The James Webb Space Telescope has captured evidence of a 'mushy' super-Earth that has fundamentally broken the traditional rules of planetary science.
Located just 35 light-years away, the planet known as L 98-59 d is covered in a global ocean of molten rock and surrounded by a thick, pungent atmosphere that smells like rotten eggs. This discovery, published in Nature Astronomy, reveals an entirely new class of volatile-rich molten planets that scientists previously thought could not exist in such hostile conditions.
A Super-Earth That Defies The Laws Of Physics
At the heart of this cosmic mystery is L 98-59 d, a planet roughly 1.6 times the size of Earth. Astronomers have long categorised small exoplanets as either airless rocky worlds or water-rich 'hycean' planets. However, new data from the James Webb Space Telescope and ground-based observatories show that L 98-59 d is neither. Despite being blasted by intense radiation from its red dwarf star, the planet has managed to hold onto a thick, hydrogen-rich atmosphere filled with heavy sulphur molecules.
Under traditional models, a rocky planet this close to its sun should have had its atmosphere stripped away billions of years ago. The fact that it remains intact is being described by researchers as 'completely bonkers'. The atmosphere is so chemically rich that it contains high concentrations of hydrogen sulphide (H2S) and sulphur dioxide (SO2), creating a toxic, yellow-tinged sky that would be instantly lethal to any known form of life.
Global Magma Ocean Sustains Stinky Atmosphere
The secret to the planet's 'impossible' survival lies beneath its surface. According to lead author Dr Harrison Nicholls of the University of Oxford, the planet is likely in a permanent molten state. Instead of a solid crust, a global magma ocean thousands of kilometres deep churns beneath the clouds. This internal reservoir of molten silicate acts as a massive storage tank for volatile gases, which are released into the sky through a process called outgassing.
This continuous volcanic activity replenishes the atmosphere faster than the star's X-ray radiation can blow it away. Scientists believe this magma ocean has persisted for nearly five billion years, effectively 'locking' the gases in place. It suggests that L 98-59 d represents a missing link in planetary evolution, potentially showing us what Earth and Mars looked like in their earliest, most violent stages of formation.
New Class Of Volatile-Rich Molten Planets
This discovery is forcing a total rewrite of the planetary textbooks. Researchers now believe that L 98-59 d is the first identified member of a broader population of sulphurous molten worlds. These planets sit in a 'transitional' zone between rocky super-Earths and gas-rich sub-Neptunes. By using computer simulations to 'turn back the clock', the team determined that L 98-59 d likely started as a much larger, puffier planet before shrinking as it cooled and lost mass over eons.
The presence of such a stable atmosphere on a molten world suggests that many planets currently labelled as 'barren' or 'airless' might actually be hiding complex chemical environments. While the temperature on L 98-59 d reaches a blistering 1,900°C, making it uninhabitable, it provides a unique laboratory for studying how atmospheres survive around active stars.
Future Of Exoplanet Characterisation
The implications of this find extend far beyond this single system. As the James Webb Space Telescope continues its survey of the L 98-59 planetary system, which contains at least five planets, astronomers are looking for similar signals on other worlds. Upcoming missions, such as the European Space Agency's Ariel and NASA's PLATO, will use these findings to refine the search for truly habitable planets.
By understanding how a world can smell like rotten eggs and be covered in lava yet still maintain its atmosphere, scientists are getting closer to answering the ultimate question: which worlds can truly support life and which are simply beautiful, toxic illusions.
