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# Bennu’s near-Earth lifetime of 1.75 million years inferred from craters on its boulders

## Abstract

An asteroid’s history is determined in large part by its strength against collisions with other objects1,2 (impact strength). Laboratory experiments on centimetre-scale meteorites3 have been extrapolated and buttressed with numerical simulations to derive the impact strength at the asteroid scale4,5. In situ evidence of impacts on boulders on airless planetary bodies has come from Apollo lunar samples6 and images of the asteroid (25143) Itokawa7. It has not yet been possible, however, to assess directly the impact strength, and thus the absolute surface age, of the boulders that constitute the building blocks of a rubble-pile asteroid. Here we report an analysis of the size and depth of craters observed on boulders on the asteroid (101955) Bennu. We show that the impact strength of metre-sized boulders is 0.44 to 1.7 megapascals, which is low compared to that of solid terrestrial materials. We infer that Bennu’s metre-sized boulders record its history of impact by millimetre- to centimetre-scale objects in near-Earth space. We conclude that this population of near-Earth impactors has a size frequency distribution similar to that of metre-scale bolides and originates from the asteroidal population. Our results indicate that Bennu has been dynamically decoupled from the main asteroid belt for 1.75 ± 0.75 million years.

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## Data availability

OCAMS images and OLA data from the Orbital A, Detailed Survey and Orbital B phases of the OSIRIS-REx mission are available in the Planetary Data System at https://sbn.psi.edu/pds/resource/orex/. Measured dimensions and locations of craters and host boulders are available in Extended Data Tables 1, 2 and Supplementary Table 1.

## Code availability

The Small Body mapping tool is available at http://sbmt.jhuapl.edu/.

## References

1. Michel, P. et al. Collisions and gravitational reaccumulation: forming asteroid families and satellites. Science 294, 1696–1700 (2001).

2. Bottke, W. F. et al. Linking the collisional history of the main asteroid belt to its dynamical excitation and depletion. Icarus 179, 63–94 (2005).

3. Flynn, G. J. et al. Physical properties of the stone meteorites: implications for the properties of their parent bodies. Chem. Erde 78, 269–298 (2018).

4. Benz, W. & Asphaug, E. Catastrophic disruptions revisited. Icarus 142, 5–20 (1999).

5. Jutzi, M. et al. Fragment properties at the catastrophic disruption threshold: the effect of the parent body’s internal structure. Icarus 207, 54–65 (2010).

6. Grün, E. et al. Collisional balance of the meteoritic complex. Icarus 62, 244–272 (1985).

7. Nakamura, A. M. et al. Impact process of boulders on the surface of asteroid 25143 Itokawa—fragments from collisional disruption. Earth Planets Space 60, 7–12 (2008).

8. Golish, D. R. et al. Ground and In-Flight Calibration of the OSIRIS-REx Camera Suite. Space Sci. Rev. 216, 12 (2020).

9. 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).

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

11. Murakami, Y. et al. Collisional disruption of highly porous targets in the strength regime: effects of mixture. Planet. Space Sci. 182, 104819 (2020).

12. Housen, K. Cumulative damage in strength-dominated collisions of rocky asteroids: rubble piles and brick piles. Planet. Space Sci. 57, 142–153 (2009).

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

14. Holsapple, K. A. & Schmidt, R. M. Point source solutions and coupling parameters in cratering mechanics. J. Geophys. Res. 92, 6350–6376 (1987).

15. Housen, K. R. & Holsapple, K. A. Ejecta from impact craters. Icarus 211, 856–875 (2011).

16. Nakamura, A. M. et al. Size dependence of the disruption threshold: laboratory examination of millimeter-centimeter porous targets. Planet. Space Sci. 107, 45–52 (2015).

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

18. Yasui, M. Effects of oblique impacts on the impact strength of porous gypsum and glass spheres: implications for the collisional disruption of planetesimals in thermal evolution. Icarus 335, 113414 (2020).

19. Holsapple, K. A. On the “strength” of the small bodies of the solar system: a review of strength theories and their implementation for analyses of impact disruptions. Planet. Space Sci. 57, 127–141 (2009).

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

21. Jenniskens, P. et al. Radar-enabled recovery of the Sutter’s Mill meteorite, a carbonaceous chondrite regolith breccia. Science 338, 1583–1587 (2012).

22. Brown, P. G. et al. An entry model for the Tagish Lake fireball using seismic, satellite and infrasound records. Meteorit. Planet. Sci. 37, 661–675 (2002).

23. Brown, P. et al. The flux of small near-Earth objects colliding with the Earth. Nature 420, 294–296 (2002).

24. Avdellidou, C. & Vaubaillon, J. Temperatures of lunar impact flashes: mass and size distribution of small impactors hitting the Moon. Mon. Not. R. Astron. Soc. 484, 5212–5222 (2019).

25. Kawamura, T. et al. Cratering asymmetry on the Moon: new insight from the Apollo Passive Seismic Experiment. Geophys. Res. Lett. 38, 15201 (2011).

26. Hörz, F. et al. Catastrophic rupture of lunar rocks: a Monte Carlo simulation. Moon 13, 235–258 (1975).

27. Pokorný, P. & Brown, P. G. A reproducible method to determine the meteoroid mass index. Astron. Astrophys. 592, A150 (2016).

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

29. Moorhead, A. V. Deconvoluting measurement uncertainty from the meteor speed distribution. Meteorit. Planet. Sci. 53, 1292–1298 (2018).

30. Nesvorný, D. et al. Cometary origin of the zodiacal cloud and carbonaceous micrometeorites. Implications for hot debris disks. Astrophys. J. 713, 816–836 (2010).

31. Michel, P. & Delbo, M. Orbital and thermal evolutions of four potential targets for a sample return space mission to a primitive near-Earth asteroid. Icarus 209, 520–534 (2010).

32. Molaro, J. L. et al. In situ evidence of thermally induced rock breakdown widespread on Bennu’s surface. Nat. Commun. 11, 2913 (2020).

33. Walsh, K. J. et al. Craters, boulders and regolith of (101955) Bennu indicative of an old and dynamic surface. Nat. Geosci. 12, 242–246 (2019); publisher correction 12, 399 (2019).

34. Britt, D. T. et al. Simulated asteroid materials based on carbonaceous chondrite mineralogies. Meteorit. Planet. Sci. 54, 2067–2082 (2019).

35. Nakamura, A. M. Impact cratering on porous targets in the strength regime. Planet. Space Sci. 149, 5–13 (2017).

36. Jutzi, M., Benz, W. & Michel, P. Numerical simulations of impacts involving porous bodies. I. Implementing sub-resolution porosity in a 3D SPH hydrocode. Icarus 198, 242–255 (2008).

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

38. Poelchau, M. H. et al. The MEMIN research unit: scaling impact cratering experiments in porous sandstones. Meteorit. Planet. Sci. 48, 8–22 (2013).

39. Housen, K. R. & Holsapple, K. A. On the fragmentation of asteroids and planetary satellites. Icarus 84, 226–253 (1990).

40. Housen, K. R. & Holsapple, K. A. Scale effects in strength-dominated collisions of rocky asteroids. Icarus 142, 21–33 (1999).

41. Holsapple, K. A. On the existence and implications of coupling parameters in cratering mechanics. In Lunar and Planetary Science Conference Vol. 14, 319–320 (Lunar and Planetary Institute, 1983).

42. Holsapple, K. A. The scaling of impact processes in planetary sciences. Annu. Rev. Earth Planet. Sci. 21, 333–373 (1993).

43. Holsapple, K. A. & Housen, K. R. Craters from impacts and explosions. V2.2.1 http://keith.aa.washington.edu/craterdata/scaling/theory.pdf (Washington Univ., 2017).

44. Holsapple, K. A. Catastrophic disruptions and cratering of solar system bodies: a review and new results. Planet. Space Sci. 42, 1067–1078 (1994).

45. Suzuki, A. I. et al. Increase in cratering efficiency with target curvature in strength-controlled craters. Icarus 301, 1–8 (2018).

46. Leinhardt, Z. M. & Stewart, S. T. Collisions between gravity-dominated bodies. I. Outcome regimes and scaling laws. Astrophys. J. 745, 79 (2012).

47. Leliwa-Kopystyński, J. et al. Impact cratering and break up of the small bodies of the Solar System. Icarus 195, 817–826 (2008).

48. Schenk, P. et al. The geologically recent giant impact basins at Vesta’s south pole. Science 336, 694–697 (2012).

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

50. Bennett, C. et al. A high-resolution global basemap of (101955) Bennu. Icarus (in the press).

51. Barnouin, O. S. et al. Shape of (101955) Bennu indicative of a rubble pile with internal stiffness. Nat. Geosci. 12, 247–252 (2019); author correction https://doi.org/10.1038/s41561-020-0643-9 (2020).

52. Ernst, C. M. et al. The Small Body Mapping Tool (SBMT) for accessing, visualizing, and analyzing spacecraft data in three dimensions. In Lunar and Planetary Science Conference Vol. 49, 1043 (Lunar and Planetary Institute, 2018).

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

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

55. Seabrook, J. A. et al. Global shape modeling using the OSIRIS-REx scanning Laser Altimeter. Planet. Space Sci. 177, 104688 (2019).

56. Farrance, I. & Frankel, R. Uncertainty of measurement: a review of the rules for calculating uncertainty components through functional relationships. Clin. Biochem. Rev. 33, 49–75 (2012).

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## Acknowledgements

We thank D. P. Hamilton, K. A. Holsapple and P. Pravec for insights and feedback. This material is based upon 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. M.D., C.A. and P.M. 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. P.M. acknowledges funding support from the European Union’s Horizon 2020 research and innovation program under grant agreement number 870377 (project NEO-MAPP) and from Academies of Excellence: Complex Systems and Space, Environment, Risk, and Resilience, part of the IDEX JEDI of Université Côte d’Azur. M.P. was supported by the Italian Space Agency (ASI) under ASI-INAF agreement number 2017-37-H.0. S.R.S. is supported by contract number 80NSSC18K0226 as part of the OSIRIS-REx Participating Scientist Program.

## Author information

Authors

### Contributions

R.-L.B. led the conceptualization of the study, the images and OLA data analysis, construction of the analytical formalism to measure boulder impact strength from crater sizes, the interpretation of results, and manuscript preparation efforts. K.J.W. contributed to the conceptualization of the study, the interpretation of results, and manuscript preparation efforts. O.S.B. created OLA DTMs of boulders, measured crater dimensions with these products, contributed to the interpretation of results and the preparation of the manuscript. D.N.D., E.R.J. and C.A.B. provided GIS guidance and expertise, contributed to the image analysis, interpretation of the results and the preparation of the manuscript. M.A.A., M.G.D. and R.T.D. contributed to the OLA data analysis, interpretation of the results and the preparation of the manuscript. W.F.B., P.M., C.A., M.D., J.L.M., E.A., E.B.B., M.C.N., M.P., H.C.C. Jr, S.R.S., D.T. and C.W.V.W. contributed to the interpretation of the results and the preparation of the manuscript. B.R. and D.R.G. processed the PolyCam images presented in the manuscript. D.S.L. leads the mission and contributed to the analysis and writing.

### Corresponding author

Correspondence to R.-L. Ballouz.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

## Additional information

Peer review information Nature thanks Dan Britt and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.

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## Extended data figures and tables

### Extended Data Fig. 1 Examples of boulders with craters and OLA profiles of the craters.

Boulders are outlined with dashed orange polygons. Craters are outlined with dashed white circles. The crater profile shown below each image corresponds to the dashed yellow line, with the letters A (start) and B (end) in the image indicating the direction of the corresponding profile (from left to right). a, Boulder 1 (image 20190328T191143S208_pol) has a circle-equivalent diameter of 2.9 m and an OLA-measured crater diameter of 1.21 ± 0.09 m. b, Boulder 2 (image 20190328T182010S618_pol) has a circle-equivalent diameter of 3.06 m and an OLA-measured crater diameter of 1.24 ± 0.07 m. c, Boulder 3 (image 20190329T205259S821_pol) has a circle-equivalent diameter of 4.24 m and an OLA-measured crater diameter of 1.60 ± 0.13 m. d, Boulder 4 (image 20190321T185825S567_pol) has a circle-equivalent diameter of 11.3 m and an OLA-measured crater diameter of 4.18 ± 0.47 m.

## Supplementary information

### 41586_2020_2846_MOESM1_ESM.pdf

Supplementary Table 1 Dimensions of craters and their host boulders. We tabulate the locations of boulders with craters and their dimensions based on shape model–projected images with pixel scales of 5 cm. We measure their largest crater radius $${R}_{{\rm{c}}}$$, the boulder areal extent $${A}_{{\rm{b}}}$$, and the ratio of the crater radius to the host boulder circle-equivalent radius $${R}_{{\rm{c}}}/{R}_{{\rm{t}}}$$. We assume 3-pixel uncertainties (15 cm) for these measurements.

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### Cite this article

Ballouz, RL., Walsh, K.J., Barnouin, O.S. et al. Bennu’s near-Earth lifetime of 1.75 million years inferred from craters on its boulders. Nature 587, 205–209 (2020). https://doi.org/10.1038/s41586-020-2846-z

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