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The end is near... well, in 7.6 billion years

2008-02-25 11:35:08 | Weblog

The end is near... well, in 7.6 billion years

The big news: Earth is doomed to fry and then be gobbled up by the dying Sun.

UV Image of the Sun

A NASA-released ultravilet image of the sun. 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.

The unusual calculations appear in the British open-access journal Astrophysics.

Robert Smith, emeritus reader in astronomy at the University of Sussex, southern 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.

Smith, working with Klaus-Peter Schroeder at the University of Guanajuato in Mexico, has taken a new run through the figures. Sadly, for our home, the number is up.

"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 says.

"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 sketches 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, says Smith.

"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 says.

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