Hubble looks at Alien World's Atmosphere

via ScienceDaily.

The Hubble Space Telescope has trained its lenses on a "hot Jupiter" exoplanet in the constellation Pegasus and examined its atmosphere in detail. The gas giant planet, HD 209458b, is only 4.7 million miles from its parent star, orbiting every 3 1/2 days. It was the first planet found by the "transit" method measuring the dip in starlight as a world blocks the light from the parent star from reaching Earth. The Hubble data shows the planet is so hot that atmospheric hydrogen is steaming off the planet.

"The Hubble data show how intense ultraviolet radiation from the host star heats the gas in the upper atmosphere, inflating the atmosphere like a balloon. The gas is so hot that it moves very fast and escapes the planet's gravitational pull at a rate of 10,000 tons a second, more than three times the rate of water flowing over Niagara Falls. The planet, however, will not wither away any time soon. Astronomers estimate its lifetime is more than 5 billion years."

Of the 200 extrasolar planets discovered so far, almost 15% are "hot Jupiters", so there are potentially billions of such planets just in our own galaxy.