An international team of scientists, led by the University of Oxford in the United Kingdom, has identified a new class of planet outside our solar system unlike any previously known. The exoplanet, dubbed L 98-59 d, is characterized by vast amounts of sulfur contained within a permanent ocean of magma. This discovery expands our understanding of the diverse range of worlds that exist beyond our own and highlights the potential for uncovering even more unusual planetary formations.
Orbiting a star approximately 35 light-years from Earth, L 98-59 d presented astronomers with a puzzling combination of characteristics: an unexpectedly low density for its size – about 1.6 times the size of Earth – and an atmosphere rich in sulfur gases. The research team published their findings in Nature Astronomy on March 16, 2026.
The discovery of this planet could significantly broaden what is known about galactic diversity, researchers say. Observations from the James Webb Space Telescope, combined with data from ground-based observatories, revealed the presence of hydrogen sulfide and other sulfur compounds in the planet’s atmosphere.
These characteristics don’t fit neatly into existing planetary categories, such as rocky ‘gas-dwarfs’ with hydrogen atmospheres or water-rich worlds composed of deep oceans and ice. To understand this unusual world, researchers utilized advanced computer simulations that reconstructed the planet’s evolution over nearly five billion years.
The models suggest that the mantle of L 98-59 d is primarily composed of molten silicate – similar to lava on Earth – creating a global magma ocean potentially extending thousands of kilometers beneath the surface. This massive molten reservoir acts as a sulfur store, capable of retaining it over geological timescales.
this magma ocean contributes to maintaining a dense atmosphere rich in hydrogen, where gases like hydrogen sulfide are found. Normally, this gas would be lost to space due to radiation from the host star, but chemical exchange between the molten interior and the atmosphere has allowed it to be preserved for billions of years.
“This discovery may force us to rethink the categories we use to describe small planets,” explained Harrison Nicholls, the study’s lead author. “While a molten planet like this is unlikely to harbor life, its study reveals the enormous diversity of worlds that exist beyond our Solar System and suggests that many more similar planets may yet be discovered.”
Observations from the James Webb Space Telescope detected sulfur dioxide in the upper layers of the planet’s atmosphere. Models indicate these gases are generated when ultraviolet radiation from its star triggers chemical reactions in the atmosphere.
Simultaneously, the magma ocean beneath the surface acts as a vast reservoir absorbing and releasing these compounds over time. This interaction between the planet’s interior and its atmosphere explains the unusual properties detected by telescopes.
The space telescope continues to provide key insights into exoplanets. Future space missions, such as ESA’s “Ariel” and “PLATO” – both designed to study hundreds of exoplanets – could further expand this knowledge and improve our understanding of how planets form and evolve, and potentially predict which ones might be habitable.
