Before the direct impact, NASA’s space probe was still able to contribute to science.

It was an exercise in avoiding a catastrophe: a direct collision of NASA’s DART spacecraft with the asteroid Dimorphos on September 27, 2022. If a kilometer-wide space rock hurtled toward Earth, it would hopefully miss the planet and be hit in time.

Before its abrupt end, DART did some quick science. In the final minutes and seconds before impact, the onboard camera snapped images of its target, a gray, oval rock filled with rocks and debris. The camera also snapped images of Didymos, the larger planet, about 780 meters in diameter, that Dimorphos orbits.

These few images have now been extracted and analyzed. that series by five Articles in Nature CommunicationsWith main conclusions: Dimorphos and Didymus are both piles of rubbleliterally “rubble piles”, accumulations of stones and gravel held together loosely by gravity.

Furthermore, Dimorphos likely formed from Didymos, according to an analysis of the dimensions of the rocks on the surface of both asteroids. In the past, under the influence of sunlight, Didymos began to rotate faster and faster on its axis, until rocks were scattered on Didymos’ equator. Shortly after, those rocks clumped together again to form the moon Dimorphos, which orbits Didymos every 11 hours and 55 minutes.

somewhat weak

The suspicion among asteroid researchers is that most asteroids between 200 meters and 10 kilometers in diameter are like that. piles of rubble It is formed from the debris of collisions between past asteroids. It is therefore quite smooth: the carrying capacity of Didymos’s surface is less than that of dry sand on Earth, say Jeanne Pihot of the University of Toulouse and her colleagues on the basis of the images.

The Didymos-Dimorphos pair’s orbit is just outside Earth’s, so they’ll never come close to us. However, the analysis isn’t just of scientific interest. Obviously, how hard an asteroid is makes a big difference if you want to knock it out of orbit. After the collision with DART, Dimorphos’ orbit appeared to change dramatically: Its orbital period became 33 minutes and 15 seconds shorter, a much larger change than expected.

The Italian LICIAcube spacecraft, which imaged the impact in the wake of DART, also saw a large plume of debris and debris after the impact. New analyses also confirm that the nature of the Dimorphos rubble pile made the impact of DART even greater, offering hope for future asteroid deflection efforts.

China has now also announced an asteroid impact mission. In October 2024, the European space mission HERA is scheduled to launch, which will travel to Dimorphos and Didymos to study the effects of the impact up close.

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