Retrograde spins of near-Earth asteroids from the Yarkovsky effect


Dynamical resonances in the asteroid belt are the gateway for the production of near-Earth asteroids1 (NEAs). To generate the observed number of NEAs, however, requires the injection of many asteroids into those resonant regions. Collisional processes have long been claimed as a possible source1,2,3, but difficulties with that idea have led to the suggestion that orbital drift arising from the Yarkovsky effect4,5,6,7 dominates the injection process8,9,10. (The Yarkovsky effect is a force arising from differential heating—the ‘afternoon’ side of an asteroid is warmer than the ‘morning’ side.) The two models predict different rotational properties of NEAs: the usual collisional theories2 are consistent with a nearly isotropic distribution of rotation vectors, whereas the ‘Yarkovsky model’ predicts an excess of retrograde rotations. Here we report that the spin vectors of NEAs show a strong and statistically significant excess of retrograde rotations, quantitatively consistent with the theoretical expectations of the Yarkovsky model.

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Figure 1: Latitude distributions for main belt asteroids and NEAs.


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This work was supported by MIUR (Italy), KBN (Poland) and the Academy of Sciences (Czech Republic). We thank D. Vokrouhlicky and S. Shore for comments and suggestions.

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Correspondence to P. Paolicchi.

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La Spina, A., Paolicchi, P., Kryszczyńska, A. et al. Retrograde spins of near-Earth asteroids from the Yarkovsky effect. Nature 428, 400–401 (2004).

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