Astronomical Institute AS CR, Fricova 1, CZ-25165 Ondrejov, Czech Republic.
Nature. 2010 Aug 26;466(7310):1085-8. doi: 10.1038/nature09315.
Pairs of asteroids sharing similar heliocentric orbits, but not bound together, were found recently. 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 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.
最近发现了一些共享相似日心轨道但没有相互束缚的成对小行星。对它们轨道的回溯积分表明它们以低相对速度缓慢分离，但并没有提供对其形成机制的更多深入了解。先前假设的旋转分裂过程可能解释了它们的形成——关键预测是质量比小于约 0.2，并且随着质量比接近这个上限，较大天体的自转周期变得很长。在这里，我们报告了一组小行星对的光度观测结果，揭示了质量比远小于 0.2 的双星对的主星旋转得很快，接近其临界裂变频率。随着质量比接近 0.2，主星周期变得很长。这是因为系统的总能量接近零，要求小行星对从主星的自转中提取越来越多的能量才能逃脱。我们没有发现质量比大于 0.2 的小行星对。超过这个极限的旋转分裂系统没有足够的能量来破坏。我们得出结论，小行星对是由母体小行星的旋转分裂形成的原始双星系统，随后在形成后不久，由于其内部系统动力学的作用而解体。
