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The unexpected surface of asteroid (101955) Bennu

Publications

Complete Citation

  • Lauretta, D. S., DellaGiustina, D. N., Bennett, C. A., Golish, D. R., Becker, K. J., Balram-Knutson, S. S., Barnouin, O. S., Becker, T. L., Bottke, W. F., Boynton, W. V., Campins, H., Clark, B. E., Connolly, H. C., Jr., d'Aubigny, C. Y. Drouet, Dworkin, J. P., Emery, J. P., Enos, H. L., Hamilton, V. E., Hergenrother, C. W., Howell, E. S., Izawa, M. R. M., Kaplan, H. H., Nolan, M. C., Rizk, B., Roper, H. L. et al. 2019. "The unexpected surface of asteroid (101955) Bennu." Nature, 568, (7750) 55. https://doi.org/10.1038/s41586-019-1033-6.

Overview

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 Earth(1). Bennu is a lowalbedo B-type asteroid(2) that has been linked to organic-rich hydrated carbonaceous chondrites(3). 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 processes(4). 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 scale(5-11). 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 inertia(12) and radar polarization ratios(13)-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 centimetres(4). 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.

Publication Date

  • 2019

Authors