Researchers have identified a brand-new class of exoplanet that represents a radical departure from the planetary categories currently known to science.

Axar.az reports that the world, designated as L 98-59 d, is located approximately 35 light-years from Earth and is described as a molten, sulphur-rich "super-Earth."

Unlike the rocky, gaseous, or water-dominated worlds typically found in our galaxy, this planet is defined by a global magma ocean and a thick atmosphere likely saturated with hydrogen sulfide and sulfur dioxide. This unique chemical makeup suggests the planet would have a pungent, toxic environment—effectively reeking of rotten eggs—driven by a permanent greenhouse effect that prevents the surface from ever cooling into a solid crust.

The discovery, published in Nature Astronomy, challenges the standard "radius valley" theories that often categorize small planets as either evolved gas dwarfs or water-rich worlds. Through advanced modeling with the PROTEUS framework, the team from the University of Oxford demonstrated that L 98-59 d likely began its life as a sub-Neptune with a large hydrogen-dominated envelope. Over billions of years, intense stellar radiation stripped away these lighter gases, leaving behind a dense, volatile-rich interior. This evolutionary pathway shows that the planet exists in a transient state, slowly transitioning between categories as its atmosphere is eroded and shaped by photochemical reactions.

One of the most significant aspects of the study is the role of the planet's interior in maintaining its extreme atmosphere. The researchers found that the global magma ocean acts as a massive reservoir for volatiles like sulfur, which are dissolved in the molten silicate and slowly degassed over gigayears. This "buffering" process allows the planet to maintain its thick, sulfurous atmosphere even as gases escape into space. By connecting the observed bulk density of the planet to its deep interior processes, the study provides a new blueprint for reconstructing the history of alien worlds, proving that even planets that cannot support life can offer critical insights into the diversity of the cosmos.