Researchers have identified a brand-new class of exoplanet unlike any previously known.
It's a molten, sulphur-rich world with a vast global magma ocean, that likely reeks of rotten eggs.
The discovery, led by the University of Oxford, centres on the planet L 98-59 d, located about 35 lightyears from Earth in the constellation of Volans.
The study reveals that the planet does not fit into established categories such as rocky, gaseous or water-rich worlds, but instead represents an entirely new type of planetary body.
More strange planets
Using advanced modelling and observational data, the team found that L 98-59 d likely possesses a mantle composed of molten silicate material – similar to lava on Earth – extending deep beneath its surface.
Unlike early Earth, however, this magma ocean appears to have persisted for billions of years rather than cooling to form a solid crust.
L 98-59 d – what we know
Planet L 98-59 d is around 1.6 times the size of Earth, but has a lower density than expected, indicating a composition that differs significantly from terrestrial planets in our Solar System.
Modelling suggests it formed and evolved under very different conditions, possibly once resembling a sub‑Neptune before shrinking and losing some of its primordial atmosphere.
The team say the planet’s unusual composition is driven by a thick atmosphere rich in heavy sulphur-bearing molecules, which creates an intense greenhouse effect.
This prevents the surface from cooling, allowing much of the planet to remain molten.
A planetary game-changer?
"This discovery suggests that the categories astronomers currently use to describe small planets may be too simple," says the study's lead author Dr Harrison Nicholls from the Department of Physics at the University of Oxford in the UK.
"While this molten planet is unlikely to support life, it reflects the wide diversity of the worlds which exist beyond the Solar System. We may then ask: what other types of planet are waiting to be uncovered?"
"What’s exciting is that we can use computer models to uncover the hidden interior of a planet we will never visit," says co-author Professor Raymond Pierrehumbert, also from the University of Oxford.
"Although astronomers can only measure a planet’s size, mass and atmospheric composition from afar, this research shows that it is possible to reconstruct the deep past of these alien worlds – and discover types of planets with no equivalent in our own Solar System."
Next-generation telescopes are expected to uncover more examples of these molten worlds, offering further insight into the processes that shape planetary systems.
