HOW NASA DEFLECTED AN ASTEROID BY CRASHING A SPACECRAFT INTO IT

NASA'S DART spacecraft made impact with its asteroid target on 27 September. Dr Tim Gregory tells us about this first-of-its-kind mission

- DR TIM GREGORY

WHAT IS THE DART MISSION?

It stands for the Double Asteroid Redirection Test. It's essentially a big science experiment to see if crashing a spacecraft into an asteroid is a good way to change its orbit around the Sun and potentially deflect an Earth-crossing asteroid away, should that happen in the future... or rather when that happens.

TELL US ABOUT THE SPACECRAFT.

DART is quite a hefty spacecraft. It weighs more than half a tonne, at 610 kilograms. One of my favourite things about this mission is that onboard is a CubeSat [LICIACube, or Light Italian CubeSat for Imaging Asteroids]. CubeSats are little, miniature satellites about the size of a champagne bottle. This particular CubeSat is Italian in origin and it's got a camera.

WHY WAS THE DIDYMOS BINARY ASTEROID SYSTEM SELECTED AS THE TARGET FOR THE MISSION?

The double asteroid is a cool little system. Much like the Earth has a celestial companion with the Moon, some asteroids have celestial companions, too. We call them binary asteroids. The target is made up of two individual objects: Didymos A, which is about 780 metres across, that's roughly seven football pitches; and its smaller companion Dimorphos, which is 160 metres across. The DART mission targeted the smaller of the two, Dimorphos.

It's important to stress that this particular asteroid system doesn't pose a threat to the Earth. It was merely chosen as a target based on its orbit around the Sun. It's got a very well-determined orbit and we will be able to track the new orbit to see if it's changed.

One of the really mind-blowing things about these asteroids is that we don't actually know a lot about them, other than their orbital parameters. We don't know what they look like. We don't know exactly what they're made of. And that's actually true, for basically every single asteroid in the Solar System.