Astronomers Discovered a Brand-New Type of Planet That Reeks of Rotten Eggs and Defies Planetary Science – Image for illustrative purposes only (Image credits: Unsplash)
Astronomers have identified an exoplanet 35 light-years away whose atmosphere carries the sharp odor of hydrogen sulfide. The world, catalogued as L 98-59 d and located in the constellation Volans, sits in a size range once thought to contain only rocky or gaseous bodies. Instead it hosts a permanent global ocean of molten silicate rock kept liquid by a dense sulfur-rich envelope that traps heat for billions of years.
Conditions No Other Known Planet Matches
The planet’s mantle never solidified. Intense greenhouse warming from the sulfur compounds prevents the surface from cooling, so the magma ocean has persisted since the planet’s formation. This state produces a low overall density that does not fit standard models for planets of its mass and radius. Researchers describe the result as a new category rather than a variation on existing ones. The combination of a fully molten interior and a sulfur-dominated atmosphere has no counterpart among the thousands of exoplanets characterised so far.
Computer Models Reconstruct a Lost History
The study combined transit and radial-velocity observations with detailed interior simulations. Early in its life the planet probably resembled a sub-Neptune with a thick hydrogen-helium envelope. Over time it lost much of that original atmosphere, leaving the sulfur-rich layer now observed. The models show that only a narrow set of starting conditions and loss rates can produce the present-day structure. “This discovery suggests that the categories astronomers currently use to describe small planets may be too simple,” said lead author Dr Harrison Nicholls of the University of Oxford. The same simulations also indicate that similar worlds could form around other stars if the right ingredients and orbital distances are present. Co-author Professor Raymond Pierrehumbert noted that the approach allows scientists to infer deep interior properties from remote measurements alone. “What’s exciting is that we can use computer models to uncover the hidden interior of a planet we will never visit,” he said. The work demonstrates that indirect data can reveal formation pathways that leave no trace in the Solar System.
Why Current Classification Schemes Fall Short
Standard divisions separate planets into rocky terrestrials, gas giants, ice giants and sub-Neptunes. L 98-59 d occupies none of these cleanly. Its radius and mass place it near the boundary between super-Earths and sub-Neptunes, yet its composition and thermal state differ sharply from both. The finding implies that additional categories will be needed once more objects are examined with comparable detail. Future observations with larger telescopes may detect similar sulfur signatures on other worlds, testing whether the process that created L 98-59 d is common or rare.
What the Detection Means Going Forward
The planet itself is far too hot and chemically extreme to support life. Its value lies in expanding the known range of planetary outcomes. As instruments improve, astronomers expect to find additional examples that further stretch existing taxonomies. Each new case will refine the computer models used to interpret distant worlds, turning remote measurements into reliable reconstructions of formation and evolution. The result is a clearer picture of how planetary systems can diverge from the patterns seen in our own Solar System.