TESS Delivers Its First Earth-sized Planet and a Warm Sub-Neptune*

The future of exoplanet science is bright, as Transiting Exoplanet Survey Satellite (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 HD 21749b to be 2.61(-0.16)(+0.17)R(circle plus), and combined archival and follow-up precision radial velocity data put the mass of the planet at 22.7(-1.9)(+2.2)M(circle plus). HD 21749b contributes to the TESS Level 1 Science Requirement of providing 50 transiting planets smaller than 4 R-circle plus with measured masses. Furthermore, we report the discovery of HD 21749c (TOI 186.02), the first Earth-sized (R-p = 0.8921(-0.058)(+0.064)R(circle plus)) planet from TESS. The HD 21749 system is a prime target for comparative studies of planetary composition and architecture in multi-planet systems.