“I think we have a good chance of hitting him,” says astronomer Özgür Karatekin.
The DART mission will be launched at the Vandenberg launch site in California on Wednesday morning around 7.20 am Dutch time. DART (Double Asteroid Redirection Test) is expected to collide with the asteroid Dimorphos, a 168 meter large piece of space rock at the end of September next year at 6.6 kilometers per second (24,000 km/h).
If such a fragment hit the Earth, it would be a worldwide catastrophe. Fortunately, Dimorphos is not on a collision course with Earth, but is in orbit around the larger asteroid Didymos, which in turn orbits the sun in elliptical orbits.
Dimorphos makes a circle around Didymos once every 11 hours and 55 minutes, “The collision with DART will take about 10 minutes from that orbital time,” says Karatekin, a researcher at the Royal Observatory of Belgium in Brussels. He was involved in computer simulations of the interior of Dimorphos and the collision with DART.
That collision is simple billiards physics at first: the mass of the colliding DART is 550 kilograms, which produces a kinetic energy comparable to the most powerful conventional military explosives.
“But how effectively that blow is translated into a change of course depends on the structure of Dimorphos,” says Karatekin. If it’s a loosely connected pile of rubble, a rubble pile, DART hits deeper, blasting a lot of debris from the impact crater. Partly due to this recoil, the speed change can be almost twice as great.
En route to its end, DART will send CCTV images of the rapidly expanding target. Hopefully there will also be images of the aftermath, shot by Italian satellite LICIACube, which split off ten days before the collision to film the collision from a safe distance. And on Earth, astronomers will map the changed orbital speed with telescopes.
But to really absorb the consequences, the European Space Agency (ESA) will send the HERA probe in 2024, which will arrive in 2027. On board are cameras and, among other things, a gravity meter. “That will allow us to determine the mass of Dimorphos,” says Karatekin, “and a probe will also land on Dimorphos to take measurements there.”
The results will teach astronomers more about the formation and history of asteroids, and thus the solar system. But they are also of more practical importance. The solar system is still full of ‘Earth snipers’, clumps of rock that occasionally come dangerously close to Earth.
1,500 injured in Russia
In 2013, such a 12,000-ton, 18-meter-wide debris fell over the Russian city of Chelyabinsk, exploding in the atmosphere. The blast damaged thousands of buildings and injured 1,500, mostly from falling glass.
It is estimated that roughly 25,000 near-Earth objects of that size still exist, of which less than one percent has yet been mapped. Larger and therefore more dangerous specimens are rarer and more visible. Yet even about 5 percent of the category of near-Earth objects – a global catastrophe if they hit the Earth – have not been mapped.
The earlier such a space rock heading toward Earth is discovered, the further it is from Earth, and the smaller the change of course required to make it miss Earth. Karatekin: “A collision is one of the simpler ways to change that course. That is also a reason for doing this research.”
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