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1. Impact-crater ejecta on Bennu indicate a surface with very low strength

Author

Edward B. Bierhaus, J. A. Seabrook, Patrick Michel, Carolyn M. Ernst, Michael Daly, Olivier S. Barnouin, Dante S. Lauretta, Daniella DellaGiustina, Michael C. Nolan, Josh Emory, William F. Bottke, Catherine Johnson, Dathon Golish, Ronald-Louis Ballouz, Erica Jawin, R. T. Daly, Manar Al Asad, Kevin J. Walsh, and Mark E. Perry

Subjects
Surface (mathematics), Impact crater, Ejecta, Geology, Astrobiology
Abstract

A planetary surface’s resistance to change is generally described as its “strength” (units of stress). The surface strength of small, rubble-pile asteroids, which consist of fragments of larger bodies that were collisionally disrupted, is poorly constrained due to their wide departure from terrestrial analogs. Here, we report the observation of an ejecta deposit surrounding an impact crater that limits the maximum surface strength of the near-Earth rubble-pile asteroid (101955) Bennu. The presence of this deposit implies that ejecta were mobilized with velocities less than the escape velocity of Bennu, 20 cm/s. Because ejecta velocities increase with surface strength, the ejecta deposit can only be explained if the effective strength of the surface material near the crater is exceedingly low, ≤100 Pa. This is three orders of magnitude below values commonly used for asteroid surfaces, but is supported by previous observations of an artificial impact crater on a similar asteroid, Ryugu. Our findings indicate a mobile surface that has likely been renewed multiple times since Bennu’s initial assembly and have far-reaching implications for interpreting observations of Bennu and other rubble piles.

Published
2021

2. Spectral analysis of craters on (101955) Bennu

Author

M. A. Barucci, D. C. Reuter, M. Fulchignoni, Beth E. Clark, Dante S. Lauretta, Edward A. Cloutis, Victoria E. Hamilton, Daniella DellaGiustina, Pedro Hasselmann, X. D. Zou, Amy Simon, Frederic Merlin, A. Praet, David Trang, R. T. Daly, E. B. Bierhaus, Cateline Lantz, John Robert Brucato, Jian-Yang Li, Sonia Fornasier, J. D. P. Deshapriya, S. Ferrone, Giovanni Poggiali, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), Lockheed Martin Space, Department of Physics, Missouri University of Science and Technology (Missouri S&T), University of Missouri System-University of Missouri System, NASA Goddard Space Flight Center (GSFC), University of Winnipeg, Institut d'astrophysique spatiale (IAS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Johns Hopkins University Applied Physics Laboratory [Laurel, MD] (APL), Hawaii Institute of Geophysics and Planetology (HIGP), University of Hawai‘i [Mānoa] (UHM), Lunar and Planetary Laboratory [Tucson] (LPL), and University of Arizona

Subjects
010504 meteorology & atmospheric sciences, Astronomy and Astrophysics, Context (language use), Astrophysics, 01 natural sciences, Regolith, Spectral line, Impact crater, 13. Climate action, Space and Planetary Science, Asteroid, Absorption band, [SDU]Sciences of the Universe [physics], 0103 physical sciences, Spectral slope, Spectroscopy, 010303 astronomy & astrophysics, Geology, 0105 earth and related environmental sciences
Abstract

Using data acquired by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) mission, we investigate spectral properties of craters on the near-Earth asteroid (101955) Bennu. We compare Bennu's craters with its global average by means of four spectral parameters: (a) minimum position of the band at 2.7 μm, (b) depth of the hydrated phyllosilicate absorption band at 2.7 μm, (c) normalized spectral slope from 0.55 to 2.0 μm, and (d) reflectance factor at 0.55 μm. We examine 45 craters using spectral data obtained under various observing conditions. For 20 craters, we find a shortward shift of the 2.7-μm band minimum relative to the global 2.7-μm band minimum, which we attribute to the presence of relatively fresh (less space-weathered) material excavated from the sub-surface by crater-forming impacts. For three craters, we find an anti-correlation between spectral slopes and reflectance factor for a series of spectra acquired during a specific scan, where we observe that spectra become redder and darker towards the center of the crater. We attribute this to the presence of fine-particulate regolith. Localized spectral heterogeneities are apparent inside a prominent equatorial crater on Bennu, which is one of the asteroid's oldest geological features. We propose that such local spectral heterogeneities could be used as a tracer of mass movement on Bennu. We show that younger craters are redder, brighter, and have deeper 2.7-μm bands. Comparing global average spectral values of Bennu and crater frequency distributions as a function of the chosen spectral parameters, we find that craters evolve to assume the global average spectral properties of Bennu. A positive correlation identified between the reflectance factor and 2.7-μm band depth suggests that brighter craters tend to be more hydrated. Finally, we put into context, the results from the Small Carry-on Impactor experiment by the Hayabusa2 spacecraft, which created an artificial crater on the near-Earth asteroid (162173) Ryugu.

Published
2021

3. The Morphometry of Impact Craters on Bennu

Author

J. A. Seabrook, R. C. Espiritu, P. Michel, H. Nair, Olivier S. Barnouin, Carolyn M. Ernst, Robert Gaskell, Dante S. Lauretta, Mark E. Perry, J. R. Weirich, Michael C. Nolan, James H. Roberts, Hannah C.M. Susorney, David Trang, R. T. Daly, Eric Palmer, E. B. Bierhaus, Kevin J. Walsh, Catherine L. Johnson, Erica Jawin, Michael Daly, Johns Hopkins University Applied Physics Laboratory [Laurel, MD] (APL), Lockheed Martin Space, Department of Earth and Space Science and Engineering [York University - Toronto] (ESSE), York University [Toronto], Planetary Science Institute [Tucson] (PSI), University of Bristol [Bristol], University of British Columbia (UBC), Southwest Research Institute [Boulder] (SwRI), Lunar and Planetary Laboratory [Tucson] (LPL), University of Arizona, Smithsonian Institution National Museum of Natural History (NMNH), Joseph Louis LAGRANGE (LAGRANGE), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Hawai'i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, and University of Hawai'i [Honolulu] (UH)

Subjects
Geophysics, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], 010504 meteorology & atmospheric sciences, Impact crater, [SDU]Sciences of the Universe [physics], 0103 physical sciences, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], General Earth and Planetary Sciences, 010303 astronomy & astrophysics, 01 natural sciences, Geomorphology, Geology, 0105 earth and related environmental sciences
Abstract

International audience; Bennu is an~500-m-diameter rubble-pile asteroid that is the target of detailed study by the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission. Here we use data from the OSIRIS-REx Laser Altimeter to assess depth-to-diameter ratios (d/D) of 108 impact craters larger than 10 m in diameter. The d/D of craters on Bennu ranges from 0.02 to 0.19. The mean is 0.10 ± 0.03. The smallest craters show the broadest range in d/D, consistent with d/D measurements on other asteroids. A few craters have central mounds, which is interpreted as evidence that a more competent substrate lies a few meters beneath them. The range of d/D narrows as crater size increases, with craters larger than 80 m tending toward smaller d/D. At large scales, increases in target strength with depth, combined with target curvature, may affect crater morphometry.

Published
2020

4. Author Correction: Shape of (101955) Bennu indicative of a rubble pile with internal stiffness

Author

M. Lefevre, Aaron S. Burton, Carina Bennett, J. A. Mapel, Renu Malhotra, Peter Fleming, J. McAdams, N. Mogk, R. L. Ballouz, P. H. Smith, V. Nifo, C. K. Maleszewski, Timothy D. Swindle, E. Dotto, Stephen R. Schwartz, C. May, J. Bayron, D. Patterson, D. Guevel, Ellen S. Howell, Humberto Campins, J. Kissell, E. Brown, J. Wood, E. Muhle, John Robert Brucato, J. Small, B. Miller, Oleksiy Golubov, R. Pennington, K. Harshman, J. Nelson, Catherine Elder, M. McGee, R. Burns, J. Contreras, S. Hull, D. Kubitschek, D. Noss, Andrew J. Liounis, J. Backer, B. May, G. Fitzgibbon, J. Donaldson, D. Worden, Bashar Rizk, R. Witherspoon, Catherine L. Johnson, Erica Jawin, G. Shaw, A. Aqueche, Dolores H. Hill, D. Folta, S. Ferrone, M. Lujan, Giovanni Poggiali, B. G. Williams, S. Selznick, Melissa A. Morris, K. Rios, Sara S. Russell, D. Lambert, J. Hong, Jeffrey B. Plescia, H. Bloomenthal, D. Drinnon, Olivier S. Barnouin, Derek S. Nelson, Amanda E. Toland, Michael C. Moreau, J. A. Seabrook, K. Dill, A. Mirfakhrai, K. Hyde, J. D. P. Deshapriya, Hannah Kaplan, Timothy P. McElrath, Juliette I. Brodbeck, N. Ramos, S. Stewart, James B. Garvin, Sei-ichiro Watanabe, M. Arvizu-Jakubicki, Jason P. Dworkin, Matthew A. Siegler, Collin Lewin, Masatoshi Hirabayashi, L. Bloomquist, S. Gardner, Keiko Nakamura-Messenger, A. H. Nair, M. Schmitzer, P. Haas, Julie Bellerose, Dolan E. Highsmith, L. Koelbel, C. C. Lorentson, J. Zareski, E. Queen, S. R. Chesley, Philip A. Bland, A. Cheuvront, V. E. Hamilton, Ronald G. Mink, N. Mastrodemos, H. C. Connolly, K. Bellamy, M. Killgore, A. Gardner, Y. Takahashi, M. Lambert, R. C. Espiritu, Z. Zeszut, E. T. Morton, Kevin J. Walsh, Timothy D. Glotch, M. Skeen, Brian Kennedy, Matthew R.M. Izawa, G. Neumann, F. Teti, D. Doerres, A. Hasten, F. Ciceri, D. Howell, A. Deguzman, J. Nagy, D. Vaughan, H. Ma, C. Lantz, D. N. Brack, David K. Hammond, Erwan Mazarico, Leilah K. McCarthy, L. Rhoads, Kathleen L. Craft, C. Welch, Jay W. McMahon, C. L. Parish, D. C. Reuter, M. Giuntini, N. Castro, Clive Dickinson, J. Kreiner, K. Kingsbury, S. Dickenshied, Joseph A. Nuth, Alan R. Hildebrand, Erik Asphaug, H. Ido, Eric M. Sahr, A. Harbison, Arlin E. Bartels, T. Forrester, D. Eckart, R. Bandrowski, Michael K. Barker, Robert Gaskell, J. Wendel, S. Freund, Marc Bernacki, Ryan S. Park, A. Taylor, E. B. Bierhaus, S. Millington-Veloza, J. Stromberg, L. B. Breitenfeld, K. Stakkestad, D. Ellis, Timothy J. McCoy, M. Susak, Richard G. Cosentino, C. Manzoni, Hisayoshi Yurimoto, C. Drouet d'Aubigny, A. Bjurstrom, Masako Yoshikawa, S. Francis, J. Peachey, J. Geeraert, K. Marchese, O. Billett, M. Rascon, F. Jaen, B. Diallo, Martin Miner, Kris J. Becker, E. Mazzotta Epifani, Florian Thuillet, A. Knight, James H. Roberts, Pasquale Tricarico, Edward A. Cloutis, T. Fisher, Dale Stanbridge, A. Colpo, Osiris-Rex Team, S. Gonzales, Q. Tran, M. K. Crombie, John Marshall, N. Bojorquez-Murphy, David Vokrouhlický, Allen W. Lunsford, H. Bowles, K. L. Edmundson, R. A. Masterson, Peter G. Antreasian, N. Gorius, Benjamin Rozitis, D. Pino Muñoz, S. Carlson-Kelly, C. Thayer, J. Elsila Cook, B. C. Clark, N. Piacentine, José C. Aponte, M. Al Asad, M. A. Barucci, D. Blum, P. Falkenstern, Neil Bowles, Matthew Chojnacki, J. M. Leonard, J. Daly, K. Yetter, M. R. Fisher, Jeffrey N. Grossman, A. Boggs, N. Jayakody, Cristina A. Thomas, C.M. Ernst, Namrah Habib, J. N. Kidd, R. J. Steele, Andrew B. Calloway, Andrew Ryan, Kimberly T. Tait, Paul O. Hayne, J. Y. Li, K. L. Berry, William V. Boynton, Yanga R. Fernandez, D. A. Lorenz, M. Wasser, Daniel J. Scheeres, K. Fortney, A. Scroggins, B. Allen, B. Sutter, T. Ferro, Jonathan Joseph, Derek C. Richardson, D. Hoak, Brian Carcich, W. Chang, P. Wren, C. Boyles, Kaj E. Williams, B. Marty, J. Liang, J. Hoffman, A. Harch, Daniel R. Wibben, Jamie Molaro, S. Rieger, R. Enos, C. W. Hergenrother, Stephen R. Sutton, J. Grindlay, E. J. Lessac-Chenen, E. Huettner, C. Norman, P. Sherman, L. Swanson, M. Coltrin, S. Van wal, B. Buck, A. Fisher, Kevin Righter, Brian Rush, David D. Rowlands, Lauren McGraw, A. Levine, K. Drozd, D. Gaudreau, A. Nguyen, S. Sides, M. Chodas, R. Dubisher, B. Ashman, Michael Caplinger, Amy Simon, W. Moore, S. S. Balram-Knutson, R. Carpenter, S. Fornasier, Shogo Tachibana, Russell Turner, Ian A. Franchi, Trevor Ireland, Chloe B. Beddingfield, D. F. Everett, M. Corvin, Lindsay P. Keller, Tammy L. Becker, S. Carter, J. L. Rizos Garcia, Mark E. Perry, E. Keates, Michael C. Nolan, P. Vasudeva, C. Fellows, K. Herzog, Mark A. Jenkins, J. R. Weirich, J. Swenson, D. R. Golish, Davide Farnocchia, Lydia C. Philpott, Rebecca R. Ghent, Hannah C.M. Susorney, S. W. Squyres, Pedro Hasselmann, J. Hill, Thomas J. Zega, B. Key, Marco Delbo, A. S. French, P. Sánchez, A. Hilbert, J. Y. Pelgrift, R. P. Binzel, L. McNamara, Vishnu Reddy, Michael Daly, Scott Messenger, Daniella DellaGiustina, Maurizio Pajola, Charles Brunet, Joshua L. Bandfield, J. Padilla, A. Janakus, M. Moreau, R. Garcia, R. A. Chicoine, P. Michel, P. Kaotira, K. S. Johnson, J. Forelli, G. Miller, K. Martin, I. Galinsky, S. Desjardins, Naru Hirata, Christine Hartzell, M. L. Jones, S. Hooven, D. Velez, R. Munoz, Carolyn M. Ernst, C. Emr, N. Martinez-Vlasoff, S. Bendall, R. Zellar, E. Church, Theodore Kareta, T. Warren, P. Wolff, V. Morrison, C. Bryan, S. Bhaskaran, N. Jones, D. Hauf, Jeremy Bauman, R. T. Daly, R. Olds, M. M. Westermann, D. K. Hamara, E. Audi, G. Johnston, Eric Palmer, Courtney Mario, Daniel P. Glavin, T. Haltigin, J. Cutts, Javier Licandro, Xiao-Duan Zou, H. L. Roper, Gregory A. Neumann, William M. Owen, S. Sugita, Y. H. Tang, Kevin Burke, H. L. Enos, D. Gallagher, William F. Bottke, K. Getzandanner, Philip R. Christensen, C. W. V. Wolner, K. Fleshman, D. Poland, J. P. Emery, M.M. Riehl, D. Fennell, D. Sallitt, A. D. Rogers, M. Fitzgibbon, John H. Jones, S. Mullen, S. Salazar, S. Oliver, A. T. Polit, J. Cerna, A. Praet, Mark E. Holdridge, E. M. Ibrahim, Coralie D. Adam, J. de León, Christopher J. Miller, M. Ryle, J. Lyzhoft, M. Loveridge, C. Hoekenga, Brent J. Bos, S. Anwar, K. Chaffin, Devin L. Schrader, B. Lovelace, Romy D. Hanna, C. D. Adam, G. L. Mehall, K. L. Donaldson Hanna, F. Merlin, B. Wright, Guy Libourel, L. F. Lim, N. Shultz, Dante S. Lauretta, K. Hanley, Beth E. Clark, L. Le Corre, K. Thomas-Keprta, Moses Milazzo, W. Hagee, B. Page, M. Fisher, E. McDonough, D. Trang, S. Clemett, A. Rubi, A. Ingegneri, Scott A. Sandford, D. Dean, J. Freemantle, Michael D. Smith, Christopher W. Haberle, L. Nguyen, M. Fulchignoni, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), MINES ParisTech - École nationale supérieure des mines de Paris, Université Paris sciences et lettres (PSL), Centre de Mise en Forme des Matériaux (CEMEF), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[PHYS]Physics [physics], 010504 meteorology & atmospheric sciences, Rubble, Stiffness, engineering.material, 010502 geochemistry & geophysics, 01 natural sciences, [SDU]Sciences of the Universe [physics], engineering, medicine, General Earth and Planetary Sciences, Geotechnical engineering, medicine.symptom, Pile, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Geology, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences
Abstract

International audience

Published
2020

5. Bennu’s near-Earth lifetime of 1.75 million years inferred from craters on its boulders

Author

M. Al Asad, Olivier S. Barnouin, P. Michel, Jamie Molaro, C. Avdellidou, Carina Bennett, E. B. Bierhaus, Dante S. Lauretta, Michael C. Nolan, Kevin J. Walsh, Harold C. Connolly, Stephen R. Schwartz, Daniella DellaGiustina, C. W. V. Wolner, Bashar Rizk, Marco Delbo, Maurizio Pajola, R. L. Ballouz, Dathon Golish, Erica Jawin, M. G. Daly, David Trang, R. T. Daly, William F. Bottke, Erik Asphaug, Lunar and Planetary Laboratory [Tucson] (LPL), University of Arizona, Southwest Research Institute [Boulder] (SwRI), Johns Hopkins University Applied Physics Laboratory [Laurel, MD] (APL), Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice, France., Joseph Louis LAGRANGE (LAGRANGE), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, and COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
education.field_of_study, Multidisciplinary, 010504 meteorology & atmospheric sciences, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], [PHYS.ASTR.EP]Physics [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], Population, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], 01 natural sciences, Astrobiology, Impact crater, Asteroid, [SDU]Sciences of the Universe [physics], 0103 physical sciences, Size frequency, Asteroid belt, education, 010303 astronomy & astrophysics, Geology, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences
Abstract

An asteroid’s history is determined in large part by its strength against collisions with other objects1,2 (impact strength). Laboratory experiments on centimetre-scale meteorites3 have been extrapolated and buttressed with numerical simulations to derive the impact strength at the asteroid scale4,5. In situ evidence of impacts on boulders on airless planetary bodies has come from Apollo lunar samples6 and images of the asteroid (25143) Itokawa7. It has not yet been possible, however, to assess directly the impact strength, and thus the absolute surface age, of the boulders that constitute the building blocks of a rubble-pile asteroid. Here we report an analysis of the size and depth of craters observed on boulders on the asteroid (101955) Bennu. We show that the impact strength of metre-sized boulders is 0.44 to 1.7 megapascals, which is low compared to that of solid terrestrial materials. We infer that Bennu’s metre-sized boulders record its history of impact by millimetre- to centimetre-scale objects in near-Earth space. We conclude that this population of near-Earth impactors has a size frequency distribution similar to that of metre-scale bolides and originates from the asteroidal population. Our results indicate that Bennu has been dynamically decoupled from the main asteroid belt for 1.75 ± 0.75 million years. Analysis of the size and depth of craters on boulders on the asteroid (101955) Bennu indicates that Bennu has been in near-Earth space for 1.75 ± 0.75 million years.

Published
2020

6. Exogenic basalt on asteroid (101955) Bennu

Author

Javier Licandro, Erica Jawin, M. Al Asad, J. A. Seabrook, Michael C. Nolan, M. A. Barucci, Kevin J. Walsh, Lydia C. Philpott, G. Poggiali, Timothy J. McCoy, R. P. Binzel, Marco Delbo, C. Avdellidou, Dante S. Lauretta, Marcel Popescu, J. L. Rizos Garcia, D. C. Reuter, Ellen S. Howell, Daniella DellaGiustina, Humberto Campins, Bashar Rizk, William F. Bottke, Hannah Kaplan, Amy Simon, Harold C. Connolly, Eri Tatsumi, V. E. Hamilton, M. G. Daly, Olivier S. Barnouin, Beth E. Clark, L. Le Corre, N. A. Porter, J. de León, Ronald-Louis Ballouz, R. T. Daly, Dathon Golish, Sonia Fornasier, Joseph Louis LAGRANGE (LAGRANGE), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), and ANR-18-CE31-0014,ORIGINS,A la recherche des planétésimaux de notre système solaire(2018)

Subjects
Basalt, Planetesimal, 010504 meteorology & atmospheric sciences, Astronomy and Astrophysics, 01 natural sciences, Parent body, Astrobiology, Igneous rock, Planetary science, Meteorite, 13. Climate action, Asteroid, [SDU]Sciences of the Universe [physics], Carbonaceous chondrite, 0103 physical sciences, 010303 astronomy & astrophysics, Geology, 0105 earth and related environmental sciences
Abstract

When rubble-pile asteroid 2008 TC3 impacted Earth on 7 October 2008, the recovered rock fragments indicated that such asteroids can contain exogenic material1,2. However, spacecraft missions to date have only observed exogenous contamination on large, monolithic asteroids that are impervious to collisional disruption3,4. Here, we report the presence of metre-scale exogenic boulders on the surface of near-Earth asteroid (101955) Bennu—the 0.5-km-diameter, rubble-pile target of the OSIRIS-REx mission5 that has been spectroscopically linked to the CM carbonaceous chondrite meteorites6. Hyperspectral data indicate that the exogenic boulders have the same distinctive pyroxene composition as the howardite–eucrite–diogenite (HED) meteorites that come from (4) Vesta, a 525-km-diameter asteroid that has undergone differentiation and extensive igneous processing7–9. Delivery scenarios include the infall of Vesta fragments directly onto Bennu or indirectly onto Bennu’s parent body, where the latter’s disruption created Bennu from a mixture of endogenous and exogenic debris. Our findings demonstrate that rubble-pile asteroids can preserve evidence of inter-asteroid mixing that took place at macroscopic scales well after planetesimal formation ended. Accordingly, the presence of HED-like material on the surface of Bennu provides previously unrecognized constraints on the collisional and dynamical evolution of the inner main belt. Six bright boulders of exotic material on near-Earth asteroid (101955) Bennu stand out from the average asteroidal surface. This unexpected record of impactors offers clues to the formation history of Bennu.

Published
2020

7. Global Patterns of Recent Mass Movement on Asteroid (101955) Bennu

Author

M. Al Asad, Daniella DellaGiustina, John Marshall, Daniel J. Scheeres, Kevin J. Walsh, E. B. Bierhaus, M. G. Daly, Olivier S. Barnouin, Jamie Molaro, Ronald-Louis Ballouz, R. T. Daly, Dante S. Lauretta, Harold C. Connolly, Carina Bennett, Erica Jawin, Timothy J. McCoy, Chloe B. Beddingfield, Michael C. Nolan, Hannah C.M. Susorney, H. L. Enos, and Hannah Kaplan

Subjects
Geophysics, Mass movement, Space and Planetary Science, Geochemistry and Petrology, Asteroid, Earth and Planetary Sciences (miscellaneous), Geology, Astrobiology
Published
2020

8. Hemispherical differences in the shape and topography of asteroid (101955) Bennu

Author

James H. Roberts, Benjamin Rozitis, Yun Zhang, E. B. Bierhaus, J. A. Seabrook, K. Getzandanner, Michael Daly, D. N. DellaGuistina, Clive Dickinson, P. Michel, Mark E. Perry, J. R. Weirich, Lydia C. Philpott, R. T. Daly, Robert Gaskell, Hannah C.M. Susorney, J. Geeraert, Andrew Ryan, Eric Palmer, G. Cunningham, Charles Brunet, M. Al Asad, Jason M. Leonard, M. C. Nolan, R. L. Ballouz, H. L. Enos, Olivier S. Barnouin, Dante S. Lauretta, D. Gaudreau, Coralie D. Adam, T. Haltigin, Bashar Rizk, Erwan Mazarico, Gregory A. Neumann, Catherine L. Johnson, Erica Jawin, Kevin J. Walsh, Johns Hopkins University Applied Physics Laboratory [Laurel, MD] (APL), Southwest Research Institute [Boulder] (SwRI), Joseph Louis LAGRANGE (LAGRANGE), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Lunar and Planetary Laboratory [Tucson] (LPL), and University of Arizona

Subjects
business.product_category, 010504 meteorology & atmospheric sciences, Longitudinal ridges, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], 01 natural sciences, 0103 physical sciences, Asymmetric distribution, Altimeter, Digital elevation model, 010303 astronomy & astrophysics, Geomorphology, Southern Hemisphere, Research Articles, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, Multidisciplinary, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Northern Hemisphere, SciAdv r-articles, Wedge (mechanical device), Asteroid, [SDU]Sciences of the Universe [physics], business, Space Sciences, Geology, Research Article
Abstract

A lidar model of asteroid (101955) Bennu has a north-south asymmetry in shape and evidence of an early partial disruption., We investigate the shape of near-Earth asteroid (101955) Bennu by constructing a high-resolution (20 cm) global digital terrain model from laser altimeter data. By modeling the northern and southern hemispheres separately, we find that longitudinal ridges previously identified in the north extend into the south but are obscured there by surface material. In the south, more numerous large boulders effectively retain surface materials and imply a higher average strength at depth to support them. The north has fewer large boulders and more evidence of boulder dynamics (toppling and downslope movement) and surface flow. These factors result in Bennu’s southern hemisphere being rounder and smoother, whereas its northern hemisphere has higher slopes and a less regular shape. We infer an originally asymmetric distribution of large boulders followed by a partial disruption, leading to wedge formation in Bennu’s history.

Published
2020
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