Scientists have found an entirely new kind of planets.
The worlds have a permanent ocean of magma inside of them, storing large amounts of sulphur.
The example found by scientists is known as L 98-59 d, and orbits a star about 35 light years from Earth.
Observations from the James Webb Space Telescope as well as from Earth show that the planet is not very dense, is roughly 1.6 times the size of Earth and has large amounts of hydrogen sulphide in its atmosphere.
Scientists would previously have thought of the planet as one of two known categories: a “gas-dwarf” made of rock with a hydrogen atmosphere, or a water world with ice and deep oceans. But the new research shows that it is something else entirely, a whole new kind of planet with heavy sulphur molecules.
In the study, researchers used computer simulations to reconstruct the life of the planet from just after it was born, five million years ago, to today. That allowed them to use the telescope observations to understand what is happening inside of the planet.
The research showed that the mantle of the planet is made of a similar substance to lava on Earth, molten silicate. Beneath that is a magma ocean that goes all the way through the planet, a reservoir storing sulphur deep underneath the planet’s surface.
The magma ocean lets the planet keep its hydrogen-rich atmosphere, sulphur-bearing gases such as hydrogen sulphide. Without that ocean, the material would go off into space, taken by X-ray radiation from the star.
There could be many more planets like this, the researchers speculate. As such, the study suggests that there might be many more kinds of planet than we had ever previously realised – some of which might support alien life.
“This discovery suggests that the categories astronomers currently use to describe small planets may be too simple,” said Harrison Nicholls, from the University of Oxford, who was lead author on the paper. “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?”
The work is published in a new paper, ‘Volatile-rich evolution of molten super-Earth L 98-59 d’, in the journal Nature Astronomy.
