Planet with a comet-like tail discovered

A planet with a fiery comet-like tail has been discovered in a distant solar system.

The gas giant HD 209458bm is orbiting so close to its star that its heated atmosphere is streaming into space.

Observations by the Hubble Space Telescope suggest that powerful stellar winds are sweeping the atmospheric material behind the scorched planet.

"We have measured gas coming off the planet at specific speeds, some coming toward Earth," said astronomer Dr Jeffrey Linsky, from the University of Colorado at Boulder in the US. "The most likely interpretation is that we have measured the velocity of material in a tail."

The planet, located 153 light years from Earth, weighs slightly less than Jupiter but is 100 times closer to its parent star.

It completes an orbit in just 3.5 days, much faster than Mercury, the closest planet to the Sun, which makes the same journey in 88 days.

The planet's super-hot atmosphere reaches temperatures of more than 1000C.

A Hubble instrument called the Cosmic Origins Spectrograph, which analyses light, showed the presence of carbon and silicon in the atmosphere.

The data also showed that material leaving the planet was not all travelling at the same speed.

"We found gas escaping at high velocities, with a large amount of this gas flowing toward us at 22,000 miles per hour," said Dr Linsky. "This large flow is likely gas swept up by the stellar wind to form the comet-like tail trailing the planet."

Despite the immense heat, it will take around a trillion years for the planet to boil away, he said.

The new findings appear in the latest issue of The Astrophysical Journal.

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