Earth is set to be sucked in and vaporised by the dying sun, and our only hope of survival is to build a fleet of interplanetary 'life-rafts', scientists say.

But we may have a little while to plan for the apocalypse, with astronomers claiming the end of the world will not be here for another 7.6 billion years.

Robert Smith, emeritus reader in astronomy at the University of Sussex, in the UK, has previously calculated that as the Sun runs out of fuel, it will gradually expand into a dangerous 'red giant', overheating the galaxy around it.

Mr Smith originally believed that this would make life on Earth uncomfortable, to say the least, but that the planet itself, though battered and burnt, would survive.

Oceans to evaporate

However, on re-examining his figures with the help of Klaus-Peter Schroeder, of Mexico's University of Guanjuato, he has discovered that the outlook is somewhat more bleak.

"The tenuous outer atmosphere of the Sun extends a long way beyond its visible surface, and it turns out the Earth would be orbiting within these... layers," he explains in the British open-access journal Astrophysics.

"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."

Mr Smith predicts that well before the planet's final destruction, life here will have become somewhat difficult, as the Sun slowly expands, evaporating the world's oceans, filling the atmosphere with water vapour, and triggering out-of-control global warming.

Asteroid rescue plan

The astronomer has two sci-fi-sounding suggestions to prevent the otherwise inevitable destruction of mankind.

One is to harness the gravitational pull of a passing asteroid to gently tug Earth out of the danger zone.

He suggests that a small nudge every 6,000 years could be enough to allow us to survive another five billion years - provided a miscalculation does not fling the asteroid back at the planet.

"A safer solution may be to build a fleet of interplanetary 'life rafts' that could manoeuvre themselves out of reach of the Sun, but close enough to use its energy," Mr Smith says.