Astronomers have discovered a strange new kind of planet beyond our solar system—one that may be covered by a vast, long-lasting ocean of molten rock and filled with sulfur deep inside.
The planet, called L 98-59 d, orbits a small red star about 35 light-years from Earth.
The findings, led by researchers at the University of Oxford, were published in Nature Astronomy.
L 98-59 d is about 1.6 times the size of Earth, but it has an unusually low density. This puzzled scientists at first.
Normally, a planet like this would be classified either as a rocky world with a thick hydrogen atmosphere or as a water-rich planet covered in deep oceans.
However, new observations from the James Webb Space Telescope and other instruments show that it doesn’t fit into either category.
Instead, the planet appears to belong to a completely new class. Its atmosphere contains large amounts of hydrogen sulfide—a gas known for its strong “rotten egg” smell.
This suggests that sulfur plays a major role in shaping the planet.
To understand what is happening, scientists used advanced computer models to simulate the planet’s history over nearly five billion years. Their results suggest that L 98-59 d has a deep global ocean of magma beneath its surface. This molten layer, made of silicate rock similar to lava on Earth, may extend thousands of kilometers down.
This magma ocean acts like a giant storage system for sulfur. It can hold large amounts of sulfur deep inside the planet and slowly release it into the atmosphere over time. This helps explain why the planet still has a thick atmosphere rich in sulfur gases, even though radiation from its star would normally strip such gases away.
The planet’s atmosphere is also shaped by strong ultraviolet radiation from its host star. This radiation triggers chemical reactions that create sulfur dioxide and other sulfur gases high above the surface. At the same time, the magma ocean below continues to exchange material with the atmosphere, maintaining this unusual balance.
Scientists think that L 98-59 d may have started out as a larger, gas-rich planet similar to a “sub-Neptune.” Over billions of years, it likely lost part of its atmosphere and cooled, shrinking into the world we see today.
Although this planet is far too hostile to support life, it provides valuable clues about how planets form and evolve. In fact, magma oceans were likely common in the early history of rocky planets, including Earth.
This discovery suggests that the current categories used to describe planets may be too simple. There could be many more types of worlds in our galaxy that scientists have not yet identified. With more data expected from powerful telescopes and future space missions, researchers hope to uncover even more unusual planets—and better understand the diversity of worlds beyond our solar system.
Source: University of Oxford.
