Distant planet is half fire, half ice

The poet Robert Frost wondered if Earth would wind up a world of fire or ice. Astronomers have discovered that a distant planet is both.

With one side always hot as lava and the other chilled possibly below freezing, Upsilon Andromeda b is a giant gas planet that orbits extremely close to Upsilon Andromeda, a star 40 light-years from our solar system in the constellation Andromeda, reports Space.

"If you were moving across the planet from the night side to the day side, the temperature jump would be equivalent to leaping into a volcano," said Brad Hansen, of the University of California, Los Angeles, who led the research.

His colleague, James Cho, of Queen Mary, University of London, said that the temperature extremes "make for a very unusual climate and weather".

This strange world, which orbits Upsilon Andromeda, a star visible with the naked eye in the constellation Andromeda, was discovered in 1996. Details of its bizarre climate, however, could be seen only after the launch in 2003 of the Spitzer telescope, which observes infra-red light. Planets orbiting other stars are difficult to detect and study because the light they emit is swamped by that of their parent suns, but they stand out better when viewed in infra-red light.

Dr Hansen’s team, who publish their results today in the journal Science, found that more infra-red light was visible when the planet’s day side was in Earth’s view than when the night side was turned towards us. This allowed them to calculate temperatures for both.

Upsilon Andromeda b is a kind of gas giant known as a "hot Jupiter", which orbits its parent star at very close quarters: its "year" lasts 4.6 days and it is one sixth as far from its star as Mercury is from the Sun, informs Times Online.