Original URL: http://www.theregister.co.uk/2008/02/27/sun_swallow_earth/

Sun will swallow Earth: Official

No escape from star's clutches

By Lester Haines

Posted in Science, 27th February 2008 10:09 GMT

Two scientists from the University of Sussex and Mexico's University of Guanajuato appear to have confirmed that if we're still around in 7.6 billion years, global warming will be the least of our worries, since our beloved Mother Earth will be drawn inexorably towards the Sun and snuffed from existence.

Sussex Uni's Robert Smith and Guanajuato's Klaus-Peter Schroeder got out their calculators to determine once and for all whether Earth would escape a blazing death by spinning into a more distant orbit around the Sun, or whether it's ultimately curtains.

The former theory suggests that, as the Sun expands into a red giant, it will eject its outer gaseous layers, thereby losing mass and weakening its gravitational grip on the Blue Marble.

However, this get-out clause doesn't factor in tidal forces or the drag of the Sun's outer layer, according to the doomsday boffins. The Earth actually exerts its own (modest) gravitational pull on the Sun, causing the face closest to us to bulge out - an extrusion which constitutes bad long-term news.

Smith explained to Space.com: "Just as the Earth is pulling on the Sun's bulge, it's pulling on the Earth, and that causes the Earth to slow in its orbit. It will spiral back and finally end up inside the Sun."

In addition to this fatal attraction, the gaseous layers escaping from the Sun will exacerbate the problem, creating drag on Earth's orbit, further slowing it.

Smith said these crucial factors had hitherto been overlooked in determining Earth's fate. He explained: "Although people have looked at these problems before, we would claim this is the best attempt that's been made to date, and probably the most reliable. What we've done is to refine existing models and to put the best calculations we can at each point in the model."

Of course, while it's interesting to ponder our planet's distant fate, we'll actually be long gone before the fireworks. Smith predicted: "After a billion years or so you've got an Earth with no atmosphere, no water and a surface temperature of hundreds of degrees, way above the boiling point of water. The Earth will become dry basically. It will become completely impossible for life of any kind to exist. It's a pretty gloomy forecast."

The researchers' findings will be published in the journal Monthly Notices of the Royal Astronomical Society. ®

On the other hand...

Last September we reported on a "red giant survivor" V 391 Pegasi b, which was spied orbiting its bloated mother star "slightly beyond" the expansion zone within which planets are doomed.

Roberto Silvotti, researcher at the INAF-Osservatorio Astronomico di Capodimonte, said: "As far as our planets are concerned, we expect Mercury and Venus to disappear in the Sun's envelope, whereas Mars should survive.

"The fate of the Earth is less clear because its position is really at the limit. All this will happen in about five billion years, when the Earth will be more or less the same age as V 391 Pegasi b, i.e. 10 billion years."