Saving Earth from asteroids – Nasa’s DART mission

On 26 September, DART successfully slammed into an asteroid in the name of planetary defence. Here’s why Nasa is hurling spacecraft at space rocks.
A week ago, Nasa tested for the first time its latest planetary defence system, designed to save Earth from asteroids heading our way. The Double Asteroid Redirection Test (DART) successfully collided with the asteroid Dimorphos, and experts are now waiting to see how effective this method is.
“DART is turning science fiction into science fact and is a testament to Nasa’s proactivity and innovation for the benefit of all,” said Nasa administrator Bill Nelson.
“In addition to all the ways Nasa studies our universe and our home planet, we’re also working to protect that home, and this test will help prove out one viable way to protect our planet from a hazardous asteroid should one ever be discovered that is headed toward Earth.”
What is DART?
DART is the world’s first test of defending the planet from asteroids using kinetic impact, but the goal is not to destroy the offending space rock but rather to alter its orbit. This is achieved by crashing into the asteroid, at speed and with force, to knock it slightly off course so it passes by Earth, instead of potentially crashing into it. Specifically, DART’s mission was to see how effective this would be as a way to protect Earth, and how much, if at all, the asteroid could be shifted.
DART was launched to deliberately collide with Dimorphos, a moonlet of a larger asteroid, Didymos. Didymos was discovered in 1996 by researcher Joseph Montani, and seven years later the existence of Dimorphus was confirmed. In Greek, dimorphos and didymos mean twin; having two forms, and the two asteroids are a binary pair, with the egg-shaped Dimorphos orbiting Didymos. Neither is actually a threat to Earth, but they are close by, so this made Dimorphos the perfect test subject.
Just like Earth, the asteroid pair orbit the Sun, and do come close to Earth at times during this rotation. At its closest, the pair passed only 0.048 AU from Earth (something like 7,180,697km) – where one unit AU is the distance from the Sun to the human planet – and at its farthest, on the other side of the Sun, around 3 AU away. Didymos, the larger of the two, is about 780 metres in diameter, while the moonlet is only 160 metres, spinning rapidly around its neighbour ...