The unexpected surface of asteroid (101955) Bennu Academic Article uri icon

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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.

authors

  • Lauretta, DS
  • DellaGiustina, DN
  • Bennett, CA
  • Golish, DR
  • Becker, KJ
  • Balram-Knutson, SS
  • Barnouin, OS
  • Becker, Tracy
  • Bottke, WF
  • Boynton, WV
  • Campins, H
  • Clark, BE
  • Connolly, HC
  • Drouet d’Aubigny, CY
  • Dworkin, JP
  • Emery, JP
  • Enos, HL
  • Hamilton, VE
  • Hergenrother, CW
  • Howell, ES
  • Izawa, MRM
  • Kaplan, HH
  • Nolan, MC
  • Rizk, B
  • Roper, HL
  • Scheeres, DJ
  • Smith, PH
  • Walsh, KJ
  • Wolner, CWV

publication date

  • April 2019