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.

Reconstructing the formation history of top-shaped asteroids from the surface boulder distribution


Finding the basic mechanism governing the surface history of asteroids of various shapes is essential for understanding their origin and evolution. In particular, the asteroids (162173) Ryugu1 and (101955) Bennu2 currently being visited by Hayabusa2 and OSIRIS-REx appear to be top shaped. This distinctive shape, characterized by a raised equatorial bulge, is shared by other similarly sized asteroids, including Didymos A3, 2008 EV54 and 1999 KW4 Alpha5. However, the possibly common formation mechanism that causes the top-like shape is still under debate. One clue may lie in the boulders on their surfaces. The distribution of these boulders, which was precisely measured in unprecedented detail by the two spacecraft1,2, constitutes a record of the geological evolution of the surface regolith since the origin of these asteroids. Here, we show that during the regolith migration driven by Yarkovsky–O’Keefe–Radzievskii–Paddack spin-up6,7,8,9 the surface boulders coevolve with the underlying regolith and exhibit diverse dynamical behaviours: they can remain undisturbed, sink into the regolith layer and become tilted, or be totally buried by the downslope deposition, depending on their latitudes. The predominant geological features commonly observed on top-shaped asteroids, including the boulder-rich region near the pole1,10, the deficiency of large boulders in the equatorial area10,11 and partially buried, oblique boulders exposed on the regolith surface12,13, are commensurate with this coevolution scenario. The surface regolith migration thus is the prevalent mechanism for the formation history of the top-shaped asteroids with stiffer cores.

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

Relevant articles

Open Access articles citing this article.

Access options

Rent or buy this article

Prices vary by article type



Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Asteroid morphological change during the YORP spin-up process.
Fig. 2: The simulated geomorphology.
Fig. 3: Visualization of the force networks excited by the creeping boulder.
Fig. 4: Typical landforms of boulders sculpted by YORP evolution.

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. Data used in Fig. 4d, e and f can be found at under image indexes hyb2_onc_20180831_101059_tvf_12a, hyb2_onc_20180801_160642_tnf_l2c and hyb2_onc_20180720_075208_tvf_l2b, respectively.

Code availability

The code used to generate the datasets is available from the corresponding authors on reasonable request.


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

    ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

  3. Benner, L. A. et al. Radar imaging and a physical model of binary asteroid 65803 Didymos. Bull. Am. Astron. Soc. 42, 1056 (2010).

  4. Busch, M. W. et al. Radar observations and the shape of near-Earth asteroid 2008 EV5. Icarus 212, 649–660 (2011).

    Article  ADS  Google Scholar 

  5. Ostro, S. J. et al. Radar imaging of binary near-Earth asteroid (66391) 1999 KW4. Science 314, 1276–1280 (2006).

    Article  ADS  Google Scholar 

  6. Walsh, K. J., Richardson, D. C. & Michel, P. Rotational breakup as the origin of small binary asteroids. Nature 454, 188–191 (2008).

    Article  ADS  Google Scholar 

  7. Hirabayashi, M., Sánchez, P. & Scheeres, D. J. Internal structure of asteroids having surface shedding due to rotational instability. Astrophys. J. 808, 63 (2015).

    Article  ADS  Google Scholar 

  8. Sánchez, P. & Scheeres, D. J. Rotational evolution of self-gravitating aggregates with cores of variable strength. Planet. Space Sci. 157, 39–47 (2018).

    Article  ADS  Google Scholar 

  9. Sánchez, P. & Scheeres, D. J. Cohesive regolith on fast rotating asteroids. Icarus 338, 113443 (2020).

    Article  Google Scholar 

  10. Michikami, T. et al. Boulder size and shape distributions on asteroid Ryugu. Icarus 331, 179–191 (2019).

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

  12. Sugita, S. et al. The geomorphology, color, and thermal properties of Ryugu: implications for parent-body processes. Science 364, 252 (2019).

    ADS  Google Scholar 

  13. 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).

    Article  ADS  Google Scholar 

  14. Cundall, P. A. & Strack, O. D. A discrete numerical model for granular assemblies. Géotechnique 29, 47–65 (1979).

    Google Scholar 

  15. Sánchez, P. & Scheeres, D. J. Simulating asteroid rubble piles with a self-gravitating soft-sphere distinct element method model. Astrophys. J. 727, 120 (2011).

    Article  ADS  Google Scholar 

  16. Schwartz, S. R., Richardson, D. C. & Michel, P. An implementation of the soft-sphere discrete element method in a high-performance parallel gravity tree-code. Granul. Matter 14, 363–380 (2012).

    Article  Google Scholar 

  17. Barnouin, O. S. et al. Shape of (101955) Bennu indicative of a rubble pile with internal stiffness. Nat. Geosci. 12, 247–252 (2019).

    Article  ADS  Google Scholar 

  18. Arakawa, M. et al. An artificial impact on the asteroid (162173) Ryugu formed a crater in the gravity-dominated regime. Science 368, 67–71 (2020).

    Article  ADS  Google Scholar 

  19. Wright, E. et al. Boulder stranding in ejecta launched by an impact generated seismic pulse. Icarus 337, 113424 (2020).

    Article  Google Scholar 

  20. Matsumura, S. et al. The Brazil nut effect and its application to asteroids. Mon. Not. R. Astron. Soc. 443, 3368–3380 (2014).

    Article  ADS  Google Scholar 

  21. Scheeres, D. J. et al. The dynamic geophysical environment of (101955) Bennu based on OSIRIS-REx measurements. Nat. Astron. 3, 352–361 (2019).

    Article  ADS  Google Scholar 

  22. Reddy, K., Forterre, Y. & Pouliquen, O. Evidence of mechanically activated processes in slow granular flows. Phys. Rev. Lett. 106, 108301 (2011).

    Article  ADS  Google Scholar 

  23. Germanovich, L. N., Kim, S. & Puzrin, A. M. Dynamic growth of slip surfaces in catastrophic landslides. Proc. Math. Phys. Eng. Sci. 472, 20150758 (2016).

    MathSciNet  MATH  Google Scholar 

  24. Nichol, K., Zanin, A., Bastien, R., Wandersman, E. & van Hecke, M. Flow-induced agitations create a granular fluid. Phys. Rev. Lett. 104, 078302 (2010).

    Article  ADS  Google Scholar 

  25. Walsh, K. J. et al. Bennu’s global geology. In Proc. 50th Lunar and Planetary Science Conference LPSC2019-1898 (LPI, 2019).

  26. Gray, J. M. N. T. Particle segregation in dense granular flows. Annu. Rev. Fluid Mech. 50, 407–433 (2018).

    Article  ADS  MathSciNet  Google Scholar 

  27. Michel, P. et al. Collisional formation of top-shaped asteroids and implications for the origins of Ryugu and Bennu. Nat. Commun. 11, 2655 (2020).

    Article  ADS  Google Scholar 

  28. Tardivel, S., Sánchez, P. & Scheeres, D. J. Equatorial cavities on asteroids, an evidence of fission events. Icarus 304, 192–208 (2018).

    Article  ADS  Google Scholar 

  29. Hirabayashi, M. et al. The western bulge of 162173 Ryugu formed as a result of a rotationally driven deformation process. Astrophys. J. Lett. 874, L10 (2019).

    Article  ADS  Google Scholar 

  30. Cheng, B., Yu, Y. & Baoyin, H. Numerical simulations of the controlled motion of a hopping asteroid lander on the regolith surface. Mon. Not. R. Astron. Soc. 485, 3088–3096 (2019).

    Article  ADS  Google Scholar 

  31. Somfai, E., Roux, J.-N., Snoeijer, J. H., Van Hecke, M. & Van Saarloos, W. Elastic wave propagation in confined granular systems. Phys. Rev. E 72, 021301 (2005).

    Article  ADS  Google Scholar 

  32. Zhang, Y. et al. Rotational failure of rubble-pile bodies: influences of shear and cohesive strengths. Astrophys. J. 857, 15 (2018).

    Article  ADS  Google Scholar 

  33. Peters, J. F., Muthuswamy, M., Wibowo, J. & Tordesillas, A. Characterization of force chains in granular material. Phys. Rev. E 72, 041307 (2005).

    Article  ADS  Google Scholar 

  34. Hayabusa2 Optical Navigation Camera (ONC) Dataset (JAXA Data Archives and Transmission System (DARTS), 2019);

Download references


This work is funded by the National Science Fund for Distinguished Young Scholars of China (no. 11525208). Y.Y. acknowledges support from the Natural Science Foundation of China (no. 11702009). P.M. acknowledges funding from the French space agency CNES, from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 870377 (project NEO-MAPP) and from Academies of Excellence: Complex systems and space, environment, risk, and resilience, part of the IDEX JEDI of the Université Côte d’Azur. We acknowledge support from the JSPS Core-to-Core programme ‘International Network of Planetary Sciences’. We are grateful to the Hayabusa2 ONC team for providing images, which are available at the JAXA Data Archives and Transmission System (DARTS) at

Author information

Authors and Affiliations



B.C. performed the soft-sphere numerical simulations and analysed the numerical results. H.B. and Y.Y. initiated the project, designed the simulations and led the research. E.A. and D.C.R. contributed to the discussion of the two-layer model and the creeping process. M.H. provided essential comments on the interior structure and deformation. P.M. initiated the collaboration between the institutions with Y.Y. and provided outstanding questions on the scope of the research with M.Y. All authors contributed to interpretation of the results and preparation of the manuscript.

Corresponding authors

Correspondence to Yang Yu or Hexi Baoyin.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature Astronomy thanks David Polishook and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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

Supplementary information

Supplementary Information

Supplementary methods, Tables 1 and 2 and Figs. 1–7.

Supplementary Video 1

Moderate friction. 75° LBx boulder. Coloured by slip heat.

Supplementary Video 2

Moderate friction. 75° LBx boulder. Coloured by latitude.

Supplementary Video 3

Moderate friction. 87° LBx boulder. Coloured by latitude.

Supplementary Video 4

Moderate friction. 45° LBx boulder. Coloured by latitude.

Supplementary Video 5

Moderate friction. 15° LBx boulder. Coloured by latitude.

Supplementary Video 6

Gravel-like friction. 75° LBx boulder. Coloured by latitude.

Supplementary Video 7

Moderate friction. Regolith bed with width of 160 m.

Supplementary Video 8

Moderate friction. Regolith bed with wedge-shaped boundaries.

Supplementary Video 9

Moderate friction. Regolith bed of both hemispheres.

Supplementary Video 10

Moderate friction. 45° LBx boulder initially buried in regolith.

Supplementary Video 11

Moderate friction. 15° LBx boulder initially buried in regolith.

Supplementary Video 12

Moderate friction. Multiple boulders.

Rights and permissions

Reprints and Permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Cheng, B., Yu, Y., Asphaug, E. et al. Reconstructing the formation history of top-shaped asteroids from the surface boulder distribution. Nat Astron 5, 134–138 (2021).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:


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