Astronomers have identified a unique class of exoplanet that challenges our current understanding of planetary evolution. New research published in Nature Astronomy details the discovery of L 98-59 d, a celestial body that maintains a persistent surface magma ocean, potentially lasting for billions of years. This finding offers a rare glimpse into the volatile-rich history of worlds that remain in a molten state far longer than rocky planets like Earth.
The study, led by Harrison Nicholls from the Department of Physics at Oxford University, suggests that the chemical composition of this exoplanet—specifically its high sulfur content—is the primary driver behind its unusual geological state. Located approximately 35 light-years away and orbiting an M-dwarf star, L 98-59 d was originally identified by NASA’s Transiting Exoplanet Survey Satellite (TESS) in 2019. By utilizing data from the James Webb Space Telescope (JWST) and other observatories, researchers have been able to characterize the planet with surprising precision.
Understanding the Composition of L 98-59 d
The physical characteristics of L 98-59 d distinguish it significantly from our own planet. According to the research published in Nature Astronomy, the exoplanet possesses 1.64 Earth masses and 1.627 Earth radii. These measurements result in an approximate density of 2.2 grams per cubic centimeter, which is only about 40% of Earth’s density. This low density serves as a key indicator that the planet’s internal structure is fundamentally different from the terrestrial worlds within our solar system.
Scientists believe that sulfur plays a pivotal role in maintaining this molten state. In the early development of rocky planets, magma oceans were common; however, as Earth cooled, its outer mantle solidified. On L 98-59 d, the high concentration of sulfur acts as a melting point depressant. Because sulfur is a siderophile element—meaning it has a strong affinity for iron—it likely influenced the formation of the planet’s core and mantle, keeping the surface in a continuous state of volcanic activity.
The research titled “Volatile-rich evolution of molten super-Earth L 98-59 d” provides a framework for understanding why this planet has avoided the cooling process that typically leads to a solid crust. This relationship between sulfur, planetary density, and magma retention may define an entirely new category of exoplanets that astronomers are only beginning to categorize.
The Significance of Magma Ocean Worlds
For planetary scientists, the existence of a long-lived magma ocean is significant because it alters the potential for habitability and our understanding of magnetospheres. On Earth, the interaction between a solid mantle and a molten outer core, combined with Coriolis forces, sustains a protective magnetic field. The discovery of L 98-59 d forces researchers to reconsider how volatile elements like sulfur influence the interior dynamics of super-Earths.
As we continue to monitor data from the JWST and other international space missions, the study of L 98-59 d serves as a benchmark for future exoplanet characterization. By analyzing the light spectra and density profiles of such planets, the scientific community can better map the diversity of planetary systems in our galaxy. This work is part of a broader effort to classify exoplanets not just by their size and distance from a star, but by their chemical composition and evolutionary stage.
Key Takeaways: The Discovery of L 98-59 d
- New Class of Planet: L 98-59 d is representative of a new class of exoplanets defined by long-lived surface magma oceans.
- Chemical Drivers: The planet’s high sulfur content is identified as the critical factor lowering its melting point and preventing solidification.
- Density Anomalies: With a density of 2.2 g/cm³, the planet is significantly less dense than Earth, pointing to a unique internal structure.
- Scientific Methodology: The findings were made possible by combining data from NASA’s TESS mission and follow-up observations from the James Webb Space Telescope.
As of late May 2026, the scientific community continues to analyze data regarding the atmospheric and surface conditions of M-dwarf orbiting planets. While the data-collection phase of certain localized instruments, such as NASA’s Atmospheric Waves Experiment (AWE), has recently concluded, the broader investigation into planetary formation remains an active priority for space agencies worldwide. We encourage our readers to share their thoughts on this discovery in the comments section below as we continue to track developments in exoplanetary science.
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