Nasa - Hubble & swift detect first - Ever changes in an exoplanet atmosphere

Just to the east of M27, the "Apple Core" nebula, there's a star that can be seen in binoculars. And this star hosts a giant planet. The star is slightly smaller and cooler than our sun. In 2005, astronomers found it's Jupiter- size planet, named HD 189733b. Incredibly, the planet orbits just 3 million miles from the star, twelve times closer than Mercury orbits our sun. It's so close that the planet whips around its star in a little over two days. But this planet pays a steep price for skirting its sun. Sometimes, the star erupts with powerful flares, flares that heat the planet's upper atmosphere so much that the gasses simply escape. Since the planet passes in front if its star as we see it from Earth, astronomers were able to use the Hubble Space Telescope to establish that the atmosphere was evaporating. But when they looked again in 2010 there was not trace of an escaping atmosphere. Yet when astronomers looked once more in 2011, they saw dramatic evidence that the atmosphere was eroding. Hydrogen gas was rushing away from the planet at speeds over 300,000 miles an hour. What had changed? The same astronomers were also watching the star with NASA's Swift satellite. Just 8 hours before Hubble was scheduled to look for the planet's atmosphere, Swift saw the star erupt in a powerful X-ray flare. Similar flares happen frequently on the sun. But because the planet is so big and so close to its star, this X-ray blast had an outsized effect, heating the planet's atmosphere and sweeping away 1,000 tons of gas each second. The escaping gas gave the planet a comet-like tail. While HD 189733b has plenty of gas to spare, atmospheric erosion is an important process, one able to whittle down any gas giant planet that hugs its star too close. Subtitle: Libera Scienza http://www.facebook.com/liberascienza