An international team of scientists, led by the University of Oxford in the United Kingdom, has identified a latest class of planet outside our solar system that doesn’t fit into any previously known categories. The planet, dubbed ‘L 98-59 d’, is characterized by vast amounts of sulfur deep within a permanent magma ocean.
Exoplanet with Sulfur-Rich Atmosphere
Orbiting a star approximately 35 light-years from Earth, the planet L 98-59 d presents a surprisingly low density and an atmosphere rich in sulfur gases, initially puzzling astronomers. The research team has published their findings in the journal Nature Astronomy.
The discovery of this planet, which is 1.6 times the size of Earth, could significantly expand our understanding of the diversity of worlds in the galaxy, researchers emphasize. 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. This finding is particularly significant as it demonstrates the power of new telescope technology to analyze exoplanetary atmospheres.
A World Unlike Any Other
These characteristics don’t align with typical classifications for small planets, such as rocky gas dwarfs with hydrogen atmospheres or water-rich worlds composed of deep oceans and ice. To understand this unusual world, the researchers utilized advanced computer simulations recreating the planet’s evolution over nearly five billion years.
The models suggest the planet’s mantle consists primarily of molten silicates, similar to Earth’s lava, creating a global ocean of magma potentially extending thousands of kilometers beneath its surface. This massive molten reservoir acts as a geological storehouse for sulfur.
this magma ocean contributes to maintaining a dense atmosphere rich in hydrogen, containing gases like hydrogen sulfide. Whereas this gas would typically be lost to space due to radiation from the host star, the constant chemical exchange between the molten interior and the atmosphere has allowed it to be preserved for billions of years.
Harrison Nicholls, the lead author of the study, explained that the discovery may require a reevaluation of the current categories astronomers employ to describe small planets. He stated, “Although a molten planet like this is unlikely to harbor life, its study reveals the enormous diversity of worlds that exist outside our Solar System and raises the possibility that there are many more similar planets yet to be discovered.”
James Webb Telescope Reveals Exoplanet Clues
Observations made in 2024 with 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 giant 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, and future space missions, such as ‘Ariel’ and ‘PLATO’ – both from the ESA, to study hundreds of exoplanets – could further expand this knowledge and better understand how they form and evolve, and predict which might be habitable.
FEW (EFE, University of Oxford, Nature Astronomy)
