Earth has been walloped by enormous asteroids in the past, and it’s going to happen again. For the first time in history, there’s a chance that we could intercept one of these objects and prevent an impact. NASA’s Double Asteroid Redirection Test (DART) mission is currently en route to a particular pair of space rocks to test that very technology, but researchers from the University of Bern and the National Centre of Competence in Research (NCCR) in Switzerland say the effects of the DART impactor might be very different than expected. Instead of leaving a crater, it might obliterate its target.
Scientists have long believed that asteroids were mostly solid chunks of rock and metal, but that was before we visited any of them. In the past few years, the Japanese Hayabusa2 and American OSIRIS-REx probes have stopped by asteroids to collect samples and return them to Earth. The teams behind those missions were surprised by the conditions they found on asteroids. NASA spotted small chunks of material floating away from the asteroid Bennu, and new research suggests the probe was almost swallowed up by the flowing, gravel-like surface. The Japanese Space Agency (JAXA) spotted more than 4,000 boulders strewn about the surface of Ryugu.
It’s possible that asteroids are less like giant rocks and more like piles of rubble, but the DART mission was conceived of before the recent NASA and JAXA missions. Its goal is to reach a binary asteroid system of Didymos and its satellite Dimorphos. The smaller Dimorphos asteroid is the target. With a diameter of just 560 feet (170 meters), NASA expected DART’s 500-kilogram impactor to leave a crater and affect the satellite’s orbit around the larger Didymos. Not so, says the new study.
If Dimorphos is anything like Bennu, which other teams have described as a gravitationally bound “ball pit,” there may not be a crater. Instead, the 4.1 mile-per-second impact could radically alter the object’s structure. It may be deflected much more strongly than planned, and substantial mass could be ejected from the impact site.
According to the study authors, the rubble model of asteroids has not been sufficiently studied because the tools to do so were not available until recently. While you can simulate impacts in a laboratory, you can’t easily create a model of a loosely associated asteroid. The modeling approach used in the new study takes into account factors like compaction, shockwave propagation, and the resulting flow of material.
We’re just a few weeks away from DART’s arrival at Didymos-Dimorphos. The mission includes a CubeSat that will monitor the impact, but the European Space Agency is planning a more robust follow-up mission called HERA to examine the effects. The HERA mission is set to launch in 2024 and will arrive in orbit of the asteroids (or maybe one asteroid and a pile of rubble) in 2026.
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