Astronomers once thought mini-Neptunes were covered by global magma oceans.
Study finds many mini-Neptunes face immense pressure, making their surfaces likely solid
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Many so-called mini-Neptunes, smaller than Neptune but with thick atmospheres of hydrogen-helium, have been found by astronomers. It is even possible that the closest type of planet in our galaxy is mini-Neptunes. It was believed that these worlds had been covered by magma oceans around the world. Nevertheless, it has been proposed by a new study that the crust would be pressed together by the heavy atmospheres in solid rock instead of molten lava. In fact, this discovery contradicts previous theories regarding these worlds.
Solid surfaces under pressure
According to the study, scientists had assumed that searing heat and thick gas layers would melt mini-Neptune crusts into global magma oceans. However, data from NASA’s James Webb Space Telescope suggested a mini-Neptune’s atmosphere contained heavier molecules than expected, implying an extremely thick, high-pressure blanket.
Models showed that this crushing pressure would force molten rock to solidify (much like carbon turning into diamond under pressure). Extending these calculations, the team found that many mini-Neptunes once assumed to be “lava worlds” likely have solid floors.
Implications for planet formation
Since mini-Neptunes are one of the most abundant planets in the galaxy, the fact that many of them contain solid surfaces makes scientists reconsider the theory of planet formation. In the past, other solar systems were predicted to be similar to the one, which cannot be the case with mini Neptuns.
It is also useful in clarifying the formation of planets by presenting a complete picture of whether the planets are molten or solid. In the end, this knowledge can inform the hunt for Earth-like worlds and help understand the history of the Earth itself.
