The Chicxulub crater in Mexico is a testament to Newton’s second law of motion. At 180km across and 20km deep it is thought to have been formed by an asteroid that was just 10km wide – but travelling very fast. The success of Nasa’s Double Asteroid Redirection Test this year means the same principles might one day prevent a repeat hit.
Dart was the first demonstration of a planetary defence technology using a kinetic impact to alter the course of an orbiting body. Nasa smashed a satellite into an asteroid to change its speed and trajectory.
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The target, harmless asteroid Dimorphos, was 160 metres across and orbited a larger asteroid called Didymos. Dart hit Dimorphos at a speed of around 22,000km per hour and managed to alter its orbit by about 1 per cent. In the vastness of space that is enough to make a difference.
The odds of an asteroid the same size as the one that formed the Chicxulub crater and wiped out the dinosaurs hitting Earth are remote. Some 66mn years have passed since it landed. But the impact from a smaller rock could still be devastating.
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No known asteroid larger than 140 metres has a chance of hitting the Earth for the next 100 years. But only half of an estimated 25,000 near-Earth objects of that size or larger are known. Even smaller asteroids can have a significant impact. The approximately 50m-sized object that exploded above Siberia in 1908 levelled trees over 2,000 sq km.
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In theory, the same principles used to create Dart could be scaled up to tackle larger and more dangerous asteroids. Bennu, with a diameter of 500 metres, ranks as one of the highest-risk known asteroids with a roughly one in 2,000 chance of impact some time between 2178 and 2290. A scaled-up satellite would need a mass of eight tonnes to have the same impact as Nasa’s test run.
More power is likely to be needed for any more substantial threat to our planet. Space scientists are studying the possibilities of nuclear payloads.
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