Extrasolar planet half hot, half freezing -- study

Using NASA's Spitzer Space Telescope, astronomers have for the first time measured the temperatures on a planet outside our Solar System, and found the planet blisteringly hot on one side, frigid on the other.

The scientists on Thursday reported their findings at a meeting of the American Astronomical Society in Pasadena, California. The study also appeared in the Oct. 12 online advance edition of the journal Science.

The planet, 40 light years (400 trillion kilometers) from Earth and named Upsilon Andromeda b, is about 75 percent the mass of Jupiter, orbiting its star every 4.6 days.

Upsilon Andromeda b was discovered in 1996 around its sun Upsilon Andromeda, which is away and visible to the naked eye at night in the constellation Andromeda.

The researchers determined that the temperature variation between the planet's light side and its dark side could reach 1,600 degrees Celsius -- its sunlit side could be hot as 1,400 to 1,650 degrees Celsius, while the dark side only minus 20 to 230 degrees Celsius.

On the other hand, Jupiter, the similar giant gas planet in our Solar System, maintains an even temperature all around.

"This planet has a giant hot spot in the hemisphere that faces the star," said Joe Harrington, the lead author of the study from the University of Central Florida, Orlando.

"The temperature difference between the day and night sides tells about how energy flows in the planet's atmosphere. Essentially, we're studying weather on an exotic planet."

The extreme temperature difference between the two sides of the planet could mean that its atmosphere absorbs and re-radiates sunlight rapidly, allowing the circling gases to quickly cool off as they move from light side to dark side, the researchers said.

The findings could completely change scientists' view about exotic gas giant planets, the researchers said.

Most astronomers expected them to be more uniformly heated like our Jupiter, but this planet clearly has a hot side and a cool side. The researchers believe that the planet is "tidally locked" to its star, meaning that it rotates slowly enough that the same side always faces its star.

Source: Xinhua