— Lasers could bore into a centimetre-sized spot on an asteroid, ejecting tiny bits of material that would push the space rock off course and away from Earth (Illustration: Don Davis/NASA)
Space lasers that zap away rogue asteroids sound like the premise for a 1980s video game. But researchers say the technique could one day be used to detect and deflect asteroids found to be barrelling towards Earth.
Previously, researchers have proposed several methods to save Earth from an asteroid impact. These include blowing it up with a nuclear bomb or putting a spacecraft beside it so the craft's gravity could tug the asteroid off course.
But these solutions have drawbacks the smaller chunks of rock created in the nuclear explosion might still threaten Earth, and the 'gravity tug' would require a relatively massive spaceship with a lot of fuel.
Now, researchers say a lightweight, space-based laser could eliminate these problems gradually altering the trajectory of a threatening asteroid. Though the technology may take two decades or so to mature, "this is something that is doable", says Richard Fork, who heads the Laser Science and Engineering Group at the University of Alabama in Huntsville, US.
One of the great advantages of using lasers is that their beams remain relatively tightly focused over long distances, allowing them to study asteroids from farther away than is currently possible.
Today, observatories such as Arecibo in Puerto Rico bounce radar off asteroids to characterise them and track their orbits. But they can only study objects from a distance equivalent to 0.1 times that between the Earth and the Sun. A laser could examine the features of an asteroid from 10 times as far away.
That could give researchers advance warning of the asteroid's likely composition and exact shape, which would help them figure out how to move it.
The laser itself could also do the moving. If its short pulses were focused on a centimetre-sized spot on the asteroid, they would repeatedly pulverise material, ejecting tiny bits of space rock at 10 kilometres per second. This would function as the asteroid's propellant, pushing it into a different orbit and safely away from Earth. From several kilometres away, each laser could operate on 25 to 40 kilowatts of power to zap a space rock for several months.
"It really doesnt take much of a push provided you do that early," Fork told New Scientist. "The key thing is to act early on."
To detect and begin deflecting dangerous asteroids as early as possible, the lasers could be placed on a fleet of eight spacecraft that would patrol the asteroid belt at different locations.
But several major technical hurdles need to be overcome before such a system could be put in place. If the spacecraft was used to characterise asteroids, it would require an antenna about 30 metres across to transmit the laser's light.
If the spacecraft was simply intended to deflect asteroids, it would not need such a large antenna. But engineers would still have to find a way to make existing laboratory lasers which are heavy more lightweight to launch them on a spacecraft about the size of a truck.
Missing the 'keyhole'
At the moment, Fork and his team are developing a titanium-sapphire laser capable of pulverising materials with its pulses. They hope their laser could be the 'grandfather' of a laser that might one day come to the aid of humanity.
There is a small chance such a life-saving laser would be needed in 2029, when the asteroid Apophis will make a close swing by Earth. If it passes through a specific region of space just 600 metres across at that time, there is a 1 in 45,000 chance it could hit Earth perhaps slamming into the Pacific Ocean on 13 April 2036.
If a laser spacecraft were going to be ready to deflect Apophis before it could reach the 600-metre-wide 'keyhole' in 2029, the government would have to start funding the mission now, says Fork.
"The chances of having it ready for the Apophis push are extremely small unless there was a sudden burst of enthusiasm for doing the laser push," he told New Scientist.
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