Diamonds in the sky over planet that defies gravity

WASP-18b is a planet where temperatures exceed 2100C - enough to create clouds of silica-based gems. Photo / Supplied

It's the planet that really shouldn't exist - or at least not for long. It is 10 times the size of Jupiter, orbits its own star in under 24 hours and should soon be spiralling into the surface of its searingly-hot sun.

Under the laws of physics, planet WASP-18b orbiting a star 1000 light years from Earth is too big and too close to its sun for comfort. The tidal interactions between the two massive objects should be pulling them together in a deadly gravitational embrace.

British astronomers say they have made a highly unusual planetary discovery in finding WASP-18b. Either they happened to have witnessed an exceptionally rare event that they have likened to winning the lottery, or they do not understand the tidal forces affecting distant planets beyond our own solar system.

"The problem with this planet is that it's very massive and very close to its star. It should be creating tidal bulging that makes it spiral into its star," said Professor Andrew Collier Cameron, of St Andrew's University.

The planet is at least one billion years old, yet at this rate it should have no more than half a million years left before it crashes into its own star.

The chances of finding it at this point in its life cycle is about 1 in 2000.

It is a Jupiter-like planet where temperatures exceed 2100C - enough to create clouds of silica-based gems, said Professor Cameron. If anyone could visit and survive, they might see a sky full of diamonds and sapphires, he said.

"The situation is analogous to the way tidal friction is gradually causing the Earth's spin to slow down, and the Moon to spiral away from the Earth," he said.

"However, the spin of the star is slower than the orbit of the planet, so the star should be spinning up, and the planet spiralling in," he said.

WASP-18b, one of more than 300 "exoplanets" orbiting distant stars, was discovered by a team led by Coel Hellier of Keele University, whose study is published in the journal Nature.

- INDEPENDENT