When the Dart mission crashed into the asteroid Dimorphos last September in what was the first-ever test of planetary defense, the Hubble Space Telescope was on the prowl. The opportunity to record remarkable images that give astronomers a unique perspective on the event.
On September 26, a spacecraft weighing just over 500 kilos deliberately crashed into the asteroid Dimorphos. The objective of the Dart mission (Double Asteroid Redirection Test) : test our ability to modify the trajectory of the asteroid to collect data that could help researchers imagine a defense strategy for our Earth against a threatening asteroid. By crashing head-on into Dimorphos at a speed of some 21,000 km/h, Dart threw more than 1,000 tons of pulverized rock into space.
The test was closely monitored by the Hubble Space Telescope. And today, the time-lapse of the images he recorded reveal, hour by hour, how this debris and this dust were torn out. Invaluable and startling information on a rather complex dispersal pattern. Because it was the very first time that astronomers witnessed a collision in the heart of a double system of asteroids. “It will take some time to understand”confie Jian-Yang Li du Planetary Science Institute of Tucson (United States), in a NASA communiqué.
An ejecta tracked
The film begins a little over an hour before impact. At that time, not even Hubble was able to separate Didymos and Dimorphos, the two asteroids that form the system. The first image after the collision with Dart was taken twenty minutes after impact. Debris is ejected from Dimorphos at around 6.5 km/h. Enough not to fall back on the asteroid. The ejecta forms a hollow cone with long stringy filaments.
About seventeen hours after impact, the debris pattern entered a second stage. The dynamic interaction within the binary system begins to deform the ejecta cone. The most important structures are revolving elements in the form of a pinwheel. The result of the gravitational pull of Didymos. “It’s really unique for this particular incidentcomments Li. When I first saw these pictures I couldn’t believe these features. I thought maybe the image was corrupted or something. »
Hubble then shows the debris being swept up into a comet-like tail by the pressure of sunlight on the tiny dust particles. It extends into a debris train where the lightest particles move fastest and furthest from the asteroid. Still later, Hubble records this tail splitting in two for a few days.
NASA’s Dart mission confirms that crashing spacecraft into asteroids can successfully knock them off course. © Nasa
The success of the Dart mission
If the researchers still plan to work on these images, they already confirm the success of the Dart mission. First, because it has proven that the interception of an asteroid with a diameter of less than one kilometer can be achieved. Even without an advanced reconnaissance mission. Provided there is sufficient warning time. Preferably decades, all the same…
Then, because the Dart mission did indeed deflect Dimorphos’ orbit by some 33 minutes. And the researchers now figured out that it was not only thanks to the thrust exerted by the collision between the spacecraft and the asteroid, but also by the recoil of the ejecta. What then, validating the principle of “the kinetic impactor” as a means of planetary defence.
But the mission goes beyond that. It offers scientists a unique opportunity to study the so-called asteroids ” assets “ – an asteroid orbiting another. Such asteroids would be the results of impact events, precisely. Thus the Dart mission made it possible to simulate and observe for the first time what could correspond to the process of formation of an active asteroid.