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Hubble telescope spies an exoplanet that snows sunscreen

It's snowing sunscreen (hallelujah) on a giant exoplanet that gets way hot on one side and collects titanium oxide on the other.

This artist's illustration depicts Kepler-13Ab and its toasty relationship with its star.
NASA, ESA, and G. Bacon (STScI)

Add exoplanet Kepler-13Ab to the list of planets you don't want to visit. It circles very close to its star, Kepler-13A, and its daylight side reaches scalding temperatures of about 5,000 degrees Fahrenheit (2,760 degrees Celsius), while its dark far side snows sunscreen.

Astronomers at Penn State are learning more about the planet's odd happenings thanks to observations from NASA's Hubble Space Telescope. The exoplanet is locked to its star so it has a permanent day side and a permanent night side. 

The research team used Hubble to observe an unexpected happening on the exoplanet: Its atmosphere gets colder at higher elevations, the opposite of what usually happens with this type of gas giant planet. That means Kepler-13Ab's day side is missing the titanium oxide gas that absorbs light and helps other planets like it heat up at higher altitudes. 

Titanium dioxide is a key ingredient in many sunscreens sold on Earth. So what happens on Kepler-13Ab? The scientists believe high winds sweep the gas around to the exoplanet's dark side, where it condenses into clouds and comes out in the form of a "sunscreen snowfall" thanks to the strong pull of the planet's surface gravity. This fascinating process is called a "cold trap."

The Penn State team published its findings in the October issue of The Astronomical Journal.

Kepler-13Ab is a big exoplanet. It's six times more massive than Jupiter. "In many ways, the atmospheric studies we're doing now on these gaseous 'hot Jupiter' kinds of planets are test beds for how we're going to do atmospheric studies of terrestrial, Earth-like planets," says Penn State astronomer and lead author Thomas Beatty.

At least we can be grateful we don't have to worry about sunscreen flurries on Earth.

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