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1h ago

L 98-59 d Identified as Sulfur-Rich Magma-Ocean World, Study Finds

A Nature Astronomy analysis ties Webb spectra to interior modeling, interpreting the low density plus sulfur gases as evidence of a long‑lived molten mantle.

An artist’s impression of the exoplanet named L 98-59 d, shown with a cutaway to reveal its interior, orbiting a red dwarf star, with two of its sibling planets, seen in this image released on March 16, 2026. Mark A. Garlick/Handout via REUTERS
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Overview

  • L 98-59 d, about 35 light-years away and roughly 1.6 times Earth’s radius, shows a bulk density near 2 g/cm³, far below typical rocky worlds.
  • JWST and ground-based spectroscopy reveal a hydrogen-rich atmosphere with abundant sulfur-bearing gases such as hydrogen sulfide and sulfur dioxide.
  • Models indicate a global magma ocean thousands of kilometers deep that stores sulfur and exchanges volatiles with the atmosphere over billions of years.
  • Researchers propose greenhouse heat trapping as the dominant reason the planet remains molten, with stellar radiation and tidal interactions as secondary sources.
  • The team frames the planet as a candidate first member of a new small-planet category, with further JWST campaigns and ESA’s Ariel and PLATO expected to test the hypothesis.