Planet Earth on the move

Moving 5.972 sextillion tonnes is relatively "simple"

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 believe - 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.

Humans would have many thousands of years to select the appropriate asteroid and develop the necessary technology to deflect the giant rock in the direction of Earth.

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 asteroid 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.

However, "as a way of preserving the entire biosphere of the Earth, this method is promising and efficient," they say.