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New 'temperate' exoplanet hints at solar system like our own

Astronomers have for the first time made detailed measurements of an exoplanet in the temperate zone around its star. Their conclusion: It looks a lot like a planet in our solar system.

By Peter N. SpottsStaff writer / March 17, 2010

An artist's impression shows CoRoT-9b, the first temperate exoplanet to be measured in detail. Scientists say it is about the size of Jupiter and orbits its parent star at about the same distance that Mercury orbits the sun.

AFP/ESO

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Astronomers have discovered a Jupiter-size planet that orbits its host star at a Mercury-like distance – a solar system that begins to look like a topsy-turvy, Alice in Wonderland version of our own.

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The discovery has allowed scientists to glean for the first time a wide range of information about an extrasolar planet so relatively distant from its "sun."

It opens the door to detailed studies of gas giants in the temperate zone around stars – the single largest group of exoplanets scientists have found so far, and a class of planets that begins look more familiar to Earth-bound eyes.

The planet, CoRoT-9b, "can start to tell us more about exoplanets which may be more akin to the giant planets in our solar system," writes David Ciardi in an e-mail exchange. Dr. Ciardi is a researcher at NASA's Exoplanet Science Institute, based at the California Institute of Technology in Pasadena, Calf., and a member of the international team reporting the discovery in tomorrow's issue of the journal Nature.

The planet, which orbits a sun-like star some 1,500 light-years from Earth in the constellation Serpens, was first detected in 2008 by instruments aboard the European Space Agency's COROT satellite. The spacecraft was designed to study the physics of distant stars and to detect any transiting planets in the process.

How it was found

Transiting planets are those that, from the telescope's perspective, pass in front of the stars it observes. When planets can be detected passing in front of or behind their parent stars, scientists can tease out a variety of data, including a planet's physical size, density, key orbital traits, and make basic measurements of its atmosphere.

But the only transiting planets scientists have been able to find are "hot Jupiters" – gas giants circling very closely to their parent stars.

By contrast, another telltale way of finding extrasolar planets – reading the gravitational pull they exert on their partent stars, apparent as a "wobble" – makes it easier to find planets at a range of distances, but it yields less information.

The discovery of CoRoT-9b marks the first time that scientists have successfully used the transit method to detect a planet at such large distances from its host star.

Once the team discovered the event in its data, it turned to ground-based telescopes to ensure it didn't get a false alarm from what is thought to be a nearby binary star system in which one star eclipses the other.

In addition, the team tapped astronomers using the radial velocity "wobble" technique to confirm 9b's existence.

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