A new model for tackling the threat of an asteroid large enough to do serious damage to Earth proposes breaking it apart bit by bit. The physicists behind the idea argue it is better suited to late discoveries than previously proposed methods, treating the world to a spectacular sky show to celebrate being saved.
Sooner or later, the Earth will definitely be hit by another asteroid large enough to do major damage. Although our minds naturally go to dinosaur-killer-sized disasters, the more likely threat is something smaller but still capable of killing millions.
Many ideas for dealing with this exist, but most rely on plenty of preparation time. Members of the University of California Santa Barbara Experimental Cosmology Group describe their alternative as: “A practical and effective method of planetary defense that allows for extremely short mitigation time scales.” It also doesn't require the invention of any advanced new technologies, like lasers powerful enough to zap space rocks to oblivion. The idea has been submitted to Advances in Space Research, but is currently on the UCSB website.
Professor Philip Lubin and Alexander Cohen propose creating a sort of minefield in the path of an oncoming object, filled with “penetrator rods” 10-30 centimeters (4-12 inches) wide and 2-3 meters (6-10 feet) long. Some of the rods would be packed with dynamite. The explosives and speed with which the asteroid will hit these rods, will cause it to break apart, the pair argue. The mass on a collision course with us will not change, but it won't hit all together. Instead, we will get a series of objects small enough to explode when they hit the atmosphere.
The asteroid bits will arrive as objects the size of a house or smaller – which may prove frightening to anyone not expecting them, but should do little damage.
"If you can reduce the big events, which are dangerous, into a bunch of little events that are harmless, you've ultimately mitigated the threat," Cohen said in a statement.
The Hollywood-approved idea of blowing an asteroid up with nuclear weapons has a similar goal, but carries multiple risks. Most existing proposals aim to shift the asteroid's orbit sufficiently that it slides harmlessly past the Earth. These all work slowly, which requires having the threat's orbit mapped out well beforehand. Lubin added these approaches; “Rely on getting an asset to deflect the threat all the way out to the asteroid long before it comes close to the Earth.”
Deflection also leaves us with a large object hurtling around the inner Solar System, likely to eventually become a threat again.
Instead, the authors propose, the rods should sit in orbit, waiting to be deployed in the path of an incoming thread. If they cause a 1 meter/second internal disruption to the asteroid, Lubin calculates in a detailed technical paper, they could reduce a 50-meter (164-foot) wide asteroid – such as the one that caused the Tunguska explosion – to safe size five hours prior to impact. Something with twice that diameter would require a day. Apophis, considered one of the prime threats to Earth at 370 meters (1,214 feet) across, would release energy greater than every nuclear weapon on Earth combined – but would be shaken to harmlessness if intercepted 10 days before arrival.
Lubin compared a penetrator array to a field of vaccine needles protecting the entire planet. Once established, they would be ready for any threat, including a long period comet, for which warning will always be limited.
The authors acknowledge small fragments might still reach the ground, but someone would have to be really unlucky to have one come through their roof.