Nasa to send asteroid away from Earth by firing a bullet at it in attempt to save the Earth from future strikes

The missile will be about the size of a fridge

Artist concept of NASA’s Double Asteroid Redirection Test (DART) spacecraft (NASA/JHUAPL)

Nasa is going to fire a bullet at an asteroid in an attempt to save the Earth.

The agency has laid out the plans for its DART mission – where it will send a space capsule the size of a fridge towards an asteroid to shoot it off course. For now, the mission is just a test, but in the future it could be used to save Earth from what scientists say is an underappreciated threat from asteroids.

The mission has now been approved by Nasa and will move into the preliminary design phase, getting ready for testing in a few years.

“DART would be NASA’s first mission to demonstrate what’s known as the kinetic impactor technique – striking the asteroid to shift its orbit – to defend against a potential future asteroid impact,” said Lindley Johnson, planetary defense officer at NASA Headquarters in Washington. “This approval step advances the project toward an historic test with a non-threatening small asteroid.”

DART's target is an asteroid that will pass by Earth in 2022, and come back two years later. More specifically, it's actually two asteroids: a binary system called Didymos B made up of a larger and a smaller rock.

It's the smaller one that Nasa will try and knock off course. But by using a binary system, scientists will be able to check with more accuracy how well their test has worked.

“A binary asteroid is the perfect natural laboratory for this test,” said Tom Statler, program scientist for DART at NASA Headquarters. “The fact that Didymos B is in orbit around Didymos A makes it easier to see the results of the impact, and ensures that the experiment doesn’t change the orbit of the pair around the sun.”

When the mission is launched, the DART craft will fly up to the asteroids, training its automatic driving tools onto Didymos B. When it finally hits the rock, it will do so at a speed nine times faster than a bullet – smashing into it with enough force that it can be seen from Earth.

Even at that speed, the difference that the collision initially makes to the asteroid would be minimal. But it would be enough to throw off its course, and that small nudge will over time lead the asteroid to change its path.

Scientists will watch that path and find out how well the system has worked for throwing it off course. That in turn will help show how well it would work for a more apocalyptic, world-ending asteroid.

“DART is a critical step in demonstrating we can protect our planet from a future asteroid impact,” said Andy Cheng of The Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, the DART investigation co-lead. “Since we don’t know that much about their internal structure or composition, we need to perform this experiment on a real asteroid. With DART, we can show how to protect Earth from an asteroid strike with a kinetic impactor by knocking the hazardous object into a different flight path that would not threaten the planet.”

Small asteroids fly to earth almost every day, but they are so little that they burn up in the atmosphere. Nasa spends its time looking for larger ones that could cause damage and estimating when they might do so – it thinks that it has found 93 per cent of asteroids of this size.

Nasa set up an office called the Planetary Defense Coordination Office (PDCO) in an attempt to keep Earth safe last year, amid increasing worryi that the planet was under threat from asteroids.