What’s New
Astronomers have discovered a planetary system that defies the standard rules of architecture. In a study published this week in Science, a team led by Thomas Wilson (University of Warwick) detailed the layout of LHS 1903, a red dwarf star 116 light-years away.
While the inner planets follow a typical pattern (a rocky world followed by two gas-rich planets), the newly discovered fourth planet, LHS 1903 e, is an anomaly. Despite orbiting at the system's outer edge, it is a small, rocky "super-Earth" (about 1.7 times Earth's size) rather than a gas giant. This creates a rare "rocky-gaseous-gaseous-rocky" sequence that contradicts the structure of our own solar system.
Why it matters
This discovery challenges the dominant theory of planet formation. For decades, the "Solar System model" has been the standard: rocky planets form close to the star where it is hot, and gas giants form further out where it is cold enough for gas and ice to accumulate.
LHS 1903 e breaks this rule. Its existence suggests that planets can form in gas-depleted environments far from their host star. This implies that planet formation is not always a simultaneous event but can happen sequentially—an "inside-out" process where outer planets form later, after the planet-building gas has already dissipated.
Background
- The Standard Model: Traditionally, astronomers believe planets form from a disk of gas and dust around a young star. Intense radiation near the star strips gas away, leaving rocky cores (like Earth). Further out, beyond the "snow line," gas remains, allowing massive giants (like Jupiter) to grow.
- LHS 1903: This star is a red dwarf, smaller and cooler than our Sun. Astronomers had previously identified its three inner planets using NASA’s TESS mission.
- CHEOPS: The new discovery was made using the European Space Agency’s CHEOPS satellite, which is designed to characterize known exoplanets in detail.
What we don’t know
- Frequency: We do not know if "inside-out" systems are rare anomalies or a common configuration that we simply haven't detected yet.
- Atmosphere: It is unclear if LHS 1903 e has any atmosphere at all, or if it is a bare rock.
- Formation Details: While the "gas-depleted" theory is the leading explanation, the exact timeline of how the disk dispersed remains theoretical.
What’s next
Astronomers will likely target LHS 1903 with the James Webb Space Telescope (JWST). Its sensitive instruments could determine if the outer rocky planet holds an atmosphere, which would provide crucial clues about its history. The team also plans to search for more "inside-out" systems to see if our own solar system is the exception rather than the rule.
Last updated: Feb 14, 2026
