Playing cosmic billiards: NASA’s Dart probe crashes into an asteroid

Photo credit: NASA

Image Description: A large, gray, textured asteroid against a stark black background. This photo was taken by the DART probe just before impact.

For most space scientists, the thought of their satellite hitting an asteroid would make them cringe. But when NASA’s DART probe did just that just after midnight on Tuesday, scientists around the world celebrated their success.

The DART probe was not just any satellite. About the size of a full-size fridge – although slightly more expensive at £300million – he’s spent the last ten months in space, traveling to his distant destination Dimorphos. Dimorphos is a small moon or moonlet orbiting the larger asteroid Didymos. Relatively inconspicuous among celestial bodies, and even nameless, it was chosen two years ago to be the first asteroid to be deflected by human intervention. The asteroid itself poses no threat to humanity: its trajectory will never bring it close enough to Earth to collide with us. Rather, it is the subject of an experiment to gauge whether asteroids can be deflected should one ever threaten Earth.

The thought of asteroids crashing into our planet and destroying life as we know it has bothered people for a long time – nobody wants to share the same fate as the dinosaurs. As NASA spokesman Glen Nagle put it, “The only thing you could do was look up and say, ‘Oh, asteroid.’ […] we want a better chance.” Movies have shown a variety of possible solutions to a celestial body coming our way, most of which involve blowing up the offending asteroid. Rather than blowing up Dimorphos, the DART, or double asteroid redirection test, involved more of a well-placed nudge. The aim of the collision between the DART probe and Dimorphos was to change the trajectory of the asteroid only slightly – still a daunting task considering its size: Dimorphos is about 160 meters in diameter, the size of 1.5 football pitches and will estimated to weigh about 5 thousand tons. DART is tiny in comparison, weighing only half a ton. So how can such a light spacecraft shift the orbit of such a large asteroid?

The method of deflection is known as “kinetic impact” and relies on DART transferring both its kinetic energy and momentum to Dimorphos upon impact. A fast-moving spacecraft possesses a lot of energy, and since DART was moving at about 20,000 kilometers per hour, over 10 billion joules were transferred to Dimorphos at the time of impact. When DART hit Dimorphos, all that energy caused a crater to form and material from the asteroid to be ejected into space. This ejection of material from the crater pushed the asteroid in the opposite direction and further helped change its orbit.

DART was moving at around 20,000 kilometers per hour, over 10 billion joules were transferred to Dimorphos at the time of impact.

All in all, the change in Dimorphos’ orbit is still small: it currently takes the asteroid just under 12 hours to orbit the larger asteroid Didymos, and it is expected to orbit Didymos just a few minutes faster than DART after impact Before. Because the target’s deflection is so small, any mission to knock an asteroid out of the way on a possible collision course with Earth would have to be done several years in advance in order for it to work. This project is therefore only part of the efforts of the international space community to protect the earth from asteroids. Both the European Space Agency and NASA track and analyze asteroids thought to be near Earth orbit, and reassuringly none of the large asteroids will collide with Earth in the next millennium. Nevertheless, even small asteroids can cause significant damage. A meteorite about 20 meters in diameter exploded in the atmosphere over Russia in 2013, causing a shock wave that injured over a thousand people, mostly from shattered glass and collapsing walls.

Such events, while frightening, are relatively rare. The publicity surrounding the DART mission has therefore sparked some debate, as scientists argue that the threat to humanity from climate change is far greater and more likely than that from Earth-bound asteroids. The parallels to the film Don’t look up, a climate change denial satire that was published just last year, are quite striking indeed. In the film, the looming threat of an asteroid hurtling toward Earth is largely ignored until someone finds a way to monetize it. In the real world, it seems to some scientists as if the imminent threat of climate change is largely ignored while asteroid deflection gets big buzz.

Despite the criticism, the DART mission is intended to benefit the scientific community in other ways besides potential earth-saving applications. Images of the impact recorded on the LiciaCube, DART’s travel companion and photographer, and on ground-based telescopes will provide data on the amount of dust released by Dimorphos. The dust cloud will depend on the type of rock that makes up Dimorphos, allowing researchers to learn more about asteroids.

Over the next few weeks, scientists will be observing the asteroid from Earth to see if Dimorphos’ orbit has actually changed. But in NASA’s eyes, the mission is already a success – it’s catapulted the concept of defending our planet from asteroids out of the realm of Hollywood and into real life.

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