Funato Yoko, Makino Junichiro, Hut Piet, Kokubo Eiichiro, Kinoshita Daisuke
General Systems Studies, University of Tokyo, Komaba, Meguro-ku, Tokyo 153, Japan.
Nature. 2004 Feb 5;427(6974):518-20. doi: 10.1038/nature02323.
Recent observations have revealed that an unexpectedly high fraction--a few per cent--of the trans-Neptunian objects (TNOs) that inhabit the Kuiper belt are binaries. The components have roughly equal masses, with very eccentric orbits that are wider than a hundred times the radius of the primary. Standard theories of binary asteroid formation tend to produce close binaries with circular orbits, so two models have been proposed to explain the unique characteristics of the TNOs. Both models, however, require extreme assumptions regarding the size distribution of the TNOs. Here we report a mechanism that is capable of producing binary TNOs with the observed properties during the early stages of their formation and growth. The only required assumption is that the TNOs were initially formed through gravitational instabilities in the protoplanetary dust disk. The basis of the mechanism is an exchange reaction in which a binary whose primary component is much more massive than the secondary interacts with a third body, whose mass is comparable to that of the primary. The low-mass secondary component is ejected and replaced by the third body in a wide but eccentric orbit.
最近的观测结果显示，在柯伊伯带中的跨海王星天体（TNO）里，有出乎意料的高比例（百分之几）是双星系统。其组成部分质量大致相等，轨道非常偏心，宽度超过主星半径的一百倍。小行星双星形成的标准理论倾向于产生具有圆形轨道的紧密双星，因此人们提出了两种模型来解释TNO的独特特征。然而，这两种模型都需要对TNO的大小分布做出极端假设。在此我们报告一种机制，该机制能够在TNO形成和生长的早期阶段产生具有观测到的特性的双星。唯一需要的假设是TNO最初是通过原行星尘埃盘中的引力不稳定性形成的。该机制的基础是一种交换反应，其中主成分比次成分质量大得多的双星与第三个天体相互作用，第三个天体的质量与主星相当。低质量的次成分被 ejected 并被第三个天体取代，进入一个宽阔但偏心的轨道。 （注：原文中“ejected”未翻译完整，推测可能是“被 eject 出去”，由于不清楚具体含义，保留英文）
