Astronomers have used the James Webb Space Telescope (JWST) to investigate a new type of planet. This molten lava world outside the solar system probably smells like rotten eggs, suggesting that there is a much wider diversity of worlds outside our solar system than previously recognized.
The extrasolar planet, or exoplanet, is designated L 98-59 d, and it orbits a small red star about 35 light-years away. Data from JWST and a number of ground-based telescopes suggest that this exoplanet, which is about 1.6 times the size of Earth, has an extremely low density. The atmosphere is full of hydrogen sulfide, a compound known for its distinct rotten egg stench.
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“This discovery suggests that the categories astronomers currently use to describe small planets may be too simple. Although this molten planet is unlikely to support life, it reflects the great diversity of worlds that exist outside the solar system,” team leader Harrison Nicholls of the University of Oxford in the UK. said in a statement. “We can then ask: what other types of planets are waiting to be discovered?”
Sea of magma
Nicholls and colleagues were able to use advanced computer simulations to retell the nearly 5-billion-year history of L 98-59 d. They then compared these models with actual telescope data to reconstruct what must be happening deep below the surface of this exoplanet.
They determined that L 98-59 d likely has a mantle of molten silicate, similar to the lava found on Earth, and an ocean of magma spanning the entire planet. This huge global magma ocean allows the exoplanet to lock away huge amounts of sulfur over long periods of time. Sulphur-rich gases have then been released into the atmosphere by L 98-59 d over billions of years. This includes the sulfur dioxide and other sulfur-based molecules JWST detected in the planet’s upper atmosphere.
The magma reservoir may also have helped L 98-59 d retain its hydrogen- and sulfur-rich atmosphere, preventing it from being lost to space as a result of X-ray bombardment from its parent star.
Over billions of years, molecules have been exchanged between the planet’s atmosphere and its interior, shaping it into the first world in a new class of gas-rich sulfurous planets that sustain long-lived magma oceans.
The team’s simulations show that L 98-59 d was likely born with huge amounts of volatile material and may once have been a much larger planet below Neptune. The world probably shrank and cooled over billions of years, losing some, but not all, of its atmosphere.
“What’s exciting is that we can use computer models to uncover the hidden interior of a planet we’ll never visit,” said team member Raymond Pierrehumbert from the University of Oxford. “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.”
The team’s results were published Monday (March 16) in the journal Natural astronomy.
