Keeler能隙内边缘的动力学现象
Dynamical phenomena at the inner edge of the Keeler gap
摘要：
我们分析了数千张卡西尼国际空间站的图像，以研究土星外A环中基勒间隙的内边缘。我们发现强有力的证据m=32扰动的径向变化的平均幅度为4.5公里。相位分析产生了与普罗米修斯的平均运动一致的模式速度，表明该模式是由32：31的内部林德布拉德共振与普罗米修斯产生的。此外，我们还发现了18瓣和20瓣模式的证据，振幅约为1.5公里。这些模式，其旋转速率对应于共振位置~4公里的间隙边缘内部，被认为是正常模式。前者可能与Pandora附近的18：17（m=18）共振有关。除了这些共振和正常模式模式，我们还观察到多个本地化的功能，似乎在本地开普勒速率移动，并持续只有几个月。一种假设是，在间隙内边缘的不同环粒子群可能对与普罗米修斯的共振有不同的反应，在强迫偏心率和/或近心上有局部变化;另一种假设是存在嵌入在基勒间隙的内边缘处或附近的几个看不见的物体，类似于怀疑存在于A环和B环外缘的那些（Spitale和Porco，2009年，2010年）。在任何一种情况下，观测环边缘相对的袢表明，本地化的功能必须在偏心轨道。
英文摘要：
We analyze several thousand Cassini ISS images in order to study the inner edge of the Keeler gap in Saturn's outer A ring. We find strong evidence for an m=32 perturbation with a mean amplitude of radial variation of 4.5 km. Phase analysis yields a pattern speed consistent with the mean motion of Prometheus, indicating that this pattern is generated by the 32:31 Inner Lindblad resonance with Prometheus. In addition, we find evidence of 18-lobed and 20-lobed patterns with amplitudes of ~1.5 km. These patterns, whose rotation rates correspond to resonance locations ~4 km interior to the gap edge, are believed to be normal modes. The former is probably related to the nearby 18:17 (m=18) resonance with Pandora. In addition to these resonant and normal mode patterns, we also observe multiple localized features that appear to move at the local keplerian rate and that persist for only a few months. One hypothesis is that different groups of ring particles at the inner edge of the gap may be reacting differently to the resonance with Prometheus, with local variations in the forced eccentricity and/or pericenter; an alternative hypothesis is the existence of several unseen objects embedded at or near the inner edge of the Keeler gap, similar to those suspected to exist at the outer edges of the A and B rings (Spitale and Porco 2009, 2010). In either case, observations of the ring edge at opposite ansae demonstrate that the localized features must be on eccentric orbits.
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