An exoplanet exists where rocks evaporate and rain back down

Planets that orbit very close to their stars, which have the potential to contain oceans of hot lava, are some of the most fascinating of all of the exoplanets that have ever been discovered. But now, a new study from McGill University suggests that one such exoplanet is even more intriguing than what has been anticipated. 

The research suggests that an Earth-size exoplanet known as K2-141b has a magma ocean that is 100 kilometers deep and supersonic winds that reach over 5,000 kilometers per hour. 

The researchers used computer simulations to predict the conditions on K2-141b. They found that the surface, ocean, and atmosphere are all made up of rocks that can evaporate and “rain” back down on the planet. 

The extreme weather that is predicted by the study would gradually and permanently change the surface and atmosphere of K2-141b over time.

“The study is the first to make predictions about weather conditions on K2-141b that can be detected from hundreds of light years away with next-generation telescopes such as the James Webb Space Telescope,” said study lead author and PhD student Giang Nguyen.

K2-141b is so close to its star that it is gravitationally locked in place – with the same side of the planet constantly facing the heat. The experts determined that about two-thirds of the surface of K2-141b experiences endless daylight, while the remaining one-third of the exoplanet experiences frigid temperatures of below -200 degrees Celsius. 

On the hot side of K2-141b, temperatures of an estimated 3,000 degrees Celsius are hot enough to not only melt rocks but also to vaporize them, ultimately creating a thin atmosphere in some areas. 

“Our finding likely means that the atmosphere extends a little beyond the shore of the magma ocean, making it easier to spot with space telescopes,” said study co-author Professor Nicolas Cowan.

The extreme heat on K2-141b would cause the rock vapor atmosphere to undergo precipitation just like the water cycle on Earth. On our planet, water evaporates and rises into the atmosphere, where it condenses and falls back as rain. This is also the case for the sodium, silicon monoxide, and silicon dioxide on K2-141b. Here, the mineral vapor formed by evaporated rock is pushed over to the frigid night side by supersonic winds, and the rocks “rain” back down into a magma ocean. The rocks are then swept back over to the hot side of the exoplanet, and the rocks evaporate all over again. 

The researchers explained that the weather cycle is not as stable on K2-141b as it is on Earth. For example, the magma flow returning to the hot side of K2-141b is slow, which could ultimately reshape the surface of the planet.

“All rocky planets­, including Earth, started off as molten worlds but then rapidly cooled and solidified,” said Professor Cowan. “Lava planets give us a rare glimpse at this stage of planetary evolution.”

The study is published in the journal Monthly Notices of the Royal Astronomical Society.

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By Chrissy Sexton, Earth.com Staff Writer