A New Class of Molten Planet Stores Abundant Sulfur in a Perpetual Magma Ocean

Why It Matters

The discovery reshapes our understanding of planetary formation and evolution, highlighting a previously unrecognized pathway for small planets to retain volatile atmospheres, which has implications for interpreting exoplanet demographics and assessing habitability criteria.

Summary

A team led by the University of Oxford has identified exoplanet L 98‑59 d as the first member of a new class of small, sulfur‑rich worlds that retain a permanent global magma ocean. JWST and ground‑based data show the planet’s low density and hydrogen sulfide‑rich atmosphere, while detailed interior‑atmosphere simulations reveal a molten silicate mantle that stores vast amounts of sulfur over billions of years, allowing a thick H₂‑rich envelope to persist despite stellar X‑ray erosion. The findings suggest that current planet classification schemes are oversimplified and that many similar magma‑ocean, sulfur‑bearing planets may exist, expanding the known diversity of exoplanets.