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Originally published in Science Express on 8 March 2007
Science 13 April 2007:
Vol. 316. no. 5822, pp. 272 - 274
DOI: 10.1126/science.1139040
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Reports

Direct Detection of the Asteroidal YORP Effect

Stephen C. Lowry,1* Alan Fitzsimmons,1 Petr Pravec,2 David Vokrouhlicky,3 Hermann Boehnhardt,4 Patrick A. Taylor,5 Jean-Luc Margot,5 Adrian Galád,6 Mike Irwin,7 Jonathan Irwin,7 Peter Kusnirák2

The Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect is believed to alter the spin states of small bodies in the solar system. However, evidence for the effect has so far been indirect. We report precise optical photometric observations of a small near-Earth asteroid, (54509) 2000 PH5, acquired over 4 years. We found that the asteroid has been continuously increasing its rotation rate {omega} over this period by d{omega}/dt = 2.0 (±0.2) x 10–4 degrees per day squared. We simulated the asteroid's close Earth approaches from 2001 to 2005, showing that gravitational torques cannot explain the observed spin rate increase. Dynamical simulations suggest that 2000 PH5 may reach a rotation period of ~20 seconds toward the end of its expected lifetime.

1 School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, UK.
2 Astronomical Institute, Academy of Sciences of the Czech Republic, Fricova 1, CZ-25165 Ondrejov, Czech Republic.
3 Institute of Astronomy, Charles University, V Holesovickách 2, 18000 Prague 8, Czech Republic.
4 Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany.
5 Department of Astronomy, Cornell University, Ithaca, NY 14853, USA.
6 Department of Astronomy, Physics of the Earth, and Meteorology, Faculty of Mathematics, Physics and Informatics, Comenius University, 842 48 Bratislava, Slovakia.
7 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK.

* To whom correspondence should be addressed. E-mail: s.c.lowry{at}qub.ac.uk

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Spin Rate of Asteroid (54509) 2000 PH5 Increasing Due to the YORP Effect.
P. A. Taylor, J.-L. Margot, D. Vokrouhlicky, D. J. Scheeres, P. Pravec, S. C. Lowry, A. Fitzsimmons, M. C. Nolan, S. J. Ostro, L. A. M. Benner, et al. (2007)
Science 316, 274-277
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Science. ISSN 0036-8075 (print), 1095-9203 (online)