Discovery of a hot, transiting, Earth-sized planet and a second temperate, non-transiting planet around the M4 dwarf GJ 3473 (TOI-488)

TL;DR

This paper reports the discovery and detailed characterization of an Earth-sized transiting planet and a second temperate, non-transiting planet around the M4 dwarf star GJ 3473, using TESS data and extensive follow-up observations.

Contribution

It provides the first precise mass and radius measurements of GJ 3473 b and reports a second non-transiting planet, enhancing understanding of such planetary systems around M dwarfs.

Findings

GJ 3473 b is a hot Earth-sized planet with a well-measured mass and radius.

A second temperate, non-transiting planet GJ 3473 c was discovered with a minimum mass and orbital period.

GJ 3473 b is among the hottest transiting Earth-sized planets known, suitable for thermal emission studies.

Abstract

We present the confirmation and characterisation of GJ 3473 b (G 50--16, TOI-488.01), a hot Earth-sized planet orbiting an M4 dwarf star, whose transiting signal ($P=1.1980035\pm0.0000018\mathrm{\,d}$) was first detected by the Transiting Exoplanet Survey Satellite (TESS). Through a joint modelling of follow-up radial velocity observations with CARMENES, IRD, and HARPS together with extensive ground-based photometric follow-up observations with LCOGT, MuSCAT, and MuSCAT2, we determined a precise planetary mass, $M_b = 1.86\pm0.30\,\mathrm{M_\oplus},$ and radius, $R_b = {1.264\pm0.050}\,\mathrm{R_\oplus}$. Additionally, we report the discovery of a second, temperate, non-transiting planet in the system, GJ 3473 c, which has a minimum mass, $M_c \sin{i} = {7.41\pm0.91}\,\mathrm{M_\oplus,}$ and orbital period, $P_c={15.509\pm0.033}\,\mathrm{d}$. The inner planet of the system, GJ 3473 b, is one of the hottest transiting Earth-sized planets known thus far, accompanied by a dynamical mass measurement, which makes it a particularly attractive target for thermal emission spectroscopy.