When astrophysicist and YouTube favourite Dr Becky Smethurst sat down to record her Night Sky News for March 2026, she had something extraordinary to share — a planet so strange that scientists have had to invent a whole new category for it.
The world in question is L 98-59 d, a rocky planet about 1.6 times the size of Earth, orbiting a small red star just 35 light-years away. And it is, by any earthly measure, remarkably strange.
A planet that doesn't fit the box
Until now, astronomers have generally sorted small exoplanets into tidy categories: rocky gas-dwarfs wrapped in hydrogen, or water-rich worlds of deep oceans and ice. L 98-59 d refuses to cooperate with either label.
An Oxford-led study published in Nature Astronomy on 16 March reveals that this planet sits atop a permanent ocean of magma — molten silicate stretching thousands of kilometres deep — and stores enormous quantities of sulphur in its interior. Its atmosphere is laced with hydrogen sulphide, 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 lead author Dr Harrison Nicholls of the University of Oxford. "We may then ask: what other types of planet are waiting to be uncovered?"
How JWST cracked the case
The breakthrough came thanks to observations from the James Webb Space Telescope, which detected sulphur dioxide and other unusual gases in the planet's upper atmosphere. The research team — spanning Oxford, Groningen, Leeds and ETH Zurich — then used advanced computer simulations to reconstruct the planet's five-billion-year history.
Their models show that L 98-59 d likely started life as a larger, sub-Neptune-sized world before gradually shrinking as it cooled and shed atmosphere. Over billions of years, chemical exchanges between its molten interior and atmosphere produced the sulphur-rich signature that JWST spotted from across the cosmos.
Co-author Professor Raymond Pierrehumbert called the work a kind of planetary archaeology: "It is possible to reconstruct the deep past of these alien worlds — and discover types of planets with no equivalent in our own Solar System."
Why it matters
Dr Smethurst — whose channel has made complex astrophysics accessible to over a million subscribers — framed the discovery as a reminder that the universe is far stranger and more varied than our models predict. If L 98-59 d is the first recognised member of a broader population of sulphurous magma worlds, the diversity of planets in our galaxy just got a whole lot richer.
And we are about to get much better at finding them.
Enter the Rubin Observatory
In February, the Vera C. Rubin Observatory in Chile issued its first scientific alerts — 800,000 in a single night — marking the dawn of real-time astronomical discovery. When fully operational, Rubin will fire off up to seven million alerts per night, flagging supernovae, variable stars, near-Earth asteroids, and more.
For exoplanet hunters, the implications are thrilling. Rubin's decade-long Legacy Survey of Space and Time will capture more objects in its first year than every other optical observatory in human history combined. Combined with JWST's atmospheric analysis and upcoming missions like Ariel and PLATO, we are entering a golden age of planetary discovery.
As Dr Smethurst put it: the universe keeps surprising us. The least we can do is keep looking up.
