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NASA’s return to the Moon coincides with explosive growth in exoplanet discovery. Missions are being formulated to search for habitable planets orbiting other stars, making this the ideal time to deploy an instrument suite to the lunar surface to help us recognize a habitable exoplanet when we see it. We present EarthShine, a technically mature, three-instrument suite to observe the whole Earth from the Moon as an exoplanet proxy. Earth Shine data will validate and improve models critical for designing missions to image and characterize exoplanets, thus informing observing strategies for flagship missions to directly image exoplanets. EarthShine will answer interconnected questions in Earth and lunar science, exoplanets, and astrobiology, related to the credo“ follow the water.” Earth Shine can take advantage of current NASA programs to conduct science from the Moon with low-cost, mature space hardware to reduce risk and assure success. Like the 1968 Apollo Earthrise image of our home planet, lonely in the black sky, the appeal of Earth Shine to a multidisciplinary array of researchers in Earth Science, Planetary Science, and astrophysics will maximize both its scientific impact and its impact on the general public.

We report the first discovery of a transiting circumbinary planet detected from a single sector of Transiting Exoplanet Survey Satellite (TESS) data. During Sector 21, the planet TIC 172900988b transited the primary star and then five days later it transited the secondary star. The binary is itself eclipsing, with a period P ≈ 19.7 days and an eccentricity e ≈ 0.45. Archival data from ASAS-SN, Evryscope, KELT, and SuperWASP reveal a prominent apsidal motion of the binary orbit, caused by the dynamical interactions between the binary and the planet. A comprehensive photodynamical analysis of the TESS, archival and follow-up data yields stellar masses and radii of M(1) = 1.2384 ± 0.0007 Mꙩ and R(1) = 1.3827 ± 0.0016 Rꙩ for the primary and M(2) = 1.2019 ± 0.0007 Mꙩ and R(2) = 1.3124 ± 0.0012 Rꙩ for the secondary. The radius of the planet is R(3) = 11.25 ± 0.44 Rꚛ (1.004 ± 0.039R(Jup)). The planet’s mass and orbital properties are not uniquely determined—there are six solutions with nearly equal likelihood. Specifically, we find that the planet’s mass is in the range of 824 ≲ M3 ≲ 981 Mꚛ (2.65 ≲ M3 ≲ 3.09M(Jup)), its orbital period could be 188.8, 190.4, 194.0, 199.0, 200.4, or 204.1 days, and the eccentricity is between 0.02 and 0.09. At V = 10.141 mag, the system is accessible for high-resolution spectroscopic observations, e.g., the Rossiter–McLaughlin effect and transit spectroscopy.

Much of the science from the exoplanets detected by the TESS mission relies on precisely predicted transit times that are needed for many follow-up characterization studies. We investigate the severity of ephemeris deterioration for simulated TESS planets and find that the ephemerides of 81% of those will have expired (i.e. mid-transit time uncertainties greater than 30 minutes, impeding the efficient scheduling of follow-up observations) one year after their TESS observations. This rapid deterioration is driven primarily by the relatively short time baseline of TESS observations. In particular, of the simulated planets that would be recommended as potential James Webb Space Telescope targets by Kempton et al. (2018), 80% will have 1 mid-transit time uncertainties greater than 30 minutes by the earliest time JWST would observe them. The recently-approved extension to the TESS mission means that the ephemerides of most (though not all) primary mission planets will eventually be rescued, but the benefits of these new observations can only be reaped two years after the primary mission observations. Moreover, even with the advent of the TESS mission extension, the ephemerides of most primary mission TESS planets (as well as those newly discovered during the extended mission) will again have expired by the time future facilities such as the ELTs, Ariel and the possible LUVOIR/OST missions come online. We identify categories of TESS planets for which the ephemeris deterioration is most severe, and provide strategies for maintaining their ephemerides fresh through additional follow- up transit observations. We find that the longer the baseline between the TESS and the follow-up observations, the longer the ephemerides stay fresh, and that 51% of simulated primary mission TESS planets will require space-based observations to refresh their ephemerides.

We report the first discovery of a thick-disk planet, LHS 1815b (TOI-704b, TIC 260004324), detected in the Transiting Exoplanet Survey Satellite (TESS) survey. LHS 1815b transits a bright (V = 12.19 mag, K = 7.99 mag) and quiet M dwarf located 29.87 ± 0.02 pc away with a mass of 0.502 ± 0.015 M⊙ and a radius of 0.501 ± 0.030 R⊙. We validate the planet by combining space- and ground-based photometry, spectroscopy, and imaging. The planet has a radius of 1.088 ± 0.064 R⊕ with a 3σ mass upper limit of 8.7 M⊕. We analyze the galactic kinematics and orbit of the host star LHS 1815 and find that it has a large probability (Pthick/Pthin = 6482) to be in the thick disk with a much higher expected maximal height (Zmax = 1.8 kpc) above the Galactic plane compared with other TESS planet host stars. Future studies of the interior structure and atmospheric properties of planets in such systems using, for example, the upcoming James Webb Space Telescope, can investigate the differences in formation efficiency and evolution for planetary systems between different Galactic components (thick disks, thin disks, and halo).

Planets occur most frequently around cool dwarfs, but only a handful of specific examples are known to orbit the latest-type M stars. Using TESS photometry, we report the discovery of two planets transiting the low-mass star called LP 791-18 (identified by TESS as TOI 736). This star has spectral type M6V, effective temperature 2960 K, and radius 0.17 Rꙩ, making it the third-coolest star known to host planets. The two planets straddle the radius gap seen for smaller exoplanets; they include a 1.1Rꚛ planet on a 0.95 day orbit and a 2.3Rꚛ planet on a 5 day orbit. Because the host star is small the decrease in light during these planets' transits is fairly large (0.4% and 1.7%). This has allowed us to detect both planets' transits from ground-based photometry, refining their radii and orbital ephemerides. In the future, radial velocity observations and transmission spectroscopy can both probe these planets' bulk interior and atmospheric compositions, and additional photometric monitoring would be sensitive to even smaller transiting planets.

We describe an algorithm which fits model planetary system parameters to light curves from Kepler Mission target stars. The algorithm begins by producing an initial model of the system which is used to seed the fit,with particular emphasis on obtaining good transit timing parameters. An attempt is then made to determine whether the observed transits are more likely due to a planet or an eclipsing binary. In the event that the transits are consistent with a transiting planet, an iterative fitting process is initiated: a wavelet-based whitening filter is used to eliminate stellar variations on timescales long compared to a transit; a robust nonlinear fitter operating on the whitened light curve produces a new model of the system; and the procedure iterates until convergence upon a self-consistent whitening filter and planet model. The fitted transits are removed from the light curve anda search for additional planet candidates is performed upon the residual light curve. The fitted models are used in additional tests which identify false positive planet detections: multiple planet candidates with near-identical fitted periods are far more likely to be an eclipsing binary, for example, while target stars in which the model lightcurve is correlated with the star centroid position may indicate a background eclipsing binary, and subtraction of all model planet candidates yields a light curve of pure noise and stellar variability, which can be used to study the probability that the planet candidates result from statistical fluctuations in the data.