For hours there was only a single pixel in view, but during its final minutes, the spacecraft DART got its sights on its target: the asteroid Dimorphos. In the final seconds, the 160-metre-sized clump of rock rapidly swelled into a gray potato shape, speckled with loose stones.
And at 1.14 am (Dutch time), DART crashed into it, just as intended. „We have loss of signal – we’ve lost the signal,” will rarely have been so enthusiastically exclaimed in NASA’s control rooms.
“It worked,” says Özgür Karatekin, a researcher at the Royal Observatory of Belgium in Brussels, involved in the DART experiment. DART (Double Asteroid Redirect Test). “For the first time, we have changed the orbit of a celestial body,” says Karatekin.
Until Monday night, Dimorphos, roughly 5 million tons, orbited the heavier Didymos once every 11 hours for 55 minutes. DART, a 570 kilogram space probe the size of a city car, hit at a speed of 23 thousand kilometers per hour. That blow should take about 10 minutes off the track period.
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Telescopes on Earth and in space are monitoring the galaxy, Karatekin says. Exactly how big the change is will become clear in the coming weeks. For example, it depends on the exact composition of Dimorphos. “From the images it looks like a loose pile of rubble, a” rubble pile”, says Karatekin. In that case, debris bounces back on impact, and that recoil causes a greater orbit change than if Dimorphos were one piece.
11 million kilometers in less than a year
Launched on November 24, 2021, DART covered 11 million kilometers to its final target in just under a year. In the weeks leading up to the impact, DART’s course was revised from time to time, something DART’s onboard algorithms did independently in the last few hours. “We could only watch and hope it went well,” said Karatekin. “Of course he could have missed, but the car navigation worked beautifully.”
The rapidly looming target asteroid was filmed by the COBRA camera, which obviously did not survive the impact. But the drifting debris plume, and possibly the impact and resulting crater, were filmed by LICIAcube, a satellite that split off from DART 15 days before the impact, to fly past three minutes after the impact.
Karatekin performed simulations in advance of the composition of Didymos, a HERA probe of the European Space Agency (ESA). It should be launched in 2024 in order to provide a more accurate picture of the aftermath of the collision.
The results are scientifically interesting, but the NASA department that ordered the mission does not have Planetary Defense in its name for nothing: planet protection. Thousands of ‘Earth snipers’ can be found in space: lumps of rock that could potentially collide with the Earth. Such a cosmic accident, for example, affected the dinosaurs, which became extinct 65 million years ago due to the impact of a piece of rock about 10 km in diameter.
Gliders of such large dimensions have probably all been mapped, and a recurrence of the dinosaur impact is not imminent. But of the smaller space rocks, which can wipe out a country or city, we have fewer in our sights. If we find one on a collision course with Earth, maybe we can nudge it with a DART successor so it just misses us. Although that will have to be a much bigger blow than DART just dealt, says Karatekin. “But I’m really happy with today’s collision.”