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

The radii of small exoplanets form two populations, super-Earths and sub-Neptunes, separated by a gap known as the radius valley. This could be produced by the removal of some atmospheres by stellar or internal heating, or the lack of an initial envelope. We use transit photometry and radial velocity measurements to detect and characterize four exoplanets orbiting LHS 1903, a red dwarf star in the Milky Way's thick disk. The planets have orbital periods from 2.2 to 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. The most distant planet from the host star, LHS 1903 e, has no gaseous envelope, indicating it formed from gas-depleted material.