With Asteroid Day on 30 June, looks at ESA’s part in a mission that is science fiction made real – to impact a near-Earth object and alter its path
e all know that accidents can happen, but 2020 will be remembered as a year of catastrophe. The upshot is we have to pay greater attention to all kinds of near misses, including those from space in the shape of incoming asteroids, and on 30 June we do just that as the world marks Asteroid Day. Similarly, 2022 should also be a year to remember but in a quite different way. That October, humankind will test out responding to the asteroid threat by slamming a desk-sized NASA spacecraft called DART, the Double Asteroid Redirection Test, into the moonlet of a near-Earth asteroid at 6.6km per second. That historic event will mark our species’ next giant leap following the Moon landing – the first time we change the orbit of a Solar System object in a measurable way.
DART’s target has been carefully chosen: the smaller of the two Didymos asteroids, in solar orbit between Mars and Earth. At 160m across, about the size of the Great Pyramid, Didymos B, or ‘Didymoon’, is in the asteroid class capable of generating casualties on a regional scale, were it to impact Earth. It orbits around the main 780m-diameter, mountain-sized asteroid. This might sound substantial, but the main asteroid has a low enough mass and gravity that Didymoon orbits around it slowly, at less than 20cm per second – a speed which makes achieving a measurable deflection
Wstraightforward. Didymoon’s degree of orbital deflection will be measurable from Earth by decoding radar signals and light curves gathered via our planet’s telescopes.
After DART’s impact, Europe will take a lead in the historic undertaking: the European Space Agency (ESA) is finalising and launching a second spacecraft to closely investigate this unique, orbitally modified body. ESA’s Hera mission, named after the Greek goddess of marriage, is due to launch in 2024. “The mission’s goal is to acquire crucial collision data we can’t obtain from long-distance observation,” says astronomer Patrick ▲ Changing lanes: in October 2022, NASA’s DART spacecraft will impact with Didymoon to make it change orbit