Goldreich Peter, Lithwick Yoram, Sari Re'em
School of Natural Science, Institute for Advanced Study, Princeton, New Jersey 08540, USA.
Nature. 2002 Dec 12;420(6916):643-6. doi: 10.1038/nature01227.
The Kuiper belt is a disk of icy bodies that orbit the Sun beyond Neptune; the largest known members are Pluto and its companion Charon. A few per cent of Kuiper-belt bodies have recently been found to be binaries with wide separations and mass ratios of the order of unity. Collisions were too infrequent to account for the observed number of binaries, implying that these binaries formed through collisionless interactions mediated by gravity. These interactions are likely to have been most effective during the period of runaway accretion, early in the Solar System's history. Here we show that a transient binary forms when two large bodies penetrate one another's Hill sphere (the region where their mutual forces are larger than the tidal force of the Sun). The loss of energy needed to stabilize the binary orbit can then occur either through dynamical friction from surrounding small bodies, or through the gravitational scattering of a third large body. Our estimates slightly favour the former mechanism. We predict that five per cent of Kuiper-belt objects are binaries with apparent separations greater than 0.2 arcsec, and that most are in tighter binaries or systems of higher multiplicity.
柯伊伯带是一个由环绕海王星之外太阳运行的冰体组成的圆盘；已知最大的成员是冥王星及其卫星卡戎。最近发现，百分之几的柯伊伯带天体是间距很宽且质量比约为1的双星。碰撞发生得过于稀少，无法解释观测到的双星数量，这意味着这些双星是通过引力介导的无碰撞相互作用形成的。在太阳系历史早期的失控吸积阶段，这些相互作用可能最为有效。我们在此表明，当两个大天体相互穿过对方的希尔球（其相互作用力大于太阳潮汐力的区域）时，会形成一个瞬态双星。稳定双星轨道所需的能量损失随后可通过周围小天体的动力摩擦，或通过第三个大天体的引力散射发生。我们的估计略倾向于前一种机制。我们预测，5%的柯伊伯带天体是视间距大于0.2角秒的双星，并且大多数处于更紧密的双星或更高多重性的系统中。
