Is the solar system unique? - space

Description

According to the standard picture of solar system formation (see "How was the solar system built?"), gas giants should not form that close to their host stars, as the heat means not enough solid material is present to make a sufficiently large rocky core. However, while the orbits of the planets in our solar system are almost circular, those of many of these giant exoplanets are often highly elliptical. This might provide a solution to the mystery: most solar systems seem to have had more chequered histories than our own, with initially distant giant planets competing for living space and bouncing each other into strange orbits closer in.

Definitive conclusions are difficult until we know the limitations of our observations. "It might be that we see solar systems with very violent histories because those are the only ones we can see," says Phil Armitage of the University of Colorado, Boulder. Results from two sensitive space-based planet hunters should help reduce the uncertainty: the French-led COROT mission, which launched in December 2006, and NASA's Kepler, scheduled to blast off in March this year.

A foretaste of what they might find is given by the 10 or so known "super-Earths" - planets with just a few times Earth's mass. If the picture of planet formation gleaned from our solar system is correct, these are rocky worlds like our own. Two of them, Gliese 581 c and d, are at the sort of distance from their parent star at which liquid water might exist on their surfaces, depending on the warming effects of greenhouse gases and cooling effects of clouds in any atmospheres they might possess.

There are other hints that rocky planets are more common than our first observations suggest. Dust close in to young stars, reported in 2008 by NASA's Spitzer Space Telescope, points to collisions connected to planet formation, and suggests that rocky worlds form around 20 to 60 per cent of stars.

But other evidence from Spitzer of dust circling much older stars dampens the prospects for tranquil rocky worlds that could harbour life. Nine in 10 solar systems seem to be more dusty than our own, in some cases by a factor of 20 or more. As planet formation is expected to be a relatively cursory process within the first 100 million years or so of a star's existence, that dust is probably the remnant of catastrophic comet collisions later in the life of these solar systems.

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http://www.newscientist.com/article/mg20126932.400-is-the-solar-system-unique.html?DCMP=OTC-rss&nsref=online-news

http://www.newscientist.com/article/mg20126932.400-is-the-solar-system-unique.html?DCMP=OTC-rss&nsref=online-news