Moving the Earth: a planetary survival guide

Space 20 October 2008

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Mark Garlick/HELAS

The clock is ticking inexorably toward doomsday even if we don’t kill ourselves by poisoning the environment or overheating the planet. You see, there’s a little problem with the Sun.




Plants and animals will have a very tough time adapting to that hothouse, although some single-celled organisms called Archaea might survive. But only for a while. Once the water vapour is in the atmosphere, ultraviolet light from the Sun will split the water molecules, and the hydrogen needed to build living cells will slowly leak into space. If our descendants – or other intelligent life-forms that follow us – want to survive, they’ll have to migrate elsewhere. But where and how?

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Humans cannot live on Mars without life support. So if large numbers of people were to take refuge there, the Red Planet would have to be made more like Earth, or ‘terraformed’

Illustration: NASA



Then there’s the matter of taking care of people once they reached their new home. Moving to any other planet would require “terraforming” it to provide food, water and oxygen to support colonists. Why not bring our own planet along with the resources we would need?

Tiny change





Moving out

Planetary dynamics seemed simple and orderly when we knew only our own solar system, but that changed with the discovery of “hot Jupiters” on tight orbits around other stars. The planets couldn’t have formed in the scorching regions where they orbit – there was not enough gas and dust there to amass such giant worlds. Instead, they must have migrated there from more distant birthplaces.




Diagram of the Kuiper Belt


These range from the gentle pull of gravity tugs – spacecraft that fly near the object and gravitationally pull them off course – to the stronger push of mass drivers, which dig into and spew out pieces of the icy body, pushing it in the opposite direction.

Their orbits could then be fine-tuned in the inner solar system using jets of ices vaporised from their surfaces by equipment sent there. Nobody’s thinking about deploying a future Bruce Willis with a rocket-load of nukes to do the job. “You need very fine-grained control, which a nuclear weapon certainly would not produce!” says Laughlin.

Sterilised biosphere

About a million such close passes would do the trick. If we spaced them evenly, that would mean about one close pass every 1000 to 6000 years, depending on whether we wanted to reach the orbit of Mars by the time the Sun started to vaporise the ocean, or when it hit its red-giant phase. Luckily, the objects could be re-used if they looped around both Jupiter and the Earth, taking energy from the giant planet and transferring it to Earth.

It would be a big job, and would take plenty of patience to move the Earth consistently outwards as the Sun grew warmer. It also carries a significant risk because the objects would have to pass just 10,000 kilometres above the Earth’s surface.

Illustration of asteroid smashing into Earth

The impact of a space rock more than 100 km across would kill most – if not all – life on Earth

Illustration: Don Davis/NASA

The objects would be much more massive than the asteroid that killed the dinosaurs, so one little “oops” could be devastating. Laughlin and colleagues take that very seriously, concluding their paper with the warning: “The collision of a 100-km diameter object with the Earth at cosmic velocity would sterilise the biosphere most effectively, at least to the level of bacteria. This danger cannot be overemphasised.”

Push from the Sun

That danger could be avoided by using a giant solar sail, says Colin McInnes, a mechanical engineer at the University of Strathclyde.

Solar sails are thin, mirror-like films that are propelled by the weak pressure of the sunlight that falls on them. McInnes’s idea is to put a free-floating solar sail at a point near the Earth where the pressure of solar radiation essentially balances the Earth’s gravitational pull.

His analysis shows that the reflection of sunlight from the sail will pull the Earth outwards along with the sail – in physical terms, increasing the Earth’s orbital energy and accelerating the centre of mass of the system outwards, away from the Sun.

McInnes calculates that moving the Earth outwards to keep pace with the Sun’s warming would require a disc-shaped sail 19.2 times the Earth’s diameter. It would have to be tilted at an angle of 35° to the line towards the Sun, and stationed at about five times the Moon’s distance from the Earth.

He envisions building it in space by refining the raw materials in a 9-km-wide metal-rich asteroid. Nickel and iron from the asteroid would be made into an 8-micron-thick film for the sail.

Thrown into chaos

The sail would be complex as well as large; it would need active control to maintain the sail’s proper shape, particularly in the face of perturbations by the Moon’s gravity. But McInnes says it would require moving 10,000 times less mass than slinging objects from the Kuiper belt past Earth.

Geoffrey Landis, a science fiction author and NASA scientist, says the concept is sound. “It looks like the physics is right, but of course there’s no technology in existence or currently proposed to make a solar sail 20 times the diameter of the Earth ¡V at the moment, that’s science fiction.”

McInnes admits that even he doesn’t take the idea too seriously: “It’s a Friday afternoon problem.”

But despite the practical difficulties of these scenarios, computer simulations by Laughlin also point out a real danger of playing with planetary orbits.

Planetary orbits are shaped by the gravitational pulls of their neighbours, so moving the Earth would change the orbits of the other inner planets in unpredictable and potentially dangerous ways.

If the move destabilised Mercury, the entire inner solar system might be thrown into a chaotic mode “that is vastly harder and possibly impossible to control”, Laughlin says. That may be the best argument for leaving the planets alone unless we have no alternatives.

More on these topics:



Physicists work out how many moons Earth could have


Interstellar meteorite may be awaiting discovery on the sea floor



What Earth’s mysterious infancy tells us about the origins of life

What Earth’s mysterious infancy tells us about the origins of life

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