Center for Interdisciplinary Exploration and Research in Astrophysics, Northwestern University, Evanston, Illinois 60208, USA.
Nature. 2011 May 12;473(7346):187-9. doi: 10.1038/nature10076.
About 25 per cent of 'hot Jupiters' (extrasolar Jovian-mass planets with close-in orbits) are actually orbiting counter to the spin direction of the star. Perturbations from a distant binary star companion can produce high inclinations, but cannot explain orbits that are retrograde with respect to the total angular momentum of the system. Such orbits in a stellar context can be produced through secular (that is, long term) perturbations in hierarchical triple-star systems. Here we report a similar analysis of planetary bodies, including both octupole-order effects and tidal friction, and find that we can produce hot Jupiters in orbits that are retrograde with respect to the total angular momentum. With distant stellar mass perturbers, such an outcome is not possible. With planetary perturbers, the inner orbit's angular momentum component parallel to the total angular momentum need not be constant. In fact, as we show here, it can even change sign, leading to a retrograde orbit. A brief excursion to very high eccentricity during the chaotic evolution of the inner orbit allows planet-star tidal interactions to rapidly circularize that orbit, decoupling the planets and forming a retrograde hot Jupiter.
大约 25%的“热木星”（在太阳系外的类木行星，其轨道非常接近恒星）实际上是在沿着与恒星自转方向相反的轨道运行。来自遥远双星伴星的扰动可以产生高倾角，但无法解释相对于系统总角动量逆行的轨道。在恒星环境中，这种轨道可以通过层次三重星系统中的长期（即长期）摄动产生。在这里，我们报告了对行星体的类似分析，包括八极阶效应和潮汐摩擦，并发现我们可以在相对于总角动量逆行的轨道上产生热木星。对于遥远的恒星质量扰动者来说，这种结果是不可能的。对于行星扰动者，内轨道的角动量分量与总角动量平行的部分不需要是恒定的。事实上，正如我们在这里所示，它甚至可以改变符号，导致逆行轨道。在内轨道混沌演化过程中短暂地进入非常高的偏心率，允许行星-恒星潮汐相互作用快速将该轨道圆化，解耦行星并形成逆行热木星。
