Planets around young stars trace the early evolution of planetary
systems. We report the discovery and validation of two planetary systems
with ages 300 Myr from observations by the Transiting Exoplanet Survey Satellite (TESS). The Myr old G star TOI-251 hosts a mini-Neptune with a day period. The Myr old K star TOI-942 hosts a system of inflated Neptune-sized planets, with TOI-942b orbiting in a period of days with a radius of and TOI-942c orbiting in a period of days with a radius of .
Though we cannot place either host star into a known stellar
association or cluster, we can estimate their ages via their photometric
and spectroscopic properties. Both stars exhibit significant
photometric variability due to spot modulation, with measured rotation
periods of ~3.5 days. These stars also exhibit significant chromospheric
activity, with age estimates from the chromospheric calcium emission
lines and X-ray fluxes matching that estimated from gyrochronology. Both
stars also exhibit significant lithium absorption, similar in
equivalent width to well-characterized young cluster members. TESS has
the potential to deliver a population of young planet-bearing field
stars, contributing significantly to tracing the properties of planets
as a function of their age.