text: 379,44,1452818407334817796,750009830786605057,"Michele L. Silverstein, Ph.D. (she/her/hers)","New paper! The LHS 1678 exoplanet system includes an M dwarf in the Gaia/Jao Gap, 2 confirmed small planets discovered by TESS (1 ultra-short period & 1 Venus-zone), a sneaky brown dwarf w/ a decades-long orbit, and a candidate 3rd planet in 4:3 resonance! <LINK> One of the coolest things about this system, in my opinion, is that in the past, the star likely expanded & contracted over billions of years. We know this bc of its association with a gap in the HR diagram. We don't know how this affected the how the planets' formed or evolved! LHS 1678 is arguably the only TESS planet host so far clearly in the gap. Until our LHS 1678 paper, no one had published a paper raising the issue of how this relates to exoplanets (to my knowledge). For reference, here's the Gaia/Jao gap discovery paper <LINK> I don't use twitter a whole lot, and it's late here. So I will stop here for now. But I think every member of this system is exciting for a different reason, and I hope you will feel compelled to look at the paper and see so for yourself. :)",https://arxiv.org/abs/2110.12079,"We present the TESS discovery of the LHS 1678 (TOI-696) exoplanet system, comprised of two approximately Earth-sized transiting planets and a likely astrometric brown dwarf orbiting a bright ($V_J$=12.5, $K_s$=8.3) M2 dwarf at 19.9 pc. The two TESS-detected planets are of radius 0.70$\pm$0.04 $R_\oplus$ and 0.98$\pm$0.06 $R_\oplus$ in 0.86-day and 3.69-day orbits, respectively. Both planets are validated and characterized via ground-based follow-up observations. HARPS RV monitoring yields 97.7 percentile mass upper limits of 0.35 $M_\oplus$ and 1.4 $M_\oplus$ for planets b and c, respectively. The astrometric companion detected by the CTIO/SMARTS 0.9m has an orbital period on the order of decades and is undetected by other means. Additional ground-based observations constrain the companion to being a high-mass brown dwarf or smaller. Each planet is of unique interest; the inner planet has an ultra-short period, and the outer planet is in the Venus zone. Both are promising targets for atmospheric characterization with the JWST and mass measurements via extreme-precision radial velocity. A third planet candidate of radius 0.9$\pm$0.1 $R_\oplus$ in a 4.97-day orbit is also identified in multi-Cycle TESS data for validation in future work. The host star is associated with an observed gap in the lower main sequence of the Hertzsprung-Russell diagram. This gap is tied to the transition from partially- to fully-convective interiors in M dwarfs, and the effect of the associated stellar astrophysics on exoplanet evolution is currently unknown. The culmination of these system properties makes LHS 1678 a unique, compelling playground for comparative exoplanet science and understanding the formation and evolution of small, short-period exoplanets orbiting low-mass stars. ","The LHS 1678 System: Two Earth-Sized Transiting Planets and an