Astronomers have used the James Webb Space Telescope to investigate a new type of planet; this molten lava world beyond the solar system likely smells like rotten eggs, and suggests that there is a much wider diversity of worlds beyond our solar system than previously recognized.
The extra-solar planet, or exoplanet, is designated L 98-59d, and it orbits a small red star located about 35 light-years away. Data from the James Webb Space Telescope and an array of Earth-based telescopes suggest that this exoplanet, which is around 1.6 times the size of the Earth, is extremely low-density. Its atmosphere is packed with hydrogen sulfide, a compound known for its distinct rotten egg stench. Under normal circumstances, L 98-59d would either be classified as rocky gas dwarf, with an atmosphere rich in hydrogen, or as a water-rich ‘’hycean’’ ocean world. However this exoplanet fits into neither category, justifying the creation of a new category of exoplanets replete with heavy sulfer molecules.
“This discovery suggests that the categories astronomers currently use to describe small planets may be too simple. While this molten planet is unlikely to support life, it reflects the wide diversity of the worlds which exist beyond the solar system,’’ Harrison Nicholls said in a statement. Nicholls and colleagues were able to use advanced computer simulations to retell the nearly 5 billion-year history of L 98-59d. They then compared these models to actual telescope data to reconstruct what must be happening deep below the surface of this exoplanet. They determined that L 98-59d likely has a mantle of molten silicate, similar to the lava found on Earth, and an ocean of magma that spans the whole planet. This vast global magma ocean allows the exoplanet to lock away huge amounts of sulphur over vast periods of time. Sulfur-rich gases have then been released into the atmosphere of L 98-59d over billions of years. This includes the sulfur dioxide and other sulfur-based molecules the James Webb Space Telescope spotted in the planet’s upper atmosphere.
The magma reservoir may have also helped L 98-59d hold on to its hydrogen and sulphur-rich atmosphere, preventing it from being lost to space as a result of bombardment of X-rays 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 sulphurous planets sustaining long-lived magma oceans. The team’s simulations show that L 98-59d was likely born with vast amounts of volatile material and may have once been a much larger sub-Neptune planet. The world likely 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 will never visit’’ team member Raymond Pierrehumbert said. They continued, ‘’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 solar system’’
