text: 194,28,895272749438054400,65010804,Hugh Osborn,"Tau Ceti is one of the closest sunlike stars. A new paper today suggests four super-Earth #exoplanets may orbit it: <LINK> <LINK> Of course, a paper in 2012 announced 5 planets... most of which turned out not to exist. Two (e & f) have survived this new analyses though. The team remove lots of noise to reveal the planetary signals which would, if confirmed, be the lowest-amplitude detections ever with RVs. <LINK> They also find the planets on orbits far more eccentric than should be possible/expected in a stable solar system. All in all: super interesting work! It's suggestive that Tau Ceti has planets, especially the long-period ones far from stellar rotation. BUT I think more data & analyses is needed before we can call them bona fide, confirmed planets (as the spurious 2012 detections showed).",https://arxiv.org/abs/1708.02051,"The removal of noise typically correlated in time and wavelength is one of the main challenges for using the radial velocity method to detect Earth analogues. We analyze radial velocity data of tau Ceti and find robust evidence for wavelength dependent noise. We find this noise can be modeled by a combination of moving average models and ""differential radial velocities"". We apply this noise model to various radial velocity data sets for tau Ceti, and find four periodic signals at 20.0, 49.3, 160 and 642 d which we interpret as planets. We identify two new signals with orbital periods of 20.0 and 49.3 d while the other two previously suspected signals around 160 and 600 d are quantified to a higher precision. The 20.0 d candidate is independently detected in KECK data. All planets detected in this work have minimum masses less than 4$M_\oplus$ with the two long period ones located around the inner and outer edges of the habitable zone, respectively. We find that the instrumental noise gives rise to a precision limit of the HARPS around 0.2 m/s. We also find correlation between the HARPS data and the central moments of the spectral line profile at around 0.5 m/s level, although these central moments may contain both noise and signals. The signals detected in this work have semi-amplitudes as low as 0.3 m/s, demonstrating the ability of the radial velocity technique to detect relatively weak signals. ","Color difference makes a difference: four planet candidates around tau