http://news.bbc.co.uk/low/english/sci/tech/newsid_1154000/1154784.stm
By BBC News Online science editor Dr David Whitehouse
Mankind will soon have the ability to move the Earth into a new orbit, say a
team of astronomers. The planetary manoeuvre may more than double the time
life can survive on our planet, they believe.
Our initial analysis shows that the general problem of long-term planetary
engineering is almost alarmingly feasible
Korycansky and colleagues
Our Sun will increase its brightness in the next billion years or so, and if
the Earth stays in its present orbit it will be fried and all life
eliminated.
Using the well-understood "gravitational sling shot" technique that has been
employed to send space probes to the outer planets, the researchers now think
a large asteroid could be used to reposition the Earth to maintain a benign
global climate.
It is an "alarmingly simple" technique, the astronomers say. It could ensure
humanity's survival and even allow our descendants to alter our Solar System
to move moons and planets to make new Earths.
The astonishing idea has been put forward by Don Korycansky, of the
University of California, along with Gregory Laughlin, of the US space Agency
Nasa, and Fred Adams, of the University of Michigan.
End of life
Astronomers believe that in a billion years from now our Sun will be over 10%
brighter than it is today. Global climate models indicate that the Earth will
react to this increase by at first becoming a "moist greenhouse".
Looking even further ahead, the Sun will increase its luminosity by about 40%
in three billion years. This will force the Earth into a "runaway greenhouse"
state, such as exists currently on the planet Venus.
According to the authors of a new study, this will "spell a definite end to
life on our planet". But there is a way to counter the increasing brightness
of the Sun, the scientists say - just increase the radius of the Earth's
orbit!
"Our initial analysis shows that the general problem of long-term planetary
engineering is almost alarmingly feasible," they say.
All that is required is for a large asteroid, about 100 km (62 miles) across,
to fly past the Earth transferring some of its orbital energy to our planet.
The asteroid would then move out to encounter Jupiter where it would acquire
more energy that it could impart to the Earth on a subsequent encounter.
Favourable position
To expand the Earth's orbit around the Sun at a rate that compensates for the
increasing brightness of the star would require an encounter every 6,000
years, or about every 240 generations.
Earth's gradual outward migration may require adjustments to be made to the
orbits of other planets as well. Recent calculations of the Solar System's
stability indicate that if the Earth was removed then Venus and Mercury would
become destabilised in a relatively short time.
Perhaps, the authors suggest, many moons and planets could be moved into more
favourable positions in the Solar System where their climates might support
life.
In the past, some astronomers have suggested that Mars could be terraformed
to make it more like the Earth. The Earth-orbital-migration technique, say
the researchers, is a far easier way to provide living space for humans in a
changing Solar System.
But it would be a procedure that required some care. If the 100 km asteroid
was to collide with the Earth then it would wipe out all life on our planet.
"This danger cannot be overemphasised," the researchers stress.
But "as a way of preserving the entire biosphere of the Earth, this method is
promising and efficient," they say.
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