Astronomers have recently identified an extraordinary planet within our galactic neighborhood that defies conventional planetary characteristics. This alien world is enveloped by a continuous ocean of molten rock and shrouded in a thick, sulfur-heavy atmosphere, creating an environment that can only be described as a hellish landscape. Situated approximately 34 light-years from Earth in the constellation Volans, this planet orbits a star smaller and dimmer than our sun, offering a rare glimpse into the diversity of planetary systems beyond our solar system.
Measuring over 60% larger in diameter than Earth, this exoplanet’s size is impressive, yet its overall density is surprisingly low—only about 40% that of our home planet. This suggests a fundamentally different internal structure compared to terrestrial planets like Earth. Unlike Earth, which has a layered interior consisting of a crust, upper mantle, and lower mantle, this planet’s interior is dominated by a vast, uninterrupted magma ocean. Harrison Nicholls, a postdoctoral researcher at the University of Cambridge Institute of Astronomy and the lead author of the study published in Nature Astronomy, the molten layer is so extensive that it forms a single, deep, and mushy mantle without distinct solid layers.
Within this turbulent magma ocean, small crystals of solid rock may be suspended, but the planet lacks a solid crust. Its metallic core is relatively small in comparison, with the magma ocean making up between 70% and 90% of the planet’s radius. This molten layer extends to depths ranging from approximately 2,775 to 3,565 miles (4,465 to 5,740 kilometers), highlighting the immense scale of the planet’s molten interior. The planet’s atmosphere is equally remarkable, composed mainly of hydrogen but containing a significant amount of sulfur compounds, including about 10% hydrogen sulfide—a gas notorious for its foul smell reminiscent of rotten eggs.
This thick, sulfur-rich atmosphere has triggered a runaway greenhouse effect, trapping heat from the host star and maintaining surface temperatures so extreme that the planet’s surface remains perpetually molten. Raymond Pierrehumbert, a planetary scientist affiliated with the University of Oxford and MIT and co-author of the study, emphasized the overwhelming nature of the atmosphere’s toxicity. He noted that while humans can detect hydrogen sulfide at incredibly low concentrations, the planet’s intense heat and toxic gases would make survival impossible, even before the stench could be noticed.
The atmospheric composition also provides clues about the planet’s interior chemistry. The high sulfur content suggests that the molten material beneath the surface likely has a mineralogical makeup distinct from any planets found within our solar system. Nicholls pointed out that while the exact composition remains uncertain, the observations imply a fundamentally different geological and chemical environment, shaped by sulfur-rich materials uncommon on Earth and its neighboring planets.
Designated L 98-59 d, this planet was initially discovered in 2019 and has since been observed by the James Webb Space Telescope in 2024, followed by ground-based telescopes in 2025. Using sophisticated computer models, researchers have reconstructed the planet’s evolutionary history, estimating its age to be nearly five billion years—slightly older than Earth. L 98-59 d orbits a red dwarf star, a common type of star that is smaller and less luminous than the sun, with just under 30% of the sun’s mass and about 1% of its brightness. It is the third planet in a system of five known planets orbiting this star.
While over 6,100 exoplanets have been discovered since the 1990s, none exhibit the unique combination of a vast magma ocean coupled with a sulfur-choked atmosphere seen on L 98-59 d. Other molten planets exist, often found extremely close to their stars where intense stellar radiation broils their surfaces. However, L 98-59 d’s molten state is sustained by a more complex interplay of factors. Nicholls explained that although all planets begin their lives molten, this planet remains in that state due to the persistent heat trapped by its thick atmosphere and the feedback loop between the magma ocean and atmospheric composition. Additional heating arises from the star’s radiation and gravitational interactions with the other planets in the system.
Despite its fascinating characteristics, L 98-59 d is not considered a candidate for life as we understand it. Surface temperatures exceed 1,500 degrees Celsius (2,732 degrees Fahrenheit), conditions far too extreme to support any known biological processes. Nevertheless, the discovery of such an alien world expands our understanding of planetary diversity and challenges existing models of planet formation and evolution. Pierrehumbert remarked that the ongoing exploration of exoplanets continues to reveal strange and unexpected worlds, often surpassing the imagination of science fiction. These findings open new avenues for applying fundamental physics in novel ways, deepening our comprehension of the cosmos and the myriad forms planets can take.
