Weird Worlds

This sulfurous hell world might change the way we classify exoplanets

- K. R. Callaway

TRILLIONS OF MILES FROM EARTH, a cluster of planets whirl around a sun of their own—and one of the worlds is a sulfur-swathed oddball. Research suggests the planet, L 98-59 d, would smell like rotten eggs and is covered in a mushy magma ocean. And it isn’t just an outlier in its home solar system. So far it’s the first exoplanet found to fit this peculiar description, and it seems to be defining a category of its own.

Scientists first observed the planet in 2019, when the Transiting Exoplanet Survey Satellite caught a glimpse of L 98-59 d passing in front of the red dwarf star at the center of its system. Afterward, observations from the Hubble and James Webb Space Telescopes hinted at the planet’s composition, but the more scientists learned, the less this newfound orb seemed to fit into existing categories for planets of its size. Neither rocky with a thick hydrogen atmosphere nor an ocean world, L 98-59 d might occupy a new class of molten, sulfurous exoplanet, according to a study in Nature Astronomy.

“It’s pretty hellish, it’s pretty alien,” says Harrison Nicholls, lead author of the study and a postdoctoral researcher at the University of Cambridge. “With more data, we might find that there are other planets like it, too.”

The first confirmed detection of an exoplanet, though long anticipated, was only 34 years ago. Increasingly powerful telescopes have since launched the field forward with more detections—now more than 6,000 in total. But it’s one thing to find an exoplanet and quite another to understand its surface conditions.