Properties of rubble-pile asteroid (101955) Bennu from OSIRIS-REx imaging and thermal analysis


Establishing the abundance and physical properties of regolith and boulders on asteroids is crucial for understanding the formation and degradation mechanisms at work on their surfaces. Using images and thermal data from NASA’s Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft, we show that asteroid (101955) Bennu’s surface is globally rough, dense with boulders, and low in albedo. The number of boulders is surprising given Bennu’s moderate thermal inertia, suggesting that simple models linking thermal inertia to particle size do not adequately capture the complexity relating these properties. At the same time, we find evidence for a wide range of particle sizes with distinct albedo characteristics. Our findings imply that ages of Bennu’s surface particles span from the disruption of the asteroid’s parent body (boulders) to recent in situ production (micrometre-scale particles).

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: Resolved phase curves of Bennu.
Fig. 2: Asteroid Bennu imaged by the OSIRIS-REx Camera Suite.
Fig. 3: Global cumulative size–frequency distribution of boulders.
Fig. 4: Albedo trends among Bennu’s boulders.
Fig. 5: Evidence of in situ boulder disaggregation.
Fig. 6: Dark diffuse units.

Code availability

The thermophysical analysis reported here uses a custom code that is based on the Advanced Thermophysical Model (ATPM) of refs. 46,59,60. The ISIS3 code used to generate the image processing data products is available from the US Geological Survey–Astrogeology Science Center:

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request. Raw (L0) through calibrated (L2, L3) OCAMS, OVIRS and OTES data will be available via the Planetary Data System (PDS) ( Data are released to the PDS according to the schedule provided in the OSIRIS-REx Data Management Plan found in the OSIRIS-REx PDS archive. Image mosaics and photometric models will be available in the PDS 1 year after departure from the asteroid.


  1. 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  Article  Google Scholar 

  2. 2.

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

    ADS  Article  Google Scholar 

  3. 3.

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

  4. 4.

    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 

  5. 5.

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

    ADS  Article  Google Scholar 

  6. 6.

    Li, J.-Y., Helfenstein, P., Buratti, B., Takir, D. & Clark, B. E. in Asteroids IV (eds Michel, P., DeMeo, F. E. & Bottke, W. F.) 277–326 (Univ. of Arizona Press, Tucson, 2015).

  7. 7.

    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 

  8. 8.

    Alí-Lagoa, V. et al. Differences between the Pallas collisional family and similarly sized B-type asteroids. Astron. Astrophys. 591, A14 (2016).

    Article  Google Scholar 

  9. 9.

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

  10. 10.

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

    ADS  Article  Google Scholar 

  11. 11.

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

  12. 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. 13.

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

    ADS  Article  Google Scholar 

  14. 14.

    Delbo’, M., Mueller, M., Emery, J. P., Rozitis, B. & Capria, M. T. in Asteroids IV (eds Michel, P., DeMeo, F. E. & Bottke, W. F.) 107–128 (Univ. of Arizona Press, Tucson, 2015).

  15. 15.

    Jakosky, B. M. On the thermal properties of Martian fines. Icarus 66, 117–124 (1986).

    ADS  Article  Google Scholar 

  16. 16.

    Opeil, C. P., Consolmagno, G. J. & Britt, D. T. The thermal conductivity of meteorites: new measurements and analysis. Icarus 208, 449–454 (2010).

    ADS  Article  Google Scholar 

  17. 17.

    Walsh, K. J. Rubble pile asteroids. Annu. Rev. Astron. Astrophys. 56, 593–624 (2018).

    ADS  Article  Google Scholar 

  18. 18.

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

  19. 19.

    Lauretta, D. S. et al. The unexpected surface of asteroid (101955) Bennu. Natur e (2019).

  20. 20.

    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 

  21. 21.

    Mazrouei, S., Daly, M. G., Barnouin, O. S., Ernst, C. M. & DeSouza, I. Block distributions on Itokawa. Icarus 229, 181–189 (2014).

    ADS  Article  Google Scholar 

  22. 22.

    Michikami, T. et al. Size-frequency statistics of boulders on global surface of asteroid 25143 Itokawa. Earth Planets Space 60, 13–20 (2008).

    ADS  Article  Google Scholar 

  23. 23.

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

  24. 24.

    Lee, P. et al. Ejecta blocks on 243 Ida and on other asteroids. Icarus 120, 87–105 (1996).

    ADS  Article  Google Scholar 

  25. 25.

    Michel, P., Benz, W., Tanga, P. & Richardson, D. C. Collisions and gravitational reaccumulation: forming asteroid families and satellites. Science 294, 1696–1700 (2001).

    ADS  Article  Google Scholar 

  26. 26.

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

    ADS  Article  Google Scholar 

  27. 27.

    Opeil, C. P., Consolmagno, G. J., Safarik, D. J. & Britt, D. T. Stony meteorite thermal properties and their relationship with meteorite chemical and physical states. Meteorit. Planet. Sci. 47, 319–329 (2012).

    ADS  Article  Google Scholar 

  28. 28.

    Müller, T. G., Sekiguchi, T., Kaasalainen, M., Abe, M. & Hasegawa, S. Thermal infrared observations of the Hayabusa spacecraft target asteroid 25143 Itokawa. Astron. Astrophys. 443, 347–355 (2005).

    ADS  Article  Google Scholar 

  29. 29.

    Rodgers, D. J., Ernst, C. M., Barnouin, O. S., Murchie, S. L. & Chabot, N. L. Methodology for finding and evaluating safe landing sites on small bodies. Planet. Space Sci. 134, 71–81 (2016).

    ADS  Article  Google Scholar 

  30. 30.

    Müller, T. G. et al. Hayabusa-2 mission target asteroid 162173 Ryugu (1999 JU 3): searching for the object’s spin-axis orientation. Astron. Astrophys. 599, A103 (2017).

    Article  Google Scholar 

  31. 31.

    Sugita, S. et al. The geomorphology, color, and thermal properties of Ryugu: implications for parent-body processes. Science (in the press).

  32. 32.

    Saito, J. et al. Detailed Images of asteroid 25143 Itokawa from Hayabusa. Science 312, 1341–1344 (2006).

    ADS  Article  Google Scholar 

  33. 33.

    Murchie, S. et al. Color variations on Eros from NEAR multispectral imaging. Icarus 155, 145–168 (2002).

    ADS  Article  Google Scholar 

  34. 34.

    Riner, M. A., Robinson, M. S., Eckart, J. M. & Desch, S. J. Global survey of color variations on 433 Eros: implications for regolith processes and asteroid environments. Icarus 198, 67–76 (2008).

    ADS  Article  Google Scholar 

  35. 35.

    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 

  36. 36.

    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  Article  Google Scholar 

  37. 37.

    Johnson, T. V. & Fanale, F. P. Optical properties of carbonaceous chondrites and their relationship to asteroids. J. Geophys. Res. 78, 8507–8518 (1973).

    ADS  Article  Google Scholar 

  38. 38.

    Sanchez, J. A. et al. Phase reddening on near-Earth asteroids: implications for mineralogical analysis, space weathering and taxonomic classification. Icarus 220, 36–50 (2012).

    ADS  Article  Google Scholar 

  39. 39.

    Li, J. et al. Spectrophotometric modeling and mapping of Ceres. Icarus 322, 144–167 (2019).

    ADS  Article  Google Scholar 

  40. 40.

    Muinonen, K. et al. Asteroid photometric and polarimetric phase curves: joint linear-exponential modeling. Meteorit. Planet. Sci. 44, 1937–1946 (2009).

    ADS  Article  Google Scholar 

  41. 41.

    Pilorget, C., Fernando, J., Ehlmann, B. L., Schmidt, F. & Hiroi, T. Wavelength dependence of scattering properties in the VIS-NIR and links with grain-scale physical and compositional properties. Icarus 267, 296–314 (2016).

    ADS  Article  Google Scholar 

  42. 42.

    Rozitis, B. The surface roughness of (433) Eros as measured by thermal-infrared beaming. Mon. Not. R. Astron. Soc. 464, 915–923 (2017).

    ADS  Article  Google Scholar 

  43. 43.

    Rozitis, B., Green, S. F., MacLennan, E. & Emery, J. P. Observing the variation of asteroid thermal inertia with heliocentric distance. Mon. Not. R. Astron. Soc. 477, 1782–1802 (2018).

    ADS  Article  Google Scholar 

  44. 44.

    Rozitis, B. & Green, S. F. Physical characterisation of near-Earth asteroid (1620) Geographos. Astron. Astrophys. 568, A43 (2014).

    ADS  Article  Google Scholar 

  45. 45.

    Spencer, J. R. A rough-surface thermophysical model for airless planets. Icarus 83, 27–38 (1990).

    ADS  Article  Google Scholar 

  46. 46.

    Rozitis, B. & Green, S. F. Directional characteristics of thermal-infrared beaming from atmosphereless planetary surfaces—a new thermophysical model. Mon. Not. R. Astron. Soc. 415, 2042–2062 (2011).

    ADS  Article  Google Scholar 

  47. 47.

    Jaumann, R. et al. Surface geomorphology of near earth asteroid (162173) Ryugu from in-situ observations: first results from the MASCOT camera. In Am. Geophys. Union Fall Meet. 2018 abstr. P21A-03 (American Geophysical Union, 2018).

  48. 48.

    Nakamura, A. M., Fujiwara, A. & Kadono, T. Velocity of finer fragments from impact. Planet. Space Sci. 42, 1043–1052 (1994).

    ADS  Article  Google Scholar 

  49. 49.

    Hanuš, J., Delbo’, M., Ďurech, J. & Alí-Lagoa, V. Thermophysical modeling of main-belt asteroids from WISE thermal data. Icarus 309, 297–337 (2018).

  50. 50.

    Nagao, K. et al. Irradiation history of Itokawa regolith material deduced from noble gases in the Hayabusa samples. Science 333, 1128–1131 (2011).

    ADS  Article  Google Scholar 

  51. 51.

    Scheeres, D. J., Hartzell, C. M., Sánchez, P. & Swift, M. Scaling forces to asteroid surfaces: the role of cohesion. Icarus 210, 968–984 (2010).

    ADS  Article  Google Scholar 

  52. 52.

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

    ADS  Article  Google Scholar 

  53. 53.

    Kieffer, H. H. & Stone, T. C. The spectral irradiance of the Moon. Astron. J. 129, 2887–2901 (2005).

    ADS  Article  Google Scholar 

  54. 54.

    McEwen, A. S. A precise lunar photometric function. Lunar Planet. Sci. 27, 841–842 (1996).

    ADS  Google Scholar 

  55. 55.

    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 

  56. 56.

    Uni-, W. et al. Standard techniques for presentation and analysis of crater size-frequency data. Icarus 37, 467–474 (1979).

    Article  Google Scholar 

  57. 57.

    Clauset, A., Shalizi, C. R. & Newman, M. E. J. Power-law distributions in empirical data. SIAM Rev. 51, 661–703 (2009).

    ADS  MathSciNet  Article  Google Scholar 

  58. 58.

    DeSouza, I., Daly, M. G., Barnouin, O. S., Ernst, C. M. & Bierhaus, E. B. Improved techniques for size-frequency distribution analysis in the planetary sciences: application to blocks on 25143 Itokawa. Icarus 247, 77–80 (2015).

    ADS  Article  Google Scholar 

  59. 59.

    Rozitis, B. & Green, S. F. The influence of rough surface thermal-infrared beaming on the Yarkovsky and YORP effects. Mon. Not. R. Astron. Soc. 423, 367–388 (2012).

    ADS  Article  Google Scholar 

  60. 60.

    Rozitis, B. & Green, S. F. The influence of global self-heating on the Yarkovsky and YORP effects. Mon. Not. R. Astron. Soc. 433, 603–621 (2013).

    ADS  Article  Google Scholar 

  61. 61.

    Gundlach, B. & Blum, J. Outgassing of icy bodies in the Solar System—II: Heat transport in dry, porous surface dust layers. Icarus 219, 618–629 (2012).

    ADS  Article  Google Scholar 

  62. 62.

    Sakatani, N. et al. Thermal conductivity model for powdered materials under vacuum based on experimental studies. AIP Adv. 7, 015310 (2017).

    ADS  Article  Google Scholar 

  63. 63.

    Sakatani, N., Ogawa, K., Arakawa, M. & Tanaka, S. Thermal conductivity of lunar regolith simulant JSC-1A under vacuum. Icarus 309, 13–24 (2018).

    ADS  Article  Google Scholar 

  64. 64.

    Ryan, A. J. Heat and Mass Transfer on Planetary Surfaces PhD thesis, Arizona State Univ. (2018).

  65. 65.

    Acton, C., Bachman, N., Semenov, B. & Wright, E. A look towards the future in the handling of space science mission geometry. Planet. Space Sci. 150, 9–12 (2018).

    ADS  Article  Google Scholar 

  66. 66.

    Gault, B. D. E., Shoemaker, E. M. & Moore, H. J. Spray Ejected From The Lunar Surface By Meteoroid Impact (NASA, 1963).

  67. 67.

    Moore, H. J. in Analysis of Apollo 10: Photography and Visual Observations 24–26 (NASA, 1971).

  68. 68.

    Bart, G. D. & Melosh, H. J. Using lunar boulders to distinguish primary from distant secondary impact craters. Geophys. Res. Lett. 34, L07203 (2007).

    ADS  Google Scholar 

Download references


This material is based upon work supported by NASA under contract NNM10AA11C issued through the New Frontiers Program. We thank C. Ernst for providing the data used in Supplementary Fig. 4 to compare the size-frequency distribution of boulders on Bennu to other small bodies. B.R. acknowledges funding support from the Royal Astronomical Society in the form of a research fellowship. P.M. acknowledges funding support from the French space agency CNES and from Academies of Excellence: Complex systems and Space, environment, risk, and resilience, part of the IDEX JEDI of the Université Côte d’Azur. M.A.B., J.D.P.D. and S.F. also acknowledge financial support from CNES the French space agency. M.P. acknowledges funding support from the Italian Space Agency (ASI) under the ASI-INAF agreement no. 2017–37-H.0. Part of this work was performed at the Jet Propulsion Laboratory, California Institute of Technology under contract with the National Aeronautics and Space Administration. S.R.S. acknowledges support from NASA Grant no. 80NSSC18K0226 as part of the OSIRIS-REx Participating Scientist Program.

Author information





D.N.D. leads the OSIRIS-REx Image Processing Working Group (IPWG). J.P.E. leads the OSIRIS-REx Thermal Analysis Working Group (TAWG). Both led the analysis and paper writing efforts. M.A.B., C.A.B., K.N.B., H.C., J.d.L., C.Y.D.d’A., S.F., D.R.G., C.H., E.S.H., H.H.K., T.K., L.L.C., J.-Y.L., J.L., J.L.R.G., P.M., M.N., M.P., D.C.R., B.R., P.H.S., E.T., C.A.T. and X.-D.Z. contributed to the image processing analysis of MapCam images. O.S.B., K.J.B., C.A.B., D.R.G. and C.H. contributed to the production of the global mosaic. E.A., R.-L.B., O.S.B., C.A.B., E.B.B., W.F.B., K.N.B., H.C., H.C.C.Jr, M.D., M.D., C.M.E., E.R.J., P.M., J.M., M.N., M.P., A.R., S.R.S., E.T. and K.J.W. contributed to the interpretation of the boulder size-frequency distribution. B.E.C., J.D.P.D., C.Y.D.d’A., S.F., D.R.G., C.H., E.S.H., J.-Y.L., B.R., N.S., A.A.S., P.H.S. and X.-D.Z. contributed to the interpretation of the photometric model. E.A., R.-L.B., J.L.B., O.S.B., R.P.B., W.F.B., N.B., P.R.C., B.C.C., M.D., C.M.E., V.E.H., E.S.H., E.R.J., T.K., L.F.L., J.M., M.N., M.P., D.C.R., B.R., A.R., S.R.S., M.A.S., A.A.S., E.T., C.A.T. and K.J.W. contributed to the interpretation of the thermophysical measurements. N.B., P.R.C., L.F.L., B.R. and M.A.S. contributed to the analysis or calibration of thermal data. D.N.D., C.Y.D.d’A., J.P.E., D.R.G., V.E.H., C.H., L.F.L., D.C.R., B.R. and A.A.S. contributed to the planning of observations. K.J.B., C.Y.D.d’A., D.R.G., E.S.H., B.R., N.S., P.H.S. and X.-D.Z. contributed to the calibration of image data. D.S.L. leads the mission and contributed significantly to the analysis. C.W.V.W. contributed substantially to the content and writing of the paper. The entire OSIRIS-REx Team made the encounter with Bennu possible.

Corresponding authors

Correspondence to D. N. DellaGiustina or J. P. Emery.

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.

Supplementary information

Supplementary Information

Supplementary Text, Supplementary Figures 1–8.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

DellaGiustina, D.N., Emery, J.P., Golish, D.R. et al. Properties of rubble-pile asteroid (101955) Bennu from OSIRIS-REx imaging and thermal analysis. Nat Astron 3, 341–351 (2019).

Download citation

Further reading


Quick links

Sign up for the Nature Briefing newsletter for a daily update on COVID-19 science.
Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing