Astronomer's three-star find


Tim Radford, science editor
Thursday July 14, 2005
The Guardian

An astronomer has identified a planet with three suns far away in the galaxy - the first of a class dubbed "Tatooine planets" after the home of Luke Skywalker, the young hero of the Star Wars films.

Maciej Konacki, of the California Institute of Technology, describes in Nature today how he trained a 10-metre telescope on three stars 149 light years from Earth, and found they shared a planet slightly larger than Jupiter.

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The stars are about as close to each other as Saturn is to the sun. "The environment in which this planet exists is quite spectacular," Dr Konacki said. "With three suns, the sky view must be out of this world, literally and figuratively."

In this region of the galaxy binary stars and even multiple star systems - heavenly bodies caught in a complex gravitational waltz - are more frequent than single stars.

But no one expected that a planet could either form or survive for long in a group of triple suns. No life could survive there, but the outlook from the planet, linked to the main star, HD 188753, would be pretty bright.

The main star, like the sun, is yellow; the larger of the other two is orange, the smaller red. A day on the mystery planet would be lurid, but its year would be brief as it completes its annual orbit in three and a half Earth days.

Researchers discovered the first "hot Jupiter" in 1995. This was an extra-solar gas giant that orbited its parent star in three to nine days. So far they have logged more than 20 such planets, among more than 100 extra-solar planetary systems.

The calculation is that a disc of gas and dust gathers around such stars at a distance of about 300m miles and this pile of rubble gradually assembles into a giant companion which is then tugged nearer its parent star. But no one has so far worked out how a giant planet would survive in the three-cornered gavotte of stars.

"How that planet formed in such a complicated setting is very puzzling. I believe there is much to be learned about how giant planets are formed," Dr Konacki said.