  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.
