Rocky planet discovered in outer orbit challenges planet formation theory
Science Daily
February 14, 2026
AI-Generated Deep Dive Summary
Astronomers have discovered a faraway planetary system that defies a widely accepted theory about planet formation. Around the red dwarf star LHS 1903, scientists initially observed three planets following the expected pattern: a rocky inner world, followed by two gas-rich planets similar to smaller Neptunes. However, the discovery of a fourth planet, designated LHS 1903 e, orbiting farthest from the star and appearing to be rocky, has turned this system into a puzzle for planetary scientists.
The traditional model suggests that young stars emit intense radiation that strips away gases from nearby developing planets, leaving behind solid, rocky worlds. Farther out, cooler temperatures allow gas giants to form by retaining their atmospheres. However, in the LHS 1903 system, this pattern is disrupted: a rocky planet exists where a gas giant would typically be expected.
To investigate, researchers led by Prof. Ryan Cloutier of McMaster University and Prof. Thomas Wilson of the University of Warwick used data from ground-based telescopes and the European Space Agency's CHEOPS satellite. They ruled out explanations such as massive collisions or planetary shifts over time through detailed computer simulations and orbital studies.
Instead, their findings suggest a new theory called "inside-out planet formation." In this scenario, planets form sequentially in a protoplanetary disk that evolves over time. By the time LHS 1903 e began forming, much of the gas in the surrounding disk may have already dissipated, leaving insufficient material to build a thick atmosphere and resulting in a rocky world.
This discovery challenges standard assumptions about planet formation and raises important questions about how planetary systems evolve. It highlights the need for scientists to rethink their models and consider alternative pathways that could explain such anomalies. As telescopes and detection methods improve, this find may pave the way for new insights into the diversity of planetary systems across the galaxy.
This breakthrough not only deepens our understanding of planet formation but also underscores how much remains unknown about the processes shaping planets in different environments. The LHS 1903 system serves as a reminder that even after decades of research, the universe continues to surprise us with unexpected configurations that push the boundaries of scientific theory.
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Originally published on Science Daily on 2/14/2026