Hurricane Katrina would be regarded as a gentle breeze on HD 209458b. The giant planet, located about 150 light-years away in the constellation Pegasus, is a hot Jupiter—nearly as big as our own gas giant, but orbiting very close to its parent star. Like Mercury and our moon, the planet is tidally locked, meaning it always shows the same face to its sun. As a result, HD 209458b's dayside surface temperature never dips below 1000˚C, while its night side temperatures are hundreds of degrees cooler. Such a large temperature gradient generates eye-popping wind speeds. How fast? By carefully analyzing the spectra of starlight streaming through its atmosphere when the planet passes in front of its star, researchers report online today in Nature that HD 209458b generates winds of toxic carbon monoxide reaching 7000 kilometers per hour. That's twice as fast as any aircraft has ever flown—not that anyone would want to fly across this world.
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