The First Habitable-zone Earth-sized Planet from TESS. II. Spitzer Confirms TOI-700 d

Abstract

© 2020. The American Astronomical Society. All rights reserved. We present Spitzer 4.5 μm 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 1.144-0.061+0.062R⊕ and orbits within its host star's conservative habitable zone with a period of 37.42 days (T eq ∼ 269 K). TOI-700 also hosts two small inner planets (R b = 1.037-0.064+0.065R⊕and R c = 2.65-0.15+0.16R⊕) with periods of 9.98 and 16.05 days, respectively. Our Spitzer observations confirm the Transiting Exoplanet Survey Satellite (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 (RV) instruments (expected RV semiamplitude of ∼70 cm s-1).