![]() Now, this precise information about Bennu’s surface can help scientists better interpret remote observations of other asteroids, which could be useful in designing future asteroid missions and for developing methods to protect Earth from asteroid collisions. (Credit: NASA/Goddard/University of Arizona/Lockheed Martin) Other image processing techniques were also applied, such as cropping and adjusting the brightness and contrast of each image. This view of asteroid Bennu ejecting particles from its surface on January 19, 2019, was created by combining two images taken on board NASA’s OSIRIS-REx spacecraft. Engineers varied the surface cohesion properties in each simulation until they found the one that most closely matched their real-life data. “By the time we fired our thrusters to leave the surface we were still plunging into the asteroid,” said Ron Ballouz, an OSIRIS-REx scientist based at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland.īallouz and the research team ran hundreds of computer simulations to deduce Bennu’s density and cohesion based on spacecraft images and acceleration information. This data revealed that as OSIRIS-REx touched the asteroid it experienced the same amount of resistance – very little – a person would feel while squeezing the plunger on a French press coffee carafe. Researchers analyzed the volume of debris visible in before and after images of the sample site, nicknamed “ Nightingale.” They also looked at acceleration data collected during the spacecraft’s touch down. The mission team decided to send the spacecraft back to take more photographs of Bennu’s surface “to see how big of a mess we made,” Lauretta said. “Every time we tested the sample pickup procedure in the lab, we barely made a divot,” Lauretta said. Even more bizarre was that the spacecraft left a big crater that was 26 feet (8 meters) wide. ![]() ![]() Mission scientists were perplexed by the abundance of pebbles strewn about, given how gently the spacecraft tapped the surface. Credit: NASA’s Goddard Space Flight Center/CI Lab/SVS Now, scientists have used data from OSIRIS-REx to revisit the sample-collection event and better understand how Bennu’s loose upper layers are held together. During this event the spacecraft’s arm sank far deeper into the asteroid than expected, confirming that Bennu’s surface is loosely bound. On October 20, 2020, NASA’s OSIRIS-REx spacecraft briefly touched down on Bennu and collected a sample for return to Earth. Near-Earth asteroid Bennu is a rubble pile of rocks and boulders left over from the formation of the solar system. “What we saw was a huge wall of debris radiating out from the sample site,” Lauretta said. The latest clue that Bennu was not what it seemed came after the OSIRIS-REx spacecraft picked up a sample and beamed stunning, close-up images of the asteroid’s surface to Earth. “Our expectations about the asteroid’s surface were completely wrong,” said Lauretta. Reasearchers also discovered that Bennu was ejecting particles of rock from its surface into space. The OSIRIS-REx team found a rough surface littered with boulders instead of the smooth, sandy beach they had expected based on observations from Earth- and space-based telescopes. The first surprise the asteroid presented was in December 2018, when NASA’s spacecraft arrived at Bennu. These surprising results add to the intrigue that has gripped scientists throughout the OSIRIS-REx mission, as Bennu has proved consistently unpredictable. The latest findings about Bennu’s surface were published on July 7, 2022, in a pair of papers in the journals Science and Science Advances, led respectively by Dante Lauretta, principal investigator of OSIRIS-REx, based at University of Arizona, Tucson, and Kevin Walsh. ![]() Credit: NASA’s Goddard Space Flight Center OSIRIS-REx touched down on Bennu at 6:08 pm EDT on October 20, 2020. Side-by-side images from NASA’s OSIRIS-REx spacecraft of the robotic arm as it descended towards the surface of asteroid Bennu (left) and as it tapped it to stir up dust and rock for sample collection (right).
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