Surprise – again! NASA spacecraft reveals that asteroid Bennu is not what it seemed

NASA’s OSIRIS-REx spacecraft leaves the surface of asteroid Bennu after collecting a sample. Credit: NASA’s Goddard Space Flight Center/CI Lab/SVS

Scientists have learned something amazing after analyzing the data collected when[{” attribute=””>NASA’s

“Our expectations about the asteroid’s surface were completely wrong.” — Dante Lauretta, principal investigator of OSIRIS-REx

Unexpectedly, it turns out that the particles making up Bennu’s exterior are so loosely packed and lightly bound to each other that if a person were to step onto the asteroid they would feel very little resistance. It would be like stepping into a pit of plastic balls that are popular play areas for kids.

“If Bennu was completely packed, that would imply nearly solid rock, but we found a lot of void space in the surface,” said Kevin Walsh, a member of the OSIRIS-REx science team from Southwest Research Institute, which is based in San Antonio.

NASA's OSIRIS REx Spacecraft Surface of Asteroid Bennu

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). OSIRIS-REx touched down on Bennu at 6:08 pm EDT on October 20, 2020. Credit: NASA’s Goddard Space Flight Center

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. These surprising results add to the intrigue that has gripped scientists throughout the OSIRIS-REx mission, as Bennu has proved consistently unpredictable.

The first surprise the asteroid presented was in December 2018, when NASA’s spacecraft arrived at Bennu. 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. Reasearchers also discovered that Bennu was ejecting particles of rock from its surface into space.

“Our expectations about the asteroid’s surface were completely wrong,” said Lauretta.

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. “What we saw was a huge wall of debris radiating out from the sample site,” Lauretta said. “We were like, ‘Holy cow!’”

Near-Earth asteroid Bennu is a rubble pile of rocks and boulders left over from the formation of the Solar System. On October 20, 2020, NASA’s OSIRIS-REx spacecraft made a brief landing on Bennu and collected a sample for return to Earth. During this event, the spacecraft’s arm sank into the asteroid more deeply than expected, confirming that Bennu’s surface is loosely bound. Now, scientists have used data from OSIRIS-REx to revisit the sampling event and better understand how the loose upper layers of Bennu hold together. Credit: NASA’s Goddard Space Flight Center/CI Lab/SVS

Mission scientists were baffled by the multitude of pebbles strewn about, given how thin the spacecraft was on the surface. Even stranger, the spacecraft left a large crater 26 feet (8 meters) wide. “Every time we tested the sample-picking procedure in the lab, we could barely make a puncture,” Loretta said. Loretta said the mission team decided to send the spacecraft back to take more pictures of Bennu’s surface “to see how much chaos we made.”

The researchers analyzed the volume of debris visible before and after images of the sample site, nicknamed the “Nightingale.” They also studied acceleration data collected during the landing of the spacecraft. This data revealed that when OSIRIS-REx touched the asteroid, it encountered the same amount of resistance — very little — that a person would feel while depressing the piston in a French pressure coffee pot. “By the time we launched our thrusts to leave the surface, we were still sinking into the asteroid,” said Ron Blose, an OSIRIS-Rex scientist at the Johns Hopkins Laboratory of Applied Physics in Laurel, Maryland.

Blues and the research team ran hundreds of computer simulations to infer Bennu’s density and coherence based on spacecraft images and acceleration information. The engineers altered the surface cohesion properties in each simulation until they found the property that most closely matches their real-world data.

asteroid benno particles

This view of the asteroid Bennu spewing particles from its surface on January 3. 19, 2019, by combining two images taken aboard NASA’s OSIRIS-REx spacecraft. Other image processing techniques, such as cropping and adjusting the brightness and contrast of each image, have also been applied. (Credit: NASA/Goddard/University of Arizona/Lockheed Martin)

Now, this accurate information about Bennu’s surface could help scientists better interpret remote observations of other asteroids, which could be useful in designing future asteroid missions and for developing ways to protect Earth from asteroid collisions.

It’s possible that asteroids like Bennu – barely held together by gravity or electrostatic force – could disintegrate in Earth’s atmosphere and thus pose a different kind of danger than solid asteroids. said Patrick Michel, OSIRIS-REx scientist and director of research at the National Center for Scientific Research at the Côte d’Azur Observatory in Nice, France.


“Spacecraft Sample Collection and Subsurface Exploration of Asteroid (101955) Bennu” by D.S. Lauretta, CD Adam, A.J. Allen, R.-L. Blues, O. S. Barnouin, K. J. Becker, T. Becker, CA Bennett, E. B. Bierhaus, B. J. Bos, R. D. Burns, H. Campins, Y. Cho, P. R. Christensen, ECA Church, B. E. Clark, HC Connolly, MG Daly, DN DellaGiustina, C. Y. Drouet d’Aubigny, J. P. Emery, H. L. Enos, S. Freund Kasper, J. B. Garvin, K. Getzandanner, D. R. Golish, V. E. Hamilton, C. W. Hergenrother, H. H. Kaplan, L. P. Keller, E. J. Lessac-Chenen, A. J. Liounis, H. Ma , L. K. McCarthy, BD Miller, M. C. Moreau, T. Morota, D. S. Nelson, JO Nolau, R. Olds, M. Pajola, J. Y. Pelgrift, AT Polit, MA Ravine, DC Reuter, B. Rizk, B. Rozitis, A. J. Ryan , E.M. Suhr, N.; Sakatani, J. A. Seabrook, S. H. Selznick, M. A. Skin, AA Simon, S. Sugita, K. J. Walsh, M. M. Westerman, CW at Woolner WK Yumoto, July 7, 2022, Sciences.
DOI: 10.1126 / science.abm1018

“Near-zero cohesion and loose packing of Bennu’s near subsurface revealed by spacecraft contact” By Kevin J. Walsh, Ronald Louis Balloz, Erica R. Gawain, Chrisa Avdelido, Olivier S. Barnwen, Karina A. Bennett, Edward B. Beerhouse, Brent J. Boss, Saverio Campione, Harold C. Connolly, Marco Delpo, Daniela N. Delagostina, Joseph de Martini, Joshua B. Michelle, Michael C. Nolan, Ryan Olds, Benjamin Rosetis, Derek C. Richardson, Bashar Rizk, Andrew J. Ryan, Paul Sanchez, Daniel J. Sherry, Stephen R. Schwartz, Sanford H. Selznick, Yoon Chang and Dante S. Loretta, Jul 7, 2022 Available here. science progress.
DOI: 10.1126 / sciadv.abm6229

NASA’s Goddard Space Flight Center provides comprehensive mission management, systems engineering, safety and mission assurance for OSIRIS-REx. Dante Loretta of the University of Arizona, Tucson, is the principal investigator. The university leads the scientific team and plans the scientific observation and data processing of the mission. Lockheed Martin Space Corporation of Littleton, Colorado built the spacecraft and provided flight operations. Goddard and KinetX Aerospace are responsible for the navigation of the OSIRIS-REx spacecraft. OSIRIS-REx is the third mission in NASA’s New Frontiers Program, which is managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the Science Mission Directorate in Washington.

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