TESS Hunt for Young and Maturing Exoplanets (THYME) IV: Three small planets orbiting a 120 Myr-old star in the Pisces--Eridanus stream

TL;DR

This paper reports the discovery and validation of three small planets orbiting a 120-million-year-old star in the Pisces--Eridanus stream, providing valuable targets for studying early planetary atmosphere evolution.

Contribution

It presents the first confirmed multi-planet system around a young star in the Psc--Eri stream, with detailed characterization and validation of the planets.

Findings

Three validated planets with periods of 1.9, 9.2, and 16 days.

Planets have radii of 1.9, 3.1, and 4.1 Earth radii.

Host star shows infrared excess indicating a debris disk.

Abstract

Young exoplanets can offer insight into the evolution of planetary atmospheres, compositions, and architectures. We present the discovery of the young planetary system TOI 451 (TIC 257605131, Gaia DR2 4844691297067063424). TOI 451 is a member of the 120-Myr-old Pisces--Eridanus stream (Psc--Eri). We confirm membership in the stream with its kinematics, its lithium abundance, and the rotation and UV excesses of both TOI 451 and its wide binary companion, TOI 451 B (itself likely an M dwarf binary). We identified three candidate planets transiting in the TESS data and followed up the signals with photometry from Spitzer and ground-based telescopes. The system comprises three validated planets at periods of 1.9, 9.2 and 16 days, with radii of 1.9, 3.1, and 4.1 Earth radii, respectively. The host star is near-solar mass with V=11.0 and H=9.3 and displays an infrared excess indicative of a debris disk. The planets offer excellent prospects for transmission spectroscopy with HST and JWST, providing the opportunity to study planetary atmospheres that may still be in the process of evolving.