TESS delivers its first Earth-sized planet and a warm sub-Neptune

Abstract

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${}_{-0.16}^{+0.17}$ $R_{\oplus }$, and combined archival and follow-up precision radial velocity data put the mass of the planet at $22.7_{-1.9}^{+2.2}$ $M_{\oplus }$. 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 ($R_p=0.892_{-0.058}^{+0.064}{R}_{\oplus }$) planet from TESS. The HD21749 system is a prime target for comparative studies of planetary composition and architecture in multi-planet systems.

Published in ApJ Letters; 5 figures, 1 table

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