Comet tail confirmed on alien planet - space - 16 July 2010 - New Scientist

The roster of weird alien worlds has a new addition: a planet with a tail.

The gaseous extrasolar planet known as HD 209458b has been suspected of having a comet-like tail since 2003 but, being 153 light years away, it has been hard to prove.

Using the Hubble Space Telescope, Jeffrey Linsky and his team at the University of Colorado in Boulder has managed to study the mass the planet is shedding. They calculated the tail's composition, direction and speed by studying changes in its host star's ultraviolet spectra as the planet passes in front of it.

HD 209458b is similar to Jupiter in size and composition. It orbits its star in just 3.5 days and its surface is roughly 3632 °C. This intense heat is causing heavy elements like carbon and silicon to boil off, and be blown away by the solar wind.

"It's a very similar phenomenon to what happens with a comet," Linsky explains. "Except it's starting off as a gas planet as opposed to ice and the material in its outer atmosphere is being heated and lost. The wind from the star is pushing it away from the planet so we see a tail."

The gas trail is blowing away from the star at more than 35,000 kilometres per hour. The team estimates that the comet-like planet has a trillion years before the entire planet disappears.

Journal reference: The Astrophysical Journal, in press

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