Scientists have identified a new type of planet capable of storing vast quantities of sulphur beneath a permanent ocean of molten rock, according to multiple reports. The study, led by researchers at the University of Oxford and published in Nature Astronomy, describes L 98-59 d, a planet orbiting a small red dwarf star 35 light years from Earth. 6 times the size of Earth but has an unexpectedly low density and an atmosphere containing significant amounts of hydrogen sulphide.
It does not fit the categories of rocky 'gas dwarf' or water-rich world, representing a new class dominated by heavy sulphur compounds. Advanced computer simulations reconstructed the planet's history from shortly after its formation nearly five billion years ago. The mantle is likely made of molten silicate, forming a global magma ocean stretching thousands of kilometres below the surface.
This magma ocean allows the planet to store huge amounts of sulphur and retain a thick hydrogen-rich atmosphere containing hydrogen sulphide. Surface temperatures on L 98-59 d reach about 1,900°C (3,500°F), according to reports. L 98-59 d is unlikely to support life.
Dr Harrison Nicholls, lead author and astrophysicist at the University of Oxford, said the discovery suggests that the categories astronomers currently use to describe small planets may be too simple. He described the planet's interior as being in a mushy, molten state, like molasses, and noted that the magma ocean efficiently stores gases, protecting them from processes that would otherwise remove them. He added that some planets in the habitable zone might not be very habitable at all, but could be molten planets like this one.
Other extreme exoplanets have also been studied. A separate planet, TOI-561 b, is a 'super Earth' with seas of molten lava, permanently stuck in daylight on one side. Located 560 light-years away, it has surface temperatures of 1,800°C and an atmosphere containing water, oxygen, and carbon dioxide.
TOI-561 b is an ultra-short-period planet with a year lasting under 11 hours. Another world, Epsilon Indi Ab, is a Jupiter-like planet with an ammonia atmosphere and clouds of water. 6 times the mass of Jupiter and has a temperature between -70°C and +20°C.
In our solar system, a tiny icy world beyond Pluto, (612533) 2002 XV93, harbors a thin atmosphere possibly created by volcanic eruptions or a comet strike. The object is about 500 km across and is the smallest in the solar system with a clearly detected global atmosphere, according to reports. Its atmosphere is 5 million to 10 million times thinner than Earth's and 50 to 100 times thinner than Pluto's.
Likely atmospheric chemicals include methane, nitrogen, or carbon monoxide. Ko Arimatsu, lead researcher at the National Astronomical Observatory of Japan, described the discovery as changing our view of small worlds in the solar system and challenging the conventional view that atmospheres are limited to large planets, dwarf planets, and some large moons. He noted that future monitoring is important to determine whether the atmosphere fades or persists.