Strange exoplanet system 116 light-years away challenges planet formation models
Feb 22nd 2026
Four planets orbit the red dwarf LHS 1903 in an unusual order—rocky, gas-rich, gas-rich, then rocky—prompting researchers to propose a reversed, gas-depleted formation sequence.
- LHS 1903 is a red dwarf about 116 light-years from Earth with four confirmed planets.
- The planets are arranged rocky, gaseous, gaseous, then rocky, with the outermost planet LHS 1903 e about 1.7 times Earths radius.
- The system was discovered with NASAs TESS and studied with ESAs Cheops along with ground-based telescopes, and the results were published in Science.
- Dynamical simulations in the study ruled out formation by giant impacts or by a gas-rich planet losing its atmosphere.
- Authors propose a gas-depleted formation in which planets formed sequentially from the inside out, so the outer rocky planet formed later when the disk had little gas.
- The arrangement contradicts the common pattern of rocky inner planets and outer gas giants and will drive further observations and model revisions, including potential follow-up with the James Webb Space Telescope.