SCIENCE

Faraway Planet is Blackest Yet Found

The planet, TrES-2b, is a gas giant about the size of Jupiter. But that’s where the similarities end

August 17, 2011

An artist's concept of what planet TrES-2b might look like David A. Aguilar (CfA)

A planet orbiting a star some 750 million light years away is extraordinarily dark, according to astronomers at the Harvard-Smithsonian Center for Astrophysics and Princeton University who report their findings in the Monthly Notices of the Royal Astronomical Society. They used data from NASA’s Kepler spacecraft to study the alien world and found that it reflects only 1 percent of the light that reaches it.

The planet, TrES-2b, is a gas giant about the size of Jupiter. But that’s where the similarities end. Jupiter is cool enough to be surrounded by bright clouds of ammonia that reflect a third or more of the sunlight that falls on it. TrES-2b is much hotter—more than 1,800 degrees Fahrenheit—and lacks the reflective clouds. It’s atmosphere is full of chemicals that absorb light, such as gaseous titanium oxide and vaporized sodium and potassium, which explain, in part at least, the planet’s dark nature. The planet is so dark, it is blacker than anything in our Solar System, blacker than paint, blacker than coal.

“It’s not clear what is responsible for making this planet so extraordinarily dark,” says study co-author David Spiegel of Princeton University. “However, it’s not completely pitch black. It’s so hot that it emits a faint red glow, much like a burning ember or the coils on an electric stove.”

TrES-2b is weird in another way—it is tidally locked, like our Moon is with Earth, so that one side always faces its sun, the star GSC 03549-02811, and one side always faces away.

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