Giant planet found in doomed orbit around star

Astronomers have found a giant planet that appears to be in the process of a slow death spiral into its star.

The odd, fiery planet is so close to its star and so large that it is triggering tremendous plasma tides on the star. Those powerful tides are in turn warping the planet's zippy less-than-a-day orbit around its star.

The result: an ever-closer tango of death, with the planet eventually spiraling into the star.

The planet WASP-18b has maybe a million years to live, said planet discoverer Coel Hellier, a professor of astrophysics at Keele University in England. Hellier's report on the planet is in Thursday's issue of the journal Nature.

"It's causing its own destruction by creating these tides," Hellier said.

The star is called WASP-18 and the planet is WASP-18b because of the Wide Angle Search for Planets team that found them.

The planet circles a star that is in the constellation Phoenix and is about 325 light-years away from Earth, which means it is in Earth's galactic neighbourhood. A light-year is about 9.3 trillion kilometres.

The planet is three million kilometres from its star, one fiftieth of the distance between Earth and its star, the sun. And because of that the temperature is about 2,100 C.

It is 10 times bigger than Jupiter, and its proximity to its star makes it likely to die, Hellier said.

Think of how the distant moon pulls Earth's oceans to form twice-daily tides. The effect the odd planet has on its star is thousands of times stronger, Hellier said. The star's tidal bulge of plasma may extend hundreds of kilometres, he said.

Have found 370 planets

Like most planets outside Earth's solar system, this planet was not seen directly by a telescope. Astronomers found it by seeing dips in light from the star every time the planet came between the star and Earth.

So far astronomers have found more than 370 planets outside the solar system. This one is "yet another weird one in the exoplanet menagerie," said planet specialist Alan Boss of the Carnegie Institution of Washington.

It is so unusual to find a planet seemingly on a suicidal path that University of Maryland astronomer Douglas Hamilton questioned whether there was another explanation.

Hamilton said it also is possible that some basic physics calculations that all astronomers rely on could be dead wrong.

The answer will become apparent in less than a decade if the planet seems to be further in a death spiral, he said.