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Register a new userThe First Habitable Zone Earth-sized Planet from TESS. I: Validation of the TOI-700 System
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We present the discovery and validation of a three-planet system orbiting the nearby (31.1 pc) M2 dwarf star TOI-700 (TIC 150428135). TOI-700 lies in the TESS continuous viewing zone in the Southern Ecliptic Hemisphere; observations spanning 11 sectors reveal three planets with radii ranging from 1 R$_oplus$ to 2.6 R$_oplus$ and orbital periods ranging from 9.98 to 37.43 days. Ground-based follow-up combined with diagnostic vetting and validation tests enable us to rule out common astrophysical false-positive scenarios and validate the system of planets. The outermost planet, TOI-700 d, has a radius of $1.19pm0.11$ R$_oplus$ and resides in the conservative habitable zone of its host star, where it receives a flux from its star that is approximately 86% of the Earths insolation. In contrast to some other low-mass stars that host Earth-sized planets in their habitable zones, TOI-700 exhibits low levels of stellar activity, presenting a valuable opportunity to study potentially-rocky planets over a wide range of conditions affecting atmospheric escape. While atmospheric characterization of TOI-700 d with the James Webb Space Telescope (JWST) will be challenging, the larger sub-Neptune, TOI-700 c (R = 2.63 R$_oplus$), will be an excellent target for JWST and beyond. TESS is scheduled to return to the Southern Hemisphere and observe TOI-700 for an additional 11 sectors in its extended mission, which should provide further constraints on the known planet parameters and searches for additional planets and transit timing variations in the system.
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We present $Spitzer$ 4.5$mu$m observations of the transit of TOI-700 d, a habitable zone Earth-sized planet in a multiplanet system transiting a nearby M-dwarf star (TIC 150428135, 2MASS J06282325-6534456). TOI-700 d has a radius of $1.144^{+0.062}_{-0.061}R_oplus$ and orbits within its host stars conservative habitable zone with a period of 37.42 days ($T_mathrm{eq} sim 269$K). TOI-700 also hosts two small inner planets (R$_b$=$1.037^{+0.065}_{-0.064}R_oplus$ & R$_c$=$2.65^{+0.16}_{-0.15}R_oplus$) with periods of 9.98 and 16.05 days, respectively. Our $Spitzer$ observations confirm the TESS detection of TOI-700 d and remove any remaining doubt that it is a genuine planet. We analyze the $Spitzer$ light curve combined with the 11 sectors of TESS observations and a transit of TOI-700 c from the LCOGT network to determine the full system parameters. Although studying the atmosphere of TOI-700 d is not likely feasible with upcoming facilities, it may be possible to measure the mass of TOI-700 d using state-of-the-art radial velocity instruments (expected RV semi-amplitude of $sim$70 cm/s).
We report the discovery of an Earth-sized planet in the habitable zone of a low-mass star called Kepler-1649. The planet, Kepler-1649 c, is 1.06$^{+0.15}_{-0.10}$ times the size of Earth and transits its 0.1977 +/- 0.0051 Msun mid M-dwarf host star every 19.5 days. It receives 74 +/- 3 % the incident flux of Earth, giving it an equilibrium temperature of 234 +/- 20K and placing it firmly inside the circumstellar habitable zone. Kepler-1649 also hosts a previously-known inner planet that orbits every 8.7 days and is roughly equivalent to Venus in size and incident flux. Kepler-1649 c was originally classified as a false positive by the Kepler pipeline, but was rescued as part of a systematic visual inspection of all automatically dispositioned Kepler false positives. This discovery highlights the value of human inspection of planet candidates even as automated techniques improve, and hints that terrestrial planets around mid to late M-dwarfs may be more common than those around more massive stars.
We report the detection of the first circumbinary planet found by TESS. The target, a known eclipsing binary, was observed in sectors 1 through 12 at 30-minute cadence and in sectors 4 through 12 at two-minute cadence. It consists of two stars with masses of 1.1 MSun and 0.3 MSun on a slightly eccentric (0.16), 14.6-day orbit, producing prominent primary eclipses and shallow secondary eclipses. The planet has a radius of ~6.9 REarth and was observed to make three transits across the primary star of roughly equal depths (~0.2%) but different durations -- a common signature of transiting circumbinary planets. Its orbit is nearly circular (e ~ 0.09) with an orbital period of 95.2 days. The orbital planes of the binary and the planet are aligned to within ~1 degree. To obtain a complete solution for the system, we combined the TESS photometry with existing ground-based radial-velocity observations in a numerical photometric-dynamical model. The system demonstrates the discovery potential of TESS for circumbinary planets, and provides further understanding of the formation and evolution of planets orbiting close binary stars.
The future of exoplanet science is bright, as TESS once again demonstrates with the discovery of its longest-period confirmed planet to date. We hereby present HD 21749b (TOI 186.01), a sub-Neptune in a 36-day orbit around a bright (V = 8.1) nearby (16 pc) K4.5 dwarf. TESS measures HD21749b to be 2.61$^{+0.17}_{-0.16}$ $R_{oplus}$, and combined archival and follow-up precision radial velocity data put the mass of the planet at $22.7^{+2.2}_{-1.9}$ $M_{oplus}$. HD 21749b contributes to the TESS Level 1 Science Requirement of providing 50 transiting planets smaller than 4 $R_{oplus}$ with measured masses. Furthermore, we report the discovery of HD 21749c (TOI 186.02), the first Earth-sized ($R_p = 0.892^{+0.064}_{-0.058} R_{oplus}$) planet from TESS. The HD21749 system is a prime target for comparative studies of planetary composition and architecture in multi-planet systems.
The bright star 55 Cancri is known to host five planets, including a transiting super-Earth. We use the CHARA Array to directly determine the following of 55 Cncs stellar astrophysical parameters: $R=0.943 pm 0.010 R_{odot}$, $T_{rm EFF} = 5196 pm 24$ K. Planet 55 Cnc f ($M sin i = 0.155 M_{Jupiter}$) spends the majority of the duration of its elliptical orbit in the circumstellar habitable zone (0.67--1.32 AU) where, with moderate greenhouse heating, it could harbor liquid water. Our determination of 55 Cancris stellar radius allows for a model-independent calculation of the physical diameter of the transiting super-Earth 55 Cnc e ($simeq 2.1 R_{earth}$), which, depending on the assumed literature value of planetary mass, implies a bulk density of 0.76 $rho_{earth}$ or 1.07 $rho_{earth}$.
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