The results of the first asteroid deflection test by the DART (Double Asteroid Redirection Test) mission are the subject of a series of five articles published in Nature, three of which involved a CNRS-INSU researcher (see box) . This NASA mission successfully completed the high-speed impact of an artificial probe on asteroid Dimorphos, the satellite of the binary asteroid Didymos, at 23:14 UTC on September 26, 2022, as part of the first planetary defense test. This is a full-scale test, the interpretation of which might be consolidated by the complete characterization of this asteroid system by ESA’s Hera probe in early 2027.
In the 1st article, an estimate of the momentum transferred by the impact of the probe to the small moon Dimorphos 151 meters in diameter is made. It initially revolved around its central body, Didymos 800 meters in diameter, in 12h55 min. The team measures a reduction in the orbital period which implies that the momentum of DART has been multiplied (by a factor between 2.2 and 4.9) due to the ejection of material on impact. These estimates indicate that the DART impact was therefore very effective in deflecting the asteroid. In the second article, the team reconstructs the impact, including the timeline leading up to it, the location and nature of the DART impact site, and the size and shape of Dimorphos that crashed into it. is revealed by the images provided by the DRACO camera (Fig. 1) on board the probe. The images show that the surface of Dimorphos presents a great geological richness, like the other small asteroids visited previously (Bennu and Ryugu). In the 3rd article, scientists interpret observations made by the Hubble Space Telescope from 15 minutes up to 18.5 days following impact, with a spatial resolution of 2.1 kilometers per pixel. The images reveal a complex evolution of the ejected material and resemble those of certain active asteroids and comets with their two characteristic tails produced however for different reasons.
