Astronomers have identified a distant planetary system that appears to upend long-standing theories of how planets form, revealing a rocky world orbiting beyond two gaseous neighbors in a configuration researchers say should not occur under conventional models.
The system, centered on a red dwarf star known as LHS 1903 about 116 light-years from Earth, contains four planets arranged in an unexpected sequence.
The innermost planet is rocky, followed by two gaseous planets, while the outermost planet is rocky again.
Such an arrangement contrasts with the prevailing model observed in our own solar system, where rocky planets orbit closest to the sun and gas giants reside farther away.
The discovery was first made using NASA’s Transiting Exoplanet Survey Satellite and later analyzed with the European Space Agency’s Cheops telescope, alongside data from other observatories.
Scientists say the system contradicts the widely accepted view that planets forming farther from their star accumulate abundant gas and ice, becoming gas-rich worlds.
“The planet-formation paradigm states that planets close to their host star should form small and rocky, with little-to-no gas or ice,” said Thomas Wilson of the University of Warwick, lead author of the study published in Science.
“This system challenges that by giving us a rocky planet outside of gas-rich planets,” Wilson added.
The outermost planet, known as LHS 1903 e, is classified as a super-Earth, with a radius about 1.7 times that of Earth and a mass roughly 5.8 times greater.
Researchers initially tested whether collisions or atmospheric loss could explain its composition but found those scenarios unlikely.
After ruling out violent impacts or stripped atmospheres, scientists proposed a “gas-depleted” formation scenario.
Under this model, the planets formed sequentially, beginning with the innermost world and moving outward.
By the time the outermost planet coalesced, much of the surrounding gas and dust had already been used by its neighboring planets.
Wilson described the fourth planet as a “late bloomer.”
The finding has sparked debate among astronomers, who say the system offers a new data point for refining models of planetary formation around red dwarf stars.
Future observations with the James Webb Space Telescope may further clarify the planet’s atmospheric properties and potential habitability.