DART, a kamikaze mission to learn how to deflect an asteroid

Artist's impression of the DART probe before it crashed into the asteroid Didymos.

Although the setting, spectacular, is worthy of a science fiction movie, the event will be framed in the real world. When ? Tuesday, September 27 at 01:14 (Paris time). Where ? Somewhere in space, 11 million miles from Earth. What ? NASA’s DART (Double Asteroid Redirection Test) probe, launched at a speed of 22,000 km/h, will crash into Dimorphos, a small asteroid about 160 meters in diameter, a satellite of a larger asteroid called Didymos. Why ? “The objective of the mission is to carry out the first deflection test of an asteroid”, summarizes Patrick Michel, director of research for the CNRS at the Côte d’Azur Observatory and a specialist in these small rocky or metallic bodies, some of which, like stray bullets in the Solar System, from time to time impact planets or one of its satellites

In the case of Earth, if the asteroid is small (10-20 meters in diameter) and rocky, it has a high chance of catching fire or exploding during its journey through the atmosphere, as we saw in 2013 with the Chelyabinsk meteor. (Russia), whose arrival still hurt a good thousand people.

Also read the file (2013): The “Chelyabinsk Superbolide”, the largest meteor since 1908

If it is a little larger (50 meters) and metallic, nothing can stop it and, in an impact releasing more than 150 times the energy of the Hiroshima bomb, it creates a crater in the ground 1.2 kilometers in diameter, as can be seen in Arizona at the site of the Meteor Crater, which appeared 50,000 years ago. And if the asteroid measures 10 kilometers, its fall causes a global cataclysm and a great extinction of life, like the one that ended the reign of the non-avian dinosaurs 66 million years ago. Hence the pleasant idea of ​​learning how to divert these killer cars from the depths of time.

Let’s make it clear from the beginning: the Didymos-Dimorphos couple does not threaten us and, just as importantly, the test that will be carried out does not risk diverting it to Earth. “We are not going to cause the danger we seek to avoid, assures Patrick Michel. We make a “toy” but this does not disturb the global trajectory of the system. »

“Involve the public”

What is going to happen ? For several days, the kamikaze probe has its target in focus, but its small camera named Draco has not yet made the difference between Didymos and Dimorphos, which form a large point. The distinction will be made “little less than an hour before impactPatrick Michel says, and it will be a critical moment: intelligent navigation software must clearly identify Didymos from Dimorphos and lock its direction on the latter.” The whole difficulty of the exercise consists in not missing a target whose shape we do not know in advance. Potatoes or cigarette? Mystery.

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