Nasa spacecraft lining up to smash into an asteroid
The Dart mission will test a technique for defending the Earth against hazardous space rocks.
Science & Tech
In the coming hours, the American space agency will crash a probe into an asteroid.
Nasa's Dart mission wants to see how difficult it would be to stop a sizeable space rock from hitting Earth.
The demonstration is taking place some 11 million km away (7 million miles) on a target called Dimorphos.
The agency says the rock is not currently on a path to hit the Earth, nor will the test accidentally send it in our direction.
The impact is timed for 23:14 GMT, Monday (00:14 BST, Tuesday). Telescopes will be watching from afar, including the new super space observatory James Webb.
We've all seen how Hollywood would do it, with brave astronauts and nuclear weapons. But how do you protect Earth from a killer asteroid for real?
Nasa is about to find out. Its idea is simply to smash a spacecraft into one.
The thinking is you would only need to change the rock's velocity by a small amount to alter its path so that it misses Earth - provided you do it far enough in advance.
The Double Asteroid Redirection Test (Dart) mission will check out this theory with a near-head-on crash into 160m-wide Dimorphos at over 20,000km/h.
This should change its orbit around a much larger asteroid, called Didymos, by just a few minutes every day.
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