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.

Fine-regolith production on asteroids controlled by rock porosity


Spacecraft missions have observed regolith blankets of unconsolidated subcentimetre particles on stony asteroids1,2,3. Telescopic data have suggested the presence of regolith blankets also on carbonaceous asteroids, including (101955) Bennu4 and (162173) Ryugu5. However, despite observations of processes that are capable of comminuting boulders into unconsolidated materials, such as meteoroid bombardment6,7 and thermal cracking8, Bennu and Ryugu lack extensive areas covered in subcentimetre particles7,9. Here we report an inverse correlation between the local abundance of subcentimetre particles and the porosity of rocks on Bennu. We interpret this finding to mean that accumulation of unconsolidated subcentimetre particles is frustrated where the rocks are highly porous, which appears to be most of the surface10. The highly porous rocks are compressed rather than fragmented by meteoroid impacts, consistent with laboratory experiments11,12, and thermal cracking proceeds more slowly than in denser rocks. We infer that regolith blankets are uncommon on carbonaceous asteroids, which are the most numerous type of asteroid13. By contrast, these terrains should be common on stony asteroids, which have less porous rocks and are the second-most populous group by composition13. The higher porosity of carbonaceous asteroid materials may have aided in their compaction and cementation to form breccias, which dominate the carbonaceous chondrite meteorites14.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: The thermal inertia of Bennu’s rocks is positively correlated with the local surface abundance of fine regolith.
Fig. 2: The porosities of most of Bennu’s and Ryugu’s rocks are much higher than that of Itokawa’s rocks.
Fig. 3: Fine-regolith production is frustrated in the presence of high-porosity rocks.

Data availability

Raw through-calibrated OTES52 and OCAMS53 data are available via the Planetary Data System ( The SPC/OLA v34 shape model is available via the Small Body Mapping Tool ( The IDs of the OTES observations used here and the best-fitting solutions for the thermophysical model are provided in Supplementary Table 1. The boulder size, location and reflectance used to test the robustness of the results are available in refs. 34,46Source data are provided with this paper.

Code availability

The thermophysical analysis reported here uses custom code based on the thermophysical model of ref. 16, available at The code to compute the geometry of the OTES acquisitions and boresight is available at (ref. 54). The code to compute Γc for the thermophysical analysis is available at (ref. 55). The rock mapping in Extended Data Fig. 3 was performed using the SAOImageDS9 software available at Other codes that support the findings of this study are available at (ref. 56).


  1. 1.

    Veverka, J. et al. The landing of the NEAR-Shoemaker spacecraft on asteroid 433 Eros. Nature 413, 390–393 (2001).

    ADS  CAS  PubMed  Article  Google Scholar 

  2. 2.

    Miyamoto, H. et al. Regolith migration and sorting on asteroid Itokawa. Science 316, 1011–1014 (2007).

    ADS  CAS  PubMed  Article  Google Scholar 

  3. 3.

    Huang, J. et al. The Ginger-shaped Asteroid 4179 Toutatis: new observations from a Successful Flyby of Chang’e-2. Sci. Rep. 3, 3411 (2013).

    PubMed  PubMed Central  Article  Google Scholar 

  4. 4.

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

    ADS  Article  Google Scholar 

  5. 5.

    Müller, T. et al. Hayabusa-2 mission target asteroid 162173 Ryugu (1999 JU3): searching for the object’s spin-axis orientation. Astron. Astrophys. 599, A103 (2017).

    Article  Google Scholar 

  6. 6.

    Ballouz, R.-L. et al. Bennu’s near-Earth lifetime of 1.75 million years inferred from craters on its boulders. Nature 587, 205–209 (2020).

    ADS  CAS  PubMed  Article  Google Scholar 

  7. 7.

    Sugita, S. et al. The geomorphology, color, and thermal properties of Ryugu: implications for parent-body processes. Science 364, eaaw0422 (2019).

    CAS  Article  Google Scholar 

  8. 8.

    Molaro, J. L. et al. Thermal fatigue as a driving mechanism for activity on asteroid Bennu. J. Geophys. Re. Planets 125, e2019JE006325 (2020).

    ADS  CAS  Google Scholar 

  9. 9.

    Lauretta, D. et al. The unexpected surface of asteroid (101955) Bennu. Nature 568, 55–60 (2019).

    ADS  CAS  PubMed  PubMed Central  Article  Google Scholar 

  10. 10.

    Rozitis, B. et al. Asteroid (101955) Bennu’s weak boulders and thermally anomalous equator. Sci. Adv. 6, eabc3699 (2020).

    ADS  PubMed  PubMed Central  Article  Google Scholar 

  11. 11.

    Flynn, G. J. et al. Hypervelocity cratering and disruption of porous pumice targets: implications for crater production, catastrophic disruption, and momentum transfer on porous asteroids. Planet. Space Sci. 107, 64–76 (2015).

    ADS  Article  Google Scholar 

  12. 12.

    Housen, K. R., Sweet, W. J. & Holsapple, K. A. Impacts into porous asteroids. Icarus 300, 72–96 (2018).

    ADS  Article  Google Scholar 

  13. 13.

    DeMeo, F., Alexander, C., Walsh, K., Chapman, C. & Binzel, R. in Asteroids Vol. IV (eds) 13–41 (2015).

  14. 14.

    Bischoff, A., Scott, E. R. D., Metzler, K. & Goodrich, C. A. in Meteorites and the Early Solar System vol. II (eds) 679 (2006).

  15. 15.

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

    ADS  Article  Google Scholar 

  16. 16.

    Delbo, M., Mueller, M., Emery, J. P., Rozitis, B. & Capria, M. T. in Asteroids Vol. IV (eds) 107–128 (2015).

  17. 17.

    Cambioni, S., Delbo, M., Ryan, A. J., Furfaro, R. & Asphaug, E. Constraining the thermal properties of planetary surfaces using machine learning: application to airless bodies. Icarus 325, 16–30 (2019).

    ADS  Article  Google Scholar 

  18. 18.

    Shimaki, Y. et al. Thermophysical properties of the surface of asteroid 162173 Ryugu: infrared observations and thermal inertia mapping. Icarus 348, 113835 (2020).

    Article  Google Scholar 

  19. 19.

    Grott, M. et al. Low thermal conductivity boulder with high porosity identified on C-type asteroid (162173) Ryugu. Nat. Astron. 3, 971–976 (2019).

    ADS  Article  Google Scholar 

  20. 20.

    Opeil, C. P., Britt, D. T., Macke, R. J. & Consolmagno, G. J. The surprising thermal properties of CM carbonaceous chondrites. Meteorit. Planet. Sci. 55, E1–E20 (2020).

    ADS  CAS  Article  Google Scholar 

  21. 21.

    Hamilton, V. et al. Evidence for widespread hydrated minerals on asteroid (101955) Bennu. Nat. Astron. 3, 332–340 (2019).

    ADS  CAS  PubMed  PubMed Central  Article  Google Scholar 

  22. 22.

    Michikami, T., Moriguchi, K., Hasegawa, S. & Fujiwara, A. Ejecta velocity distribution for impact cratering experiments on porous and low strength targets. Planet. Space Sci. 55, 70–88 (2007).

    ADS  Article  Google Scholar 

  23. 23.

    Avdellidou, C. et al. Very weak carbonaceous asteroid simulants I: mechanical properties and response to hypervelocity impacts. Icarus 341, 113648 (2020).

    Article  Google Scholar 

  24. 24.

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

    ADS  CAS  PubMed  Article  PubMed Central  Google Scholar 

  25. 25.

    Okada, T. et al. Highly porous nature of a primitive asteroid revealed by thermal imaging. Nature 579, 518–522 (2020).

    ADS  CAS  PubMed  Article  PubMed Central  Google Scholar 

  26. 26.

    Jawin, E. et al. Global patterns of recent mass movement on asteroid (101955) Bennu. J. Geophys. Res. Planets 125, e2020JE006475 (2020).

    ADS  Article  Google Scholar 

  27. 27.

    Hsu, H., Wang, X., Carroll, A., Hood, N. & Horanyi, M. Electrostatic removal of fine-grained regolith on sub-km asteroids. In AAS/Division for Planetary Sciences Meeting Abstracts Vol. 52, 402.06 (2020).

  28. 28.

    Walsh, K. et al. Craters, boulders and regolith of (101955) Bennu indicative of an old and dynamic surface. Nat. Geosci. 12, 242–246 (2019).

    ADS  CAS  Article  Google Scholar 

  29. 29.

    Ruesch, O. et al. In situ fragmentation of lunar blocks and implications for impacts and solar-induced thermal stresses. Icarus 336, 113431 (2020).

    Article  Google Scholar 

  30. 30.

    Scott, E. R. D. & Bottke, W. F. Impact histories of angrites, eucrites, and their parent bodies. Meteorit. Planet. Sci. 46, 1878–1887 (2011).

    ADS  CAS  Article  Google Scholar 

  31. 31.

    Bland, P. A. et al. Pressure-temperature evolution of primordial solar system solids during impact-induced compaction. Nat. Commun. 5, 5451 (2014).

    ADS  CAS  PubMed  Article  Google Scholar 

  32. 32.

    Bennett, C. et al. A high-resolution global basemap of (101955) Bennu. Icarus 357, 113690 (2021).

    Article  Google Scholar 

  33. 33.

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

    ADS  Article  Google Scholar 

  34. 34.

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

    ADS  Article  Google Scholar 

  35. 35.

    Barnouin, O. et al. Digital terrain mapping by the OSIRIS-REx mission. Planet. Space Sci. 180, 104764 (2020).

    Article  Google Scholar 

  36. 36.

    Horz, F. & Cintala, M. Impact experiments related to the evolution of planetary regoliths. Meteorit. Planet. Sci. 31 (Suppl.), A65 (1996).

    Google Scholar 

  37. 37.

    Flynn, G. J., Consolmagno, G. J., Brown, P. & Macke, R. J. Physical properties of the stone meteorites: implications for the properties of their parent bodies. Chem. Erde 78, 269–298 (2018).

    CAS  Article  Google Scholar 

  38. 38.

    Macke, R. J., Consolmagno, G. J. & Britt, D. T. Density, porosity, and magnetic susceptibility of carbonaceous chondrites. Meteorit. Planet. Sci. 46, 1842–1862 (2011).

    ADS  CAS  Article  Google Scholar 

  39. 39.

    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 

  40. 40.

    Wada, K. et al. Asteroid Ryugu before the Hayabusa2 encounter. Prog. Earth Planet. Sci. 5, 82 (2018).

    ADS  Article  Google Scholar 

  41. 41.

    Ryan, A. J., Pino Muñoz, D., Bernacki, M. & Delbo, M. Full-field modeling of heat transfer in asteroid regolith: radiative thermal conductivity of polydisperse particulates. J. Geophys. Ress Planets 125, e2019JE006100 (2020).

    ADS  Google Scholar 

  42. 42.

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

    ADS  Article  Google Scholar 

  43. 43.

    Burke, K. N. et al. Particle size-frequency distributions of the OSIRIS-REx candidate sample sites on asteroid (101955) Bennu. Remote Sens. 13, 1315 (2021).

    ADS  Article  Google Scholar 

  44. 44.

    Biele, J. et al. Macroporosity and grain density of rubble pile asteroid (101955) Bennu. In AGU Fall Meeting 2020 Vol. 1, P037–04 (2020).

  45. 45.

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

    ADS  Article  Google Scholar 

  46. 46.

    DellaGiustina, D. N. et al. Variations in color and reflectance on the surface of asteroid (101955) Bennu. Science 370, eabc3660 (2020).

    ADS  CAS  PubMed  Article  PubMed Central  Google Scholar 

  47. 47.

    Nakamura, T. et al. Itokawa dust particles: a direct link between S-type asteroids and ordinary chondrites. Science 333, 1113–1116 (2011).

    ADS  CAS  PubMed  Article  PubMed Central  Google Scholar 

  48. 48.

    El Mir, C., Ramesh, K. T. & Delbo, M. The efficiency of thermal fatigue in regolith generation on small airless bodies. Icarus 333, 356–370 (2019).

    ADS  Article  Google Scholar 

  49. 49.

    Hergenrother, C. W. et al. The operational environment and rotational acceleration of asteroid (101955) Bennu from OSIRIS-REx observations. Nat. Commun. 10, 1291 (2019).

    ADS  CAS  PubMed  PubMed Central  Article  Google Scholar 

  50. 50.

    Watanabe, S. et al. Hayabusa2 arrives at the carbonaceous asteroid 162173 Ryugu—a spinning top-shaped rubble pile. Science 364, 268–272 (2019).

    ADS  CAS  PubMed  Google Scholar 

  51. 51.

    Demura, H. et al. Pole and global shape of 25143 Itokawa. Science 312, 1347–1349 (2006).

    ADS  CAS  PubMed  Article  Google Scholar 

  52. 52.

    Christensen, P., Hamilton, V., Anwar, S., Mehall, G. & Lauretta, D. OSIRIS-REx Thermal Emission Spectrometer Bundle urn:nasa:pds:orex.otes, (NASA Planetary Data System, 2019).

  53. 53.

    Rizk, B., Golish, D., DellaGiustina, D. & Lauretta, D. OSIRIS-REx Camera Suite Bundle urn:nasa:pds:orex.ocams, (NASA Planetary Data System, 2019).

  54. 54.

    Deshapriya, J. D. P. OTES geoWriter (2021).

  55. 55.

    Ryan, A. Regolith Heat Transfer Code for Manuscript “Rock Porosity Drives Regolith Buildup on Carbon-Rich Versus Stony Asteroids” (2021).

  56. 56.

    Cambioni, S., Delbo, M. & Poggiali, G. Codes for Two-Component Thermophysical Analysis of Asteroid (101955) Bennu (2021).

Download references


This material is based on work supported by NASA under contract NNM10AA11C issued through the New Frontiers Program. We are grateful to the entire OSIRIS-REx team for making the encounter with Bennu possible, to C. Wolner and F. Murphy for editorial help, and to the OPAL infrastructure of the Observatoire de la Côte d’Azur (CRIMSON) for providing computational resources and support. S.C. thanks the University of Arizona for supporting this study. M.D., C.A., J.D.P.D. and  M.A.B. acknowledge the French space agency CNES. C.A. and M.D. acknowledge support from ANR “ORIGINS” (ANR-18-CE31-0014). C.A. was supported by the French National Research Agency under the project “Investissements d’Avenir” UCAJEDI ANR-15-IDEX-01. G.P. and J.R.B. were supported by Italian Space Agency grant agreement INAF/ASI number 2017-37-H.0. B.R. acknowledges financial support from the UK Science and Technology Facilities Council (STFC). E.C. thanks CSA, NSERC, CFI, MRIF and UWinnipeg for supporting this study.

Author information




S.C. led the project, the interpretation of the results and the manuscript development, and performed the thermophysical simulations and data analysis. M.D. provided the thermophysical software, performed the thermal cracking calculations, and contributed to the interpretation of the results and the development of the manuscript. G.P. developed the pipeline to retrieve OTES detailed survey data and performed rock mapping in PolyCam images. C.A. curated the discussion on meteoroid bombardment and contributed to writing the manuscript. A.J.R. contributed with the code to convert thermal inertia values in fine-regolith particle size and developed the iterative approach to determine the cut-off value of thermal inertia, together with S.C. J.D.P.D. extracted the observation geometry of the spacecraft and Bennu from mission kernels. R.-L.B. proposed important tests of the robustness of the results. E.A., W.F.B. and J.R.B. contributed to the interpretation of the data and writing of the manuscript. D.N.D., K.N.B., C.A.B. and K.J.W. provided support in the interpretation of spacecraft imagery. J.P.E. and B.R. contributed to the data interpretation during the OSIRIS-REx Thermal Analysis Working Group meetings, and to the design of the observations and data acquisition. M.A.B. and E.C. contributed to the interpretation of the results. D.S.L. made this study possible as the PI of the OSIRIS-REx mission and contributed to the discussion of the results.

Corresponding author

Correspondence to S. Cambioni.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature thanks Guy Consolmagno and Seiji Sugita for their contribution to the peer review of this work. Peer reviewer reports are available.

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

Extended data figures and tables

Extended Data Fig. 1 The thermal inertia of Bennu’s rocks and the surface abundance of fine regolith were measured in 122 quasi-randomly–distributed regions.

a, OTES spots on Bennu plotted on the global basemap of Bennu32 as function of longitude and latitude (red: Equatorial Station 1 at 3:00 pm, or EQ1; blue: Equatorial Station 2 at 3:20 am, or EQ2). b, comparison between modelled and observed radiance for one of the 122 areas (ID: 609491396:610102222). c, comparison between the emissivity of Bennu and the residuals of the analysis for the spots 609491396:610102222; the residual curves closely resemble Bennu’s emissivity, which is not modelled by our thermophysical model. The error bars correspond to 3 times the Noise Equivalent Spectral Radiance of the OTES instrument15. Credit for global mosaic in panel a: NASA/Goddard/University of Arizona.

Extended Data Fig. 2 There is less fine regolith at the OSIRIS-REx’s backup sampling site Osprey than at the primary sampling site Nightingale.

Blue and yellow pixels represent areas where no particles bigger than 2 cm, ~ls, were mapped by ref. 43. The value DPls is the upper limit for the sizes of fine regolith detected by our thermophysical model. There are fewer blue and yellow pixels at Osprey (image resolution: 0.3 cm per pixel, panels a, b) than at Nightingale (image resolution: 0.4 cm per pixel, panels c, d), implying that Osprey has less unresolved material than Nightingale. Consistently and independently, our thermophysical model indicates αOsprey<αNightingale (Supplementary Table 1, spots 609505286:610098718 and 609504794:610100730, respectively). Credit for bird graphics and PolyCam images: NASA/Goddard/University of Arizona.

Extended Data Fig. 3 The fine-regolith abundance derived from OTES data is lower than the area of unresolved material measured in Bennu’s images.

Our visual mapping and size measurement of rocks within two OTES spots: a, OTES spots 609493058:610103962; b, OTES spots 609487186:610098206. In both areas, the values of α from our thermophysical solution are smaller than the areas of unresolved materials seen in the images. Given the coarse PolyCam32 resolution, it is possible that there are unmapped particles larger than ls (but smaller than the image resolution) that our thermophysical model detects as rocks and thus do not contribute to the value of α. Credit for PolyCam images: NASA/Goddard/University of Arizona.

Source data

Extended Data Fig. 4 The correlation between ΓR and α is statistically significant.

a, Spearman correlation coefficient. b, Spearman P-value; a Spearman P < 0.05 indicates that the correlation between ΓR and α is statistically significant. The figure corresponds to the results for a value of regolith macroporosity of φ = 40%.

Extended Data Fig. 5 The correlation between ΓR and α is robust against the choice of the fine-regolith macroporosity.

The results for macroporosity φ = 15% and φ = 60% have Spearman correlation coefficients 0.56 ± 0.06 and 0.58 ± 0.06, probability of non-correlation P < 0.05, and are within 3 standard deviations of the best-fit values for regolith macroporosity of φ = 40% in 99% and 92% of the cases, respectively. The correlations are robust against removing the areas whose solutions are statistically distinct from the data set with macroporosity φ = 40% (Spearman correlation index: 0.55 ± 0.07 and P < 0.05 in 100% of 10,000 trials). The error bars correspond to 1 standard deviation (Supplementary Table 1; Methods) computed on ~450 and ~880 samples on average. The results for a regolith macroporosity of φ = 40% are described in the main text (Fig. 1).

Source data

Extended Data Fig. 6 The correlation between ΓR and α is not an artefact of thermophysical modelling.

We fit model radiances emitted by a single triangular facet with zero roughness; if the thermal inertia Γ ≤ Γc = 100 Jm−2K−1s−0.5, then α = 100%, and if Γc<Γ<2,500 Jm−2K−1s−0.5, then α = 0%. We retrieve the expected step function of α as a function of Γ, indicating that the correlation in Fig. 1 is unlikely to be an artefact of the model. The error bars correspond to 1 standard deviation computed on ~ 1.76 × 104 samples on average (Methods).

Source data

Extended Data Fig. 7 The correlation between ΓR and α is not a geometric effect due to boulders’ sizes.

a, PolyCam image of the surface corresponding to spots 609486110:610097198 where α is low probably because the spots are filled by a large, dark boulder. b, PolyCam image of the surface corresponding to spots 609495164:610106090 where α does not correlate with the size of the largest boulder; this is representative of most of the surveyed areas. c, plot of α as function of the percentage of the OTES spot covered by the largest boulder on the surface. The Spearman test reveals that these two quantities have a probability of non-correlation above the critical threshold of 0.05 in 99.99% of 10,000 trials. This indicates that the ΓR-α correlation of Fig. 1 is not the result of geometric effects. The error bars in panel c correspond to 1 standard deviation (Supplementary Table 1; Methods) computed on ~ 670 samples on average. Credit for global mosaic: NASA/Goddard/University of Arizona.

Source data

Extended Data Fig. 8 The time required to thermally break rocks is shorter for low-porosity rocks than for high-porosity rocks.

We consider the asteroid to be in near-Earth space and explore a range of rotation periods corresponding to the shaded areas. The latter is to take into account changes in the current rotation periods (4.296 h and 12.1 h for Bennu and Itokawa, respectively) that these asteroids may have experienced in the past49 due to the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect. We estimate that in their main belt source region, at about 2.3 au from the Sun, the time to break is ~60 times longer.

Source data

Extended Data Fig. 9 Examples of in-situ boulder fragmentation on Bennu.

a, a 5.4 m-diameter boulder located at 22° N 157° E. b, a 5.6 m-diameter boulder located at 42° N 170° E. c, a 5.3 m-diameter boulder located at 57° N 304° E. d, a 5 m-diameter boulder located at 39° S 203° E. The images are from the global mosaic32 acquired by the PolyCam33 imager of OCAMS. Credit for PolyCam images: NASA/Goddard/University of Arizona.

Supplementary information

Peer Review File

Supplementary Table 1

This table contains 4 spreadsheets; properties of the OTES spots (including the unique data identifiers); two-component thermophysical solution for a regolith macroporosity of 40%; two-component thermophysical solution for a regolith macroporosity of 15%; two-component thermophysical solution for a regolith macroporosity of 60%.

Source data

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Cambioni, S., Delbo, M., Poggiali, G. et al. Fine-regolith production on asteroids controlled by rock porosity. Nature 598, 49–52 (2021).

Download citation


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