Forget The Upside Down, Astronomers Discover A Bizarre Inside-Out Planetary System

by Aaron Leong — Friday, February 13, 2026, 10:28 AM EDT

A team of international astronomers has announced the discovery of an "inside-out" planetary system that defies the established understanding of planetary patterns. The system features four planets orbiting around a faint red host star called LHS 1903: the innermost is rocky, the next two are gaseous, whereas oddly, the outermost one is rocky. Huh?

lhs1903 planets — Four planets orbit LHS 1903, which is a small red M-dwarf star that is cooler and shines less brightly than our sun. Note that the distances and sizes of the planets are not to scale – the outer fourth planet is much smaller than the other three planets in the system. (Credit: ESA.)

Located roughly 116 light-years away, the LHS 1903 system was initially identified by NASA’s Transiting Exoplanet Survey Satellite (TESS) in 2019, but its true nature only became clear through recent follow-up observations by the European Space Agency’s (ESA) CHEOPS telescope.

This four-planet system follows a rocky-gaseous-gaseous-rocky sequence, a configuration that has left the research community scratching their collective heads. In our current understanding of planetary system formation, intense radiation from a young star strips away the light gases of nearby protoplanets, leaving behind rocky cores. Farther out, where it is cooler, planets can accumulate massive envelopes of hydrogen and helium to become gas giants like Jupiter.

*Cheops open questions: How do planets evolve? (Credit: ESA)*

LHS 1903 defies this logic. The fourth and outermost planet (LHS 1903 e) in the system is not a gas giant, but a rocky world similar in composition to Venus, but 1.7 times that of Earth. Lead author Dr. Thomas Wilson, from the University of Warwick, described the discovery as likely the first evidence of a planet forming in a "gas-depleted environment." According to the team’s findings published in EurekaAlert!, this inside-out formation suggests that the planets may have formed sequentially, with the inner planets sweeping up so much material that by the time the final outer planet began to coalesce, there was no gas left to build a giant atmosphere.

Beyond its formation, the system’s compact nature is equally interesting. All four planets are packed into orbits tighter than Mercury’s path around our sun, completing their year in less than 30 days. This proximity suggests a history of gravitational instability or "violence," where planets may have migrated from their original birthplaces. Co-author Andrew Cameron of the School of Physics and Astronomy at University of St. Andrews noted that the system looks like it has been "turned inside out," potentially due to ancient gravitational interactions that shifted the worlds into their current, bizarre alignment.