L 98-59 d is a ~1.6 R⊕ exoplanet orbiting the M dwarf l-98-59 ~35 light-years from Earth in Volans. In a 2026 Oxford-led study (src-l-98-59-d-sulphur-magma-world-2026-05), the planet is proposed as the prototype of a new small-planet class: a persistent, global sulphur-rich silicate magma-ocean-world sustained by a heavy sulphur-bearing atmosphere driving a runaway greenhouse.
Key properties
- Radius: ~1.6 R⊕
- Density: lower than expected for a purely terrestrial composition
- Distance: ~35 ly in Volans
- Host: M dwarf l-98-59
- Atmosphere: heavy sulphur-bearing molecules → intense greenhouse → mantle stays molten over Gyr timescales
- Surface: uninhabitable; persistent global magma ocean
- Likely formation pathway: shrunken former sub-Neptune that lost most of its primordial envelope
Significance
- Lead author harrison-nicholls argues the result shows current small-planet taxonomy (rocky / gaseous / water-rich) is too coarse.
- Co-author raymond-pierrehumbert frames the methodology as a demonstration that coupled atmosphere–interior modelling can reconstruct deep planetary history from mass, radius, and atmospheric composition.
- Widens the planetary diversity catalogue against which biosignatures and false-positive-biosignatures are interpreted.
Related Pages
- l-98-59 · m-dwarf-stars
- magma-ocean-world · sulphur-atmosphere · outgassing · secondary-atmosphere
- mini-neptune · high-mean-molecular-weight-atmosphere
- exoplanet-habitability · exoplanet-atmosphere-models
- 55-cancri-e — sibling lava planet with contrasting hydrogen/CO-rich atmosphere (low oxygen-fugacity interior vs. L 98-59 d’s sulphur-rich high-fugacity interior)
- k2-18b · toi-1130b
- lhs-1140b — another 2026 M-dwarf rocky-world atmosphere study, contrasting outcomes (potentially life-favorable world vs. L 98-59 d’s uninhabitable magma-ocean class)
- harrison-nicholls · raymond-pierrehumbert · university-of-oxford
- src-l-98-59-d-sulphur-magma-world-2026-05
- src-55-cancri-e-hydrogen-atmosphere-2026-06