Serious sunburn: An artist's impression of a planet being devoured by its red giant star.

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PARIS: The big news: Earth is doomed to fry and then be gobbled up by the dying Sun. But don't blow your savings on an apocalypse party just yet, for astronomers say the planet's demise is 7.6 billion years away.

Robert Smith, an astronomer at the University of Sussex, England, previously calculated that as the Sun runs out of fuel, it will expand into a dangerous "red giant". But Earth – while battered and burnt to a crisp – would escape ultimate destruction, he had thought.

Now, working with Klaus-Peter Schroeder at the University of Guanajuato in Mexico, Smith has taken a new run through the figures. Sadly, for our home, the number is up. The unusual calculations appear online in the British open-access journal arXiv.

Captured and vaporised

"The tenuous outer atmosphere of the Sun extends a long way beyond its visible surface, and it turns out the Earth would actually be orbiting within these very low-density outer layers," Smith said. "The drag caused by this low-density gas is enough to cause the Earth to drift inwards, and finally to be captured and vaporised by the Sun."

Life on Earth will have become rather uncomfortable before then, however. A billion years from now, as the Sun slowly expands, the oceans will evaporate, filling the atmosphere with water vapour (a potent greenhouse gas) and triggering runaway global warming.

Smith sketched two options, both admittedly sci-fi in feel, for escaping this fate.

One is to harness the gravitational pull of a passing asteroid to gently tug Earth out of the danger zone. A wee nudge every 6,000 years could be enough to survive for at least five billion years – provided a miscalculation does not send the asteroid barrelling into Earth instead of doing a close flyby, said Smith.

If humans are even still around at that point "a safer solution may be to build a fleet of interplanetary 'life rafts' that could manoeuvre themselves always out of reach of the Sun but close enough to use its energy," he added.