This exoplanet’s atmosphere is going full steam ahead.

A planet beyond our solar system called GJ 9827d has an atmosphere composed almost completely of hot water molecules, astronomers report in the Astrophysical Journal Letters October 4.

“We’re using the term ‘steam world,’” says astronomer Ryan MacDonald at the University of Michigan in Ann Arbor.

GJ 9827d was discovered in 2017 orbiting a star about 100 light-years from Earth. At about twice Earth’s size and three times Earth’s mass, it’s a type of planet called a sub-Neptune (SN: 8/8/22). Worlds like this are the most common in the galaxy, although our solar system doesn’t have any.

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