Leeds and Oxford researchers help uncover magma ocean world unlike any known planet
New research has revealed a previously unknown type of exoplanet, with a vast magma ocean and sulphur-rich atmosphere unlike any world yet observed.
Researchers at the University of Leeds have contributed to a major international study, led by the University of Oxford, that identifies a new class of planet that stores significant amounts of sulphur deep within its molten interior. The findings, published in Nature Astronomy, centre on the exoplanet L 98-59 d, located around 35 light-years from Earth.
The planet orbits a small red dwarf star and has long puzzled astronomers. Despite being about 1.6 times Earth's size, it has an unusually low density and an atmosphere containing hydrogen sulphide. Such characteristics do not align with existing classifications, which typically group similar worlds as either rocky planets with thin gaseous envelopes or water-rich bodies dominated by deep oceans.
To investigate further, the team combined observations from the James Webb Space Telescope with ground-based data and advanced computer simulations. These models reconstructed the planet’s evolution over nearly five billion years, allowing researchers to probe processes occurring far beneath its surface.
Results indicate that L 98-59 d likely hosts a global ocean of molten silicate which is thousands of kilometres deep. This magma reservoir acts as a long-term store for sulphur, regulating its release into the atmosphere. In turn, this helps sustain a thick, hydrogen-rich envelope containing sulphur-bearing gases that would otherwise be stripped away by stellar radiation.
A whole new category of planet?
This interplay between interior and atmosphere could define a new category of planet: gas-rich, sulphur-dominated worlds maintained by enduring magma oceans. If it’s confirmed, these may represent a broader population of unrecognised planets.
Lead author Dr Harrison Nicholls, of the University of Oxford, said: “This discovery suggests that the categories astronomers currently use to describe small planets may be too simple. While this molten planet is unlikely to support life, it reflects the wide diversity of the worlds which exist beyond the Solar System. We may then ask: what other types of planet are waiting to be uncovered?”
The study also highlights how sulphur chemistry shapes the planet’s observable features. Ultraviolet radiation from its host star drives reactions in the upper atmosphere, producing sulphur gases, while the molten interior acts as a buffer, absorbing and releasing these compounds over geological timescales.
Dr Richard Chatterjee, a Research Fellow in Exoplanets in the School of Physics and Astronomy, added: “Our computer models simulate various planetary processes, effectively enabling us to turn back the clock and understand how this unusual rocky exoplanet, L 98-59 d, evolved.
“Hydrogen sulphide gas, responsible for the smell of rotten eggs, appears to play a starring role there. But, as always, more observations are needed to understand this planet and others like it. Further investigation may yet show that rather pungent planets are surprisingly common.”
Further information
- Image title and credit: Illustration of the exoplanet L 98-59 d, by Mark A. Garlick.
- For media enquiries, please contact Faculty Communications Manager Matt Gardner at M.D.Gardner@leeds.ac.uk.
