The remarkable extrasolar planet HD 209458b is a gas giant a little smaller than Jupiter that's constantly venting its atmosphere into space, giving it a very comet-like tail, all thanks to its super-close orbit around its sun.

The planet is found about 153 light-years away from Earth. As you can see above in an artist's conception, it's very close to its star - its orbit only takes 3.5 days, whereas even Mercury takes 88 days to revolve around our Sun. That unusual proximity has created this comet tail effect, as the star's intense radiation heats up the atmosphere so much that some of it escapes into space.

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Study leader Jeffrey Linsky, an astronomer at the University of Colorado, explains that this amazing find is long in the making:"

"Since 2003 scientists have theorized the lost mass is being pushed back into a tail, and they have even calculated what it looks like. We think we have the best observational evidence to support that theory. We have measured gas coming off the planet at specific speeds, some coming toward Earth. The most likely interpretation is that we have measured the velocity of material in a tail."

The Hubble Telescope's Cosmic Origins Spectrograph was able to detect the powerful solar winds that shape the tail and the turbulent nature of the planet's internal chemistry. The astronomers were able to find carbon and silicon in the planet's atmosphere, meaning the entire body is being super-heated and even the heavy elements are getting thrown up into space. Even so, the star won't destroy its planet anytime soon: at its present rate of evaporation, HD 209458b has enough material left to stick around for a trillion years.

[The Astrophysical Journal]