Space is typically imagined as a silent, scentless vacuum, but 35 light-years away in the constellation of Volans, there is a world that would be an assault on the senses. According to a new study led by researchers at the University of Oxford, the exoplanet L 98-59 d is a molten, sulphur-rich wasteland that likely reeks of rotten eggs.
For decades, astronomers have categorized planets into a few convenient buckets: rocky worlds like Earth, gas giants like Jupiter, or ice giants like Neptune. L 98-59 d, however, refuses to fit. It represents a brand-new class of planetary body—a world defined not by a solid crust or a gaseous envelope, but by a global, persistent ocean of magma.
The discovery challenges the fundamental way scientists classify small planets. While the search for “Earth 2.0” often focuses on temperate, rocky spheres with liquid water, L 98-59 d proves that the universe is far more imaginative—and far more hostile—than our own solar system suggests. This is not just a weird outlier; it is a glimpse into a planetary evolution path we previously didn’t know existed.
A world that refused to cool
At first glance, L 98-59 d shares some superficial similarities with Earth. It is roughly 1.6 times the size of our home planet. However, its density tells a different story. The planet is significantly less dense than a typical terrestrial world, suggesting a composition that deviates sharply from the iron-and-silicate balance found in our neighborhood.
The team’s modeling reveals a terrifying interior: a mantle composed of molten silicate material. On Earth, such a state existed billions of years ago during the planet’s infancy, before it cooled enough to form a solid crust. But L 98-59 d has remained in this molten state for eons. Instead of hardening into a stable surface, the planet has remained a shimmering, liquid hellscape.
The reason for this permanent heat is an atmospheric “blanket” of heavy sulphur-bearing molecules. This thick atmosphere creates an intense greenhouse effect, trapping heat so effectively that the surface cannot radiate it away into space. The result is a feedback loop that keeps the silicate mantle liquid, ensuring the planet remains a global magma ocean.
| Feature | Earth | L 98-59 d |
|---|---|---|
| Relative Size | 1.0x | ~1.6x |
| Surface State | Solid Crust | Global Magma Ocean |
| Primary Atmosphere | Nitrogen/Oxygen | Sulphur-rich |
| Core Density | High (Rocky/Iron) | Lower than expected |
From sub-Neptune to sulphur wasteland
How does a planet end up as a stinking, molten ball? The researchers believe L 98-59 d didn’t start this way. The current modelling suggests the planet may have once resembled a “sub-Neptune”—a world slightly larger than Earth but shrouded in a thick, primordial envelope of hydrogen and helium.
Over millions of years, the planet likely lost this outer layer, perhaps due to the radiation and heat from its parent star. As the lighter gases stripped away, the heavier sulphur compounds remained and concentrated. This transition transformed the planet from a gaseous mini-giant into the dense, sulphur-choked world observed today.
This evolutionary path suggests that many of the “small” planets we see in the galaxy might be the stripped-down remains of larger worlds, hiding complex chemical histories beneath their atmospheres.
Reconstructing worlds we will never visit
One of the most significant aspects of this discovery is not the planet itself, but how it was found. Because L 98-59 d is 35 light-years away, we cannot send a probe to sample its magma or smell its atmosphere. Instead, the Oxford team relied on a combination of observational data—measuring the planet’s mass and radius—and advanced computer modelling.
“What’s exciting is that we can use computer models to uncover the hidden interior of a planet we will never visit,” said Professor Raymond Pierrehumbert, co-author of the study. By plugging known variables into physics-based simulations, the team could reconstruct the planet’s deep past and current interior structure.
This methodology marks a shift in exoplanetary science. We are moving past the era of simply “finding” planets and into an era of “characterizing” them. Astronomers are no longer just counting dots in the dark; they are performing forensic geology on worlds trillions of miles away.
Expanding the planetary menu
The discovery of L 98-59 d serves as a humbling reminder of the limitations of human categorization. For a long time, the “rocky vs. Gas” binary was sufficient. But as our tools improve, the gaps in that binary are filling with worlds that defy definition.
“This discovery suggests that the categories astronomers currently use to describe small planets may be too simple,” noted Dr. Harrison Nicholls, the study’s lead author. While L 98-59 d is virtually certain to be uninhabitable, its existence broadens the scope of what is possible in the cosmos.
If a molten sulphur world can exist, it raises the question of what other “impossible” planets are orbiting distant stars. We may find worlds made of diamond, planets with atmospheres of vaporized metal, or oceans of liquid carbon, all of which would have been unthinkable a few decades ago.
The next phase of this research will rely on next-generation telescopes, including the James Webb Space Telescope (JWST), which are capable of more precise atmospheric spectroscopy. These tools will allow astronomers to search for other molten worlds and confirm if L 98-59 d is a lonely anomaly or the first member of a vast, stinking family of planets.
Do you think we’ll find more of these “impossible” worlds in our lifetime? Share your thoughts in the comments below.
