A hot gas giant planet discovered in 2008 is losing its atmosphere to its star at a rate of 189 million billion tonnes a year, astronomers in China say.

The planet, WASP-12b, is very close to its star, just two per cent of the distance between the Earth and the sun, and has a surface temperature of 2,250 C, as hot as some stars and half as hot as the surface of the sun.

The gas giant planet is both larger and more massive than Jupiter but orbits its star at an incredible speed, completing a "year" in just 26 hours. The planetary system is 871 light-years away.

The planet is so close to its star that the star's tidal forces are distorting the planet into an egg shape and pulling away its atmosphere at a rate of 189 million billion tonnes every year.

That sounds like a lot, like there shouldn't be any planet left, but it's only one-10 millionth of the mass of Jupiter.

The astronomers found that the planet was losing mass by analyzing the amount of the star's light the planet was blocking when it passed between the star and the Earth.

The researchers, led by Shu-lin Li of Peking University, predict that the gas being pulled off the planet by the star's tides is forming a disk around the star, and that disk should be detectible by infrared telescopes.

The astronomers' calculations, appearing this week in the journal Nature, also indicate that there could be a second planet, a so-called super-Earth, that orbits the star within the disk of gas in resonance with WASP-12b.