NASA sends the Dart probe to crash against an asteroid: “We want to prevent future generations from having to improvise”

This is a first of its kind for NASA. The American space agency launched from California on the morning of Wednesday, November 24 (7.20 a.m. Paris time, and on the night of Tuesday to Wednesday in the United States), a space mission of a new kind. Objective: send a probe to crash into an asteroid.

Dart is its name – “dart” in French and acronym for Double Astroid Redirection Test (link to an article in English) – should reach its target in a little less than a year and change its trajectory. In 2026, another probe called Hera, European this time, will be sent into space in turn to study the result of this impact as closely as possible.

What is the target?

Dart’s target is called Dimorphos, the name given to this small asteroid present in our solar system. It is a pebble 160 meters in diameter that revolves around another, a little larger called Didymos, which is 800 meters in diameter.

The duo, identified twenty-five years ago, is one of those 15% of asteroids that are double, a bit like mini Earth-Moon systems. They are also near-Earths, that is to say asteroids whose orbit can cross that of the Earth.

What is the risk for the Earth?

By tapping on the little moon of Didymos to deviate its trajectory, which is enough for a test, “we deviate its trajectory around its main body but we do not deviate it from its trajectory around the sun, so we avoid causing a risk that we are trying to avoid”, explains Patrick Michel, astrophysicist at the Observatory of the Cote d’Azur, world expert on asteroids, and scientific manager of the Hera space mission. This mission “whatever happens, will not increase any risk with the Earth”, reassures Patrick Michel.

What is the interest of this mission?

Even if there is no major risk identified today, and for at least a few hundred thousand years, for a large near-Earth asteroid to destroy our existence, we continue to list those of smaller size. , a few hundred meters. These asteroids could one day, but it does not seem for tomorrow, to have a destructive effect on the scale of a city or a region. As it is better to prevent than to cure and to put all the assets on our side, we therefore seek to know if by crashing a probe on this type of object, we can very slightly modify their trajectory and thus save our planet from a potentially devastating collision.

“We know that this kind of problem with low probability and high consequences is multiparameter, explains astrophysicist Patrick Michel. There is the scientific parameter: knowing how to identify the threat and knowing what to do. There is the technological parameter: how we deal with it. There is also political decision-making, crisis management and legal issues. The advantage is that we have the means to prepare for it. “

“What we want to avoid is that future generations, when they are faced with this risk, are forced to improvise and it is too late because it is extremely complex.”

Patrick Michel, astrophysicist

to franceinfo

We are really talking about space defense. For the moment there is no way to protect yourself against a large stone from space. This mission is therefore clearly made to validate an avoidance technique.

How will the impact be studied?

After ten months of space travel and a few million kilometers traveled, the Dart probe will propel its almost 600 kg on its target, at more than 20 000 km / h. The impact, expected in October 2022, will be filmed by a mini satellite dropped a few days before the final fall. Scientists also hope to be able to measure the consequences of this crash from Earth, using radars and telescopes. “Dart, which weighs 560 kg and will tap at 6 km per second, will produce an instantaneous difference in trajectory. As it (the asteroid) passes 11 million km from Earth at the time of impact, it is ie relatively close to observe it with terrestrial telescopes, we can at least have a first measurement of the difference in the time it takes for the moon to revolve around its central body before and after impact. “

“The telescopes won’t fully respond to what happened, but it will give us a first indication.”

Patrick Michel, astrophysicist

to franceinfo

Additional data on NASA’s Dart mission will also be collected in a few years thanks to another mission, this time piloted by the European Space Agency. In 2026, ESA will send the Hera probe to Dimorphos. She will then be able to better visualize the shape of the crater on the asteroid left by the impact and will also make it possible to do more fundamental science, in particular by studying the internal structure of these asteroids, of which much remains to be discovered.

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