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Planetary News: Extrasolar Planets (2007)Spitzer Detects Supersonic Winds on Distant PlanetMay 10, 2007:
Supersonic winds measuring around 4500 miles per hour are blasting through the atmosphere of a Jupiter-sized planet orbiting star HD 189733. So say scientists who have been studying conditions on the planet using the Spitzer Space Telescope. The research team led by Heather Knutson of the Harvard-Smithsonian Center for Astrophysics used the Spitzer Space Telescope to measure the infrared light, or heat, as the planet orbited its sun-like star. “We have mapped the temperature variations with longitude across the entire surface of a planet that is so far away, it takes 60 years to reach us” explained Knutson. The planet, which is in constellation Vulpecula, is "tidally locked" to itsstar, so that one side always faces the star and the other side is always dark ,just as the moon is tidally locked to the Earth. This means that one side of the planet is in a perpetual “day,” while the other is in a permanent “night.” Despite this, the map shows that temperatures on the the planet differ by a relatively modest 500 degrees Fahrenheit, ranging from 1,200 degrees F on the nightside to 1,700 degrees F on the dayside. "At these high temperatures, air cools off rapidly when it moves from the dayside to the nightside," said Adam Showman of the University of Arizona Lunar and Planetary Laboratory (LPL). "That relatively small temperature difference implies that fierce winds redistribute a lot of the heat." Showman and fellow LPL research associate Curtis Cooper analyzed Spitzer data on planet HD 189733b using the numerical models they've been developing for exoplanet atmospheres. "We need to do more detailed modeling to calculate actual wind speeds” Showman said. "However, we can be certain the speeds are FAST, probably a couple of kilometers per second," or about 4,500 mph. According to Showman’s and Curtis’s calculations the supersonic exoplanet winds might be as strong as 10 kilometers per second, or about 22,000 mph. By comparison, its wind speeds on Earth rarely exceed 200 mph in the Jet Stream, and wind speeds on Jupiter range from 70 to 340 mph. "This isn't just the case where you need winds, but winds that are fast enough to move air from one side of the gas giant planet to the other before it has time to cool off," Showman said. "These hot Jupiter exoplanets are blasted by 20,000 times more energy per second than Jupiter,” Added co-author David Charbonneau of the Harvard-Smithsonian Center for Astrophysics. “Now we can see how these planets deal with all that energy. " |
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