Hottest, darkest planet discovered

Stephen Withers
Thursday, 10 May 2007 05:15

Science - Space

NASA's Spitzer space telescope has revealed the hottest planet yet discovered: a 2000 Celsius (3700 Fahrenheit) gas giant described as a "chunk of hot coal in space".

Planet HD 149026b is 279 light years away in the constellation Hercules. Despite being of similar size to Saturn, it is the smallest and densest known transiting planet. (A transiting planet crosses in front and behind its star as viewed from Earth.) Researchers say it is probably also the darkest, absorbing almost all of its star's light rather than reflecting it.

"This planet is off the temperature scale that we expect for planets," said Drake Deming of NASA's Goddard Space Flight Center, co-author of the Nature paper describing the findings.

Another exoplanet studied using Spitzer appears to be extremely windy.

Surface temperatures on HD 189733b (located 60 light-years away in the constellation Vulpecula) have been mapped by measuring the infrared light from the planet. Even though one side of HD 189733b permanently faces its star, the temperature difference between the light and dark sides is relatively minor - 900 Celsius (1700 Fahrenheit) versus 650 Celsius (1200 Fahrenheit). Scientists theorise winds of up to 9500 kph (6000mph) transfer heat to the dark side.

"These hot Jupiter exoplanets are blasted by 20,000 times more energy per second than Jupiter," said Harvard-Smithsonian Center for Astrophysics researcher David Charbonneau, co-author of the Nature paper describing HD 189733b. "Now we can see how these planets deal with all that energy."

'Hot Jupiters' are gas giants orbiting close to their stars. Around half of the 200-plus exoplanets discovered so far are hot Jupiters.