THE regenerating liquid-metal robots in the Terminator movies have a cosmic relation: incoming asteroids that quickly reassemble if blasted by a nuclear bomb.
If a sizeable asteroid is found heading towards Earth with little warning, the only way to prevent an impact may be to blast it to bits with a nuke.
But too small a bomb would cause the fragments to fly apart only slowly, allowing them to clump together under their mutual gravity. Simulations now show this can happen in an alarmingly short time.
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Don Korycansky of the University of California, Santa Cruz, and Catherine Plesko of the Los Alamos National Laboratory in New Mexico simulated blowing up asteroids 1 kilometre across. When the speed of dispersal was relatively low, it took only hours for the fragments to coalesce into a new rock.
鈥淭he high-speed stuff goes away but the low-speed stuff reassembles [in] 2 to 18 hours,鈥� Korycansky says. The simulations were in March at the Lunar and Planetary Science Conference in Houston, Texas.
As a result, the asteroid could still wallop Earth.
Fewer fragments
But in scenarios in which we have more warning time, asteroids鈥� ability to reassemble would actually be a good thing, since fragments flying near Earth could still cause damage by knocking out satellites, Plesko says.
The goal in such a situation would be to nudge the asteroid off its collision course without breaking it up, a delicate balancing act. If the push is too weak, the asteroid might not move quickly enough off course to avoid a collision with Earth. On the other hand, if the push is too strong, the asteroid could break apart 鈥� a worry that has often been raised in connection with using nuclear blasts in particular.
But even if the asteroid breaks up, the new study shows it may quickly reassemble, saving Earth from a blizzard of fragments, Plesko says. The momentum from a nuclear blast would give the reassembled asteroid a slightly different trajectory, so it would miss Earth if it was nuked far enough in advance, she says. 鈥淵es, it flies apart, but when it reassembles it鈥檚 been pushed off course,鈥� she told 快猫短视频. 鈥淭he harder you can push it, the less lead time you need.鈥�
Still, it is best to avoid breaking up the asteroid to begin with, if possible, because even if most of it reassembles, some stray fragments could still cause harm, she says.
If we ever did need to destroy an asteroid on short notice, a 2009 study led by David Dearborn of the Lawrence Livermore National Laboratory in California reassuringly showed that a 900-kiloton nuclear device 鈥� which is within our capability 鈥� would permanently disperse a 1-kilometre asteroid.
