If you enjoy a steam bath, the galaxy may offer a lot of planets for you to visit. These worlds may be completely covered by water. And they’re so close to their stars that a lot of the water evaporates, forming a deep, steamy atmosphere.

Astronomers have confirmed more than 4,000 planets in other star systems, with many more candidate worlds. Some of them are classified as “super-Earths.” These planets are a little wider and heavier than Earth. They’re also quite dense, so they’re probably balls of rock and metal, just like Earth.

Some other planets are “mini-Neptunes.” They’re about twice the size of the super-Earths, but they’re not nearly as dense. That could mean they have solid cores surrounded by layers of hydrogen and helium, the lightest elements.

But recent studies by research teams in France suggest another possibility: The planets are hot and wet, with atmospheres made of steam.

The mini-Neptunes in this category are quite close to their parent stars — millions to perhaps tens of millions of miles. At that close range, they’d be extremely hot. If they have deep oceans, all that heat would vaporize a lot of the water. The water vapor would form a puffed-up atmosphere. That would make the planets look a lot wider than they really are.

If that’s the case, then a lot of “mini-Neptunes” are really super-Earths in disguise — hidden below a blanket of steam.

Tomorrow: the Great Silence.

Script by Damond Benningfield

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