By Jesse Emspak
Lumps of rock flying through space could cause catastrophic damage to our planet. What could we do if we found one on a collision course?
Imagine the day observatories confirm that an asteroid is on a collision course with Earth; space-faring nations agree we need to stop it. What happens next depends on how much time the asteroid watchers say we have. None of these options are easy, and at least one of them would require the use of nuclear weapons.
Major asteroid strikes are rare. The last one that could have caused massive loss of life was the Tunguska event of 1908, in which what was believed to be a meteorite exploded some 10 kilometres above a remote area of Siberia.
That type of impact occurs once every few centuries. Siberia, however, is remote; even today the population is small and scattered across a huge area. Had the same object arrived four of five hours later, the major city of St Petersburg would have been hit with the equivalent of a megaton-scale nuclear explosion.
We have seen a smaller version of this nightmare scenario more recently. In 2013, the Chelyabinsk Meteor, which disintegrated at an altitude of 30 kilometres, shattered windows and injured 1,400 people in the western Russian city. It delivered an explosion equal to about 500 kilotons – about 30 or so Hiroshima bombs – though it exploded high enough to not cause too much structural damage. That kind of impact is much more common, occurring about three times per year. Most occur over the ocean or in remote areas, so we usually don’t notice. But the question isn’t if an impact will happen, but when.
Governments are taking this seriously; taking the first tentative steps to preventing a dangerous impact. In January, Nasa formed the Planetary Defense Coordination Office to act as a clearing house for asteroid observations and work with other space agencies to discuss how large space rocks on a collision course with Earth might be dealt with.
Right now, the PDCO spends much of its effort in detection, coordinating various observation programs, says Lindley Johnson, Nasa’s planetary defense officer. That’s because you can’t deal with the space rocks until you know where they are. “We try to detect anything that might be a threat years, if not decades, in advance,” he says. Once a dangerous asteroid is identified, the actual plans for stopping one enter the picture.
The simplest method is a kind of planetary billiards, using a space probe to send a heavy object (or the probe itself) smashing into it. The asteroid will then, hopefully, be pushed off course and miss the Earth.
The idea is to find out exactly how much one can move an asteroid without running the risk of sending it on a dangerous trajectory
A joint European Space Agency and Nasa mission will test such technology in the next few years, under the name Asteroid Impact and Deflection Assessment (Aida). The mission consists of two spacecraft, one called the Asteroid Impact Mission (Aim), which will launch in late 2020, and the second, the Double Asteroid Redirection Test (Dart), in 2021.
In 2022 they’ll arrive at a double asteroid called 65803 Didymos, which is accompanied by a companion called Didymoon. Didymos measures some 780 metres across, whileDidymoon is about 170 metres. The smaller of the two orbits the larger one every 11.9 hours, and they are close, only 1,100 metres apart. The Aim craft will rendezvous with the asteroid and study its composition. Once Dart arrives it will crash into Didymoon, and Aim will see what the effect on the smaller rock’s orbit is. The idea is to find out exactly how much one can move an asteroid without running the risk of sending it on a dangerous trajectory, a kind of baby step to actually redirecting it.