The universe just got a little stranger — and a lot more fascinating. Astronomers using NASA's James Webb Space Telescope have discovered what appears to be an entirely new type of exoplanet, one defined by a sulfur-rich atmosphere and a partially molten interior unlike anything scientists have catalogued before.
The findings, published this week in Nature Astronomy, center on a planet called L 98-59 d, which orbits a small red dwarf star just 35 light-years from Earth. At about 1.6 times the size of our planet but with an unusually low density, this world doesn't fit neatly into any existing category of small planets.
A Global Ocean of Magma
What makes L 98-59 d so remarkable is what lies beneath its atmosphere. Scientists believe much of the planet could be covered by a global magma ocean infused with dissolved sulfur. Its atmosphere, meanwhile, is loaded with sulfur compounds, including hydrogen sulfide — the chemical responsible for the smell of rotten eggs.
"This discovery suggests that the categories astronomers currently use to describe small planets may be too simple," said Dr. Harrison Nicholls, the study's lead author from the University of Oxford. "While this molten planet is unlikely to support life, it reflects the wide diversity of worlds which exist beyond the solar system."
Why Sulfur Matters
On Earth, sulfur compounds are closely tied to volcanic activity and can create harsh, toxic environments. But on L 98-59 d, those same compounds exist on a planetary scale, shaping both the atmosphere and the planet's internal structure in ways scientists have never observed before.
The presence of hydrogen sulfide is particularly significant for researchers. Beyond its distinctive odor, it provides crucial clues about how the planet formed and evolved — and how materials like rock and gas interacted over billions of years. It's like finding a chemical fingerprint that tells the story of an entire world's history.
Expanding Our Cosmic Vocabulary
Before this discovery, astronomers had identified several broad categories for small planets: rocky worlds like Earth, water-rich "hycean" planets, and various types of super-Earths. L 98-59 d doesn't fit any of these templates. It may represent the first confirmed member of a new class — sulfur-dominated worlds with molten interiors.
"We may then ask: what other types of planets are waiting to be uncovered?" Nicholls said.
The discovery is a powerful reminder of how much we still have to learn about the cosmos. From gas giants to ocean worlds, and now sulfur-drenched magma planets, the James Webb Space Telescope continues to reveal a universe far more diverse and surprising than anyone imagined. And the telescope is just getting started.
