Star "Eating" Superhot Planet's Atmosphere

One of the hottest known planets outside our solar system is slowly being "eaten" by its parent star, astronomers report.

First described in 2008, the extrasolar planet—or exoplanet—WASP-12b is a Jupiter-like world that orbits its host star so tightly a year lasts just 26 hours.

This closeness means that a combination of heat from the star and from a gravitational tug-of-war called tidal heating brings the surface temperature to more than 4,700 degrees Fahrenheit (2,600 degrees Celsius).

New data show that WASP-12b's atmosphere is also being puffed up by the star's heat to the point that some of its gases are escaping.

But rather than being blown away by stellar winds, the lost atmosphere might be getting pulled toward the star to form a hot ring around the star, said study leader Shu-lin Li, an astronomer at Peking University in Beijing.

In fact, WASP-12b is losing mass so fast it will likely disappear before its aging star has a chance to swallow the planet whole. (Related: "New 'Impossible' Planet May Be on a Death Spiral.")

The sunlike host star, known as WASP-12, is now about two billion years old, which means it's nearing the end of its life, said Heather Knutson, an astronomer and exoplanet researcher at the University of California, Berkeley.

Normally, dying sunlike stars grow into red giants, and their outer atmospheres expand to engulf nearby planets, said Knutson, who was not involved in the study. WASP-12 is predicted to become a red giant within about a hundred million years.

But "this star will not have WASP-12b to 'eat,' because the planet would have been totally disrupted long before then, within ten million years,” said study co-author Douglas Lin of the University of California, Santa Cruz.