Rocky planet discovered in outer orbit challenges planet formation theory

Astronomers have discovered a rocky planet orbiting far from its host star in a planetary system that defies established models of planet formation. The system, centered on the small red dwarf star LHS 1903, was found to host four planets: three inner planets following the expected pattern of a rocky world closest to the star and two gas giants farther out. However, new data from the European Space Agency’s CHEOPS satellite revealed a surprising fourth planet, LHS 1903 e, located in the outermost orbit but composed primarily of rock rather than gas. This finding challenges the widely accepted theory that rocky planets form close to their stars where intense radiation strips away gaseous envelopes, while gas giants develop in cooler, more distant orbits where thick atmospheres can be retained. The discovery of a rocky planet in the outer region of the system suggests that the processes governing planet formation and atmospheric retention may be more complex than previously thought. The research, led by Professors Ryan Cloutier of McMaster University and Thomas Wilson of the University of Warwick, combined observations from space- and ground-based telescopes to analyze the system’s composition and orbital dynamics. The team investigated alternative explanations such as planetary collisions or orbital migrations but found these scenarios insufficient to explain the presence of a rocky planet so far from its star. The LHS 1903 system’s unique configuration raises questions about the timing and environmental conditions necessary for rocky planet formation and suggests that red dwarf stars may host diverse planetary architectures. This discovery could have significant implications for understanding planet formation across the galaxy and may influence the search for potentially habitable exoplanets around low-mass stars. As red dwarfs are the most common type of star in the Milky Way, uncovering exceptions to established planetary formation patterns around them broadens the scope of planetary science. Further study of LHS 1903 and similar systems will be crucial to refining models of planetary evolution and assessing the variety of worlds that exist beyond our Solar System.