Editor's Summary

26 August 2010

Asteroids two-by-two


The increased interest in the observation of main-belt asteroids in recent years has led to the identification of tens of asteroid pairs, which follow near-identical orbits around the Sun even though they are not physically bound together. Rotational fission of larger bodies has been hypothesized as a mechanism for their formation, an idea that gains support with some new observations. Theory predicts that the mass ratios of two asteroids in a pair will be less than about 0.2 and that as the mass ratio approaches this upper limit, the spin period of the larger body is extended. Accordingly, photometric observations of 35 asteroid pairs reveal none with mass ratios greater than 0.2, and as mass ratios approach 0.2, primary periods grow longer. This suggests that asteroid pairs form by rotational fusion of a parent asteroid into a short-lived proto-binary system.

LetterFormation of asteroid pairs by rotational fission

P. Pravec, D. Vokrouhlický, D. Polishook, D. J. Scheeres, A. W. Harris, A. Galád, O. Vaduvescu, F. Pozo, A. Barr, P. Longa, F. Vachier, F. Colas, D. P. Pray, J. Pollock, D. Reichart, K. Ivarsen, J. Haislip, A. LaCluyze, P. Kušnirák, T. Henych, F. Marchis, B. Macomber, S. A. Jacobson, Yu. N. Krugly, A. V. Sergeev & A. Leroy

doi:10.1038/nature09315