In September 2022, a space probe, the Dart mission, hit the asteroid Dimorphos for the first time. Goal: deviate from its trajectory. But the collision didn't just have this effect, researchers tell us today. It completely changed the shape of the asteroid.
In November 2021, NASA launched an unprecedented mission. The Double Asteroid Redirection Test mission, better known by the acronym DartDart. Its goal: a collision with the asteroid Dimorphos to assess humanity's ability to deflect the trajectory of such an object, which could risk a collision with Earth. The high-speed, head-on collision occurred several million kilometers away. It was September 2022.
It didn't take long for NASA to announce the mission's success.
Mission Dart: Humanity has managed to repel an asteroid for the first time in its history!
For the first time, humanity had succeeded in repelling an asteroid. And not just a little. Before colliding with Dart, Dimorphos took 11 hours and 55 minutes to orbit its parent asteroid – because the target object is part of a binary star system. A modification of this duration of 73 seconds would be a real success, the scientists assured at the time. But after impact, Dimorphos rotated in just 11 hours and 23 minutes!
Dart on Dimorphos, an impact with serious consequences
The publication today of new results from the Dart mission in the journal Nature Astronomy reveals some surprising details of the operation. The impact – although comparable in mass to that of an ant in two buses – appears to have left more than just a crater on the asteroid. Dimorphos may actually have completely changed its shape.
“We wondered if we hadn’t pulverized the asteroid! » The dart mission tells about Patrick Michel
A few weeks after the collision, one of the fathers of the mission and research director at CNRS at the Côte d'Azur Observatory, Patrick Michel, told us that for a moment he thought Dart had pulverized dimorphos. So maybe he wasn't so far from the truth. Based on simulations and various observations, astronomers now estimate that the asteroid, which weighs around 5 million tons, still lost around 20 million kilos. That's the equivalent of six Saturn V rockets that took the Apollo program astronauts to the moon!
Simulations revealing the nature of the asteroid
The astronomers arrived at these results using an algorithm that has already proven itself elsewhere. It breaks down the impact between two bodies into millions of particles, whose behavior is determined by the interaction of various reconfigurable variables such as gravity, density or resistance of the asteroid's material. In around 250 simulations, the researchers had a lot of time to visualize the effects of variations on parameters that were unknown to them.
By comparing the results of all these simulations with data collected by some satellites, the James-Webb and HubbleHubble space telescopes, and instruments on Earth, the researchers conclude that “Dimorphos is a 'debris pile' asteroid, which is held together by extremely weak gravity” and not by its cohesive force. » Enough to explain the astonishing effectiveness of the orbital deviation caused by Dart.
While we wait for confirmation, the planet's defense is moving forward
Astronomers therefore now assume that the Hera mission led by ESA, the European Space Agency, which is scheduled to reach Dimorphos at the end of 2026, will find an asteroid with a completely different shape. He was like someone had bitten into the M&Ms before he hit darts.
If this is confirmed, astronomers will note that dimorphs like RyuguRyugu and Bennu ultimately appear to exhibit some lack of cohesion. Although the first asteroid is rich in silicate silicates and the other two are rich in carboncarbon. “It is fascinating to imagine that all small asteroids lack cohesion. But it would be good news for the defense of the planet, because knowing in advance the reaction of a body will facilitate the development of the tools necessary for our protection,” concludes Patrick Michel in an ESA press release.