- L 98-59 d is a super-Earth exoplanet about 35 light-years from Earth. Scientists thought it was likely volcanically active due to its sulfur atmosphere.
- The planet has a deep, global ocean of magma below its mantle, a new study of data from the James Webb Space Telescope suggests.
- It represents a new type of super-Earth planet not known before. It is likely just one of many such worlds in our galaxy.
You deserve a daily dose of good news. For the latest in science and the night sky, subscribe to EarthSky’s free daily newsletter.
A molten super-Earth exoplanet 35 light-years away
A super-Earth exoplanet about 35 light-years away is unlike any others seen before. Researchers from Europe said on March 16, 2026, that the planet – L 98-59 d – represents a new class of rocky molten planet. The mantle is likely molten silicate, similar to lava on Earth. And beneath it is a deep global ocean of magma. Scientists think the magma ocean extends for thousands of miles below the mantle.
The University of Oxford in the U.K. led the study, based on new observations by the James Webb Space Telescope. Researchers from the University of Groningen, the University of Leeds and ETH Zurich were also involved.
L 98-59 d is about 1.6 times the diameter of Earth, making it a super-Earth type exoplanet. But the planet’s unusually low density puzzled scientists. Its atmosphere also contains large amounts of hydrogen sulfide. Being largely molten on the inside could explain both of these observations. The planet orbits a red dwarf star. Red dwarfs are smaller and dimmer than the sun.
A previous study from 2024 had also hinted that L 98-59 d might be a volcanic exoplanet. Researchers had tentatively found the gases sulfur dioxide (SO2) and hydrogen sulfide (H2S) in its atmosphere.
The journal Nature Astronomy published the new peer-reviewed findings on March 16, 2026.
Harrison Nicholls and colleagues suggest that exoplanet L 98-59 d could be entirely composed of molten lava: a magma ocean covering a mushy core. ??@nichollsh.bsky.social
— Nature Astronomy (@natastron.nature.com) 2026-03-16T17:41:18Z
A subsurface global ocean of magma
Why was the planet’s density so low for its size? The researchers used data from recent observations of L 98-59 d and advanced computer simulations to find the answer. They were able to simulate the planet’s geological history during its nearly 5-billion-year lifetime. This provided clues as to what the planet is like on the inside. What the researchers found was surprising.
The mantle of the lava is likely molten silicate. That’s similar to lava on Earth. But unlike Earth, the study results suggest that below the mantle, there is a global ocean of magma. That ocean is estimated to extend for thousands of miles deep into the planet’s interior.
Part of a broader population
The researchers say that L 98-59 d might be just one of many such worlds. It’s just the first one that astronomers have found. The researchers characterize them as “gas-rich sulfurous planets with long-lived magma oceans.” Lead author Harrison Nicholls at the University of Oxford said:
This discovery suggests that the categories astronomers currently use to describe small planets may be too simple. 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?
Sulfur feeds the atmosphere
As noted above, astronomers had already tentatively detected sulfur dioxide (SO2) and hydrogen sulfide (H2S) in the planet’s atmosphere. This hinted that the planet was volcanically active and/or had a magma ocean under its surface.
Now, the new findings suggest that ultraviolet light from the planet’s star creates those gases when it hits the planet’s atmosphere. In turn, the subsurface magma ocean acts as a reservoir for the gases. It’s been storing and releasing them for billions of years. Together, the atmospheric chemistry and subsurface storage have helped make L 98-59 d the planet it is today.
A larger world that shrank
The new findings also suggest that L 98-59 d was once larger than it is now. Early on, it was more sub-Neptune in size. Sub-Neptunes are smaller than Neptune but larger than super-Earths. But then it gradually shrank and cooled. And it lost some of its atmosphere in the process.
Scientists also said magma oceans are common in the early stages of rocky planets. So L 98-59 d can provide important clues about Earth’s primordial history billions of years ago. As co-author Raymond Pierrehumbert at the University of Oxford explained:
What’s exciting is that we can use computer models to uncover the hidden interior of a planet we will never visit. Although astronomers can only measure a planet’s size, mass and atmospheric composition from afar, this research shows that 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.
Does L 98-59 d smell like rotten eggs?
Notably, hydrogen sulfide is one of the main components of the planet’s atmosphere. It is pungent, with an odor similar to rotten eggs. Does this mean smelly planets are common? As Richard Chatterjee at the University of Leeds and University of Oxford noted:
Our computer models simulate various planetary processes, effectively enabling us to turn back the clock and understand how this unusual rocky exoplanet, L 98-59 d, evolved. Hydrogen sulfide gas, responsible for the smell of rotten eggs, appears to play a starring role there. But, as always, more observations are needed to understand this planet and others like it. Further investigation may yet show that rather pungent planets are surprisingly common.
Bottom line: L 98-59 d is a molten super-Earth exoplanet, with a deep subsurface global ocean of magma. The study’s results come from new analysis of data from the James Webb Space Telescope.
Source: Volatile-rich evolution of molten super-Earth L 98-59 d
Via University of Oxford
Read more: Is this a volcanic exoplanet? Hints are in its atmosphere
Read more: Atmosphere on lava planet is an exciting surprise