Thursday, May 17, 2007

Strange Alien World

A bizarre world of scorching hot ice shrouded in a steamy atmosphere may have been found, according to new observations. Characterising the Neptune-size planet is an important milestone on the way to detecting and characterising Earth-like planets that could harbour life.

Astronomers have discovered more than 200 planets orbiting other stars, called extrasolar planets or exoplanets. Almost all of these were detected by the way their gravity makes their parent stars wobble. But this technique, called the radial velocity method, reveals very little about the planet except for the size of its orbit and an estimate of its mass.

Astronomers can learn a lot more by watching "transits" of planets that pass in front of their parent stars as seen from Earth. Careful analysis of the dimming this causes can provide clues to the planet's composition and structure. But the brightness dips are small and difficult to detect for all but the largest planets.

Now, astronomers have observed the smallest ever transiting planet. It has turned out to be a strange world, unlike anything seen before.

The planet, which orbits a small star located 30 light years from Earth called GJ 436, was actually discovered in 2004 using the radial velocity method (see Two new rocky super Earths found). At that point, astronomers deduced that it was about as massive as Neptune.

Exotic ice
But now, a team led by Michael Gillon of Geneva University in Switzerland have observed the planet transiting its host star using a telescope at the Observatoire Francois-Xavier Bagnoud (OFXB) in Saint-Luc, Switzerland.

They have been able to measure the planet's width, which provides clues to its composition and structure. It turns out to be about 50,000 kilometres wide, roughly four times the width of Earth and about the size of Neptune.

The planet is therefore too compact to be made mostly of hydrogen gas, like Jupiter, the researchers say, but not compact enough to be a rocky 'super Earth', as some had speculated. Instead, they believe it must be made mostly of an exotic form of water.

Although the parent star is much cooler than the Sun, the planet orbits 13 times closer to the star than Mercury's orbit around the Sun. That means the surface must be a blazing hot 300° C or more, keeping water in its atmosphere in vapour form.

But the high pressures in the planet's interior would compress the water so much that it would stay solid even at hundreds of degrees Celsius – the expected temperatures inside the planet. There are a variety of exotic 'hot ice' states possible in such conditions, with names like 'Ice VII' and 'Ice X."
More at:http://space.newscientist.com/article/dn11864-strange-alien-world-made-of-hot-ice-and-steam.html
Posted by Ajay :: 3:52 PM :: 0 comments

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