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. TOI-251 is a 40-320 Myr old G star hosting a 2.74 +0.18/-0.18 REarth mini-Neptune with a 4.94 day period. TOI-942 is a 20-160 Myr old K star hosting a system of inflated Neptune-sized planets, with TOI-942b orbiting with a period of 4.32 days, with a radius of 4.81 +0.20/-0.20 REarth, and TOI-942c orbiting in a period of 10.16 days with a radius of 5.79 +0.19/-0.18 REarth. 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.
@article{arxiv.2011.13349,
title = {Two young planetary systems around field stars with ages between 20-320 Myr from TESS},
author = {George Zhou and Samuel N. Quinn and Jonathan Irwin and Chelsea X. Huang and Karen A. Collins and Luke G. Bouma and Lamisha Khan and Anaka Landrigan and Andrew M. Vanderburg and Joseph E. Rodriguez and David W. Latham and Guillermo Torres and Stephanie T. Douglas and Allyson Bieryla and Gilbert A. Esquerdo and Perry Berlind and Michael L. Calkins and Lars A. Buchhave and David Charbonneau and Kevin I. Collins and John F. Kielkopf and Eric L. N. Jensen and Thiam-Guan Tan and Rhodes Hart and Brad Carter and Christopher Stockdale and Carl Ziegler and Nicholas Law and Andrew W. Mann and Steve B. Howell and Rachel A. Matson and Nicholas J. Scott and Elise Furlan and Russel J. White and Coel Hellier and David R. Anderson and Richard G. West and George Ricker and Roland Vanderspek and Sara Seager and Jon M. Jenkins and Joshua N. Winn and Ismael Mireles and Pamela Rowden and Daniel A. Yahalomi and Bill Wohler and Clara. E. Brasseur and Tansu Daylan and Knicole D. Coloń},
journal= {arXiv preprint arXiv:2011.13349},
year = {2020}
}