abstract
stringlengths 3
192k
| title
stringlengths 4
857
|
|---|---|
we study the feasibility of measuring the d/h ratio in the atmospheres of exoplanets using current and future telescopes. the deuterium content of the atmosphere can tell us something about the formation and evolution of the exoplanet, but requires detailed consideration of the molecular absorption. | probing atmospheric escape and evolution in exoplanets: the feasibility of measuring d/h in exoplanet atmospheres using current and future observatories |
low-density, transiting exoplanets present outstanding opportunities to study planetary atmospheres due to their relatively large atmospheric scale heights, and large expected absorption features in transmission. in this dissertation talk i will present observations of two of the most rarefied planets known to science - wasp-107b and wasp-127b. on wasp-107b we detected helium on an exoplanet for the first time, and showed a new way to study extended, escaping exoplanet atmospheres. helium is the second most abundant element in the universe after hydrogen and is a major constituent of gas-giant planets in our solar system. early theoretical models predicted helium to be among the most readily-detectable species in the atmospheres of exoplanets, especially in extended and escaping atmospheres. however, searches for helium have until recently been unsuccessful. we detected helium wasp-107b at a confidence level of 4.5-sigma by measuring its near-infrared transmission spectrum with the hubble space telescope. we identified the narrow absorption feature of excited, metastable helium at 10,830 angstroms. the large amplitude of the helium absorption feature suggests that wasp-107b has an extended atmosphere that is eroding at a total rate of 1010- 3x1011g s-1(0.1-4% of its total mass per gyr). the detection demonstrates a new way to study the diffuse upper layers of exoplanet atmospheres and their mass-loss histories, and it comes at a fortuitous time. several ground-based, high-resolution, infrared spectrographs have recently become (or will soon become) available, and they are capable of measuring 10,830 angstrom absorption on exoplanets at high enough resolution to probe the shape of escaping planetary winds. our hubble space telescope and spitzer space telescope transmission spectrum for wasp-127b shows sodium, potassium, water, and carbon-bearing molecules in its atmosphere. wasp-127b is therefore a treasure trove of measurable atmospheric abundances. | helium, water, and carbon on low-density exoplanets |
we constructed 1-d atmospheric semi-empirical models of the m dwarf exoplanet hosts gj 832 (m2), gj 581 (m3), and gj 876 (m5), with the primary goal of synthesizing ultraviolet (uv) spectra of these stars. uv radiation drives photochemical processes in exoplanet atmospheres and can lead to atmospheric escape via hydrodynamic outflow. we compute our models in full non-lte using the radiative transfer code ssrpm (stellar-solar radiation physical modelling), and our model atmospheres extend from the photosphere to the corona. we use spectral data from the muscles treasury survey and the 2.15 m telescope casleo in san juan, argentina. our models fit spectra in the range from x-ray to visible, including key chromospheric lines such as lyman alpha, ca ii h & k, mg ii h & k, c ii (133.3 nm), and si iv (140.0 nm). thus, we can synthesize in a self-consistent manner the parts of electromagnetic spectra that are usually not available due to interstellar hydrogen absorption, specifically, far-uv (110 - 170 nm) continuum and all extreme-uv (10 - 91.2 nm) radiation. the output of our models can, therefore, be used as input for exoplanet atmosphere models. | semi-empirical modeling of the m dwarf exoplanet hosts gj 832, gj 581, and gj 876: uv radiation and implications for exoplanet atmospheres |
atmosphere escape is observed in the solar system for a variety of objects, including the sun all the way down to pluto. it should, therefore, come as no surprise that planets orbiting other stars may exhibit similar phenomena, providing an opportunity to explore the effects of atmosphere escape across a range of conditions not encountered in the solar system. improvements in understanding the upper atmospheres of exoplanets and the time evolution of stellar x-ray to ultraviolet fluxes for a range of stellar masses have, together, enabled careful models of planet evolution that include the impact of atmospheric escape. a clear picture is emerging where some planets are left relatively unscathed, while others may experience substantial planetary evaporation that completely determines their bulk properties and ultimate fate. this chapter introduces some of the basic concepts for understanding the role of atmospheric escape and large-scale planetary evaporation in the long-term evolution of jupiter-mass down to super-earth-mass exoplanets. | planetary evaporation through evolution |
planets lose mass over the course of their lives, shaping the observed population. the hubble space telescope has been our premier tool for observing this process in action over the past fifteen years, using uv spectroscopy targeting escaping hydrogen and, more recently, ir spectroscopy targeting escaping helium. we have now observed atmospheric escape from over half a dozen planets. hst has studied many of these planets extensively using transmission spectroscopy during transit, revealing that most of these planets, from hot jupiters, to warm neptunes, to low-gravity 'super puffs', have muted transmission spectra compared to cloud-free model atmospheres. wang and dai (2019) recently proposed that these two observations-atmospheric escape and muted spectra-could be intrinsically linked for very low-gravity planets, with dust entrained in outflows obscuring observed spectra. we propose to use theoretical simulations of mass loss, exospheric transmission spectra, and cloud/haze formation and destruction to investigate this proposed mechanism. we will apply these new models to a broad range of planets, including 3 hot jupiters, 3 warm neptunes, and 2 super puffs. each planet we consider has an observed transmission spectrum with hst; the jupiters and neptunes have detected h or he exospheres; and the super puffs are expected to be in the process of losing their envelopes. using these simulations, we seek to investigate whether this dusty outflow mechanism well above the hydrostatic atmosphere is obscuring our views of exoplanets during transit, muting their features. if so, this has broad implications for past and future exoplanet observations with hst and jwst. | can dust in outflows obscure exoplanet transmission spectra? |
we simulate the space environment around the planet au microscopii b and the response of the escaping planetary atmospheric to space weather conditions of a time-varying ambient stellar wind and coronal mass ejection (cme). we calculate the lyman alpha line profile and its variations as a result of the space weather conditions. the synthetic ly alpha line profile shows stronger absorption in the blue wing around velocities of -100 km/s, as seen from observations. however, our simulations show that: i) the line profile is highly variable and sensitive to the stellar wind conditions; ii) for extreme stellar wind conditions (i.e., cme conditions), the absorption completely disappears; iii) the velocity of the escaping atmosphere is less than -20 km/s in magnitude, suggesting that the higher blue-shift velocity in the ly alpha profile may be attributed to the stellar wind via sweeping the escaping atmospheric material. we also find that the atmospheric escape, which is driven by a pressure gradient between the dense planetary atmospheric base and space, may be significantly suppressed in the case of close-in exoplanets, and extreme space weather conditions. this is due to the fact that the stellar wind conditions for close-in exoplanets hold a pressure (thermal, dynamic, and magnetic) that is not much smaller, and even greater than that of the top of the exoplanet atmosphere. our findings show that interpretations of the ly alpha line profile in the context of exoplanetary atmospheric escape must be supported by information of the varying stellar wind conditions near the planet. our findings also show that it is imperative for models of exoplanetary hydrodynamic escape to include the stellar wind conditions as the upper boundary condition. | space weather-driven variations in lyman alpha absorption signatures of exoplanet atmospheric escape: mhd simulations and the case of au mic b |
the heating by photo-ionization in the thermosphere of short-period exoplanets can drive hydrodynamic escape, which is key to understanding the evolution of the planet atmosphere and explaining the atmospheric measurements. besides powering the atmosphere escape, the energy deposited by euv photons from the host star can also be radiated away through collisional excited atomic spectral lines, leading the mass loss rate to fall significantly below the energy limit. recent observations have detected evidence of atomic mg and fe absorptions in the nuv transmission spectrum of hot jupiter wasp-121b and hd 209458b. studying the signature of these atomic lines not only can reveal the structure of the upper atmosphere, but also constrain the radiative cooling rates. these lines will also be detectable by the colorado ultraviolet transit experiment (cute) satellite that will monitor extrasolar giant planets for evidence of mass loss and magnetic fields. in this work, we expand the capability of the exoplanet hydrodynamic atmosphere code of koskinen et al. (2013) to calculate processes of atomic metal species and compare the results with available observations. | a hydrodynamic study of radiative cooling and escape of metal species in hot jupiter atmospheres |
in this work the height profiles of temperature, velocity, and density were obtained for the hot neptune gj 436b, using a one-dimensional self-consistent aeronomic model. we traced the expansion of the gas envelope affected by heating from the extreme radiation of the host star from the thin atmospheric layer 1.02r 0 up to 5r 0 . the model used takes into account the contribution of suprathermal particles, which significantly refines the atmospheric heating function. it was found that the structure of the atmosphere is being formed with two characteristic altitude scales corresponding to a relatively dense atmosphere and a more rarefied corona. the atmospheric mass loss rate was also calculated, it was found to be about 1.6 × 10 9 g s -1 , which is lower than the results obtained by the authors of other calculations. | on the thermal atmosphere evaporation of hot neptune gj 436b |
we propose to adapt an existing modeling framework to interpret ultraviolet observations of atmospheric escape in exoplanets, aiming to provide the community with a scalable, open-source code that will be used to understand the evolution of exoplanets at the population level. our motivation lies in that understanding the complex evolution of planetary atmospheres and how they respond to a changing space environment is a critical factor in the search for earth-like worlds. most of the exoplanets discovered to date orbit extremely close to their host stars, driving their atmospheres to quickly evaporate to space. recent transmission spectroscopy observations of atmospheric escape in several hot exoplanets have sparked a new wave of theoretical efforts in modeling photoevaporation and its impacts in the evolution of hot gas giants to rocky planets. as more and more observations are executed, we need to develop simplified theoretical frameworks that allow us to effectively probe exoplanet atmospheres as a sample, which in turn allows us to perform comparative studies. the code we propose to develop allows for fast calculations that yield bayesian estimates of mass loss rates and other properties of the planet's upper atmosphere. hst has already observed more than 10 exoplanets in the uv using the transmission spectroscopy technique, and several other planets are slated to be observed in cycle 29. at the end of the project, we will leverage these archival and future datasets to uniformly study all observed planets using this new framework, yielding for the first time a comparative study of photoevaporation in exoplanets based on hst data. | the great escape: a comparative study of photoevaporation in exoplanets observed with hst |
we simulate the space environment around au microscopii b and the interaction between the magnetized stellar wind with a planetary atmospheric outflow for ambient stellar wind conditions and coronal mass ejection (cme) conditions. we also calculate synthetic lyα" role="presentation" tabindex="0">α absorption due to neutral hydrogen in the ambient and the escaping planetary atmosphere affected by this interaction. we find that the lyα" role="presentation" tabindex="0">α absorption is highly variable due to the highly-varying stellar wind conditions. a strong doppler blue-shift component is observed in the lyα" role="presentation" tabindex="0">α profile, in contradiction to the actual escape velocity observed in the simulations themselves. this result suggest that the strong doppler blue-shift is likely attributed to the stellar wind, not the escaping neutral atmosphere, either through its advection of neutral planetary gas, or through the creation of a fast neutral flow via charge exchange between the stellar wind ions and the planetary neutrals. indeed, our cme simulations indicate a strong stripping of magnetospheric material from the planet, including some of the neutral escaping atmosphere. our simulations show that the pressure around close-in exoplanets is not much lower, and may be even higher, than the pressure at the top of the planetary atmosphere. thus, the neutral atmosphere is hydrodynamically escaping with a very small velocity (<15 km s‑1" role="presentation" tabindex="0"><15 km s‑1). moreover, our simulations show that an mhd treatment is essential in order to properly capture the coupled magnetized stellar wind and the escaping atmosphere, despite of the atmosphere being neutral. this coupling should be considered when interpreting lyα" role="presentation" tabindex="0">αobservations in the context of exoplanets atmospheric escape. | space weather-driven variations in ly-alpha absorption signatures of exoplanet atmospheric escape: mhd simulations and the case of au mic b |
the recently discovered strongly irradiated terrestrial exoplanet lhs3844b presents a first opportunity to understand the impact of the uv environment produced by an m dwarf star on planetary atmospheric escape processes. astronomers were recently awarded 100 hours with spitzer to measure the infrared phase curve of lhs 3844b and determine if this planet has retained an atmosphere. whether we learn that the planet has retained or lost its atmosphere, we argue that it essential to constrain the uv spectrum of its host star, lhs 3844, which in turn will allow us to test models of uv-driven hydrodynamic escape. due to the faintness of lhs 3844, it would be prohibitive to directly observe the uv spectrum to high precision over the full wavelength range. instead, we propose to leverage the results of the muscles treasury program and use line-to-line emission correlations in order to obtain a robust estimate of the uv spectrum of lhs 3844 from only 10 spacecraft orbits. | a first opportunity to test models of atmospheric escape for a terrestrial exoplanet |
lyα (1216 å) and the o i triplet (1302, 1305, and 1306 å) are bright stellar emission lines in the far-ultraviolet (fuv) that trace the stellar chromosphere. lyα in particular is used to predict the flux in other high-energy wavelength regimes and serve as a backlight for probing the atmospheric escape of transiting exoplanets. in addition to absorption in the line core of lyα by the interstellar medium (ism), observations of stellar lyα and o i are contaminated with geocoronal emission, or airglow. airglow contamination is particularly strong with the hubble space telescope's (hst) most sensitive fuv spectrograph, the cosmic origins spectrograph (cos), due to the instrument's wide spectroscopic aperture. we have explored the stability of the lyα and o i airglow emission profiles observed with the cos g130m grating for different lifetime and grating positions. this analysis demonstrates that the profiles are sufficiently stable to create airglow templates that can be used to remove contaminating airglow from stellar spectra observed by cos. we find that one o i template is sufficient across all g130m grating setups, whereas separate templates for specific grating setups are required for lyα. we developed a graphical user interface (gui) to implement the airglow subtraction on a sample of 172 f, g, k, and m-type dwarfs to recover airglow-free stellar emission lines. we investigate correlations between recovered stellar fluxes and several measures of stellar activity such as the r'hk index, stellar rotation, and other chromospheric and coronal tracers. the airglow subtraction results indicate that the recovery tool developed in this work can produce acceptable recovered spectra for late type stars. | recovering stellar lyα and o i emission from hst-cos spectra: separating stellar and geocoronal signals |
hot jupiters are massive gaseous planets which orbit closely to their parent star. the strong stellar irradiation at these small orbital separations causes the temperature of the upper atmosphere of the planet to rise. this can cause the planet's atmosphere to escape into space, creating an exoplanet outflow. we ascertained which factors determine the presence and structure of these outflows by creating one dimensional simulations of the density, pressure, velocity, optical depth, and neutral fraction of hot jupiter atmospheres. this was done for planets of masses and radii ranging from 0.5-1.5 mj and 0.5-1.5 rj. we found the outflow rate to be highest for a planet of 0.5 mj and 1.5 rj at 5.3×10-14 mj/yr. we also found that the higher the escape velocity, the lower the chance of the planet having an outflow. | the escaping upper atmospheres of hot jupiters |
the helium triplet at 1083 nm has recently emerged as a powerful new observational probe of exoplanet atmospheric loss. we are using this new technique to conduct a survey of atmospheric escape in inflated hot gas giants using the nirspec instrument on the keck ii telescope. here we present the detection of helium in the atmosphere of wasp-52b, extending over 66 ± 5 scale heights, and find tentative evidence of helium in the atmosphere of wasp-177b at around 23 scale heights. by modeling the helium absorption profile, we find wasp-52b is losing its mass at a rate of ~1.6 × 1011 g/s. finally, we place our results into the context of the ~30 exoplanets that have been the focus of helium studies to date. | keck/nirspec studies of helium in the atmospheres of two inflated hot gas giants orbiting k dwarfs: wasp-52b and wasp-177b |
recent atmospheric models and observations of transiting exoplanets have shown that metastable helium is an invaluable tracer of their upper atmospheres. ground-based, high-resolution spectrographs are able to resolve the strong absorption line of metastable helium at 10830 angstroms, and probe the morphology and kinematics of escaping planetary winds. these data will help answer long-standing questions about stellar wind strengths; planetary magnetic fields; and the nature of sub-neptunes. i will present three helium studies with keck/nirspec: a post-transit tail sculpted by a strong stellar wind; an emission spectrum of a hot jupiter with implications for its magnetic field; and a transmission spectrum of a sub-neptune which is inconsistent with a previously reported detection. | what exoplanetary helium can tell us about stellar winds, magnetic fields, and the nature of sub-neptunes |
in other solar systems, the radiation streaming from the central star can have a destructive impact on the atmospheres of the stars close-in planets. a new study suggests that these exoplanets may also have a much harder time keeping their moons.where are the exomoons?moons are more common in our solar system than planets by far (just look at jupiters enormous collection of satellites!) and yet we havent made a single confirmed discovery of a moon around an planet outside of our solar system. is this just because moons have smaller signals and are more difficult to detect? or might there also be a physical reason for there to be fewer moons around the planets were observing?led by ming yang, a team of scientists from nanjing university in china have explored one mechanism that could limit the number of moons we might find around exoplanets: photoevaporation.artists illustration of the process of photoevaporation, in which the atmosphere of a planet is stripped by radiation from its star. [nasa goddard sfc]effects of radiationphotoevaporation is a process by which the harsh high-energy radiation from a star blasts a close-in planet, imparting enough energy to the atoms of the planets atmosphere for those atoms to escape. as the planets atmosphere gradually erodes, significant mass loss occurs on timescales of tens or hundreds of millions of years.how might this process affect such a planets moons? to answer this question, yang and collaborators used an n-body code called mercury to model solar systems in which a neptune-like planet at 0.1 au gradually loses mass. the planet starts out with a large system of moons, and the team tracks the moons motions to determine their ultimate fates.escaping bodiesevolution of the planet mass (top) in a simulation containing 500 small moons. the evolution of the semimajor axes of the moons (middle) and their eccentricities (bottom) are shown, with three example moons, starting at different radii, highlighted in blue, red and green. the black dotted line shows how the critical semimajor axis for stability evolves with time as the planet loses mass. [yang et al. 2016]yang and collaborators find that the photoevaporation process has a critical impact on whether or not the moons remain in stable orbits. as the photoevaporation drives mass loss of the planet, the planets gravitational influence shrinks and the orbits of its exomoons expand and become more eccentric. eventually these orbits can reach critical values where theyre no longer stable, often resulting in systems with only one or no surviving moons.the team finds that even in the best-case scenario of only small moons, no more than roughly a quarter of them survive the simulation still in orbit around their planet. in simulations that include larger moons further out, the system is even more likely to become unstable as the planet loses mass, with more moons ultimately escaping.what happens to the moons that escape? some leave the planetmoon system to become planet-like objects that remain in orbit around the host star. others are smashed to bits when they collide with other moons or with the planet. and some can even escape their entire solar system to become a free-floating object in the galaxy!based on their simulations, the authors speculate that exomoons are less common around planets that are close to their host stars (0.1 au). furthermore, exomoons are likely less common in solar systems around especially x-ray-luminous stars (e.g., m dwarfs) that can more easily drive photoevaporation. for these reasons, our best chances for finding exomoons in future missions will be aroundstars that are more sun-like, orbitingplanets that arent too close to their hosts.citationming yang et al 2016 apj 833 7. doi:10.3847/0004-637x/833/1/7 | the impact of stars on moons |
in exoplanet atmospheres, lyman alpha radiation can ionize atoms, dissociate molecules, and exert pressure forces that drive an outflow. monte carlo simulations of such phenomena have a large computational cost due to the extreme optical depths at lya line center. we present a novel, semi-analytic solution to the radiative transfer equation for resonant scattering that is shown to correct discrepancies in previous models as compared with monte carlo. we also present a time-dependent solution that can be used to accelerate monte carlo simulations by sampling the photon escape time distribution directly. | a novel solution to an old problem in lyman alpha radiative transfer |
the super-earth hip116454b was the first exoplanet detected by the k2 mission, in transit across a bright and nearby k1 dwarf (v=10.2, d=55 pc). the low density of the planet suggests it must have at least 30% water or a 0.5% h-he envelope. given the strong xuv irradiation from the young (2 gyr) host star, this h-he envelope should have been lost through evaporation in a few hundred millions year, suggesting that hip 116454b likely contains a large mass fraction of water. the shallow transit depth makes difficult the search for water vapor in the lower atmosphere with hst/wfc3. the moderate orbital distance of this warm ( 700 k) planet favors the formation of a super-critical steam envelope, which should be promptly dissociated at high altitude by the xuv irradiation and become observable as hydrogen flowing within and beyond the roche lobe. the host star is similar to hd 189733, host to an evaporating hot jupiter, and numerical simulations of hip116454b show that the hydrogen exosphere resulting from the dissociation of water is observable with hst/stis at ly-alpha. the detection of this exosphere would be the first signature of an evolved evaporating ocean on an extrasolar planet, as well as the first validation of internal structure models of exoplanets in this mass regime. it would also determine how to best search for water in the lower atmosphere of hip116454b with the jwst. a non-detection of escaping hydrogen, as with 55 cnc e and hd 97658b, would bring useful constraints on the nature of the planetary atmosphere, the evolutionary path of close-in super-earths, and the progenitors of the rocky evaporation remnants detected by kepler. | search for an evaporating ocean on the super-earth hip 116454b |
ultraviolet transit observations probe the upper atmosphere of exoplanets, where mass loss occurs. our analysis of nuv transmission observations of hd 209458b shows evidence for ionized iron beyond the planet's roche lobe, and no evidence for neutral iron, neutral magnesium, nor ionized magnesium. these results pose a conundrum for current theoretical models. while the upper-atmosphere observations indicate that hydrodynamic escape can carry up the heavy iron atoms, the lower-atmosphere observations indicate that iron should be trapped into aerosol condensates. this intricate relationship between lower- and upper-atmosphere properties makes the combination uv and optical/infrared observations more valuable than the sum of it parts when characterizing an atmosphere. only a few targets enable both upper- and lower-atmosphere characterization, thus, further nuv observations of hd 209458b would be invaluable to improve our understanding of exoplanet atmospheres. | signs of ionized iron beyond the roche lobe of hd 209458b from nuv observations |
currently, active studies on the formation, stability and evolution of exoplanet atmospheres are being conducted through observations by ground and space telescopes, as well as mathematical modeling. shortly after the observation of the extended hydrogen cloud around the exoplanet - transit hot jupiter hd209458b, a number of models were developed to study the thermal atmospheric escape in hydrodynamic mode from close in exoplanets. these studies have improved our understanding of the atmospheric escape process. it can be expected that future observations of exoplanets will present stronger constrains and lead to improved models of atmospheric dissipation, the use of which will lead to a better understanding of the paleoclimate and the evolution of the terrestrial planets in the solar system. | on dissipation of the exoplanetary atmospheres |
using a global 3d, fully self-consistent, multi-fluid gas-dynamic aeronomic model, we simulate the dynamically expanding upper atmosphere of an exoplanet hd 209458b. the complex spatial structure of the escaping upper atmospheric planetary material, energized by the stellar xuv and driven further by tidal forces, while interacting with the stellar wind plasma is revealed in course of the modelling. we calculate transit absorption in lyα and find that it is produced by both, dense exosphere inside the roche lobe, due to the natural line broadening mechanism, and by the fast energetic neutral atoms (so-called enas) outside the roche lobe, due to the resonant thermal line broadening. | global 3d multi-fluid aeronomy simulation of the hd 209458b |
one of the proposed explanations for the observed lack of close-in exoplanets with sizes between 1.5 and 2.0 earth-radii is that this valley is carved by atmospheric erosion: sub-neptune-sized planets begin their lives with large h/he-rich envelopes, which are lost during their early ages due to photoevaporation. the recent discovery of the young exoplanetary systems in k2-136 and k2-233 provides an excellent opportunity to test this hypothesis using lyman-alpha transmission spectroscopy, but first we need to evaluate the fuv flux of the stars, which is the main objective of this project. we realistically estimate that the lyman-alpha emission of these k-type stars are promptly detectable with hst/stis, despite their distance, owing to their young age. these observations will allow us to study the uv environment and evolution around young low-mass exoplanetary systems, and in the future could lead to the first evidence of atmospheric escape in a young sub- neptune. | far-ultraviolet exploration of nearby young exoplanet-hosting stars |
recent kepler observations revealed hundreds of terrestrial type exoplanets around g to m dwarfs. many of the detected exoplanets are located close to their host stars and are exposed to large fluxes of ionizing radiation. how do exoplanetary atmospheres respond to such harsh stellar environments? this presentation discusses modeling the upper atmospheres of exoplanets with a focus on three key parts. | modeling the upper atmospheres of exoplanets: energy deposition and escape |
induced magnetospheres of non-magnetized atmospheric bodies like mars and venus are formed by magnetic fields of ionospheric currents induced by the convective electric field e = - v x b/c of the solar wind. the induced magnetic fields create a magnetic barrier which forms a void of the solar wind plasma, an induced magnetosphere. but what happens when the interplanetary magnetic field is mostly radial and the convective field e ≈ 0? do a magnetic barrier and solar wind void form? if yes, how such a degenerate induced magnetosphere work? the question is directly related to the problem of the atmospheric escape due to the interaction with the solar and stellar winds. the radial interplanetary magnetic field in the inner solar system is typical for the ancient sun conditions and exoplanets on near-star orbits. also, the radial interplanetary field may provide stronger coupling of the near-planet environment with the solar/stellar winds and thus effectively channels the solar/stellar wind energy to the ionospheric ions. we review the current works on the subject, show examples of degenerate induced magnetospheres of mars and venus from mars express, venus express, and maven measurements and hybrid simulations, discuss physics of degenerate induced magnetospheres, and impact of such configurations on the escape processes. | degenerate induced magnetospheres |
the heating by photo-ionization in the thermosphere of short-period exoplanets can drive hydrodynamic escape, which is key to understanding the evolution of the planet atmosphere and explaining the atmospheric measurements. besides powering the atmosphere escape, the energy deposited by euv photons from the host star can also be radiated away through collisional excited atomic spectral lines, leading the mass loss rate to fall significantly below the energy limit. recent observations have detected atomic mg and fe features in the transmission spectrum of several hot jupiters. studying the signature of these atomic lines not only can reveal the structure of the upper atmosphere, but also constrain the radiative cooling rates. to understand these features, we construct a sophisticated forward model by expanding the capability of the exoplanet hydrodynamic atmosphere code of koskinen et al. (2013) to calculate processes of atomic metal species and compare the results with available observations. in the talk, i will explain our model and show the effect of metal species and roche lobe overflow. | a hydrodynamic study of radiative cooling and escape of metal species in hot jupiter atmospheres |
exoplanets' atmospheres and exospheres have been observed for more than a decade. on the observational side, a large number of atmospheres have been probed. in particular, uv observations have provided detailed information on the physical processes at work in the upper atmospheres and exospheres in various type of exoplanets (with diversity in planetary masses and orbital distances). simultaneous observations of planetary atmosphere and x-ray stellar radiations have been undertaken to understand the links between the high-energy stellar radiations, their variations and the stellar flares on the one side, and the atmospheric escape and variations of physical conditions in the exoplanets' atmosphere on the other side. these observations has triggered significant modeling efforts to understand the effect of stellar radiations and flares on the planetary atmospheres, using theoretical works and numerical simulations. all these new results are the building blocks of a new domain in the field of exoplanet, which could be called the "exoplanetary space-weather". | exoplanetary atmospheres under the effects of stellar flares |
exoplanets in extreme irradiation environments, close to their parent stars, could lose some fraction of their atmospheres because of the extreme irradiation. atmospheric mass loss has been observed during the past 12 years for hot gas giants, as large (~10%) ultraviolet absorption signals during transits. meanwhile, no confident detection have been obtained for lower-mass planets, which are most likely to be significantly affected by atmospheric escape. in fact, hot rocky planets observed by corot and kepler might have lost all of their atmosphere, having begun as neptune-like. the signature of this loss could be observed in the ultraviolet, when the planet and its escaping atmosphere transit the star, giving rise to deeper and longer transit signatures than in the optical. i will report on new hubble observations of the neptune-mass exoplanet gj 436b, around which an extended atmosphere has been tentatively detected in 2014. the new data reveal that gj 436b has huge transit depths of 56.3±3.5% in the hydrogen lyman-alpha line, far beyond the 0.69% optical transit depth, and even far beyond mass loss signatures observed at the same wavelength from more irradiated gas giants. we infer from this repeated observations that the planet is surrounded and trailed by a large exospheric cloud of hydrogen, shaped as a giant comet, much bigger than the star. we estimate a mass-loss rate, which today is far too small to deplete the atmosphere of a neptune-like planet in the lifetime of the parent star, but would have been much greater in the past. this 16-sigma detection opens exciting perspectives for the atmospheric characterization of low-mass and moderately-irradiated exoplanets, a large number of which will be detected by forthcoming transit surveys. | a giant cloud of hydrogen escaping the warm neptune-mass planet gj 436b |
to investigate how an intrinsic magnetic field affects atmospheric escape, one has to look at the whole chain, from the precipitation of solar wind particles (and electromagnetic waves) onto the atmosphere, to heating and acceleration of ionospheric ions, to the possible escape of the ions through the magnetosphere. here we investigate the first link in this chain, the energy input from a stellar wind to a magnetosphere. this energy could provide an upper limit on the escape, since it represent the available energy (the escape rate can be also limited by the ionospheric ion supply). we study different intrinsic magnetic field strengths, making the results applicable to solar system planets, and to exoplanets. apart from the total energy flux, we will also study the morphology, and velocity spectra, of the precipitating ion flux. we use a hybrid plasma solver for this study (particle ions, fluid electrons). | stellar wind energy influx to intrinsic magnetospheres |
radio emission is known to be produced by magnetized solar system planets via the cyclotron maser instability (cmi). it is very probable that this is also true for magnetized exoplanets but radio emission from planets outside the solar system has not been found yet. up to now it was thought that so-called hot jupiters, jupiter-like planets at distances below 0.1 au to their host star, are the best candidates for detection of exoplanetary radio emission. this thesis treats several new aspects in the search for radio emission from exoplanets. the rst is expanding the currently existing predictions for radio uxes and powers of exoplanets based on dipole magnetic elds by including deviations from the dipole. this comprises the inclusion of multipoles and the study of the inuence of a magnetodisk on the dipole predictions. it is found that multipoles enhance the frequency and power of the emission. a magnetodisk yields an enhancement in radio power and ux. growth rates of radio waves potentially generated at exoplanets are studied as well. it is found that for close-in gas giants at orbits smaller than 0.1 au the densities in possible source regions are too high to lead to sucient growth rates for propagating radio waves. this is investigated in detail for three hot jupiters, two typical close-in gas giants and a supermassive gas giant. it is already known that close-in, hot planets sustain strong mass-loss and heating due to stronger radiation from their host stars. this results in extended ionospheres and atmospheres. this thesis shows that this leads to unfavourable conditions for the cmi generation mechanism. for typical hot jupiters the escape of potential radio waves is impossible. for a supermassive gas giant the situation is more favourable. finally, the feasibilty of observations of exoplanetary radio emission is discussed, emphasizing that planets at orbits larger than 0.2 au are better candidates for observations. | investigation of exoplanetary radio emission - new aspects in the search for exoplanets at radio wavelengths |
the heating by photoionization in the thermosphere of short-period exoplanets can drive hydrodynamic escape, which is key to understanding the evolution of planetary atmospheres and explaining transit observations. besides powering atmospheric escape, the energy deposited by extreme uv photons from the host star can also be radiated away through collisionally excited atomic spectral lines. in addition, metals and excited state hydrogen, which have lower ionization potentials than 13.6 ev, can absorb the longer wavelength photons in the stellar spectrum. these two factors, in addition to roche lobe overflow, can cause the mass loss rate to exceed the traditional energy-limited value. in the near uv and optical transmission spectrum of the hot jupiter wasp-121b, recent observations have detected strong absorption features of mg, fe, ca, and hα, extending outside the planet's roche lobe. studying these atomic signatures can directly trace the escaping atmosphere and constrain the thermal processes in the upper atmosphere. to understand these features, we construct a sophisticated forward model by expanding the capability of the exoplanet hydrodynamic atmosphere code introduced in koskinen et al. 2013, to include important processes of atomic metal species and excited hydrogen. using this model, we can reproduce and interpret detected atomic features in the transmission spectrum of wasp-121b self-consistently. | a hydrodynamic study of the escape of metal species and excited hydrogen in the atmosphere of the hot jupiter wasp-121b |
the young magnetically active solar-like stars are efficient generators of ionizing radiation in the form of x-ray and extreme-uv (euv) flux, stellar winds, and eruptive events. the eruptive events include (super)flares with energies 100 times greater than that observed on the sun. these outputs represent the critical factors affecting atmospheric escape and chemistry of (exo)planets around active stars. while x-ray fluxes and surface magnetic fields can be derived from observations, the euv emission, and wind mass fluxes, coronal mass ejections and associated stellar energetic particle events cannot be directly observed, and thus remain elusive. here, we present a new data constrained star-as-the-sun modeling approach as a viable way to reconstruct the coronal and wind environments of these stars. this approach is based on the results of our coordinated international multi-observatory "evolving magnetic lives of young suns" that incorporates the data of four young solar-like stars, k1 ceti, be ceti, eps eri and v993 tau. the derived hst data and stellar magnetograms retrieved from spectropolarimetry observations are used to constrain the poynting flux via alfven waves at the lower computational boundary of the three-dimensional magnetohydrodynamic model, alfven wave solar model (awsom). we present the results of 3d mhd simulations of stellar coronae and winds from young suns and show how the modeled background coronal environments are used to set the conditions for initiation and propagation of stellar coronal mass ejections and associated stellar energetic particle events. | living with the young sun: first results of hst-xmm newton and tess coordinated observations of young suns and modeling of their coronae, winds and eruptive events |
observations of exoplanets used to characterize the chemistry and dynamics of atmospheres have developed considerably throughout the years. nonetheless, it remains a difficult task to give a full and detailed description using solely observations. with future space missions such as jwst and ariel, both expected to be launched within this decade, it becomes even more crucial to be able to fully explain and predict the underlying chemistry and physics involved. in this research, we focus on modeling star-planet interactions by using synthetic flare spectra to predict chemical tracers for future missions. we make use of a chemical kinetics code that includes synthetic time-dependent stellar spectra and thermal atmospheric escape to simulate the atmospheres of known exoplanets. using a radiative transfer model we then retrieve emission spectra. this ongoing study is focused on various known planetary systems of which the stellar spectrum has been obtained by the (mega-)muscles collaboration. preliminary results on these systems show that stellar flares and thermal escape can have a significant effect on the chemistry in atmospheres. | the impact of time-dependent stellar activity on the atmospheric chemistry and observability of exoplanets |
the d/h ratio is a powerful window into the evolution of atmospheres. atmospheric escape results loss of the lighter isotope, which, in the solar system, has allowed us to conclude that mars and venus lost significant amount of water. measuring the d/h ratio in exoplanet atmospheres is possible by looking at the absorption/emission features of water or methane in the mid-infrared. even at natural isotopic abundances, the deuterated isotopes have regions where the absorption surpasses the main isotopes. the ro-vibrational opacities of the relevant couples (i.e. h2o/hdo and ch4/ch3d) have to be very well constrained however. combining both experimental and ab-initio line lists offers the most complete and accurate way to calculate molecular absorptions. we combine these datasets, and the feasibility of detecting d/h in exoplanets is assessed using both ground and space based observatories, and considering a number of different atmospheres and planetary sizes. | ground and space based observatories: the feasibility of measuring d/h in exoplanet atmospheres |
a lack of close-in neptune-sized planets, and the recently-discoveredbimodal distribution of super-earths and sub-neptunes from kepler, haveboth been interpreted as evidence that exoplanet evolution is profoundlyaffected by xuv- driven atmospheric evaporation. the key uncertainty inthis interpretation is the energetic efficiency of the atmospheric escape,which can be measured by combining hst uv and xmm x-ray observations,but only for nearby and young transiting systems. the kepler planets aretoo far away, but fortunately k2 and mearth are finding small planets thatare nearby and/or situated in clusters with known young ages. we proposexmm measurements that will be combined with scheduled hst observationsto determine how mass loss efficiency depends on planet size. | xuv irradiation of the youngest and nearest transiting super-earths and neptunes |
the recent discovery of a super-earth transiting the bright starhd219134 provides an unprecedented opportunity for detailed study of theatmosphere of low-mass exoplanet. the k3v star is located at a distanceof only 6.5pc, enabling sensitive measurements of its x-ray flux andspectrum. this is important because x-ray/euv irradiation is believedto drive the observed evaporation of hot jupiters (hd209458b, hd189733b)and neptunes (gj436b), and hd219134b will extended these studies to thesuper-earth regime. here we propose an xmm-newton observation that willdefine the high-energy environment of the planet and allow estimatesof its atmospheric escape rate. this will aid the interpretation ofatmosphere observations with hst, spitzer, jwst etc. | the x-ray irradiation of the nearest transiting super-earth |
recent observations, especially space telescope missions, reveal that there are many kinds of exoplanets. especially, earth-mass to several earth-mass planets has two types of planets: the bare-rocky planets and planets possessing significant atmosphere. they are divided by the planetary radius since the hydrogen-helium atmosphere expands its radius. focusing on the planets whose radius larger than typically 1.8 earth radius, those planets have 1-30 % of atmospheres by mass. such diversities are essential to understand the diversities of the formation processes of exoplanets. here we focus on the late stage of the formation process. planets have experienced giant impact events that cause atmospheric escape. we perform the smoothed particle hydrodynamic simulation to reveal the impact-induced atmospheric escape. we find that the kinetic energy of escaped atmospheric mass is simply proportional to the kinetic energy of the giant impact. we demonstrate the relationship between the kinetic energy of the escaped mass and the escaped atmospheric mass fraction. we find two regimes that determine the atmospheric escape: the momentum-driven regime and the other is the energy-driven regime. combined the relationships among the kinetic impact energy, kinetic escape energy, and the escaped atmospheric mass, we can derive an analytic expression for the atmospheric escape as a function of the impact energy. the present study provides strong constraints on the formation scenarios of observed rocky planets. since the giant impact removes the primordial atmosphere, rocky planets expected to have atmospheres should have formed before the protoplanetary disk dissipation. | catastrophic atmospheric loss event induced by the giant impact |
hot exoplanets with semi-major axes smaller than 0.05 au can go considerable alteration from the high energy radiation of their host stars radiation from driving winds to altering the thermal profiles to disintegrating nearby planets. a variety of exoplanets are studied in this high irradiation environment with different consequences on their atmospheres. the escaping winds from the transiting hot jupiter hd 209458b are measured with a novel limb brightened transit model for ultraviolet wavelengths. the hot exoplanet corot-1b is used as a test case for the hypothesis that tio and vo molecules (which can exist in equilibrium at high temperatures) can create a temperature inversion in the planet by absorbing stellar ultraviolet radiation. finally, the escaping debris from the disintegrating planet candidate kic 12557548b are characterized with spectroscopy to constrain the size of dust particless in its escaping winds. | observations of disintegrating, evaporating and hot planet atmospheres with transmission spectra |
the atmospheres of highly irradiated exoplanets are observed to undergo hydrodynamic escape, resulting in planetary mass loss. however, stellar winds can shape and even prevent atmospheric escape, affecting observable signatures of escape such as lyman-alpha and h-alpha line profiles. in this work, we simulate atmospheric escape of close-in exoplanets using 3d magnetohydrodynamics simulations to investigate how they are affected by stellar winds. we show that, although younger hot-jupiters experience higher levels of atmospheric escape, owing to a favourable combination of higher irradiation levels and weaker planetary gravity, stellar winds are also stronger at this young age, which can act as to reduce escape rates of young exoplanets. even when this reduction is not significant, we demonstrate that transit signatures can be erased due to the presence of a stellar wind and that neglecting stellar winds in the interpretation of spectroscopic transits can lead to underestimation of planetary escape rates. | effects of stellar winds on spectroscopic transits of close-in exoplanets |
our hst and keck observational campaigns have detected, for thefirst time, escaping atmospheres around multiple young mini-neptunes.photoevaporation from these planets shapes exoplanet demographics,but one of the biggest sources of uncertainty in modelling the outflowis the x-ray and extreme uv spectrum of the star. stellar euv cannotbe measured due to interstellar absorption, and must be inferred fromthe x-ray luminosity. we propose a survey to measure the x-ray spectraof four new young, active stars hosting small (<3.5 r_earth) planets,all of which we are targeting for helium outflow observations with keck.as a bonus, xmm's om will measure the muv (~200 nm) flux, which destroysmetastable helium and is therefore critical to modelling the heliumsignal we observe. | photoevaporation from small planets orbiting young, active stars (ii) |
planetary thermal escape, the so-called jeans escape, occurs in the uppermost layer of the atmosphere, the exosphere. there, the medium is not collisional enough to maintain the velocity distribution function maxwellian and a part of the gas overcomes the escape velocity. however, there is another mechanism which emphasizes the thermal hydrogen escape: the radiation pressure. the radiation pressure results from the resonant scattering of stellar photons by an atom or molecule. this phenomenon is particularly efficient on hermean sodium but also on hydrogen around any planet/exoplanet. in this study, we will quantify the increase of the jeans escape induced by the radiation pressure on terrestrial planets (up to 30% at earth) and exoplanets and show the existence of an upper limit for this escape which is none other than the blow-off regime. | how does the stellar lyman alpha flux drive the planetary hydrogen exospheric escape? |
near-uv transit measurements could be used to investigate a variety ofexoplanet phenomena including atmospheric escape, vertical distributionof aerosols, and interactions of the planetary atmosphere with a stellarwind. xmm-newton is one of only three nuv capable space telescopes with aguest observer program, and -- due to having the longest orbital period-- the telescope most well-suited to monitoring exoplanet transits inthe nuv. we propose to observe four hot jupiter transits to fill in gapsin the range of exoplanet equilibrium temperatures probed, in order toconfirm or refute the tentative trends observed through a similar studywith swift. | uv transmission spectroscopy of hot jupiter atmospheres with the xmm-newton |
ultra-hot jupiters (uhjs), jovian exoplanets with equilibrium temperatures greater than 2250 k, have quickly become recognized as unique laboratories for understanding the effect of irradiation on planetary atmospheres. to properly understand atmospheric heating and escape on exoplanets, we must observe how exoplanets respond to the irradiation they receive by measuring atmospheric mass loss and by detecting the opacity sources that determine the atmosphere's energy balance. we propose to observe the entire near-ultraviolet and optical transmission spectrum of a new high signal-to-noise ultra-hot jupiter, wasp-178b. this planet shares many characteristics with the well-studied wasp-121b, but orbits the second hottest know exoplanet host star, allowing us to test the effects of host star irradiation spectrum on the atmosphere. by observing a transit in the uv at high spectral resolution with stis/e230m, we will search for escaping metals, including fe ii and mg ii, and constrain the roche lobe filling factor of the atmosphere. we can directly compare these results with recent observations of wasp-121b, providing insight into atmospheric escape mechanisms. we will also observe the entire nuv and optical transit spectrum at low spectral resolution with wfc3/uvis/g280, allowing us to infer the presence of species like fe, tio, and vo while contributing necessary context to interpret the high resolution observations. this program will be the first comparative study of escaping metals and heat deposition in uhjs, some of the highest signal-to-noise exoplanet targets. | comparing escaping metals and heat deposition in ultra-hot jupiters |
hydrodynamic atmospheric escape is thought to be the main avenue for early evolution in exoplanets ranging from gas giants to terrestrial worlds, as shown by demographic studies resulting from the kepler survey. however, with only three exoplanets to date that display smoking gun evidence of hydrodynamic escape, most modeling efforts to understand this process have been limited to semi-arbitrary assumptions and artificial test cases. this has a downstream effect that limits our capacity to assess if sub-jovian planets are able to retain their volatile-rich atmospheres. while hot jupiters are under no threat of losing significant fractions of their mass, they are the best targets to study hydrodynamic escape because they have detectable signals of exospheric metals in transmission spectroscopy. these signatures can only be observed by hst in the ultraviolet. in this program, we propose to observe the transmission spectrum of the ultra-hot jupiter wasp-76b. we predict that this planet is losing mass at a rate 10 times larger than that of hd 209458b, and we can detect escape of mg and fe at more than 5-sigma confidence in high resolution. we further predict that the escaping material fills the roche lobe of the planet and is in a state of geometric blow-off. our results will automatically yield a precise near-uv transmission spectrum of wasp-76 b, a crucial measurement to probe opacity sources in its stratosphere and rainout of metallic species. | hydrodynamic atmospheric escape in a benchmark ultra-hot jupiter |
the young magnetically active solar-like stars are efficient generators of ionizing radiation in the form of x-ray and extreme uv (euv) flux, stellar wind and eruptive events. these outputs are the critical factors affecting atmospheric escape and chemistry of (exo)planets around active stars. while x-ray fluxes and surface magnetic fields can be derived from observations, the euv emission and wind mass fluxes, coronal mass ejections and associated stellar energetic particle events cannot be directly observed. here, we present the results of a three-dimensional magnetohydrodynamic (mhd) model of a young solar analog kappa 1 ceti representing our sun at the time when life started on earth with inputs constrained by spectropolarimetric data, hst/stis far uv, x-ray data data and stellar magnetic maps reconstructed at two epochs separated by 11 months. the simulations suggest that the global stellar corona had undergone a drastic transition from a simple dipole-like to a tilted dipole with multipole field components, and thus, provided favorable conditions for corotating interaction events (cirs) that drive strong shocks. the dynamic pressure exerted by cirs are 1300 times larger than those observed from the sun and can contribute to the atmospheric erosion of early venus, earth, mars and young earth-like exoplanets. our data-constrained mhd model provides the framework to model coronal environments of g-m planet hosting dwarfs. the model outputs can serve as a realistic input for exoplanetary atmospheric models to evaluate the impact of stellar coronal emission, stellar winds and cirs on their atmospheric escape and chemistry that can be tested in the upcoming jwst and ground-based observations. | magnetic life of young suns: data constrained model of the corona and wind from k1 ceti |
photo-evaporation of planetary atmospheres plays a key role in the evolution of exoplanets, carving their whole population. however, direct observations of atmospheric escape are scarce and almost non-existent in the mass range of super-earths and mini-neptunes, while these planets are among the most impacted by the phenomenon. a huge step forward could be made by achieving a comparative study of several super-earths, volatile-rich or not, in a single multi-planet system: such planets would indeed experience the same evolution of the stellar x and euv flux that are driving atmospheric escape. the perfect system for such a study has just been identified: the nearby, solar-type, and naked-eye star nu^2 lupi hosts transiting planets spanning a remarkably large range of insolation (~100 to ~5x the insolation of earth). tess found the transits of the two inner planets and cheops detected the transit of planet d, a volatile-rich super-earth with an exceptional period of 107 day. these super-earths straddle the radius gap of the "evaporation valley" and could have retained different fractions of gas and volatiles. like for previously observed warm neptunes, they could be enshrouded in huge comet-like exospheric clouds of escaping gas, which could have built up in the mild radiative environment. the system unique combination of proximity, brightness and favorable planet characteristics offers a fantastic opportunity to exploit hst ultraviolet capabilities to search for the hydrogen, oxygen and carbon escaping three planets in whole new mass and irradiation regimes. it is the ideal testbed for advancing both observations and theories of atmospheric evaporation of exoplanets. | a comparative study of atmospheric escape in the brightest system of super-earths straddling the evaporation valley |
transmission spectroscopy is one of our most powerful tools for characterizing exoplanet atmospheres, and thanks to the recent launch of nasa's tess mission we will soon have a large sample of planets around bright stars, ideally suited to this technique. with it's unique combination of uv to nir wavelength coverage and incredibly high s/n, luvoir would build upon the powerful legacy of hubble and revolutionize our ability to characterize the atmospheres of a wide range of transiting exoplanets. at fuv wavelengths the luvoir ultravoilet multi object spectrograph (lumos) will obtain high s/n transmission spectra and high spectral resolution, allowing us to detect transiting planetary exospheres and constrain the physics of atmospheric escape. meanwhile, using the uvis channel on the high definition imager (hdi) instrument we can obtain high s/n r = 500 spectra in the optical and nuv, which allow us to constrain the properties of clouds and search for absorption from alkali metals. finally, with the nir channel in hdi we will be able to detect molecular absorption and measure abundances for a wide range of species including h2o, co2, and o2. | transmission spectroscopy of exoplanets with luvoir |
hot jupiters (hj) are exoplanets, gas giants with low orbits (≤ 0.1 a.u.). the stellar x-ray and ultraviolet (xuv) radiation energy deposition result in heating ionization and the consequent expansion of planetary atmosphere. expansion of upper atmosphere under certain conditions could be so large that the majority of light atmospheric constituents overcome the gravitational binding and escape from the planet in a form of hydrodynamic wind. besides interaction of two counter-streaming plasma flows (stellar wind and ionized upper layers of planet atmosphere), each of this flows interact with planetary magnetic field. in such complex situation laboratory simulation can provide data that can’t be obtained by computer simulation or observation. experiment was carried out on ki-1 facility: high-vacuum chamber 5m long, 1.2 m in diameter with pressure ∼ 10-6 torr. magnetic dipole with two attached laser targets played the role of a planet, and background plasma from θ-pinch used for simulation of stellar wind. as a result, data on a behavior of plasma density and magnetic field were obtained. the novel phenomenon was registered: magnetic field is transferred by the cloud of laser plasma, which was not observed before in experiments or calculations. | laboratory simulation of hot jupiters atmosphere expansion |
large-scale exoplanet search surveys have shown evidence that atmospheric escape is a ubiquitous process that shapes the evolution and demographics of planets. however, we lack a detailed understanding of this process because very few exoplanets discovered to date could be probed for signatures of atmospheric escape. recently, the metastable helium triplet at 1.083 μm has been shown to be a viable window for the presence of he-rich escaping envelopes around short-period exoplanets. our objective is to use, for the first time, the phoenix spectrograph to search for helium in the upper atmosphere of the inflated hot jupiter wasp-127 b. we observed one transit and reduced the data manually since there is no pipeline available. we did not find a significant in-transit absorption signal indicative of the presence of helium around wasp-127 b, and set a 90% confidence upper limit for excess absorption at 0.87% in a 0.75 å passband covering the he triplet. given the large scale height of this planet, the lack of a detectable feature is likely due to unfavorable photoionization conditions to populate the metastable he i triplet. this conclusion is supported by the inferred low coronal and chromospheric activity of the host star and the old age of the system, which result in a relatively mild high-energy environment around the planet. | search for helium in the upper atmosphere of the hot jupiter wasp-127 b using phoenix/gemini |
the characterization of exoplanet atmospheres will be a major scientific endeavor in the coming decades, in particular the search for biosignatures in the atmospheres of temperate, rocky exoplanets. it is a primary science driver for upcoming space-based (e.g., jwst) and ground-based (e.g., gmt) facilities. there are currently several different research directions in exoplanet atmosphere characterization that probe fundamental questions in exoplanet formation and evolution, as well as provide stepping stones to developing the facilities and techniques to ultimately detect biosignatures in the atmospheres of small planets. observations of extended atmospheres provide an opportunity to not only measure the current conditions in the planetary atmosphere, but also put constraints on formation history and interior structure (owen et al. 1999), interactions with host star (cauley et al. 2017), and atmospheric and planetary evolution (oberg et al. 2011). one such research direction is the characterization of extended exoplanetary atmospheres with different spectral absorption lines, namely lyman-α, h-α, or hei at different wavelengths. here, we present an analysis aimed to estimate the planetary mass-loss rate and the signal of these lines starting from the properties of the tess candidates sample. this allows to select the more promising targets for a follow-up with radial velocities and possibly atmospheric characterization. we also present a summary of our follow-up observations to characterize the planets in the system gj9827, the nearest planetary system that kepler or k2 has ever found, with three super-earth planets in 1:3:5 commensurability. gj9827b has a relatively hot atmosphere, which makes it an ideal target for measuring atmospheric escape, particularly given the high activity of its host star. | characterizing exoplanetary atmospheres in the tess era |
observing and understanding potentially habitable exoplanet systems, like trappist-1, is one of the field's top priorities. one challenge to habitability planets orbiting m type stars face is extreme x-ray and ultraviolet (xuv) radiation at the beginning of the system's lifetime. during this time, any water existent on the planet's surface will be vaporized at which point water molecules may be broken up into their constituent parts. as time goes on, hydrogen will escape, leaving behind oxygen, and effectively causing the planet to lose water overall. although single cases of atmospheric escape in super-heated atmospheres have been explored, we still need to better understand the full range of possibilities for water evolution on the trappist-1 planets. this study identifies the range of possible water evolution histories for these worlds, assuming a pure water atmosphere. this work will contextualize future ground-based and james webb space telescope observations of trappist-1, along with helping us to assess the strength of oxygen as a sign of life or habitability in these environments. | bayesian calculations of water inventories and oxygen accumulation on the trappist-1 planets |
the habitability of earth-like planets is an increasingly important subject in astrophysics and in planetary sciences. atmospheric escape plays a vital role in the evolution of the habitability of earth-like planets. by systematically analyzing the numerical simulation results of the interactions between the planetary atmospheres and the stellar winds, in this work, we evaluate various factors related to the atmospheric nonthermal ion escape rates, including planetary parameters (e.g., mass, density, radius, semimajor axis, etc.) and stellar wind parameters (e.g., density, velocity, and interplanetary magnetic field (imf) strength). furthermore, we determine and quantify the key factors affecting the planetary atmospheric nonthermal ion escape rates. our results show that the correlation coefficients between planetary atmospheric nonthermal ion escape rates and stellar wind density, imf strength, and the ratio of the planetary radius to the planetary semimajor axis are 0.98 (0.88), 0.95 (0.81), and 0.87 (0.59), respectively, in the scenario of maximum (minimum) dynamic wind pressure. this means that the planetary atmospheric nonthermal ion escape rates increase with the increasing stellar wind density, the increasing imf strength, and the increasing ratio of the planetary radius to the planetary semimajor axis. generally, the nonthermal ion escape rates of planetary atmospheres are more sensitive to stellar wind parameters than to others. in addition, we determine the functional relations of the above three significant parameters for evaluating and quantifying the effects of such key physical factors on the nonthermal ion escape rates of the planetary atmospheres. our findings will be very useful for better understanding the key factors that influence the escapes of planetary atmospheres. | quantifying the key factors affecting the escape of planetary atmospheres |
we report the detections of photoevaporative atmospheric escape from four young mini neptunes (< 3 r⊕, < 1 gyr), the smallest and youngest planets for which escaping atmospheres have been detected. out of the five we observed, we obtained one detection in ly alpha and three detections in the metastable helium line at 1083 nm. these detections suggest that most mini neptunes have primordial hydrogen/helium envelopes. when combined with 3d hydrodynamic models, our helium observations show that the mass loss is vigorous enough to strip most of the envelope within ~1 gyr, although additional modeling work is still needed to match the detailed properties of the outflow. these data constitute strong evidence that photoevaporation dramatically shapes the demographics of small exoplanets, creating the super earth population and carving out the radius gap separating super earths from mini neptunes. | first detections of escaping atmospheres from young mini neptunes |
in this work we applied the previously developed self-consistent 1d model of hydrogen-helium atmosphere with suprathermal electrons to close-in hot neptune gj 436 b. the obtained height profile of density shows the two-scale structure of the planetary atmosphere. the mass-loss rate is found to be about. | thermal atmospheric escape of close-in exoplanets |
low-mass close-in exoplanets are susceptible to intense atmospheric escape. recent studies suggested that such escaping outflow can deliver abundant aerosols to upper atmospheres and drastically inflate the observed transit radius. here, we investigate how aerosols grow and move in escaping atmospheres and influence transit observations of exoplanets using a detailed microphysical model. we find that aerosols formed at low altitudes, such as condensation clouds, are barely transported by the outflow owing to efficient particle growth and gravitational settling, while aerosols formed at high altitudes, such as photochemical hazes, are susceptible to be entrained in escaping outflow. with sufficiently high aerosol production altitudes and rates, the outflowing aerosols can enhance the observable radius by a factor of ∼2 or even more. the outflowing aerosols produce featureless nir transmission spectra, in agreement with the spectra observed for extremely low-density planets called super-puffs. the spectrum also shows a broad spectral slope ranging from the visible to the mid-ir as well as absorption features of the aerosols themselves, which can be tested by upcoming jwst observations. lastly, using an interior structure model, we show that the radius inflation by outflowing aerosols is drastic only when the planets verge on total atmospheric loss. this potentially explains why super-puffs are uncommon despite the suggested prevalence of photochemical hazes on exoplanets. | aerosols in escaping atmospheres: implications for transmission spectra and origin of super-puffs |
kelt-9b is the hottest discovered exoplanet to date and ground-based transmission spectroscopy of this ultra-hot jupiter has revealed a wealth of atoms and ions entrapped in its escaping atmosphere. here we present new near-ultraviolet (nuv) observations of the planet obtained with the colorado ultraviolet transit experiment (cute) cubesat. the cute transmission spectra show regions of extended absorption at altitudes beyond the planet's roche lobe, including a spectral region containing mg ii. we present and explore the kelt-9b nuv transmission spectrum and place it in the context of previous observations. | near-ultraviolet transmission spectroscopy of the ultra-hot jupiter kelt-9b from the colorado ultraviolet transit experiment |
the lyman alpha emission line is the brightest uv emission line in m and k dwarfs and serves as an important tool for studies of stellar chromospheres, the interstellar medium, and exoplanet atmospheres. however, lyman-alpha observations are proven difficult due to the strong obstruction by the interstellar medium (ism), necessitating a reconstruction of the intrinsic stellar line from the observed spectrum. we have performed new lyman alpha reconstructions on the muscles treasury survey stars, incorporating improved parameterizations for the intrinsic line wings and line core, such as self-reversal. most of the m dwarfs' new fluxes are 4% to 65% fainter than what was presented originally in the muscles high level science products, although gj 1214 is 2x fainter. the k dwarfs are generally 2x - 5x fainter, primarily because they are more greatly affected by self-reversal than m dwarfs. we present an analysis of how the updated lyman alpha fluxes could impact photochemical and atmospheric escape studies and flux-flux scaling relations with other chromospheric emission lines such as ca ii h&k. | new and improved lyman-α reconstructions of m & k dwarfs from the muscles treasury survey |
one of the most well-studied exoplanets to date, hd 189733b stands out as an archetypal hot jupiter with a wide collection of observations and theoretical models aimed at characterizing its atmosphere, interior, host star, and environment. we report here on the results of an extensive campaign to observe atmospheric escape signatures in hd 189733b using the hubble space telescope and its unique ultraviolet capabilities. we have found a repeatable in-transit absorption of singly-ionized carbon and neutral oxygen in the epoch of june-july/2017. this result is, however, in tension with a previous observation with the same configuration performed in 2009. finally, we also reproduce the observation of escaping hydrogen using a different instrument than previous detections. our results reinforce the conclusion that the exosphere of hd 189733b is highly variable from epoch to epoch, likely in response to the changes in the high-energy input from its variable host star. | atmospheric escape in hd 189733b: variable signatures of hydrogen, oxygen and carbon measured with hst |
the last couple of years has seen a significant increase in detections of evaporating exoplanets, owing mainly to the discovery of the metastable helium as a probe for atmospheric escape. this process is thought to be an important factor to explain features in the exoplanet population, such as the hot-neptune desert and the radius valley. while part of exoplanet community, in general, enjoys a swath of open-source codes that help them plan and interpret observations, the same cannot be said about those who study atmospheric escape. at least, not until recently. we developed a new open-source code, named p-winds, with the objective of supplying the community with an easy to use, well-documented tool designed for observations of evaporating exoplanets. this code allows the forward modeling of spectral signatures (e.g., the metastable he triplet), as well as the statistical retrieval of the atmospheric escape rate and outflow temperature. in this presentation, i will discuss the motivation, implementation, and use cases for p-winds. i will showcase retrievals for several warm neptunes and hot jupiters using both new and archival datasets. we use this technique to uniformly search for trends between the atmospheric escape rate vs. the incident high-energy irradiation, as predicted by the energy-limited mass loss hypothesis. | an open-source framework to plan and interpret observations of atmospheric escape in exoplanets |
ultraviolet observations of ultra-hot jupiters (uhjs; teff > 2000 k) provide us with an opportunity to investigate previously unexplored parameters of exoplanet atmospheres. wasp-189b is one of the hottest planets discovered to date with a day side temperature of about 2640 k. it orbits a bright (v = 6.64) a-type star every 2.7 days and has a radius of about 1.4 jupiter radii. we present preliminary results of observations of wasp-189b conducted with the cute smallsat. cute, launched in september of 2021 to a low earth orbit, is a 6u nasa-funded smallsat carrying on-board a near ultraviolet low-resolution spectrograph. wasp-189b was one of the cute early science targets and was observed during april and may 2022. we present data reduction, analysis, and initial results, which indicates significant atmospheric absorption at near-ultraviolet wavelengths when compared to the optical, suggestive of the presence of an extended, possibly escaping, atmosphere. | near ultraviolet observations of wasp-189b with cute telescope |
hydrodynamic escape from exoplanet atmospheres may be an important evolutionary process for many irradiated gas-rich planets, and could help explain trends in the observed exoplanet population. observational evidence for atmospheric escape has usually come from observations of excess hydrogen ly-α absorption in exoplanet transit spectra. however, because the ly-α line core can be heavily affected by interstellar absorption and geocoronal emission, recent studies (both observational and theoretical) have turned to the 10830 å line of metastable helium as an alternative probe of escaping exoplanet atmospheres. the primary advantages of this line over the ly-α are its resilience to interstellar contamination and its accessibility from high-resolution ground-based spectrographs. in this work, we present simulated high-resolution transmission spectra at the 10830 å helium line for two exoplanets: hat-p-11b, a warm neptune-mass planet, and wasp-69b, a hot jupiter. using a 1d atmospheric model of hydrogen and helium, we simulate possible outflow conditions for the two planets, then couple our model outputs to a new radiative transfer solver to predict spectra. we then compare our results to recent observations of hat-p-11b and wasp-69b to place constraints on their outflow temperatures and mass loss rates. we find that a range of hydrodynamic models can reasonably reproduce the observations, with our most-likely model of hat-p-11b having an isothermal outflow temperature of t0 = 7300 k and a total mass loss rate of mdot = 3.16 × 1010 g s-1, and our most-likely wasp-69b model having t0 = 10000 k and mdot = 5.01 × 1011 g s-1. we attribute the degeneracy between t0 and mdot to the quality of the observations and suggest that higher precision measurements and resolved time-series spectra may help to mitigate the degeneracy in future efforts. the sao reu program is funded in part by the national science foundation reu and department of defense assure programs under nsf grant no. ast-1852268, and by the smithsonian institution. | new insights into the escaping atmospheres of hat-p-11b and wasp-69b: simulated 10830 \\r{a} helium line transmission spectra |
we review atmospheric escape processes from mars as measured by the maven mission, and consider how the martian atmosphere would fare if mars orbited an active m dwarf star. | atmospheric escape from mars: lessons for studies of exoplanets |
the martian atmosphere and climate system will respond as the solar luminosity continues to increase over the next 5 billion years. the mars surface will heat up to above the melting temperature of water ice, even without greenhouse warming. water ice currently in the polar caps and ground ice will melt, potentially repopulating crater lakes or a very small ocean, with the abundance possibly enhanced due to diffusion outward of water currently locked in the crust. the co2 currently adsorbed in the regolith and locked up in the polar ice cap will diffuse into the atmosphere, providing up to 50 mbar total; this would increase the temperature further (albeit only slightly) via greenhouse warming. there are two end-member scenarios of what the climate could look like: (i) surface water could drive an atmospheric water cycle somewhat analogous to present-day earth's; this would create a global clement climate conducive to the existence of widespread life. while earth's climate could have a transition to be more venus-like as the sun heats up, mars could become more earth-like. (ii) the widespread presence of liquid water could cause h2o to hydrate surface/subsurface minerals (or allow h released from water to escape to space) and co2 to form carbonates, leaving mars to continue with a dry, lifeless environment. it's not possible to determine which of these end-members (or where in between) actually will occur – the water cycle under these conditions is too different from any well-constrained model to allow us to predict how robust it would be or how effective in producing the sustained physical and chemical weathering required to remove co2 and h2o from the atmosphere. this changing climate reminds us that exoplanet evolution and habitability can be driven by endogenous processes associated with a terrestrial planet as well as by the ability of euv and a stellar wind from the host star to strip away atmosphere. | mars' atmosphere, volatiles, and climate as the sun heats up over the next 5 billion years |
atmospheric escape is believed to significantly influence the evolution of close-in exoplanets, and has been proposed to shape planetary demographics in the form of the hot neptune desert and evaporation valley. in order to test these theories, it is crucial to obtain accurate estimates of the atmospheric mass-loss rate for evaporating exoplanets. strong absorption during transit in the helium line at 1083 nm has recently proven a powerful direct observational tracer of atmospheric escape. a common approach to extracting mass-loss rates from these observations is to fit synthetic line profiles based on models that parametrize the planetary outflow in terms of the mass-loss rate and a constant temperature. however, such analyses often result in degeneracies between the mass-loss rate and temperature, making it difficult to narrowly constrain either parameter. we place additional theoretical constraints on the allowed temperature by simulating outflow models with the photo-ionization code cloudy, which ensures a highly detailed nlte treatment of the gas. combining the two constraints allows us to find much tighter estimates for the atmospheric mass-loss rate. we demonstrate this here for the helium line, but our methods can be applied to many other spectral lines in the visible and ultraviolet wavelength range, which are inherently included in cloudy, in order to probe different layers of the escaping atmospheres and thus get a better insight into their properties. | constraining atmospheric mass-loss rates of exoplanets by simulating spectral lines of multiple species |
the rocky planets in our solar system each have their own complicated stories to tell, and we have decades of data observing them up close. yet, looking at the innermost worlds of mercury and venus, we still don't have complete answers to simple questions. how much bigger would mercury need to be, in order for it to have retained an atmosphere? how much more closely to the sun could venus orbit, without its thick atmosphere eroding into space? observations of exoplanets can help answer these questions. both thanks to exoplanet discovery efforts that have provided worlds starting to resemble those our solar system and thanks to webb for providing the long-wavelength sensitivity needed to observe these cool planets, we can start to directly observe planets that resemble our own. here, we propose to use miri/lrs to observe the emission spectrum of the exoplanet ltt1445ab and use its dayside temperature to determine whether or not it has an atmosphere. at mere 6.9pc away, the ltt1445 system is the closest m dwarf know to host a transiting planet, and determining whether or not it has an atmosphere provides crucial context for the decade of exoplanetary science ahead. this work would provide valuable insight to atmospheric escape from rocky planets both within the solar system and beyond. | the thermal emission spectrum of the closest m dwarf transiting rocky planet |
atmospheres of close-in exoplanets around k and m dwarfs are subject to large fluxes of ionizing radiation from the hosts stars. first, the stellar radiative flux in the x-ray and extreme uv (xuv) ionizes and heats the upper atmosphere, driving atmospheric heating, affecting the conductance, and enhancing atmospheric escape. second, the stellar wind's interaction with the planet's intrinsic magnetosphere transfers energy to the atmosphere through field aligned currents and poynting flux. that energy is dissipated in the high latitude cusp and auroral regions through joule heating which can inflate the atmosphere and also enhance the escape rate. these two mechanisms also modify the atmospheric chemistry via ionization, dissociation of molecular species and through initiation of ion, neutral and photochemical chemical reactions. this presentation will introduce a newly developed exoplanet ionosphere-thermosphere response (itr) tool, a three-dimensional multi-fluid atmospheric code that models the hydrodynamics, kinetic effects of particle precipitation and coupled atmospheric chemistry of a wide range of atmospheric layers: from ionosphere to mesosphere of an exoplanet exposed to the effects of space weather. we discuss its application to wide range of exoplanetary environments exposed to extreme space weather. | studying impact of space weather factors on exoplanetary atmospheric thermodynamics and chemistry with exoplanet-itr tool |
in this talk, i will give an overview of recent key results from ultraviolet studies of cool stars (focusing on the "extreme ultraviolet" bandpass, 10 – 91 nm), with an emphasis on implications for atmospheric escape. i will conclude by presenting the landscape for stellar and exoplanetary investigations utilizing ultraviolet observations over the next two decades. missions of all sizes have important roles to play in this area: i will highlight planned or proposed missions ranging from cubesats and smallsats to explorer class missions to flagships. | ultraviolet spectra of exoplanet host stars as inputs for atmospheric escape calculations |
the lyman alpha emission line is the brightest uv emission line in m and k dwarfs and serves as an important tool for studies of stellar chromospheres, the interstellar medium, and exoplanet atmospheres. however, lyman-alpha observations are proven difficult due to the strong obstruction by the interstellar medium (ism), necessitating a reconstruction of the intrinsic stellar line from the observed spectrum. we have performed new lyman alpha reconstructions on the muscles treasury survey stars, incorporating improved parameterizations for the intrinsic line wings and line core. we present an analysis of how the updated lyman alpha fluxes could impact photochemical and atmospheric escape studies and flux-flux scaling relations with other chromospheric emission lines such as ca ii h&k. | new and improved lyman alpha reconstructions of m and k dwarfs |
using the global 3d multi-fluid hd and its extension to mhd we simulated the measured hd209458b transit absorption depths at the fuv lines, and at the nir line (10830 å) of metastable helium hei(23s) triplet, paying attention to possible change of the absorption profiles due to the presence of planetary intrinsic magnetic field. as continuation of our previous studies of hd209458b (shaikhislamov et al. 2018, 2020), the inclusion of the hei(23s) line into consideration and the comparison with corresponding measurements allows to constrain the helium abundance by he/h ~ 0.02, and stellar xuv flux at 1 a.u. by fxuv ~10 erg cm2 s-1 at 1 a.u. for the first time, we studied the influence of the planetary dipole magnetic field with a model which self-consistently describes the generation of the escaping upper atmospheric flow of a magnetized hot jupiter, formation of magnetosphere and its interaction with the stellar wind. we simulated the absorption in the most of spectral lines for which measurements have been made. mhd simulations have shown that the planetary magnetic dipole moment µp = 0.61 of the jovian value, which produces the magnetic field equatorial surface value of 1 g, profoundly changes the character of the escaping planetary upper atmosphere. the total mass loss rate in this case is reduced by 2 times, as compared to the non-magnetized planet. in particular, we see the formation of the dead- and the wind- zones around the planet with the different character of plasma motion there. the 3d mhd modelling also confirmed the previous 2d mhd simulations result of khodachenko et al (2015) that the escaping pw forms a thin magnetodisk in the equatorial region around the planet. the significantly reduced velocity of pw at the low altitudes around the planet, and especially at the night side, results in the stronger photo-ionization of species and significantly lower densities of the corresponding absorbing elements. altogether, the reduced velocities and lower densities result in significant decrease of the absorption at lyα (hi), oi, and cii lines, though the absorption at hei(23s) line remains nearly the same.as it was shown in our previous papers, the dense and fast stellar wind, interacting with the escaping upper atmosphere of hd209458b, generates sufficient amount of energetic neutral atoms (enas) to produce significant absorption in the high-velocity blue wing of the lyα line. however, according to the performed 3d mhd modelling reported here, the planetary magnetic dipole field with the equatorial surface value of bp=1 g prevents the formation of enas, especially in the trailing tail. this effect opens a possibility to constrain the range of planetary magnetic field values for the evaporating hot jupiters and warm neptunes in the stellar-planetary systems where sufficiently strong sw is expected.the presented results fitted to the available measurements indicate that the magnetic field of hd209458b should be at least an order of magnitude less than that of the jupiter. this conclusion agrees with the previous estimates, based on more simplified models (e.g., kislyakova et al. 2014) and much less observational data, when only lyα absorption was considered. we believe that the application of 3d mhd models simulating the escape of upper atmospheres of hot exoplanets and the related transits at the available for measurement spectral lines, sensitive to the dynamics of planetary plasma affected by the mf, opens a way for probing and quantifying of exoplanetary magnetic fields and sheds more light on their nature.this work was supported by grant № 18-12-00080 of the russian science foundation and grant № 075-15-2020-780 of the russian ministry of education and science. khodachenko, m.l., shaikhislamov, i.f., lammer, h., et al., 2015, apj, 813, 50.shaikhislamov, i. f., khodachenko, m. l., lammer, h., et al., 2018, apj, 866(1), 47.shaikhislamov, i. f., khodachenko, m. l., lammer, et al., 2020, mnras, 491(3), 3435-3447 | magnetosphere of hot jupiter hd209458b and transit absorption in lines related to the upper atmosphere |
photo-evaporation of planetary atmospheres plays a key role in the evolution of exoplanets, carving their whole population. however, direct observations of atmospheric escape are scarce and almost non-existent in the mass range of super-earths and mini-neptunes, while these planets are among the most impacted by the phenomenon. a huge step forward could be made by achieving a comparative study of several super-earths, volatile-rich or not, in a single multi-planet system: such planets would indeed experience the same evolution of the stellar x and euv flux that are driving atmospheric escape. the perfect system for such a study has just been identified: the nearby, solar-type, and naked-eye star nu^2 lupi hosts transiting planets spanning a remarkably large range of insolation (~100 to ~5x the insolation of earth). tess found the transits of the two inner planets and cheops detected the transit of planet d, a volatile-rich super-earth with an exceptional period of 107 day. these super-earths straddle the radius gap of the "evaporation valley" and could have retained different fractions of gas and volatiles. like for previously observed warm neptunes, they could be enshrouded in huge comet-like exospheric clouds of escaping gas, which could have built up in the mild radiative environment. the system unique combination of proximity, brightness and favorable planet characteristics offers a fantastic opportunity to exploit hst ultraviolet capabilities to search for the hydrogen, oxygen and carbon escaping three planets in whole new mass and irradiation regimes. it is the ideal testbed for advancing both observations and theories of atmospheric evaporation of exoplanets. | a comparative study of atmospheric escape in the brightest system of super-earths straddling the evaporation valley |
au mic is an m1ve star in the β pic moving group and therefore has an age of 23 ± 3 myr. at 9.79 ± 0.04 pc, it is one of the closest pre-main sequence stars to earth. two exoplanets transiting au mic have been discovered using data from tess. au mic b orbits closer to its host, with a period of 8.46 days. it has a radius measurement of 4.20 earth radii, placing it on the edge of the hot neptune desert. we expect planets at this size (indicating a large gaseous envelope) and orbital period (highly irradiated) to be experiencing significant photoevaporation. this and its youth prompt the detailed study of au mic b's potentially escaping atmosphere. we obtained lyman-alpha transits of au mic b with hst/stis. we present a detailed analysis of the flares within these observations. the flare-removed lyman-alpha light curves do not exhibit any evidence of escaping neutral hydrogen. this supports theoretical work done by owen & murray-clay (2021) showing that some hot neptunes and sub-saturns will have their escaping envelopes photoionized too quickly to be observable in lyman-alpha. | au mic b, or not au mic b: the question of the young planet's escaping atmosphere |
the escape of hydrogen atoms to space from the upper atmosphere is an important process at mars, responsible for the depletion of much of the planet's initial water. most modern-day hydrogen loss at mars is considered to be via thermal (jeans) escape, in which some atoms in the high-energy tail of a collisional velocity distribution have sufficient energy to be removed. however, the relative importance of the escape of nonthermal or "hot" hydrogen, which is a higher-velocity population that has gained energy though chemical processes, is yet to be fully determined, as existing models generally predict less nonthermal escape than is inferred from h corona observations. here, we use a new monte carlo model, which tracks the trajectories of simulated hot particles through the upper atmosphere, to estimate nonthermal h escape magnitudes from more mechanisms than have previously been studied and identify the key production mechanisms. we present new escape probability profiles, showing that up to 82-91% of the hot h generated above the ionospheric peak escapes, and utilize them to compute initial escape estimates for 46 nonthermal h-producing mechanisms. our results show that hco+ dissociative recombination (hco+ + e- → co + h) and the exothermic photochemical reactions o+ + h2 → oh+ + h, co2+ + h2 → ocoh+ + h and oh+ + o → o2+ + h are among the most important processes producing escaping nonthermal h for both low and high solar activity conditions. cumulatively, we estimate that the escape flux from nonthermal mechanisms is ~10% of the thermal escape flux. hco+ dissociative recombination makes the largest contribution (up to 5.2%), and when modelled in detail, we find escape rates of 3.5-6.5% of the thermal hydrogen escape rate from this mechanism alone. hco+ dissociative recombination is therefore an important escape and planetary desiccation mechanism, which has not been considered before. it has likely also influenced venus' atmospheric evolution, where thermal escape is known to be negligible, and by extension, the evolution of co2-rich atmospheres of venus-sized exoplanets. | hco+ dissociative recombination and other significant drivers of nonthermal hydrogen loss at mars |
photoevaporating planetary winds have been proposed as important mechanism contributing to the evolution of the volatile inventory for close-in planets, potentially explaining the observed radius valley seen in the population of low-mass exoplanets at around r ~ 1.7rearth. molecules originating in a planets' lower atmosphere can be entrained in the escaping hydrogen wind and dissociated by energetic photons on their way to higher altitudes. this process results in outflows containing varying amounts of c and o atoms, in their neutral and ionized states. these minor species can contribute strongly to the total cooling capability in the outflow, and hence impact the mass loss rates significantly. in this work, i use a 1-d multi-species radiation hydrodynamics code in conjunction with photochemistry, in order to investigate the c/o-dependent mass loss-rates and thermal structure of outflows from those exoplanets. i will discuss impacts of the birth properties of exoplanets, parameterized by their atmospheric c/o and c/h values. furthermore i will investigate the evolution of exo-atmospheres under the uv-rich irradiation conditions of m and k dwarves. finally, those radius evolution scenarios will give rise to predictions of the observable transit radii of planets at a given age. incorporating constraints of c/o measurements from jwst as well as ground-based high-resolution spectroscopy will help test those predictions and understand the role of atomic cooling in planetary evolution. | the c/o ratio and its influence on hydrodynamic escape from super-earth exoplanets |
kepler observations revealed two striking features in the distribution of exoplanet radii: a dearth of short period sub-neptune-sized planets, and a relatively clean gap around 2 earth radii. atmospheric escape of planetary h/he envelopes driven by the high-energy x-ray and uv irradiation from the host star can explain the presence of the desert at short periods as well as the radius valley. the very young (~ 25 myr) v1298 tau system with its four neptune- to jupiter-sized planets is an excellent system to test planet formation and evolution models.to investigate the fate of the four planets, we obtained x-ray measurements of v1298 tau with chandra. we then calculated the future photoevaporative mass loss rates using platypos, an open-source tool to model the (energy-limited) atmospheric escape of planetary systems over several giga years. we allowed for the host star to spin down at three different ages, which translates into a low, intermediate, and high activity stellar evolutionary track. our findings show that in certain planetary mass and orbital distance regimes, the stellar high-energy evolution determines if a planet is stripped completely or can retain some fraction of its initial gaseous envelope. | estimating the atmospheric mass loss of v1298 tau's four young planets & the role of the host star in planet population studies |
the transition between rocky and volatile/gas-rich planets is one of the main open questions in exoplanetary research. population studies show that this transition is not smooth, but rocky super-earths and gas-rich mini-neptunes with masses within 7-15 earth masses should co-exist. atmospheric escape is surmised to control this transition, causing some planets to lose their atmospheres to space while others retain most of their volatiles and gas. the hd 3167 planetary system, hosting two transiting close-in planets, has been identified from k2 photometry in august 2016. through a large collaborative effort, we recently pinned down the planetary masses, revealing a duo of super-earths: one rocky planet (b) and one volatile/gas-rich 'mini-neptune' (planet c). thanks to its bright host star (v=8.9), this system is poised to become a benchmark target for studies of super-earth evolution and atmospheres. hd 3167c, in particular, is the mini-neptune transiting the brightest host star, providing a unique opportunity to access, for the first time, the atmospheric properties of this mysterious class of low-mass, low-density exoplanets. we propose 5 hst orbits to cover one transit of planet c and measure the stellar h i lyman-alpha emission line. we hope to detect a signature from an extended exosphere escaping the planet. this has never been observed for an exoplanet below 10 earth masses and would prove that exoplanets in this mass regime can host hydrogen envelopes. a negative result will allow us to assess the far- and extreme-uv environment of both exoplanets, which is critical for planning optimal follow-up strategies. | atmospheric escape from a mini-neptune |
ultraviolet transit observations probe the upper atmosphere of exoplanets, where mass loss occurs. our analysis of the archival hst/stis nuv transmission observations of hd 209458b shows evidence for ionized iron, but no evidence for neutral iron, neutral magnesium, nor ionized magnesium. while our non-detection of neutral magnesium resolves the tension with theoretical models from previous results, our results are at still odds with lower-atmosphere models resulting from optical and infrared observations. these upper-atmosphere observations indicate that hydrodynamic escape is strong enough to carry heavy atoms like iron beyond the planetary roche lobe; however, lower-atmosphere observations suggest the presence of cloud condensates. with iron-bearing aerosols condensating more strongly than magnesium-bearing aerosols, if magnesium is trapped in the lower atmosphere, iron should be as well. the intricate relationship between lower- and upper-atmosphere properties makes the combination uv and optical/infrared observations more valuable than the sum of its individual parts. the unique properties of the hd 209458 system place its transiting hot jupiter in a pivotal role in our understanding of planetary atmospheres, few other planets will ever enable such precise measurements of both their upper- and lower-atmosphere properties. here, i will present the analysis and theoretical interpretation of the hd 209458b nuv observations. then i will discuss the prospects of future observations to elucidate the puzzling nature of this planet's atmosphere as a whole, which is of particular value before the the imminent launch of the james webb space telescope. | revisiting the nuv transmission spectrum of hd 209458b: signs of ionized iron beyond the roche lobe |
the atmospheres of highly irradiated exoplanets are observed to undergo hydrodynamic escape, resulting in planetary mass loss. however, stellar winds can shape and even prevent atmospheric escape, affecting observable signatures of escape such as lyman-α and h-α line profiles. in this work, we simulate atmospheric escape of close-in exoplanets and investigate whether they are affected by stellar winds. we show that, although younger hot-jupiters experience higher levels of atmospheric escape, owing to a favourable combination of higher irradiation levels and weaker planetary gravity, stellar winds are also stronger at this young age, which act to reduce/inhibit escape rates of young exoplanets. | leaking exoplanets: understanding how stars affect atmospheric escape in exoplanets |
because of rare collisions, the motion of light species (h, h2) in the planetary exospheres is essentially determined by the external forces: the gravitation from the planet and the radiation pressure, ... currently, the only analytical model used to model exospheric neutral density profiles is the well-known chamberlain model which takes into account only the gravity. in this work and in the same way as chamberlain, we solve rigorously and analytically, based on the hamiltonian mechanics and liouville theorem, the additional effect of the radiation pressure in particular for hydrogen (the model works for any species sensitive to the radiation pressure) on the structure of the exosphere and on the density profiles of ballistic particles. this approach was initially developed by bishop and chamberlain (1989) only in the sun-planet direction. we extend it here to the whole exosphere with a 2d model. also, we determine analytically the escape flux on the dayside at sza=0, which can be compared with the jeans' escape flux. we thus show that the radiation pressure induces : 1. strong density asymmetries at high altitudes in the planetary exospheres, leading to the phenomenon of geotail at earth for example 2. the natural existence of an external limit (or exopause) for the exosphere, whose location is analytically determined 3. an increase of the exospheric densities compared with chamberlain profiles without radiation pressure (e.g. up to +150% at 5 martian radius) 4. a significant increase of the thermal escape flux (up to 30/35% for earth/mars today), until a «blow-off » regime with a constant escape flux for an extreme radiation pressure. the influence of the radiation pressure on the escape flux may thus bring conditions on the size of primary atmospheres, because of a strong radiation pressure in the sun's young years. finally, we show that this model may be applied to exoplanets, in particular to the hot jupiters that are also subject to additional effects: centrifugal force and stellar gravity. we show the influence of the radiation pressure on the equipotentials of the circular restricted three body problem. we also demonstrate that the hot jupiter hd 209458b is actually in a blow-off regime induced by the radiation pressure, which allows us to propose an alternative scenario for the evolution of its atmosphere. | analysis of the effect of the radiation pressure on planetary exospheres : application to earth, mars, titan and hot jupiters |
in recent years, nasa has prioritized the discovery and characterization of habitable exoplanets, including investigating which star-planet systems are conducive to habitable conditions. the escape small explorer mission, currently in phase a development, supports this goal by measuring the euv and fuv spectra of nearby stars and modeling their effects on planetary atmospheres. we have simulated escape spectra of sun-like and m dwarf stars, taking into account effects of the ism, airglow, order overlap, instrumental background, and photon noise. these models, projecting signal-to-noise ratio vs. wavelength, provide the expectations for escape's ability to measure the uv spectral irradiance of stars observed in two spectral surveys. we will present representative stellar spectra and signal-to-noise metrics in key euv and fuv lines for the escape baseline mission. | america's next top uv spectral model: building an snr calculator for the escape small explorer mission |
this work estimates the effect of the extreme ultraviolet (uv) radiation of the parent star on the production of the suprathermal fraction of atomic hydrogen in the h 2 → h transition region in the upper atmosphere of gj 436b. we also consider the formation of the escaping flux of h atoms created by this effect. we calculate the production rate and energy spectrum of the hydrogen atoms with excess kinetic energy during the dissociation of h 2 . using the numerical stochastic model for a hot planetary corona, we investigate the kinetics and transfer of suprathermal hydrogen atoms in the upper atmosphere and the emergent flux of atoms evaporating from the atmosphere. the latter is estimated as 4.0×10 11 cm -2 s -1 for a moderate stellar activity level of uv radiation, which leads to a planetary atmosphere evaporation rate of 2.5×10 8 g s -1 due to the process of the dissociation of h 2 . this estimate is close to the upper boundary of observational estimates in the range (3.7 × 10 6 - 1.1 × 10 9 ) g s -1 for the rate of atmospheric loss of gj 436b. | on non-thermal atmospheric loss for exoplanet gj 436b caused by the h 2 photodissociation input |
the habitability of exoplanets like earth around red dwarfs - a population of stars smaller than the sun, that are 70% of the stars in our galaxy - can be affected by large emissions of energy, called flares, produced by these stars. flares can heat the upper planetary atmosphere and drive the escape of water of these planets. to fully understand this process and how these high energy events could impact the water reservoir in planets like earth, we simulated several scenarios of this interaction using a code called \vplanet. with this, we saw that these events can remove 2 times the actual amount of water of the earth from these planets. | the contribution of m dwarf flares to the thermal escape of potentially habitable planet atmospheres |
the evaporating exoplanets (eve) code allows to model an escaping atmosphere on a transiting exoplanet in three dimensions. with eve we are then able to make predictions on the signatures caused by the absorbing atmosphere, in the observed transmitted stellar spectrum. a key ingredient in our model is the local synthetic stellar spectrum that we use to construct the total flux emitted by the star. the synthetic spectrum has to be as faithful as possible to the actual observed stellar spectrum. indeed, the knowledge of the local stellar spectrum allows to identify, at each instant of the transit, the actual part of the stellar flux that is hidden and absorbed by the planet. thus, giving the possibility to generate realistic absorption signatures comparable to observations. in this work we show how we model the local stellar spectrum for the helium triplet lines at 1083nm, directly based on the observed stellar flux. these chromospheric lines are of interest for transit observations, as helium is easily found at high altitudes in planetary atmosphere. additionally, the conditions for the formation of the metastable helium triplet are met around young stars which radiate higher levels of extreme uv flux. | building local stellar spectra from observations: the neutral helium chromospheric lines |
planets transiting m dwarfs offer our best opportunities to observe the atmospheres of potentially habitable planets outside the solar system. models predict that m dwarfs can significantly erode their planets' atmospheres, but no observations yet exist to investigate this atmospheric escape. gj1132b is a warm, rocky, earth-size planet transiting a star that is both very nearby (12pc) and very small (0.21 solar radii). here, we propose to use gj1132b as a laboratory to examine the process of hydrogen escape from terrestrial planets, a topic that is important for understanding the evolution of habitable worlds. we will use stis to observe two transits of gj1132b at lyman-alpha wavelengths, to measure the size of the neutral hydrogen cloud escaping from the planet. such a cloud might be fed by the dissociation of trace amounts of water or hydrogen halides in the planet's upper atmosphere. in a cycle 23 pilot study, we proved the star is bright enough at ly-alpha to serve as a backlight for these observations, and we tentatively detected a 40% flux decrement when the planet was in front the star. gj1132b is subject to less radiation pressure than the comet-tailed exoplanet gl436b; this allows neutral hydrogen to develop into an inflated coma and leading arm, with substantial absorption before and during the time of optical transits. these observations would provide the first constraints on atmospheric escape from an earth-size planet around an m dwarf, and they make use of hubble's precious uv capabilities to inform future jwst atmospheric observations of gj1132b and other rocky planets. | hydrogen escape from a rocky earth-size exoplanet |
atmospheric escape has first been detected through transit observations of massive hot jupiters like hd209458b and hd189733b. absorption signatures in the lyman-alpha line of their host stars have been attributed to comet-like tails of escaping neutral hydrogen, blown away by the stellar radiation pressure or stellar wind interactions. the recent detection of a giant exosphere surrounding the warm neptune gj 436 b has shed new light on the evaporation of close-in planets, revealing that moderately irradiated, low-mass exoplanets could make exceptional targets for studying this mechanism and its impact on exoplanets. in this talk, i will show the role played by stellar radiation pressure on the structure of gj436b exosphere and its transmission spectrum, highlighting its differences with the known evaporating hot jupiters. furthermore, while the three observations performed in the lyman-α line of gj 436 show repeatable transit variations, the spectra observed at each of epoch display specific features that require additional physics. i will present preliminary results as for the origin of this temporal variability. | evaporating atmospheres: from hot-jupiters to warm-neptunes |
the key role that hydrodynamic escape has on the mass loss of the planets and their evolution is well known. this is particularly important for close-in planets because the extreme stellar xuv irradiation they receive causes them to undergo hydrodynamic atmospheric escape. although the mass loss caused by this mechanism may not be high enough to significantly alter the state of hot jupiters, it strongly affects the evolution of lower-mass planets. for the latter, atmospheric escape drives and controls their evolution, shaping our currently observed exoplanet population. the whole process, from stellar irradiation to the planet, is not currently well understood, mainly because of the scarcity of appropriate observations. recently though, high-resolution absorption measurements of the metastable he i triplet state at 10830 å have become available. these have opened a new window to study the upper atmospheres of exoplanets. in particular, the carmenes high-resolution spectrograph at caha has provided in the last few years he i triplet absorption measurements of about ten diverse exoplanets. this talk will present those observations and a thorough analysis of them. in particular, we will show results about key parameters of those planets' upper atmospheres like their mass-loss rates, h/he abundances, and their diverse hydrodynamic escape regimes. the number of planets observed is already large enough that we can draw some general conclusions. | on the study of atmospheric escape of exoplanets using the new window of the he 10830 line |
recent data suggest that most of rocky exoplanets around active g-m planet hosts should be exposed to high ionizing radiation fluxes from stellar coronae, flares, magnetized winds and coronal mass ejections. this raises the question of the atmospheric plasma dynamics and subsequent plasma escape driven by the energy deposited via x-ray and extreme uv driven (xuv) photoionization. the atmospheric escape is one of the central issues to exoplanetary habitability, because the presence of a thick high molecular weight secondary atmosphere over sufficiently long timescales is a crucial factor associated with planetary surface pressure due to the exposure to stellar uv and particle irradiation. here, we extend our previous results of airapetian et al. (2017) by applying the exo-global ionosphere-thermosphere (exo-gitm) model of thermodynamics and atmospheric dynamics of an earth-like exoplanet controlled by the coronal xuv emission from trappist-1 and toi-700 rocky exoplanets. we show that at relatively low xuv energy deposition in the atmosphere (<60 times of the solar flux), the atmospheric escape is mostly driven by the ion escape, which is characteristic of conditions for a recently discovered rocky exoplanet toi-700d. our models suggest that the transition from the xuv driven ion escape to hydrodynamic atmospheric scape occurs at > 60 times of the xuv solar flux. we discuss the implications of the atmospheric escape due to xuv photoionization driven heating and joule heating rates for unmagnetized and a magnetized planet and habitability conditions for trappist b-h rocky exoplanets. | transition from xuv driven ion escape to hydrodynamic escape: implications for habitability of trappist1 b-h and toi-700d rocky exoplanets |
atmospheric escape is an important factor shaping the exoplanet population and hence drives our understanding of planet formation. atmospheric escape from giant planets is driven primarily by the stellar x-ray and extreme-ultraviolet (euv) radiation. euv and longer wavelength uv radiation also power disequilibrium chemistry in the middle and upper atmosphere of exoplanets. hence our knowledge of stellar uv fluxes play a vital role in the understanding of atmospheric escape and chemistry. while the far-ultraviolet fluxes can be observed for some stars, most of the euv range is unobservable due to the lack of a space telescope with euv capabilities and, for the more distant stars, to interstellar medium absorption. thus, it becomes essential to have indirect means for inferring euv fluxes from features observable at other wavelengths. we present here analytic functions for predicting the euv emission of f-, g-, k-, and m-type stars from the log r'hk activity parameter that is commonly obtained from ground-based optical observations of the caii h&k lines. the scaling relations are based on a collection of about 100 nearby stars with published log r'hk and euv flux values, where the latter are either direct measurements or inferences from high-quality far-ultraviolet (fuv) spectra. the scaling relations presented here return euv flux values with an accuracy of about three, which is slightly lower than that of other similar methods based on fuv or x-ray measurements.spheric escape is an important factor shaping the exoplanet population and hence drives our understanding of planet formation. atmospheric escape from giant planets is driven primarily by the stellar x-ray and extreme-ultraviolet (euv) radiation. euv and longer wavelength uv radiation also power disequilibrium chemistry in the middle and upper atmosphere of exoplanets. hence our knowledge of stellar uv fluxes play a vital role in the understanding of atmospheric escape and chemistry. while the far-ultraviolet fluxes can be observed for some stars, most of the euv range is unobservable due to the lack of a space telescope with euv capabilities and, for the more distant stars, to interstellar medium absorption. thus, it becomes essential to have indirect means for inferring euv fluxes from features observable at other wavelengths. we present here analytic functions for predicting the euv emission of f-, g-, k-, and m-type stars from the log r'hk activity parameter that is commonly obtained from ground-based optical observations of the caii h&k lines. the scaling relations are based on a collection of about 100 nearby stars with published log r'hk and euv flux values, where the latter are either direct measurements or inferences from high-quality far-ultraviolet (fuv) spectra. the scaling relations presented here return euv flux values with an accuracy of about three, which is slightly lower than that of other similar methods based on fuv or x-ray measurements. | stellar activity parameter as a proxy for stellar extreme ultraviolet fluxes |
multi-planet systems which display transit timing variations (ttvs) have produced one of the most surprising and impactful results of the kepler mission: the existence of very low-density "puffy" exoplanets. these planets are controversial, since their rate of atmospheric escape according to standard models means they should not exist. we propose to obtain high-quality hires spectra for four kepler ttv host stars as a means of testing this important result. building upon our previous work with kepler-11, we will measure the bulk densities of four other kepler stars which host very low-density planets using high-resolution, high signal-to-noise spectra. this independent measurement of stellar density will reveal any systematic biases that may be present in the ttv model. our results will not only improve the measured physical properties of key points in the exoplanet mass-radius diagram (and potential near-future jwst targets), but also make a necessary check on the ttv method itself. | precise stellar characterization as a critical test of ttv mass measurements |
this paper presents an analysis of the influence of the neutral atmosphere state on non-thermal processes in the upper atmosphere of the exoplanet π men c. namely, the contribution of exothermic photochemistry reactions to the formation of the suprathermal atomic hydrogen fraction in the h 2 →h transition region of the exoplanet's extended upper atmosphere provided by the aeronomic model [1] is considered. two different — weak and moderate, — values of the stellar wind [1] were concidered in the aeronomic model used. studies have been carried out at the molecular level of description of the kinetics and transport of hydrogen atoms formed with an kinetic energy excess using a numerical stochastic model of a hot planetary corona. the calculated non-thermal escape fluxes are 2.2×10 13 cm ‑2 s ‑1 for a weak stellar wind (sw) and 2.9 ×10 12 cm ‑2 s ‑1 in the case of a moderate level of stellar activity in uv radiation. the values of atmospheric loss rate averaged over the illuminated hemisphere are equal to 9.7 × 10 9 g s ‑1 for weak sw flux and 1.5 × 10 9 g s ‑1 for a moderate sw flux. | photochemical losses in the upper atmosphere of exoplanet π men c depending on the state of the neutral atmosphere |
we make use of the one-way coupled framework (linking our gcm, dsmc, and mhd models), known to accurately reproduce maven observations, for studying the atmospheric ion and photochemical escape rates and climate evolution over the history of mars. | modeling martian atmospheric losses over time: implications for (exo)planetary climate evolution and habitability |
atmospheric escape rate is a key parameter to measure in order to understand the evolution of exoplanets. in this presentation, we will show that the balmer series, observed with high-resolution transmission spectroscopy, is a precise probe to measure exoplanet evaporation, especially for ultra hot jupiters orbiting early-type star. these hot gaseous giant exoplanets (such as kelt-9 b) are presumed to have an atmosphere dominated by neutral and ionized atomic species. in particular, hydrogen balmer lines have been detected in some of their upper atmospheres, suggesting that hydrogen is filling the planetary roche lobe and escaping from these planets. here, we will present new significant absorptions of the balmer series in the kelt-9b atmosphere obtained with harps-n. the precise line shapes of the hα, hβ, and hγ absorptions allow us to put constraints on the thermospheric temperature. moreover, the mass loss rate, and the excited hydrogen population of kelt-9 b are also constrained, thanks to a retrieval analysis performed with a new atmospheric model (the pawn model). we retrieved a thermospheric temperature of t = 13 200+800-720 k and a mass loss rate of log10(mlr) = 10^(12.8+-0.3) g/s when the atmosphere was assumed to be in hydrodynamical expansion and in local thermodynamic equilibrium (lte). since the thermospheres of hot jupiters are not expected to be in lte, we explored atmospheric structures with non-boltzmann equilibrium for the population of the excited hydrogen. we do not find strong statistical evidence in favor of a departure from lte. however, our non-lte scenario suggests that a departure from the boltzmann equilibrium may not be sufficient to explain the retrieved low number densities of the excited hydrogen. in non-lte, saha equilibrium departure via photo-ionization, is also likely to be necessary to explain the data. | measuring and modeling the balmer series in hot gaseous giant exoplanets |
atmospheric escape from exoplanets is a topic of great interest for the exoplanet community since atmospheric retention is an important component of surface habitability. while atmospheric escape has been detected from large exoplanets, it remains difficult to measure for smaller (rocky) planets. indeed, for rocky planets orbiting active stars it is thought that it may be difficult for atmospheres to be retained at all. in the absence of detailed observations, one option is to leverage observations and models for planets in our own solar system.here we consider atmospheric escape from mars - if it orbited an m dwarf star similar to barnard's star. our analysis considers five escape processes: hydrodynamic escape, thermal escape, photochemical escape, ion escape, and sputtering. to estimate the escape rate via each process from our hypothetical "exomars", we employ models for escape that have either been validated using observations or verified against other models. we provide escape rate estimates for important species in the martian upper atmosphere: o, o2, h, and co2, and use them to estimate the lifetime of the martian atmosphere. | atmospheric lifetime from a hypothetical mars-sized planet orbiting barnard's star |
a vast amount--over 700 orbits--of hubble time has been dedicated to characterizing the high energy radiation from m dwarfs over their lifetimes; one key goal is to understand exoplanet environments. the smallest m dwarfs are very different from sun-like stars, with long pre-main sequence lifetimes and a higher fraction of their bolometric luminosity emitted at uv and x-ray wavelengths. of critical importance to the next era of exoplanet science is connecting what we have learned from this vast library of hst spectra to the physics of planets themselves. perhaps the highest impact observations in the first cycles of jwst will be the first measurements of planetary atmospheres around terrestrial planets, which are accessible only for planets orbiting the smallest stars. these atmospheres will be shaped by outgassing from the planet and atmospheric escape over billions of years. we propose a two-part effort: first, we will use archival hst uv spectra and x-ray data of 0.1-0.25 m_sun stars to model the high energy emission, creating reconstructed spectra of the currently-unobservable extreme ultraviolet (euv). next, we will use these reconstructed spectra as inputs to our atmospheric escape model for terrestrial planets, coupling the atmospheric escape driven by irradiation from the host star and the thermal emission of the planet, which controls outgassing rates. we will focus first on the atmospheres most amenable to jwst observations: warm venus-like planets with co2 atmospheres. we will digest the results of our models for observers, providing descriptions of which planets are most likely to have atmospheres and where new uv observations are most needed. | extending the legacy of hst observations of m dwarfs: coupled models of terrestrial planet thermal evolution and atmosphere loss |
the atmosphere of mars is co2 dominated at lower altitudes, below around 225-250km altitude. through multiple photochemistry paths, the dominant ion species is o2+. dissociative recombination of o2+ ions produces neutral o atoms which have sufficient energy to escape from the planet. the amount of oxygen lost over geological time periods due to this process is very large(several meters of equivalent water over the surface). in this talk we describe the results of an investigation of how photochemical loss of o from mars is altered when the n2 and no neutral densities are enhanced over current abundances. higher n2 and no density profiles lead to higher n2+ density, and more importantly, higher no+ density, and thus, lower o2+ density. but the dissociative recombination of no+ does not produce atomic o atoms that exceed the escape energy. additionally, higher abundances of n2 would lead to more neutral-neutral collisions between n2 and o, which would lead to energy loss of hot o atoms. thus, for a mars atmosphere (or a mars-like exoplanet) atmospheric loss could be inhibited with higher atmospheric n2 abundances. | the effect of nitrogen chemistry on photochemical escape of oxygen from mars |
one out of four terrestrial planet atmospheres accessible to jwst orbits a flaring m-dwarf. the x-ray light from these flares drives variability in planetary atmospheres, breaking apart molecules, causing atmospheric escape, and complicating interpretation of transit spectra. upcoming jwst observations of a rocky exoplanet orbiting the m-dwarf flare star ltt 1445a provide a unique opportunity to probe the effects of flares on the planet. these observations are part of the approved jwst cycle 1 large program 2512. ltt 1445 is a hierarchical triple system of mid to late m-dwarfs, with 2 terrestrial planets transiting the a component on 3.1 and 5.4 d periods. both components are confirmed flare stars, as new chandra observations spatially resolve a and bc, and observe frequent flares from each. chandra will detect ~1 flare in the sxr during the flare-affected period of jwst observations. we request the first simultaneous x-ray and nir observation of activity on a rocky planet atmosphere. | a chandra and jwst view of m-dwarf rocky planet atmospheres |
with r~150,000 resolving power and fast tip-tilt image stabilization, the extreme precision spectrometer at the 4.3m lowell discovery telescope is ideally suited for measuring line broadening in planetary gases (jurgenson et al. 2016; petersburg et al. 2020; brewer et al. 2020). here we present measurements sampling between 0 and 5 planetary radii along the cometlike tail of mercury's sodium and potassium exosphere. data were obtained surrounding maximum radiation pressure and at a 90° phase angle, where mercury's tail is oriented perpendicular to the line of sight. spectra show steadily broadening linewidths in both sodium and potassium with distance from the planet. effective temperature estimates are obtained by convolving a model of the doppler-broadened hyperfine structure with the instrumental line spread function. the result is a dramatic heating in sodium gas from ~1,200 k to nearly 10,000 k as the gas is sampled from 0 to 5 mercury radii downtail. potassium effective temperatures over this range show an even greater increase from ~700 k to 11,000 k. small-scale effective temperature variations are also seen on mercury's dayside with sodium at high latitudes being 100-200 k hotter than gas at the sub-solar point. we theorize that this heating results from the recoil of photon momenta as light is re-emitted from the excited atoms. photon re-emission is nearly isotropic in alkali d line transitions, and while direction vectors cancel on average, recoil events could still heat the gas by imparting a momentum of ℎ/ onto each atom at a variable resonance scattering rate. due to radiation pressure, resonance scattering rates increase down-tail since the incident sunlight available to excite the gases doppler shifts from the fraunhofer absorption wells into the solar continuum. as atoms move down-tail with mercury in the outbound portion of its orbit, there is positive feedback in the scattering rate and each photon scatter imparts its momentum, steadily heating the population in a random-walk. the observed difference between sodium and potassium heating supports this theory: heating would scale with radiation pressure, which is nearly 50% higher in potassium. observations have not yet been made at the inbound leg of mercury's orbit where negative feedback occurs, however, and numerical modelling is needed to test this hypothesis. this heating mechanism is previously unconsidered in dynamical models of escaping planetary atmospheres. the finding has broad implications to collisionless gas dynamics and is relevant to studies of the lunar exosphere, cometary comae and exoplanetary transit spectra. | measurement of heating in mercury's alkali exotail |
one of the biggest aims in exoplanet science is to understand how planets and their atmospheres evolve. among the several challenges faced while inching towards this goal is the severe lack of observational constraints on the high-energy environments of young exoplanets and their early history of atmospheric escape. in particular, we do not know how well neptune-sized and smaller planets can survive atmospheric erosion during the first billion years and retain their primary atmospheres. in this context, the recently discovered planet ds tuc a b (45 myr) is the best target to study atmospheric escape in the first 100 myr in the life of a neptune-sized exoplanet, and is likely going to become a testbed to investigate the primordial chemistry of exoplanetary atmospheres with jwst. a previous transit observation with hst suggest that this planet is currently undergoing intense hydrodynamic escape, but the result is ambiguous due to insufficient phase coverage and potential stellar activity contamination. in this program, we aim to observe two more transits, which are necessary to confirm that the feature is not spurious and to study the shape of the planet's exosphere. either a detection or a non-detection will be crucial to interpret the evolution of exoplanetary atmospheres of this young planet and other similar worlds. | resolving the dichotomy of atmospheric escape in the young planet ds tuc a b |
hydrogen escapes to space and iron sinks to the core, leaving oxygen in the middle. does this ever lead to o2 atmospheres? yes, if conditions are right! | a generalized approach to rocky planet oxidation via gravitational differentiation: implications for exoplanets and the solar system |
atmospheric escape from exoplanets is a topic of great interest for the exoplanet community since atmospheric retention is an important component of surface habitability. while atmospheric escape has been detected from large exoplanets, it remains difficult to measure for smaller (rocky) planets. indeed, for rocky planets orbiting active stars it is thought that it may be difficult for atmospheres to be retained at all. in the absence of detailed observations, one option is to leverage observations and models for planets in our own solar system. here we consider atmospheric escape from mars – if it orbited an m dwarf star similar to barnard's star. our analysis considers five escape processes: hydrodynamic escape, thermal escape, photochemical escape, ion escape, and sputtering. to estimate the escape rate via each process from our hypothetical "exomars", we employ models for escape that have either been validated using observations or verified against other models. we provide escape rate estimates for important species in the martian upper atmosphere: o, o2, h, and co2, and use them to estimate the lifetime of the martian atmosphere. | atmospheric lifetime for a hypothetical mars-sized planet orbiting barnard's star |
atmospheric escape from exoplanets is a topic of great interest for the exoplanet community since atmospheric retention is an important component of surface habitability. while atmospheric escape has been detected from large exoplanets, it remains difficult to measure for smaller (rocky) planets. indeed, for rocky planets orbiting active stars it is thought that it may be difficult for atmospheres to be retained at all. in the absence of detailed observations, one option is to leverage observations and models for planets in our own solar system. here we consider atmospheric escape from mars if it orbited an m dwarf star similar to barnards star. our analysis considers five escape processes: hydrodynamic escape, thermal escape, photochemical escape, ion escape, and sputtering. to estimate the escape rate via each process from our hypothetical exomars, we use a combination of scaling laws derived from spacecraft observations of escape from present day mars, and models for escape that have been validated using observations. we provide escape rate estimates for important species in the martian upper atmosphere: o, o2, h, and co2, and use them to estimate the lifetime of the martian atmosphere. | atmospheric escape rates from mars if it orbited an m dwarf star |
hst is the only facility capable of probing the uppermost planetary layers in the ultraviolet, which is key to understanding and modeling the vigorous atmospheric mass-loss seen in highly irradiated exoplanets. recent hst nuv observations of an ultra hot jupiter (uhj) have definitively shown that ionized heavy elements including iron and magnesium are driven by atmospheric escape beyond the roche lobe. these observations indicate the gas is not gravitationally bound to the planet, resulting in enormous signals when seen in transit. these ionized species may be hydrodynamically escaping or could be magnetically confined to the planet. here we propose to observe escaping ions from the atmospheres of two ultra-hot jupiters orbiting two of the most uv-bright exoplanet host stars. by observing in the nuv, we can compare the escape rates of heavy elements, measure the velocity profiles, and determine the extent to which the roche lobe is filled of several uhjs orbiting different spectral type host stars, thus testing mass-loss mechanisms across differing xuv irradiation levels. we will also search for asymmetries in the nuv transit light curves, which will constrain post-cometary evaporation tails and magnetically controlled outflow. | heavy metal bands: a study of ions escaping from the hottest jovian atmospheres |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.