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yesterday

Astronomers Find Rare ‘Inside-Out’ Planetary System With Rocky Outer World

A peer-reviewed study of the red dwarf LHS 1903 points to sequential planet formation in a gas-depleted disc after simulations ruled out collisions or orbital swapping.

An artist's impression of a planetary system with four planets, around a small red star, called LHS1903 with a large reddish-brown rocky planet with craters is visible in the foreground and three smaller planets: one with blue and white colors, another with blue and brown bands, the third with a rocky surface behind it and in the top right corner of the image, a small but bright red star illuminates the scene, with space dust and distant stars visible in the background, in this illustration released on February 12, 2026. ESA/Handout via REUTERS
NASA's Transiting Exoplanet Survey Satellite, or TESS, was launched in 2018 to find new planets orbiting other stars.
A conceptual view of a red dwarf star, the same type as LHS 1903 and the most common type of star in the universe.

Overview

  • The four-planet system around LHS 1903, about 116 light-years away, is ordered rocky–gaseous–gaseous–rocky with all worlds orbiting in under 30 days.
  • ESA’s CHEOPS follow-up to NASA’s TESS detections revealed the outer planet, LHS 1903 e, as a rocky super-Earth rather than a sub-Neptune.
  • The findings, published February 12 in Science, combine space- and ground-based observations to pin down radii, densities and stable orbits.
  • Dynamical modeling disfavors giant impacts, atmospheric stripping or large-scale orbital rearrangement as the cause of the unusual architecture.
  • Authors favor an inside-out, one-by-one formation scenario in a gas-poor environment, a rare configuration that researchers say warrants targeted atmospheric studies.