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.

Formation of asteroid pairs by rotational fission


Pairs of asteroids sharing similar heliocentric orbits, but not bound together, were found recently1,2,3. Backward integrations of their orbits indicated that they separated gently with low relative velocities, but did not provide additional insight into their formation mechanism. A previously hypothesized rotational fission process4 may explain their formation—critical predictions are that the mass ratios are less than about 0.2 and, as the mass ratio approaches this upper limit, the spin period of the larger body becomes long. Here we report photometric observations of a sample of asteroid pairs, revealing that the primaries of pairs with mass ratios much less than 0.2 rotate rapidly, near their critical fission frequency. As the mass ratio approaches 0.2, the primary period grows long. This occurs as the total energy of the system approaches zero, requiring the asteroid pair to extract an increasing fraction of energy from the primary's spin in order to escape. We do not find asteroid pairs with mass ratios larger than 0.2. Rotationally fissioned systems beyond this limit have insufficient energy to disrupt. We conclude that asteroid pairs are formed by the rotational fission of a parent asteroid into a proto-binary system, which subsequently disrupts under its own internal system dynamics soon after formation.

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

Get just this article for as long as you need it


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

Figure 1: Primary rotation periods P 1 versus mass ratios q of asteroid pairs.
Figure 2: A disparity between the lightcurve amplitudes of the primary components in asteroid pairs and binary systems.


  1. Vokrouhlický, D. & Nesvorný, D. Pairs of asteroids probably of a common origin. Astron. J. 136, 280–290 (2008)

    Article  ADS  Google Scholar 

  2. Pravec, P. & Vokrouhlický, D. Significance analysis of asteroid pairs. Icarus 204, 580–588 (2009)

    Article  ADS  Google Scholar 

  3. Vokrouhlický, D. & Nesvorný, D. The common roots of asteroids (6070) Rheinland and (54827) 2001 NQ8. Astron. J. 137, 111–117 (2009)

    Article  ADS  Google Scholar 

  4. Scheeres, D. J. Rotational fission of contact binary asteroids. Icarus 189, 370–385 (2007)

    Article  ADS  Google Scholar 

  5. Milani, A., Knežević, Z., Novaković, B. & Cellino, A. Dynamics of the Hungaria asteroids. Icarus 207, 769–794 (2010)

    Article  ADS  Google Scholar 

  6. Pravec, P. & Harris, A. W. Binary asteroid population. 1. Angular momentum content. Icarus 190, 250–259 (2007)

    Article  ADS  Google Scholar 

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

    Article  ADS  CAS  Google Scholar 

  8. Scheeres, D. J. Stability of the planar full 2-body problem. Celest. Mech. Dyn. Astron. 104, 103–128 (2009)

    Article  ADS  MathSciNet  Google Scholar 

  9. Scheeres, D. J. Stability in the full two-body problem. Celest. Mech. Dyn. Astron. 83, 155–169 (2002)

    Article  ADS  MathSciNet  Google Scholar 

  10. Warner, B. D., Harris, A. W. & Pravec, P. The asteroid lightcurve database. Icarus 202, 134–146 (2009)

    Article  ADS  Google Scholar 

  11. Scheeres, D. J. Minimum energy asteroid reconfigurations and catastrophic disruptions. Planet. Space Sci. 57, 154–164 (2009)

    Article  ADS  Google Scholar 

  12. Bottke, W. F., Jr, Vokrouhlický, D., Rubincam, D. P. & Nesvorný, D. The Yarkovsky and Yorp effects: implications for asteroid dynamics. Annu. Rev. Earth Planet. Sci. 34, 157–191 (2006)

    Article  ADS  CAS  Google Scholar 

  13. Warner, B. D. Asteroid lightcurve analysis at the Palmer Divide Observatory: 2008 May – September. Minor Planet Bull. 36, 7–13 (2009)

    ADS  Google Scholar 

  14. Galád, A., Kornoš, L. & Világi, J. An ensemble of lightcurves from Modra. Minor Planet Bull. 37, 9–15 (2009)

    ADS  Google Scholar 

Download references


Research at Ondřejov was supported by the Grant Agency of the Czech Republic. D.V. was supported by the Czech Ministry of Education. D.P. was supported by an Ilan Ramon grant from the Israeli Ministry of Science, and is grateful for the guidance of N. Brosch and D. Prialnik. D.J.S. and S.A.J. acknowledge support by NASA's PG&G and OPR research programs. A.W.H. was supported by NASA and NSF. Work at Modra Observatory was supported by the Slovak Grant Agency for Science. The observations at Cerro Tololo were performed with the support of CTIO and J. Vasquez, using telescopes operated by the SMARTS Consortium. Work at Pic du Midi Observatory was supported by CNRS, Programme de Planétologie. Operations at Carbuncle Hill Observatory were supported by the Planetary Society’s Gene Shoemaker NEO Grant. Support for PROMPT has been provided by the NSF. F.M. and B.M. were supported by the NSF. We thank O. Bautista, T. Moulinier and P. Eclancher for assistance with observations with the T60 on Pic du Midi.

Author information

Authors and Affiliations



This work was a team effort; here we specify only the most important contributions by individual authors. P.P. led the project and worked on most of its parts, except Supplementary Information sections 1 and 4. D.V. performed the backward orbit integrations and contributed to interpretations of the results. D.P. ran the observations and data reduction, and contributed to interpretations. D.J.S. developed the fission theory and worked out its implications for the observational data. A.W.H. contributed to interpretations and implications of the data. A.G., O.V., F.P., A.B., P.L., F.V., F.C., D.P.P., J.P., D.R., K.I., J.H., A.L., P.K., T.H., F.M., B.M., Yu.N.K., A.V.S. and A.L. carried out the observations, data reduction and analyses. S.A.J. ran simulations of the satellite ejection process in a proto-binary after fission.

Corresponding author

Correspondence to P. Pravec.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Figures 1- 45 with Legends, Supplementary Methods, Supplementary Data, Supplementary Discussions 1-2 with additional References and Supplementary Tables 1-2. (PDF 10292 kb)

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Pravec, P., Vokrouhlický, D., Polishook, D. et al. Formation of asteroid pairs by rotational fission. Nature 466, 1085–1088 (2010).

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI:

This article is cited by


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