The unexpected surface of asteroid (101955) Bennu

the OSIRIS-REx Team

Research output: Contribution to journalLetter

25 Citations (Scopus)

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 low-albedo 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.

Original languageEnglish (US)
Pages (from-to)55-60
Number of pages6
JournalNature
Volume568
Issue number7750
DOIs
StatePublished - Apr 4 2019

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Minor Planets
Spacecraft
Meteoroids
Radar
Prebiotics
Particle Size
Hot Temperature
Water

ASJC Scopus subject areas

  • General

Cite this

The unexpected surface of asteroid (101955) Bennu. / the OSIRIS-REx Team.

In: Nature, Vol. 568, No. 7750, 04.04.2019, p. 55-60.

Research output: Contribution to journalLetter

the OSIRIS-REx Team. / The unexpected surface of asteroid (101955) Bennu. In: Nature. 2019 ; Vol. 568, No. 7750. pp. 55-60.
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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 Earth 1 . Bennu is a low-albedo 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.",
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AU - the OSIRIS-REx Team

AU - Lauretta, Dante

AU - DellaGiustina, D. N.

AU - Bennett, C. A.

AU - Golish, D. R.

AU - Becker, K. J.

AU - Balram-Knutson, S. S.

AU - Barnouin, O. S.

AU - Becker, T. L.

AU - Bottke, W. F.

AU - Boynton, W. V.

AU - Campins, H.

AU - Clark, B. E.

AU - Connolly, H. C.

AU - Drouet d’Aubigny, C. Y.

AU - Dworkin, J. P.

AU - Emery, J. P.

AU - Enos, H. L.

AU - Hamilton, V. E.

AU - Hergenrother, C. W.

AU - Howell, E. S.

AU - Izawa, M. R.M.

AU - Kaplan, H. H.

AU - Nolan, M. C.

AU - Rizk, B.

AU - Roper, H. L.

AU - Scheeres, D. J.

AU - Smith, P. H.

AU - Walsh, K. J.

AU - Wolner, C. W.V.

AU - Highsmith, D. E.

AU - Small, J.

AU - Vokrouhlický, D.

AU - Bowles, N. E.

AU - Brown, E.

AU - Donaldson Hanna, K. L.

AU - Warren, T.

AU - Brunet, C.

AU - Chicoine, R. A.

AU - Desjardins, S.

AU - Gaudreau, D.

AU - Haltigin, T.

AU - Millington-Veloza, S.

AU - Rubi, A.

AU - Aponte, J.

AU - Gorius, N.

AU - Boynton, William V.

AU - Malhotra, Renu

AU - Smith, Peter

AU - Swindle, Timothy

AU - Zega, Thomas

PY - 2019/4/4

Y1 - 2019/4/4

N2 - 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 low-albedo 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.

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