Skip to main content


Size-frequency statistics of boulders on global surface of asteroid 25143 Itokawa


The surface of asteroid 25143 Itokawa is covered with numerous boulders although gravity is very small compared with that of other asteroids previously observed from spacecraft. Here we report the size-frequency statistics of boulders on the entire surface of Itokawa based on high-resolution images (1 pixel ≈0.4 m) obtained by the Hayabusa spacecraft. There are 373 boulders larger than 5 m in mean horizontal dimension on the entire surface—0.393 km2—and the number density is nearly 103/km2. The cumulative boulder size distribution on the entire surface has a power-index of −3.1 ± 0.1. For the east and west sides and the head and body portions of Itokawa, the power-index of the size distributions and the number densities of boulders of these areas are thought to be similar from the statistical point of view. A global mapping of boulders shows that there is no apparent correlation in the locations of boulders and craters. The ratio of the total volume of the boulders to the total excavated volume of the craters on Itokawa is ≈25% when only craters larger than 50 m in mean diameter are considered, and this ratio is extremely larger than that on Eros and the Moon, respectively. The origin of boulders on the surface of Itokawa was examined quantitatively by calculating the number of boulders and the size of the largest boulder using a model based on impact cratering experiments. The result indicated that the boulders on the surface of Itokawa cannot solely be the product of craters. Our results suggest that the boulders originated from the disruption of the larger parent body of Itokawa, as has been described in previous papers (Fujiwata et al., Science, 312, 1330–1334, 2006; Saito et al., Science, 312, 1341–1344, 2006).


  1. Abe, S., T. Mukai, N. Hirata, O. S. Barnouin-Jha, A. F. Cheng, H. Demura, R. W. Gaskell, T. Hashimoto, K. Hiraoka, T. Honda, T. Kubota, M. Matsuoka, T. Mizuno, R. Nakamura, D. Scheeres, and M. Yoshikawa, Mass and local topography measurements of Itokawa by Hayabusa, Science, 312, 1344–1347, 2006.

  2. Britt, D. T., D. Yeomans, K. Housen, and G. Consolmagno, Asteroid density, porosity, and structure, Asteroid III (Univ. Arizona Press), 485–500, 20

  3. Cintala, M. J. and K. M. McBride, Block distributions on the lunar surface: A comparison between measurements obtained from surface and orbital photography, NASA Technical Memorandum 104804, NASA, Washington D.C., 1995.

  4. Cintala, M. J., J. B. Garvin, and S. J. Wetzel, The distribution of blocks around a fresh lunar mare crater, Proc. Lunar Planet. Sci. Conf., 13, 100–101, 1982.

  5. Colwell, J. E., Power-law confusion: You say incremental, I say differential, Lunar Planet. Sci. Conf., 24, abstr. 325–326, 1993.

  6. Demura, H., S. Kobayashi, E. Nemoto, N. Matsumoto, M. Furuya, A. Yukishita, N. Muranaka, H. Morita, K. Shirakawa, M. Maruya, H. Ohyama, M. Uo, T. Kubota, T. Hashimoto, J. Kawaguchi, A. Fujiwara, J. Saito, S. Sasaki, H. Miyamoto, and N. Hirata, Pole and global shape of 25143 Itokawa, Science, 312, 1347–1349, 2006.

  7. Dombard, A. J. and A. M. Freed, Thermal stresses on asteroids: application to Eros, American Geophysical Union, Spring Meeting, abstract #P22B-02, 2001.

  8. Fujiwara, A., J. Kawaguchi, D. K. Yeomans, M. Abe, T. Mukai, T. Okada, J. Saito, H. Yano, M. Yoshikawa, D. J. Scheeres, O. Barnouin-Jha, A. F. Cheng, H. Demura, R.W. Gaskell, N. Hirata, H. Ikeda, T. Kominato, H. Miyamoto, A. M. Nakamura, R. Nakamura, S. Sasaki, and K. Uesugi, The rubble-pile asteroid Itokawa as observed by Hayabusa, Science, 312, 1330–1334, 2006.

  9. Gaskell, R. W., O. S. Barnoiun-Jha, and D. J. Scheeres, Characterizing small bodies from imaging data, AGU Fall Meeting Abstracts, #G52B- 03, 2006.

  10. Geissler, P., J. M. Petit, and R. Greenberg, Ida: Distribution and origin of surface blocks, Lunar Planet. Sci. Conf., 25, abstr. 411–412, 1994.

  11. Geissler, P., J. M. Petit, and R. Greenberg, Ejecta reaccretion on rapidly rotating asteroid: Implications for 243 Ida and 433 Eros, Proc. Astron. Soc. Pacific, 107, 57–67, 1996a.

  12. Geissler, P., J. M. Petit, D. D. Durda, R. Greenberg, W. Bottke, M. Nolan, and J. Moore, Erosion and Ejecta Reaccretion on 243 Ida and Its Moon, Icarus, 120, 140–157, 1996b.

  13. Housen, K. R., Crater ejecta velocities for impact on rocky bodies, Lunar Planet. Sci. Conf., 23, abstr. 555–556, 1992.

  14. Housen, K. R. and K. A. Holsapple, Impact cratering on porous asteroids, Icarus, 163, 102–119, 2003.

  15. Housen, K. R., R. M. Schmidt, and K. A. Holsapple, Crater Ejection Scaling Laws: Fundamental forms based on dimensional analysis, J. Geophys. Res., 88, 2485–2499, 1983.

  16. Hirata, N. and A. M. Nakamura, Secondary craters of Tycho: Sizefrequency distributions and estimated fragment size-velocity relationships, J. Geophys. Res., 111, E03005, 2006.

  17. Hirata, N., C. Honda, R. Nakamura, H. Miyamoto, S. Sasaki, H. Demura, A. M. Nakamura, T. Michikami, O. S. Barnouin-Jha, R.W. Gaskell, and J. Saito, Survey of craters and impact structures on the Asteroid Itokawa, Lunar Planet. Sci. Conf., 38, abstr. 1572–1573, 2007.

  18. Lee, S. W., P. C. Thomas, and J. Veverka, Phobos, Deimos, and the Moon: Size and distribution of crater ejecta blocks, Icarus, 68, 77–86, 1986.

  19. Lee, P., J. Veverka, P. C. Thomas, P. Helfenstein, M. J. S. Belton, C. R. Chapman, R. Greeley, R. T. Pappalardo, R. Sullivan, and J. W. Head, Ejecta blocks on 243 Ida and on other asteroids, Icarus, 120, 87–105, 1996.

  20. Melosh, H. J., Impact ejection, spallation, and the origin of meteorites, Icarus, 59, 234–260, 1984.

  21. Michikami, T., Evolution of Asteroid regolith layers by cratering, PhD Thesis, University of Tokyo, 2001.

  22. Michikami, T., K. Moriguchi, and R. Nakamura, Application to Large Blocks on Asteroid 25143 Itokawa: Ejecta Mass Distribution with Low Velocity for Impact Cratering Experiment on Porous Target, Lunar Planet. Sci. Conf., 36, abstr. 1729–1730, 2005.

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

  24. Miyamoto, H., H. Yano, D. J. Scheeres, S. Abe, O. Barnouin-Jha, A. F. Cheng, H. Demura, R. W. Gaskell, N. Hirata, M. Ishiguro, T. Michikami, A. M. Nakamura, R. Nakamura, J. Saito, and S. Sasaki, Regolith Migration and Sorting on Asteroid Itokawa, Science, 316, 1011–1014, 2

  25. Saito, J., H. Miyamoto, R. Nakamura, M. Ishiguro, T. Michikami, A. M. Nakamura, H. Demura, S. Sasaki, N. Hirata, C. Honda, A. Yamamoto, Y. Yokota, T. Fuse, F. Yoshida, D. J. Tholen, R. W. Gaskell, T. Hashimoto, T. Kubota, Y. Higuchi, T. Nakamura, P. Smith, K. Hiraoka, T. Honda, S. Kobayashi, M. Furuya, N. Matsumoto, E. Nemoto, A. Yukishita, K. Kitazato, B. Dermawan, A. Sogame, J. Terazono, C. Shinohara, and H. Akiyama, Detailed images of asteroid 25143 Itokawa from Hayabusa, Science, 312, 1341–1344, 2006.

  26. Thomas, P. C., J. Veverka, A. Bloom, and T. Duxbury, Grooves on Phobos: Their distribution, morphology, and possible origin, J. Geophys. Res., 84, 8457–8477, 1979.

  27. Thomas, P. C., J. Veverka, R. Sullivan, D. P. Simonelli, M. C. Malin, M. Caplinger, W. K. Hartmann, and P. B. James, Phobos: regolith and ejecta blocks investigated with Mars Orbiter Camera images, J. Geophys. Res., 105, 15091–15106, 2000.

  28. Thomas, P. C., J. Veverka, M. S. Robinson, and S. Murchie, Shoemaker crater as the source of most ejecta blocks on the asteroid 433 Eros, Nature, 413, 394–396, 2001.

Download references

Author information

Correspondence to Tatsuhiro Michikami.

Rights and permissions

This article is published under an open access license. Please check the 'Copyright Information' section for details of this license and what re-use is permitted. If your intended use exceeds what is permitted by the license or if you are unable to locate the licence and re-use information, please contact the Rights and Permissions team.

About this article

Cite this article

Michikami, T., Nakamura, A.M., Hirata, N. et al. Size-frequency statistics of boulders on global surface of asteroid 25143 Itokawa. Earth Planet Sp 60, 13–20 (2008).

Download citation

Key words

  • Boulder
  • size distribution
  • Itokawa
  • asteroid