Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

The unexpected surface of asteroid (101955) Bennu


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 scale5,6,7,8,9,10,11. 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.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: Range of albedo on the surface of Bennu.
Fig. 2: OCAMS imaging data elucidate Bennu’s diverse surface reflectance and composition.
Fig. 3: OCAMS global mosaic overlain with elevation data and four regions of interest for sampling.

Data availability

Data used in the plots in Figs. 1, 2 are available with this manuscript as Source Data. Raw and calibrated datasets will be available via the Planetary Data System (PDS) ( Data are delivered to the PDS according to the OSIRIS-REx Data Management Plan, available in the OSIRIS-REx PDS archive. Higher-level products—for example, global mosaics and elevation maps—will be available in the Planetary Data System PDS one year after departure from the asteroid.


  1. Lauretta, D. S. et al. The OSIRIS-REx target asteroid (101955) Bennu: constraints on its physical, geological, and dynamical nature from astronomical observations. Meteorit. Planet. Sci. 50, 834–849 (2015).

    ADS  CAS  Article  Google Scholar 

  2. Hergenrother, C. W. et al. Lightcurve, color and phase function photometry of the OSIRIS-REx target asteroid (101955) Bennu. Icarus 226, 663–670 (2013).

    ADS  Article  Google Scholar 

  3. Clark, B. E. et al. Asteroid (101955) 1999 RQ36: spectroscopy from 0.4 to 2.4 μm and meteorite analogs. Icarus 216, 462–475 (2011).

    ADS  CAS  Article  Google Scholar 

  4. Lauretta, D. S. et al. OSIRIS-REx: sample return from asteroid (101955) Bennu. Space Sci. Rev. 212, 925–984 (2017).

    ADS  Article  Google Scholar 

  5. Daly, M. G. et al. The OSIRIS-REx Laser Altimeter (OLA) investigation and instrument. Space Sci. Rev. 212, 899–924 (2017).

    ADS  Article  Google Scholar 

  6. Bierhaus, E. B. et al. The OSIRIS-REx spacecraft and the Touch-and-Go Sample Acquisition Mechanism (TAGSAM). Space Sci. Rev. 214, 107 (2018).

    ADS  Article  Google Scholar 

  7. Christensen, P. R. et al. The OSIRIS-REx thermal emission spectrometer (OTES) instrument. Space Sci. Rev. 214, 87 (2018).

    ADS  Article  Google Scholar 

  8. Reuter, D. C. et al. The OSIRIS-REx visible and infrared spectrometer (OVIRS): spectral maps of the asteroid Bennu. Space Sci. Rev. 214, 54 (2018).

    ADS  Article  Google Scholar 

  9. Rizk, B. et al. OCAMS: the OSIRIS-REx camera suite. Space Sci. Rev. 214, 26 (2018).

    ADS  Article  Google Scholar 

  10. Masterson, R. A. et al. Regolith X-Ray Imaging Spectrometer (REXIS) aboard the OSIRIS-REx asteroid sample return mission. Space Sci. Rev. 214, 48 (2018).

    ADS  Article  Google Scholar 

  11. McMahon, J. W. et al. The OSIRIS-REx radio science experiment at Bennu. Space Sci. Rev. 214, 43 (2018).

    ADS  Article  Google Scholar 

  12. Emery, J. P. et al. Thermal infrared observations and thermophysical characterization of OSIRIS-REx target asteroid (101955) Bennu. Icarus 234, 17–35 (2014).

    ADS  Article  Google Scholar 

  13. Nolan, M. C. et al. Shape model and surface properties of the OSIRIS-REx target asteroid (101955) Bennu from radar and lightcurve observations. Icarus 226, 629–640 (2013).

    ADS  Article  Google Scholar 

  14. Hergenrother, C. W. et al. The design reference asteroid for the OSIRIS-REx mission target (101955) Bennu. Preprint at (2014).

  15. Hamilton, V. E. et al. Evidence for widespread hydrated minerals on asteroid (101955) Bennu. Nat. Astron. (2019).

  16. Barnouin, O. S. et al. Shape of (101955) Bennu indicative of a rubble pile with internal stiffness. Nat. Geosci. (2019).

  17. Scheeres, D. J. et al. The dynamic geophysical environment of (101955) Bennu based on OSIRIS-REx measurements. Nat. Astron. (2019).

  18. Walsh, K. J. et al. Craters, boulders and regolith of (101955) Bennu indicative of an old and dynamic surface. Nat. Geosci. (2019).

  19. DellaGiustina, D. N. et al. Properties of rubble-pile asteroid (101955) Bennu from OSIRIS-REx imaging and thermal analysis. Nat. Astron. (2019).

  20. Hergenrother, C. W. et al. Operational environment and rotational acceleration of asteroid (101955) Bennu from OSIRIS-REx observations. Nat. Commun. (2019).

  21. Campins, H. et al. Compositional diversity among primitive asteroids. Prim. Meteor. Aster. 2018, 345–369 (2018).

    Article  Google Scholar 

  22. Izawa, M. R. M. et al. Spectral reflectance properties of magnetites: implications for remote sensing. Icarus 319, 525–539 (2019).

    ADS  CAS  Article  Google Scholar 

  23. Kerridge, J. F., Mackay, A. L. & Boynton, W. V. Magnetite in CI carbonaceous meteorites: origin by aqueous activity on a planetesimal surface. Science 205, 395–397 (1979).

    ADS  CAS  Article  Google Scholar 

  24. Rubin, A. E., Trigo-Rodríguez, J. M., Huber, H. & Wasson, J. T. Progressive aqueous alteration of CM carbonaceous chondrites. Geochim. Cosmochim. Acta 71, 2361–2382 (2007).

    ADS  CAS  Article  Google Scholar 

  25. Brearley, A. J. in Meteorites and the Early Solar System II (eds Lauretta, D. S. & McSween Jr, H. Y.), 587–624 (Univ. Arizona Press, Tucson, 2006).

  26. Lantz, C., Binzel, R. P. & DeMeo, F. E. Space weathering trends on carbonaceous asteroids: a possible explanation for Bennu’s blue slope? Icarus 302, 10–17 (2018).

    ADS  Article  Google Scholar 

  27. Thompson, M. S., Loeffler, M. J., Morris, R. V., Keller, L. P. & Christoffersen, R. Spectral and chemical effects of simulated space weathering of the Murchison CM2 carbonaceous chondrite. Icarus 319, 499–511 (2019).

    ADS  CAS  Article  Google Scholar 

  28. Bischoff, A., Scott, E. R., Metzler, K. & Goodrich, C. A. in Meteorites and the Early Solar System II (eds Lauretta, D. S. & McSween Jr, H. Y.), 679–712 (Univ. Arizona Press, Tucson, 2006).

  29. Delbo, M. et al. Thermal fatigue as the origin of regolith on small asteroids. Nature 508, 233–236 (2014).

    ADS  CAS  Article  Google Scholar 

  30. Gundlach, B. & Blum, J. A new method to determine the grain size of planetary regolith. Icarus 223, 479–492 (2013).

    ADS  Article  Google Scholar 

  31. Scheeres, D. J. et al. The geophysical environment of Bennu. Icarus 276, 116–140 (2016).

    ADS  Article  Google Scholar 

  32. Binzel, R. P. et al. Spectral slope variations for OSIRIS-REx target asteroid (101955) Bennu: possible evidence for a fine-grained regolith equatorial ridge. Icarus 256, 22–29 (2015).

    ADS  Article  Google Scholar 

  33. OSIRIS-REx Mission Status Update, Feb 11, 2019 (2019).

  34. Li, J.-Y., Helfenstein, P., Buratti, B. J., Takir, D. & Clark, B. E. in Asteroids IV (eds Michel, P. et al.) 129–150 (Univ. Arizona Press, Tucson, 2015).

  35. DellaGiustina, D. N. et al. Overcoming the challenges associated with image-based mapping of small bodies in preparation for the OSIRIS-REx mission to (101955) Bennu. Earth Space Sci. 5, 929–949 (2018).

    ADS  Article  Google Scholar 

Download references


This material is based on work supported by NASA under contract NNM10AA11C, issued through the New Frontiers Program.

Reviewer information

Nature thanks Harry Y. McSween Jr and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Author information

Authors and Affiliations




D.S.L. led the OSIRIS-REx mission, analysis and writing of the paper. D.N.D. leads the Image Processing Working Group (IPWG), which includes C.A.B., D.R.G., K.J.B., T.L.B., H.C., E.S.H. and P.H.S. The IPWG developed the image calibration pipeline, produced the global mosaic, analysed the surface for albedo variations and calculated the relative reflectance in the different MapCam filters. O.S.B. led the altimetry investigation and produced the elevation data. W.F.B. performed dynamical analysis linking Bennu to dark asteroids in the main asteroid belt. S.S.B.-K., W.V.B., B.E.C., C.Y.D.d’A., H.L.E., C.W.H., M.C.N. and B.R. designed the observation profiles and OCAMS operation plans for mission design and data acquisition. C.W.H. also led the astronomical characterization. H.C.C. Jr, J.P.D. and C.W.V.W. contributed to the content and writing of the manuscript. J.P.E. led the thermal analysis. V.E.H. led the spectral analysis, and M.R.M.I. and H.H.K. led the characterization and interpretation of the magnetite visible spectral properties. H.L.R. led the graphic design and figure development. D.J.S. led the radio science analysis and K.J.W. led the geological investigation of Bennu. The entire OSIRIS-REx Team made the encounter with Bennu possible.

Corresponding author

Correspondence to D. S. Lauretta.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 The global mosaic of Bennu, projected onto a sinusoidal map that preserves area.

The PolyCam images were photometrically corrected to mimic imaging conditions with phase, emission and incidence angles of 0°. The map has a pixel scale of 1.2 m per pixel. Images were taken on 25 November 2018.

Extended Data Fig. 2 Areas used for the calculation of the albedo variation in Fig. 1d.

Blue and orange outlines represent dark and bright clasts, respectively.

Extended Data Fig. 3 Timeline of the various observations made during the Approach phase.

The figure shows the key parameters affecting imaging conditions as a function of range to the asteroid and calendar date.

Extended Data Fig. 4 Schematic of Preliminary Survey, showing passes over the north pole, equator, and south pole.

Each trajectory leg lasts two days. The observations consist of MapCam mosaics made far from Bennu, both on the inbound and outbound legs from the closest approach, OLA observations made near the closest approach, both inbound and outbound, and additional MapCam mosaics made soon after the OLA observations but on the outbound legs of the polar flybys only. The time of closest approach to the pole was set at a nominal 17:00 utc for all flybys.

Extended Data Table 1 Observation parameters for early PolyCam images
Extended Data Table 2 Observation parameters for late PolyCam images
Extended Data Table 3 Observation parameters for Preliminary Survey distant MapCam activities
Extended Data Table 4 Observation parameters for close MapCam activities

Source data

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Lauretta, D.S., DellaGiustina, D.N., Bennett, C.A. et al. The unexpected surface of asteroid (101955) Bennu. Nature 568, 55–60 (2019).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing