WE鈥橵E been told to nuke 鈥檈m, tug 鈥檈m and even paint 鈥檈m. But burrowing into killer asteroids on a collision course with Earth might be the best way to deflect them.
In 2029, the asteroid Apophis will pass near Earth, and our planet鈥檚 gravity may then put it on collision course for when it comes back round in 2036. Although the chance of an impact is only 1 in 45,000, developing methods to save us from such near-Earth asteroids (NEAs) is vital, and current proposals simply aren鈥檛 up to the job, says Daniele Fargion of the University of Rome La Sapienza, Italy.
Proposals for deflecting NEAs have included blasting them with nuclear explosives, tugging them with nuclear-powered spacecraft or painting them white on one side so that reflected solar energy will nudge the asteroid off course. Blowing up the asteroid could leave vast fragments still Earthbound, however, and tugging and painting can only push the asteroid a few kilometres off course, says Fargion.
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He proposes an alternative, inspired by the way rockets are propelled forward as they eject mass when burning fuel. He suggests dropping nuclear-powered rockets, each tipped with a screw-shaped drill, onto the asteroid from a mother ship. After latching onto the asteroid鈥檚 surface 鈥� not easy in almost zero gravity 鈥� each 鈥渟crew rocket鈥� will drill deep into the asteroid, projecting the rocky spoil behind it into space at high speed and pushing the asteroid off course.
鈥淓ach rocket will drill into the asteroid, projecting the rocky spoil into space鈥�
Fargion鈥檚 calculations show that over 10 years, screw rockets could deflect a 1-cubic-kilometre asteroid by 30,000 kilometres. 鈥淚nstead of carrying huge amounts of fuel from Earth to propel the asteroid this large distance, we simply exploit the asteroid鈥檚 own material,鈥� he says.
Nick Bailey, an expert on asteroid tracking at Southampton University, UK, calls the solution 鈥渆legant鈥� but says that many asteroids are made of piles of rubble, not large chunks of rock, and that it will be tough to get screw rockets to latch onto these.
Another difficulty is that the asteroid may well be rotating. To account for this, screw rockets will be fitted with guidance systems, allowing them to track their position and fire only when they are on the right side of the asteroid to push it off collision course.
To test the idea of screw rockets, Fargion proposes sending them to the moon, where they could also be used to dig out underground shelters for human use.
