The unexpected surface of asteroid (101955) Bennu

D. S. Lauretta (), D. N. DellaGiustina, C. A. Bennett, D. R. Golish, K. J. Becker, S. S. Balram-Knutson, O. S. Barnouin, T. L. Becker, W. F. Bottke, W. V. Boynton, H. Campins, B. E. Clark, H. C. Connolly, C. Y. Drouet d’Aubigny, J. P. Dworkin, J. P. Emery, H. L. Enos, V. E. Hamilton, C. W. Hergenrother, E. S. Howell, M. R. M. Izawa, H. H. Kaplan, M. C. Nolan, B. Rizk, H. L. Roper, D. J. Scheeres, P. H. Smith, K. J. Walsh and C. W. V. Wolner
Additional contact information
D. S. Lauretta: University of Arizona
D. N. DellaGiustina: University of Arizona
C. A. Bennett: University of Arizona
D. R. Golish: University of Arizona
K. J. Becker: University of Arizona
S. S. Balram-Knutson: University of Arizona
O. S. Barnouin: The Johns Hopkins University Applied Physics Laboratory
T. L. Becker: University of Arizona
W. F. Bottke: Southwest Research Institute
W. V. Boynton: University of Arizona
H. Campins: University of Central Florida
B. E. Clark: Ithaca College
H. C. Connolly: Rowan University
C. Y. Drouet d’Aubigny: University of Arizona
J. P. Dworkin: NASA Goddard Space Flight Center
J. P. Emery: University of Tennessee
H. L. Enos: University of Arizona
V. E. Hamilton: Southwest Research Institute
C. W. Hergenrother: University of Arizona
E. S. Howell: University of Arizona
M. R. M. Izawa: Okayama University–Misasa
H. H. Kaplan: Southwest Research Institute
M. C. Nolan: University of Arizona
B. Rizk: University of Arizona
H. L. Roper: University of Arizona
D. J. Scheeres: University of Colorado
P. H. Smith: University of Arizona
K. J. Walsh: Southwest Research Institute
C. W. V. Wolner: University of Arizona

Nature, 2019, vol. 568, issue 7750, 55-60

Abstract: Abstract NASA’S Origins, Spectral Interpretation, Resource Identification and Security-Regolith Explorer (OSIRIS-REx) spacecraft recently arrived at the near-Earth asteroid (101955) Bennu, a primitive body that represents the objects that may have brought prebiotic molecules and volatiles such as water to Earth1. Bennu is a low-albedo B-type asteroid2 that has been linked to organic-rich hydrated carbonaceous chondrites3. Such meteorites are altered by ejection from their parent body and contaminated by atmospheric entry and terrestrial microbes. Therefore, the primary mission objective is to return a sample of Bennu to Earth that is pristine—that is, not affected by these processes4. The OSIRIS-REx spacecraft carries a sophisticated suite of instruments to characterize Bennu’s global properties, support the selection of a sampling site and document that site at a sub-centimetre scale5–11. Here we consider early OSIRIS-REx observations of Bennu to understand how the asteroid’s properties compare to pre-encounter expectations and to assess the prospects for sample return. The bulk composition of Bennu appears to be hydrated and volatile-rich, as expected. However, in contrast to pre-encounter modelling of Bennu’s thermal inertia12 and radar polarization ratios13—which indicated a generally smooth surface covered by centimetre-scale particles—resolved imaging reveals an unexpected surficial diversity. The albedo, texture, particle size and roughness are beyond the spacecraft design specifications. On the basis of our pre-encounter knowledge, we developed a sampling strategy to target 50-metre-diameter patches of loose regolith with grain sizes smaller than two centimetres4. We observe only a small number of apparently hazard-free regions, of the order of 5 to 20 metres in extent, the sampling of which poses a substantial challenge to mission success.

Date: 2019
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DOI: 10.1038/s41586-019-1033-6

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