When analyzing the characteristics and distribution of the asteroid’s craters, the scientists realized that unlike the moon, Bennu doesn’t keep a very long record of its past encounters. “By studying rubble-pile asteroids, we are not only gaining insight into the history and evolution of the solar system, but also into our potential ability to protect Earth.” Youngest surface in the solar systemīennu has offered other surprises as well. “Our ability to do this is very dependent upon our understanding of the construction of these objects, how they are put together and how they respond to energetic events,” Bierhaus said. If one day a sizable asteroid is found on a collision course with Earth, humankind will have to send an artificial impactor its way, in an attempt to avert the collision. Scientists believe that the vast majority of near-Earth asteroids - those that could possibly impact our planet - are rubble piles. Understanding how rubble-pile asteroids behave during impacts is interesting not only from the scientific perspective, Bierhaus said. It’s not allowed to propagate into the rest of the surface and make a crater.” “It might be entirely absorbed by one boulder or a small number of boulders. “When something hits Bennu, the energy of the impact is not efficiently transmitted into the bulk volume of the asteroid,” Bierhaus said. Scientists call the production of that crumple zone “impact armoring.”
This structure, Bierhaus said, works like “the crumple zone in a car,” absorbing many impacts, especially less energetic ones, nearly without a trace. “It’s extremely rugged, covered with boulders, and very different from the moon or Mars.”īennu is what scientists call a rubble-pile asteroid: Rather than a solid block of rock, the little world is essentially a clump of boulders, pebbles and sand, all produced in earlier collisions, that are held together only by gravity. “We think this absence of small craters has to do with the character of Bennu’s surface,” said Bierhaus. That asteroid, somewhat smaller than Bennu, didn’t have many craters at all, Bierhaus said. Without a proper weather-producing atmosphere and little to no volcanism, these barren worlds keep an accurate record of their past battering.īut on Bennu, things don’t seem to work the same way.īierhaus said that what the scientists found on Bennu was somewhat similar to what Japanese spacecraft Haybusa discovered on the asteroid Itokawa, which it visited in 2005. Scientists base their understanding about crater-forming asteroid collisions on observations of surfaces of rocky planets, like Mars and Mercury, or the moon. “But they are not there.” Missing craters “Statistically, we would expect to see many more small craters,” Bierhaus said. Those calculations show that the scientists should have found many more such impact scars. But then the researchers compared these numbers with data about the frequency and intensity of crater-forming collisions on Earth, the moon and other bodies. The 1,590-foot-wide (484 meters) Bennu is pockmarked with craters - the scientists found over 1,500 of them, ranging from 3 feet (1 m) to 660 feet (200 m) wide. Bierhaus and his colleagues spent months going through those images with the aim to learn more about how craters form on the asteroid, and what the researchers found surprised them.
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