Letter | Published:

Acceleration of the rotation of asteroid 1862 Apollo by radiation torques

Nature volume 446, pages 420422 (22 March 2007) | Download Citation

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Abstract

The anisotropic reflection and thermal re-emission of sunlight from an asteroid’s surface acts as a propulsion engine. The net propulsion force (Yarkovsky effect) changes the orbital dynamics of the body at a rate that depends on its physical properties; for irregularly shaped bodies, the propulsion causes a net torque (the Yarkovsky–O'Keefe–Radzievskii–Paddack or YORP effect) that can change the object’s rotation period and the direction of its rotation axis1,2. The Yarkovsky effect has been observed directly3, and there is also indirect evidence of its role in the orbital evolution of asteroids over long time intervals4,5,6. So far, however, only indirect evidence exists for the YORP effect through the clustering of the directions of rotation axes in asteroid families6,7,8. Here we report a change in the rotation rate of the asteroid 1862 Apollo, which is best explained by the YORP mechanism. The change is fairly large and clearly visible in photometric lightcurves, amounting to one extra rotation cycle in just 40 years even though Apollo’s size is well over one kilometre. This confirms the prediction that the YORP effect plays a significant part in the dynamical evolution of asteroids.

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Acknowledgements

We thank D. Vokrouhlický for assistance and discussions, P. Pravec for Apollo data, and W. Bottke and A. Harris for comments. The work of M.K. was supported by the Academy of Finland, that of J.Ď. by the Grant Agency of the Czech Republic, and that of Y.N.K. and N.M.G. by the Ministry of Education and Science of the Ukraine.

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Affiliations

  1. Department of Mathematics and Statistics, Rolf Nevanlinna Institute, PO Box 68, FI-00014 University of Helsinki, Finland

    • Mikko Kaasalainen
  2. Astronomical Institute, Charles University, V Holešovičkách 2, 18000 Prague, Czech Republic

    • Josef Ďurech
  3. Palmer Divide Observatory, Colorado Springs, Colorado 80908, USA

    • Brian D. Warner
  4. Institute of Astronomy of Kharkiv National University, Sumska str. 35, Kharkiv 61022, Ukraine

    • Yurij N. Krugly
  5. Crimean Astrophysical Observatory, Simeiz 98680, Ukraine

    • Ninel M. Gaftonyuk

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Competing interests

Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests.

Corresponding author

Correspondence to Mikko Kaasalainen.

Supplementary information

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  1. 1.

    Supplementary Information

    This file contains Supplementary Table S1 (observations of Apollo) and Supplementary Figures S1-S4 illustrating Apollo lightcurves (S1), Apollo shape model (S2), simulated YORP behaviour of the model (S3), orbital evolution of Apollo( S4).

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https://doi.org/10.1038/nature05614

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