but now nasa is preparing to launch a spacecraft from california that will be guided remotely to crash into a pair of asteroids called didymos and dimorphous. neither present any risk to earth, but scientists want to test whether it is possible to change the course of the large asteroids, even by a tiny fraction. this is a big dealfor nasa, the first time the agency will intentionally crash a spacecraft into an asteroid for a planetary defence mission. the impact won t happen until september next year. but when it does, it will deliberately strike at around 15,000 mph. essentially, this spacecraft is going to act like a cue ball in a game of pool orsnooker, right? it s going to smash into this asteroid and give it a little bit of a boost in energy. if you can change the speed of the asteroid so that it just misses the earth, that s all you need to do. no known asteroid wider than 140 metres is expected to hit the earth
this is a computer simulation of dart, the double asteroid redirection test, which could be our first line of defence if one of those lumps of rock comes heading our way. nature has given us a setup where we have an asteroid, a binary asteroid, that s approaching close to earth so that we can observe from earth based observatories, but this is a test. and this is how the test will work. astronomers have long been aware of a pair of asteroids called didymos and dimorphous. sometime later next year, dart will target then, smash into them, trying to alter their course. these asteroids are no danger to us, but others might well be. if there was an asteroid that was a threat to the earth, what you d want to do, this technique with would, be many years in advance, decades in advance, such that you would just give this asteroid a small nudge