This artist's concept shows a Jupiter-like planet soaking up the scorching rays of its nearby "sun." NASA's Spitzer Space Telescope used its heat-seeking infrared eyes to figure out that a gas-giant planet like the one depicted here is two-faced, with one side perpetually in the cold dark, and the other forever blistering under the heat of its star.
Image credit: NASA/JPL-Caltech
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NASA has announced that its Spitzer Space Telescope has made the first measurements of the day and night temperatures of a planet outside our solar system. An international team of scientists, including Professor Kristen Menou of Columbia University, used infrared data from Spitzer to reveal that the Jupiter-like gas giant planet circling very close to its sun is always as hot as fire on one side, and potentially as cold as ice on the other.
"This planet has a giant hot spot in the hemisphere that faces the star," said Joe Harrington of the University of Central Florida, Orlando. Harrington is lead author of a paper appearing online today in Science. He and the project's principal investigator, Brad Hansen of the University of California, Los Angeles, presented the results today at the 38th meeting of the Division for Planetary Sciences of the American Astronomical Society in Pasadena, California. "This is a spectacular result," said Michael Werner, project scientist for Spitzer at NASA's Jet Propulsion Laboratory. "When we designed Spitzer years ago, we did not anticipate that it would be revolutionizing extrasolar planet science."
Kristen Menou, professor of astronomy and a member of Columbia's Astrobiology Center, is a co-investigator on the Spitzer program. He is interpreting the data from the Spitzer Space Telescope, data that revealed the extrasolar planet's 'phase curve' (plotting of the amount of light emitted by the planet as it orbits its sun). Menou studies how wind affects planetary temperatures. "At Columbia", says Menou, "we've been studying what the global winds may be like on exotic planets such as Upsilon Andromedae b. This measurement indicates that the planet's winds may be far less efficient at redistributing heat across the planetary surface than we expected."
The Spitzer data is also a valuable proof of principle, demonstrating that the telescope can detect the planet's extreme temperature variations. "We are thrilled by this result and the prospects carried with it", says Menou. "There are other solar systems where we can perform similar observations in the future. We are truly opening the door to studying a whole new class of planets, looking at diversity, and thus learning from differences with our own solar system."
Upsilon Andromedae b is a so-called hot-Jupiter planet made of gas like Jupiter, and circles closely around its scorching star every 4.6 days. Scientists believe the planet, with a temperature variation of about 2,550 degrees Fahrenheit, is tidally locked to its star. This means it is rotating slowly enough that the same side always faces the star, just as our tidally locked moon never shows us its back side. However, since this planet is gas, not rock, its outer atmosphere could be moving around faster than its locked interior. According to the astronomers, the observed temperature difference between the two sides of Upsilon Andromedae b is extreme and indicates that the planet's atmosphere absorbs and reradiates sunlight so fast that gas circling around cools off quickly.
The Spitzer Space Telescope used its heat-seeking infrared eyes to periodically stare at the Upsilon Andromedae planetary system over about five days. It found that the system's light dimmed and brightened in time with Upsilon Andromedae b's orbit. This change in observed light, or heat, is the result of the planet showing its different faces to Spitzer as it travels around the star. When the planet's sunlit side was in Earth's view, Spitzer detected more light from the system; when its dark side was facing us, Spitzer picked up less light.
Upsilon Andromedae b was discovered in 1996 around the star Upsilon Andromedae, which is 40 light-years away and visible to the naked eye at night in the constellation Andromeda. It is circled by two other known planets located farther out than Upsilon Andromedae b. The plane of this planetary system is tilted relative to our solar system in such a way that the planets are always in Earth's line of sight.
Other authors of this work include: Statia H. Luszcz of Cornell University, Ithaca, N.Y., and University of California, Berkeley; Sara Seager of the Carnegie Institution of Washington, D.C.; Drake Deming and Jeremy Richardson of NASA's Goddard Space Flight Center, Greenbelt, Maryland; and James Y-K Cho of Queen Mary, University of London.
Columbia University Astrobiology Center: http://www.astro.columbia.edu/~astrobio/
For graphics and more information about Spitzer, visit www.spitzer.caltech.edu/spitzer.
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