[tt] Science Daily: Sun Will Vaporize Earth Unless We Can Change Our Orbit

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Sun Will Vaporize Earth Unless We Can Change Our Orbit
http://www.sciencedaily.com/releases/2008/02/080223130020.htm

ScienceDaily (Feb. 24, 2008) -- New calculations by University of
Sussex astronomers predict that the Earth will be swallowed up by
the Sun in about 7.6 billion years unless the Earth's orbit can be
altered.

Dr Robert Smith, Emeritus Reader in Astronomy, said his team
previously calculated that the Earth would escape ultimate
destruction, although be battered and burnt to a cinder. But this
did not take into account the effect of the drag caused by the outer
atmosphere of the dying Sun.

He says: "We showed previously that, as the Sun expanded, it would
lose mass in the form of a strong wind, much more powerful than the
current solar wind. This would reduce the gravitational pull of the
Sun on the Earth, allowing the Earth's orbit to move outwards, ahead
of the expanding Sun.

"If that were the only effect the Earth would indeed escape final
destruction. However, 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. 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."

The new paper was written in collaboration with Dr Klaus-Peter
Schroeder, previously at Sussex, who is now in the Astronomy
Department of the University of Guanajuato in Mexico.

Life on Earth will have disappeared long before 7.6 billion years,
however. Scientists have shown that the Sun's slow expansion will
cause the temperature at the surface of the Earth to rise. Oceans
will evaporate, and the atmosphere will become laden with water
vapour, which (like carbon dioxide) is a very effective greenhouse
gas. Eventually, the oceans will boil dry and the water vapour will
escape into space. In a billion years from now the Earth will be a
very hot, dry and uninhabitable ball.

Can anything be done to prevent this fate? Professor Smith points to
a remarkable scheme proposed by a team at Santa Cruz University, who
suggest harnessing the gravitational effects of a close passage by a
large asteroid to "nudge" the Earth's orbit gradually outwards away
from the encroaching Sun. A suitable passage every 6000 years or so
would be enough to keep the Earth out of trouble and allow life to
survive for at least 5 billion years, and possibly even to survive
the Sun's red giant phase.

"This sounds like science fiction," says Professor Smith. "But it
seems that the energy requirements are just about possible and the
technology could be developed over the next few centuries." However,
it is a high-risk strategy - a slight miscalculation, and the
asteroid could actually hit the Earth, with catastrophic
consequences. "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
adds.

Journal reference: "Astronomical engineering: a strategy for
modifying planetary orbits". D G Korycansky of the University of
California at Santa Cruz, with colleagues Greg Laughlin and Fred
Adams: (Astrophysics & Space Science, 275, 349-366, 2001)

Adapted from materials provided by University of Sussex.