The machine struck Tuesday at 1:14 am The Dimorphos asteroid at 22,000 km/h. Objective: slightly deviate from its trajectory. But it will take several days, or even several weeks to know if it has succeeded.
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In English, Dart means dart. And Tuesday, September 27, at 1:14 am (Paris time), the NASA dart reached its target: the Dart-suicide mission (Double Asteroid Redirection Test) crushed well on the small asteroid Dimorphos, 160 meters in diameter, itself satellite of a larger asteroid, Didymos. All 11 million kilometers from the earth.
During the hour preceding the collision, we were able to follow the double asteroid approach on the NASA chain thanks to Draco, the camera equipping Dart. Even if the film was more similar to a slideshow, since only one image per second was broadcast, you could feel almost transported to a spacecraft. Fifty minutes before the impact, while Dimorphos was still only a small pale point, was announced that the target was “locked”, just like a fighter plane targeted by a missile.
Two trajectory corrections later, carried out by the autonomous navigation software, we distinguished Didymos and its diamond shape. It was not until the final minutes that the oval of Dimorphos, whose scientists ignored the form before that, began to take shape on the screen. During the final seconds, when he was no longer in doubt that Dart would reach his target, Draco was sending more and more details of a rocky surface. It occupied the whole field of vision, then nothing. By dying, the probe signed the success of its mission.
Next step, the HERA mission
Dart’s objective, which struck Dimorphos at a speed of 22,000 km/h, consists in slightly modifying the trajectory of its target, in order to learn to deflect an asteroid potentially dangerous for earthlings. An army of telescopes is robbed on the couple Didymos-Dimorphos in order to measure how long the period of revolution of the second around the first will be modified. The results of these observations are not expected for several days, or even several weeks. It is also the time that the retransmission of the images taken by Licicube will take, an Italian nanosatellite accompanying Dart, who, holding cautiously at a distance so as not to risk being destroyed by rocks ejected during the impact, filmed the scene and its result.
That said, Dart’s-suicide mission is only act I of history. In 2027, the HERA mission of the European Space Agency (which will take off in October 2024) scrutinized Dimorphos from every angle to fully analyze the consequences of the collision. As Patrick Michel explains, CNRS research director at the Côte d’Azur observatory and Héra scientific manager, the latter “will give two series of crucial information: the final result of the impact and all the Internal properties of the target thanks to a radar. We will know if it is an aggregate or a monolith, its mineralogy, its geological properties, its mass … “All this information is crucial to model what happened this Tuesday and allow To understand how effective the impact of a machine is to deviate an asteroid from its trajectory. In order to prepare the right dart for the day when the threat of a large pebble, hypothetical will become real.