The Most Common Planets in the Galaxy Look Nothing Like Earth. JWST Just Proved It.
The most common planets in the galaxy do not look like Earth. They have no solid silicate crust, no layered mantle, no convenient geology to stand on. They are covered in oceans of magma, saturated with sulfur, and wrapped in atmospheres that would kill you in seconds. One of them is 35 light-years away, orbiting a dim red star in the constellation Volans — and a paper published in March 2026 in Nature Astronomy has now confirmed exactly what it looks like on the inside.
The planet is L 98-59 d. It is a super-Earth, roughly 1.6 times the diameter of our world, orbiting an M-dwarf star. It has been on astronomers' radar since 2024, when JWST detected sulfur dioxide in its upper atmosphere — a first for exoplanet science. What happened next is the subject of research by a team led by Dr. Harrison Nicholls at the University of Oxford, along with collaborators from the University of Groningen, the University of Leeds, and ETH Zurich. Their conclusion: L 98-59 d does not fit any existing category. It is not a gas dwarf, not a water world. It is something else entirely.
The planet's interior is a permanent magma ocean. Molten silicate — lava, essentially — extending thousands of kilometers below what would pass for a surface. The mantle is chemically reducing, saturated with more than 1.8 percent sulfur and hydrogen by mass. Its atmosphere is dominated by hydrogen sulfide, the compound responsible for the smell of rotten eggs. This is not a world that could support life as we recognize it. It is a world that looks like what Earth might have been, if our planet had never cooled.
"Magma oceans represent the universal initial states of all rocky planets," the paper notes — including Earth and Mars. In the early history of our solar system, both worlds were covered in molten rock. Earth cooled. L 98-59 d did not, or at least not all the way. The difference, the authors suggest, is that L 98-59 d formed with an unusually large inventory of volatile material — sulfur, hydrogen, water — and has been cooking in it ever since, held in a permanent molten state by the heat of decay and the proximity of its host star.
The planet may also be a former sub-Neptune in exile. The models suggest it could have begun life as a larger, gas-rich world, gradually shrinking over five billion years as it cooled and bled atmosphere into space. What was left is this: a rocky core wrapped in magma, dripping sulfur into an atmosphere that should have been stripped away by the star's ultraviolet radiation long ago. The magma ocean acts as a reservoir, buffering the atmosphere and releasing gas as fast as the star removes it. A self-replenishing rotten-egg world, 35 light-years away.
"This discovery suggests that the categories astronomers currently use to describe small planets may be too simple," Nicholls said in a statement accompanying the paper. "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?"
That question is the story. Super-Earths — planets between one and four times Earth's diameter — are the most common type of planet in the galaxy. The Kepler mission established this more than a decade ago. What it did not establish is what those super-Earths look like on the inside. Earth-based assumptions — that rocky planets cool, differentiate, form crusts — were always provisional. L 98-59 d is the first direct evidence that the majority of worlds in the galaxy may have followed entirely different evolutionary paths.
The implications for habitability research are not minor. If the most common planets are magma-ocean worlds with sulfur atmospheres, then the search for life as we understand it is searching on the rare exceptions, not the rule. "We may then ask," Nicholls said, "what other types of planet are waiting to be uncovered?" Good question. The answer, at least for now, appears to be: stranger ones than we thought.
The paper is titled "Volatile-rich evolution of molten super-Earth L 98-59 d," published in Nature Astronomy, March 16, 2026. The JWST observations that seeded the study date to 2024. Ariel and PLATO, upcoming exoplanet missions, will add more data. The team intends to apply their models to new targets as they come in. If L 98-59 d is the first confirmed member of a new planet class, the second and third are probably already in the archive, waiting to be modeled.