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Exoplanet Sees Extreme Heat Waves

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Author Topic: Exoplanet Sees Extreme Heat Waves  (Read 62 times)
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« on: January 29, 2009, 08:56:40 am »

One extrasolar planet takes heat waves to the extreme: Within six hours, temperatures on the gas giant can soar by more than 1,000 degrees Fahrenheit (555 degrees C).

The intense baking triggers shock-wave storms that whip around the planet quicker than the speed of sound, carrying with them skyrocketing heat and high-speed winds.

Known as HD 80606b, the gaseous planet was discovered in 2001 by a Swiss planet-hunting team led by Dominique Naef of the Geneva Observatory. It is about four times the mass of Jupiter and is located 200 light-years from Earth.

Wild orbit

HD 80606b's orbit around its host star it's year is 111.4 Earth-days long. Its day one rotation about its axis is thought to last about 34 hours (though the scientists don't measure this value directly). The interesting thing is that its orbit is very elongated, the most eccentric of any known planet.

The giant planet spends most of its year at relatively comfortable distances that would place it between Venus and Earth in our own solar system. But for just a fraction of one day each year, the planet swings to within 0.03 astronomical units (AU) of its star. (One AU is the average distance between the Earth and sun.)

"If you could float above the clouds of this planet, you'd see its sun growing larger and larger at faster and faster rates, increasing in brightness by almost a factor of 1,000," said Gregory Laughlin, an astrophysicist at the University of California, Santa Cruz. Laughlin is lead author of a new report on the findings published in the Jan. 29 issue of the journal Nature.

Hyper heat wave

Laughlin and his colleagues used NASA's Spitzer Space Telescope to measure heat emanating from the planet before, during and after its closest approach to its host star.

The team found that in just six hours, the planet's temperature rose from 980 to 2,240 degrees Fahrenheit (527 to 1,227 degrees C). At its closest approach, the planet receives 825 times more irradiation than it does at its farthest point from the star.

While other hot exoplanets close to their stars, called hot Jupiters, are known to have temperatures that reach up to 3,000 degrees F (1,600 degrees C), none has shown such a temperature swing in such a brief period of time.

That kind of temperature change suggests the intense irradiation from the star is absorbed in a layer of the planet's upper atmosphere that absorbs and loses heat rapidly, Laughlin said, adding that if the sun suddenly became 1,000 times brighter, it would take much longer before the Earth would double its temperature.

Something strange must be going on.

Shock-wave storms

To figure out how the heat affected the planet's atmosphere, study researcher and UCSC colleague, Jonathan Langton, fed the Spitzer data into a computer model. The simulation revealed global storms and shock waves unleashed in the planet's atmosphere every 111 days as it swings close to its star.

"As the atmosphere heats up and expands, it produces very high winds, on the order of 5 kilometers per second (3 miles per second, or more than 11,000 mph), flowing away from the day side toward the night side," Langton said. "The rotation of the planet causes these winds to curl up into large-scale storm systems that gradually die down as the planet cools over the course of its orbit."

So even on the side of the planet facing away from the star, "you'd feel the effect of these shock-wave storms as they pass over you. It's not a place you would want to visit," Laughlin said.

"That heating is so intense it's basically like an explosion on the side of the planet that's getting baked by the star," Laughlin told SPACE.com. "That generates these extraordinary storms that begin to echo around the planet."

If the planet's orbit is aligned just right, it will pass in front of the star, an event known as a transit, on Feb. 14. The transit would allow astronomers to refine their calculations of the planet's radius and make other measurements.

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