Astronomers at the University of Sussex claim to have calculated that the Sun will vapourise Earth in about 7.6 billion years unless our planet’s orbit is altered.
According to them, the Sun’s slow expansion will cause the temperature on the surface of the Earth to rise — oceans will evaporate and the atmosphere will become laden with water vapour, which 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.
The team previously calculated that the Earth would escape ultimate destruction, although be battered and burnt to a cinder. But they did not take into account the effect of the drag caused by the outer atmosphere of the dying Sun.
"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," lead astronomer Dr Robert Smith was quoted by the ‘ScienceDaily’ as saying.
But, can anything be done to prevent this fate? By altering the orbit of our planet, according to Dr Smith.
He pointed to a remarkable scheme proposed by Santa Cruz University astronomers 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 6,000 years or so would be enough to keep the Earth out of trouble and allow life to survive for at least five billion years, and possibly even to survive the Sun’s red giant phase.
"This sounds like science fiction. But it seems that the energy requirements are just about possible and the technology could be developed over the next few centuries," Dr Smith said.
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 said.