Hubble Probes Layer-cake Structure of Alien World's Atmosphere [HD 209458b]

HubbleSite ^ | January 31, 2007 | Donna Weaver/Ray Villard

[SunkenCiv]

The planet, designated HD 209458b, is unlike any world in our solar system. It orbits so close to its star and gets so hot that its gas is streaming into space, making the planet appear to have a comet-like tail... 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. The scorched planet is a big puffy version of Jupiter. In fact, it is called a "hot Jupiter," a large gaseous planet orbiting very close to its parent star... The planet completes an orbit around its star every 3.5 days. It orbits 4.7 million miles from its host, 20 times closer than the Earth is to the Sun. By comparison, Mercury, the closest planet to our Sun, is 10 times farther away from the Sun than HD 209458b is from its star. Unlike HD 209458b, Mercury is a small ball of iron with a rocky crust... HD 209458b is one of the most intensely studied extrasolar planets because it is one of the few known alien worlds that can be seen passing in front of, or transiting, its star, causing the star to dim slightly. In fact, the gas giant is the first such alien world discovered to transit its star. HD 209458b is 150 light-years from Earth in the constellation Pegasus.

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from PhysOrg:

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The solar-type star, HD 209458, and its 'hot Jupiter' planet in transit are shown in simulated violet light. As in this illustration, the star would appear as a limb-darkened purple disk if seen in near-ultraviolet and violet light. The newly detected dense, narrow layer of hot hydrogen atoms is represented by the dark absorbing ring around the opaque planetary disk. The bulk of hydrogen atoms in the upper atmosphere, which forms an extensive cloud and also a comet-like tail, is shown in white. The absorbing layer was drawn at twice the altitude and 10 times the thickness to be more easily visible in this illustration, the rest of which has been drawn to scale. (Art credit: Loretta McKibben, UA Lunar and Planetary Lab).

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Image: Hubble Measures Atmospheric Structure of Extrasolar Planet HD 209458b

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[Ernest_at_the_Beach]

The Universe is a fascinating story...

[SunkenCiv]

story about discovery is linked here:

Great Collection of SPACE Links
Hall of Science | 2-9-05 | Editorial Staff
Posted on 03/09/2005 5:15:07 PM EST by vannrox
http://www.freerepublic.com/focus/f-news/1359500/posts

also:

Too Close For Comfort: Hubble Discovers An Evaporating Planet
Science Daily | FR Post 3-15-03 | Editorial Staff
Posted on 03/14/2003 9:03:50 AM EST by vannrox
http://www.freerepublic.com/focus/f-news/864636/posts

[SunkenCiv]

Wrong Group Credited with Being First in Recent Planet Discovery
by Robert Roy Britt
17 December 1999

[T]iming was on Greg Henry's side recently after he observed a decrease in light from a distant star on November 7, providing what seemed to be the first conclusive evidence that planets exist around other stars. A press release was issued within a week and Henry, an astronomer at Tennessee State University, became known as the first scientist to make a direct observation of an extrasolar planet... Another group of researchers, David Charbonneau and Tim Brown of the Harvard-Smithsonian Center for Astrophysics and the National Center for Atmospheric Research... back in September... had already observed the dip in starlight from the planet passing in front of HD 209458. And their observations were more thorough, covering two full transits (on September 9th and 16th) of the planet across the disk of the star... HD 209458... 153 light-years away (roughly 1.4 million billion kilometers or 859,000 billion miles) in the constellation Pegasus.