Journal Article

Formation of asteroid pairs by rotational fission

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

2010

Overview

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 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. Rotational fission may explain the formation of pairs of asteroids that have similar heliocentric orbits but are not bound together. These authors 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. In agreement with crucial predictions, they do not find asteroid pairs with mass ratios larger than 0.2, and as the mass ratio approaches 0.2 the primary period grows long. Pairs of asteroids sharing similar heliocentric orbits, but not bound together, were found recently 1 , 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 process 4 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.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 639/33/445/848 / Asteroids / Asteroids (minor planets) / Astronomy / Astrophysics / Earth and Planetary Astrophysics / Earth, ocean, space / Estimates / Exact sciences and technology / Humanities and Social Sciences / letter / multidisciplinary / Natural history / Nuclear fission / Physics / Planets, their satellites and rings. Asteroids / Ratios / Science / Science (multidisciplinary) / Sciences of the Universe / Solar system