The surprising architecture of LHS 1903
The system around LHS 1903 features four known planets arranged in a pattern that immediately caught astronomers’ attention: two inner rocky worlds, labeled LHS 1903 b and LHS 1903 c, followed by a pair of larger gaseous planets, LHS 1903 d and LHS 1903 e, with the outermost object unexpectedly turning out to be rocky again. In the
Science paper associated with DOI
10.1126/science.adl2348, the team reports that the planets’ measured radii and densities fall on both sides of the so-called “radius valley,” the statistical divide between compact, likely rocky super-Earths and puffier, gas-rich mini-Neptunes. Lead author Thomas Wilson attributes the precise density measurements to a combination of transit data and stellar characterization that allowed the team to pin down the planets’ sizes and masses with unusual confidence.
Those measurements relied heavily on the CHEOPS space telescope, which was able to watch LHS 1903 for repeated, shallow dips in brightness as each planet crossed the face of the star. According to the
Preprint version of the study, CHEOPS recorded distinct transit depths for all four worlds, with the inner planets producing relatively small signals consistent with compact rocky bodies and the middle planets generating deeper transits that match larger, gas-enveloped planets. The authors note that LHS 1903 e, despite occupying the system’s outermost known orbit, presents a transit signature and inferred density that indicate a rocky composition with little or no gaseous envelope, a configuration they argue is best explained by “gas-depleted” formation at a late stage in the system’s history.