3, 2018, it began wrapping Bennu in a complex web of observations. Credit: NASA's Goddard Space Flight Center This narrated video presents the mission's complete trajectory during its time at Bennu. The sampling experiment at Bennu shows that it's almost impossible to predict how such a rubble pile might respond to an impact."We flew the spacecraft closer to this object than any spacecraft has ever been flown before we did maneuvers that were centimeters per second, or millimeters per second, in order to get the spacecraft exactly where it needed to be and to change its orbit." "From a trajectory and navigation perspective, the team really did things that have never been done before in planetary exploration," said Mike Moreau, deputy project manager for OSIRIS-REx at NASA Goddard. Moreover, scientists assume that many asteroids sport a similar "rubble pile" structure: essentially conglomerations of rock, gravel and dirt held together by weak gravitational forces. And even though NASA estimates the chance of collision at 1 in 2,700 between the years 21, Bennu is still one of the most dangerous asteroids currently known. At 1,640 feet wide, a strike by Bennu would cause continent-wide disruption on our planet. But it's not there."īennu's soft, fluffy nature may complicate a possible future deflection attempt, should astronomers determine the rock threatens to hit Earth. "We expected that small, fine grains and dust would stick to the large boulders and fill the void space and act as a glue to provide some strength, which would allow the surface to push back against the spacecraft more. "The boulders are very porous and there is a lot of void space between them," Kevin Walsh, a geologist at the Southwest Research Institute in Colorado and lead author of the second study, told. (Image credit: NASA/Goddard/University of Arizona/Lockheed Martin) For comparison, "a typical Earth rock" has a density about six times higher, more like 190 pounds per cubic foot (3,000 kilograms) per cubic meter.Ī second study, based on measurements of forces exerted on the probe during the impact, confirmed those numbers.ĭebris ejected from the surface of asteroid Bennu. The probe sank as deep as 30 inches (70 cm), revealing pristine material that, unlike the asteroid's surface, was unaltered by the steady battering of cosmic rays and the solar wind, the streams of high-energy particles from the sun.įrom the measurements acquired during this repeat visit, Lauretta's team calculated that the density of the surface material was only about 31 to 44 pounds per cubic foot (500 to 700 kilograms per cubic meter), Lauretta said. The surface was soft and flowed away like a fluid." "There clearly was no resistance whatsoever. That's a surprisingly large scar scientists had expected to scoop out a bit about as wide as the sample collector itself, 12 inches (30 centimeters). After touchdown, mission scientists found a brand new 26-foot-wide (8 m) gaping hole in the surface, with displaced rubble and boulders scattered around the site. When the spacecraft first arrived at Bennu, that site, called Nightingale, sat within a 65-foot-wide (20 m) impact crater. Six months after sample collection, in April 2021, the researchers got another glimpse of the OSIRIS-REx touchdown site. The impact aftermath was so unexpected that Lauretta, lead author of one of the two studies, campaigned for the spacecraft to revisit the area to understand what happened.
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