Thirty-four light-years away, in the constellation Volans, there is a world that would kill you before you could take a second breath. Not because of the heat, though the surface temperature exceeds 1,500 degrees Celsius and the ground is a global ocean of liquid rock. Not because of the pressure, though the atmosphere presses down in a chemistry unlike anything in our solar system.
You would notice, in those first moments, that the air smells of rotten eggs.
A Planet That Broke the Classification System
In March 2026, researchers at the University of Oxford published findings in Nature Astronomy identifying the exoplanet L 98-59 d as the first confirmed member of a new class of world. Using observations from the James Webb Space Telescope, the team found that the planet is about 1.6 times the size of Earth but significantly less dense than its size would suggest. That anomaly pointed to the answer: vast amounts of sulphur, trapped inside a permanent, planet-wide magma ocean.
The atmosphere contains hydrogen sulphide, the compound responsible for the smell of rotten eggs, alongside sulphur dioxide and other heavy sulphur gases. Webb had first detected a sulphur dioxide signature in 2024 observations; the new analysis assembled the full picture of what kind of world could produce it. The answer required a new category entirely.
Why the Universe Needed a New Shelf
For most of the history of planetary science, we worked with three broad archetypes: rocky worlds like Earth and Mars, gas giants like Jupiter and Saturn, and icy bodies like Europa or Pluto. The discovery of thousands of exoplanets has been steadily complicating that picture. L 98-59 d now suggests a fourth type: volatile-rich, sulphur-dominated worlds with long-lived magma oceans that act as deep reservoirs, storing and cycling gases in ways our models never predicted.
The planet orbits L 98-59, a small red dwarf star. Close-in worlds around red dwarfs are irradiated intensely; lighter elements escape, and heavier ones accumulate. In the case of L 98-59 d, the result is a planet that is simultaneously rocky and volcanic, gaseous and molten, its interior and atmosphere locked in a sulphurous exchange that the Oxford team suggests could persist for billions of years.
Our solar system has nothing like it. That is precisely why it matters. The researchers propose that L 98-59 d may be the first identified representative of a broader population, common around red dwarfs, whose existence our formation models simply hadn’t accounted for. The environments where planets form turn out to produce a far stranger range of outcomes than we assumed.
What Comes Next
L 98-59 d is the third of at least five known planets orbiting L 98-59. One of the outermost, designated L 98-59 f, sits within the habitable zone of its star and is a candidate for future atmospheric characterisation with Webb. Each observation of this compact multi-planet system sharpens the picture of how planetary diversity arises around red dwarfs, which are the most common type of star in the galaxy.
Future Webb observations will refine the atmospheric composition of L 98-59 d further and may reveal whether the sulphur cycle operating inside it has any analogues elsewhere. Given how many red dwarf systems exist, a new class of world found just 34 light-years away is unlikely to be alone.
Every time we build a new category for the worlds we find, the universe quietly adds another shelf.
