Astronomers using the James Webb Space Telescope (JWST) have discovered a new type of exoplanet that likely has an atmosphere reminiscent of rotten eggs. This finding, which underscores the considerable diversity of planets beyond our solar system, involves the exoplanet named L 98-59 d, located approximately 35 light-years from Earth. The data collected from both the JWST and various Earth-based telescopes indicate that this planet is about 1.6 times the size of Earth and possesses an extremely low density.
The atmosphere of L 98-59 d is rich in hydrogen sulfide, a gas known for its pungent smell. Traditionally, such a planet would be categorized as either a rocky gas dwarf or a water-rich “hycean” ocean world. However, L 98-59 d does not fit neatly into either classification, prompting scientists to propose a new category of planets characterized by heavy sulfur molecules.
New Insights into Planetary Diversity
According to Harrison Nicholls, team leader from the University of Oxford, “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 worlds that exist beyond our solar system.” He further emphasized the potential for uncovering more unique planetary types in the future.
Nicholls and his colleagues utilized advanced computer simulations to analyze the nearly 5 billion-year history of L 98-59 d. By comparing these models to actual observations from telescopes, they reconstructed the conditions present beneath the planet’s surface. Their findings indicate that L 98-59 d likely has a mantle of molten silicate and a global ocean of magma, similar to lava on Earth. This expansive magma ocean enables the planet to retain vast amounts of sulfur over extended periods.
The release of sulfur-rich gases into the atmosphere has occurred over billions of years, including sulfur dioxide and other sulfur-based molecules identified by the JWST. The magma reservoir appears to have played a critical role in maintaining the planet’s hydrogen and sulfur-rich atmosphere, shielding it from being stripped away by X-ray bombardment from its parent star.
Exploration of Alien Worlds
The research also suggests that L 98-59 d was initially formed with substantial volatile materials, potentially making it a much larger sub-Neptune planet in its early stages. Over billions of years, the planet has likely shrunk and cooled, losing some of its atmosphere but retaining key elements.
Raymond Pierrehumbert, another member of the research team at the University of Oxford, remarked, “What’s exciting is that we can use computer models to uncover the hidden interior of a planet we will never visit. 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, revealing types of planets with no equivalent in our own solar system.”
The findings from this investigation were published on March 16, 2024, in the journal Nature Astronomy. As astronomers continue to explore the cosmos, discoveries like L 98-59 d open new avenues for understanding the complexities of planetary systems beyond our own.
