Planet observed with comet-like tail

Posted by Emma Woollacott

Astronomers using NASA's Hubble Space Telescope have confirmed the existence of what they're calling a 'cometary planet' - one that's so close to its star that its heated atmosphere is escaping into space.

Hubble's Cosmic Origins Spectrograph (COS) indicates that strong stellar winds are sweeping the cast-off atmospheric material behind the planet and shaping it into a comet-like tail.

"Since 2003, scientists have theorized the lost mass is being pushed back into a tail, and they have even calculated what it looks like," said astronomer Jeffrey Linsky of the University of Colorado in Boulder, leader of the NASA study.

"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."

HD 209458b, located 153 light-years from Earth, weighs slightly less than Jupiter but is 100 times closer to its star, with an orbit of just three and a half days.

Linsky and his team used COS to analyze the planet's atmosphere during transiting events.

They detected the heavy elements carbon and silicon in the planet's super-hot, 2,000-degree-Fahrenheit atmosphere. This shows that the planet's star is heating the entire atmosphere, dredging up the heavier elements and allowing them to escape the planet.

The COS data also showed the material leaving the planet was not all traveling 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," Linsky said. "This large gas flow is likely gas swept up by the stellar wind to form the comet-like tail trailing the planet."

But HD 209458b won't be destroyed anytime soon. "It will take about a trillion years for the planet to evaporate," Linsky said.