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Rocky Outer World in 'Inside-Out' Star System Challenges Planet Formation Theory

The Science study points to sequential, gas-depleted formation, prompting calls for atmospheric follow-up.

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

  • Astronomers report four planets around the red dwarf LHS 1903, arranged rocky–gaseous–gaseous–rocky about 116 light-years from Earth.
  • The outermost planet, LHS 1903 e, is a rocky super-Earth roughly 1.7 times Earth’s radius, contrary to expectations for distant worlds.
  • NASA’s TESS flagged the system, while ESA’s CHEOPS and additional observatories refined sizes and densities and revealed the fourth planet.
  • Dynamical and impact simulations ruled out giant collisions, atmospheric stripping, and simple orbital swapping as explanations for the architecture.
  • Researchers favor sequential, inside-out formation in a gas-depleted disk, and outside experts urge atmospheric characterization to test the scenario.