The Dart – or Double Asteroid Redirection Test – mission will see Nasa test whether it might be possible to redirect a future asteroid that could be coming to collide with Earth.
It will do so by slamming into an otherwise harmless double asteroid known as Didymos. Scientists will then be able to examine whether and how that worked to inform their work if an asteroid really was on its way to collide with us.
That mission launched at 6.20am UK time on Wednesday morning, or 10.20pm local pacific time. It lifted off on board a SpaceX Falcon 9 rocket from Vandenberg Space Force Base in California.
It will then fly through space on its way to the pair of asteroids. It will look to catch Didymos when it is 6.7 million miles from Earth.
That long distance is intentional. The mission will only knock the asteroid off its orbit by a little – but that is all that might be needed, so long as scientists are able to spot potentially hazardous asteroids early enough.
Dart will smash into the asteroid, going at 15,000mph, in September 2022. Scientists should know not long after that whether it is successful, thanks in part to an Italian satellite that will be deployed about 10 days before so that it can watch the impact and send back images to Earth.
Astronomers will then be able to chart the change in the orbit from telescopes back on Earth. That will really answer the question of whether the test has been successful, and how any future asteroids might be able to be diverted.
It could take years before we fully understand the effects of the experiment, however. The European Space Agency is working on another spacecraft, known as Hera, which will arrive at the asteroid in 2027 and look to examine what has happened, five years on.