Gas-depleted planet formation occurred in the four-planet system around the red dwarf LHS 1903

TL;DR

This study characterizes four planets around the red dwarf LHS 1903, revealing that the outermost planet formed in a gas-depleted environment, providing insights into planet formation and atmospheric evolution.

Contribution

First detailed characterization of a four-planet system around a red dwarf showing formation in a gas-depleted environment.

Findings

LHS 1903 b is rocky with no atmosphere

LHS 1903 c and d have extended atmospheres

LHS 1903 e formed from gas-depleted material

Abstract

Small exoplanet radii show two populations, referred to as super-Earths and sub-Neptunes, separated by a gap known as the radius valley. This may be produced by the removal of atmospheres due to stellar or internal heating, or lack of an initial envelope. We us transit photometry and radial velocity measurements to detect and characterize four planets orbiting LHS 1903, a red dwarf (M-dwarf) star in the Milky Way's thick disk. The planets have orbital periods between 2.2 and 29.3 days, and span the radius valley within a single planetary system. The derived densities indicate that LHS 1903 b is rocky, while LHS 1903 c and LHS 1903 d have extended atmospheres. Although the most distant planet from the host star, LHS 1903 e, has no gaseous envelope, indicating it formed from gas-depleted material.