Dynamics of Saturn's F ring and satellites from Cassini images

土星的F环对我们对行星环和相邻的小卫星之间的引力相互作用的理解提出了最严峻的考验，这种相互作用的过程类似于影响原行星及其周围物质的过程。尽管它的两颗“牧牧者”卫星——普罗米修斯和潘多拉——对土星环产生了可探测到的影响，但仍有一些不寻常的特征使土星环令人费解。从卡西尼号的掩星数据中，有越来越多的证据表明，土星环附近有一群小卫星（小于1公里）在运行。此外，卡西尼号的图像显示，环上大的（~500公里）扭曲与环上大的（~10公里）物体穿过环轨道的影响是一致的。在环的核心也有较小的（~50km）畸变，这与被普罗米修斯扰动的轨道上嵌入的卫星（半径<1km）一致。提议的研究将对卡西尼号F环的图像进行全面调查，以便(i)识别和改进大物体的轨道，以便了解它们与环的相互作用；（ii）识别和跟踪较小的物体，以建立人口分布的图片；（iii）寻找环的不寻常特征，表明存在更多的嵌入物体，并解释与之相关的动力学过程。在授权的时间尺度上，卡西尼号将见证F环和月亮普罗米修斯之间最接近的距离，我们预计那时F环的扭曲是最大的。延长任务意味着我们将对F环进行6年的观测。这将使我们有机会研究和理解影响环的所有动力学过程，从而使我们对环-卫星和原行星-盘相互作用等更普遍的问题有一个独特的见解。

Saturn's F ring poses the most severe test of our understanding of the gravitational interaction between planetary rings and small, adjacent satellites in processes that are analagous to those affecting protoplanets and the surrounding matertial out of which they accreted. Although its two 'shepherding' satellites, Prometheus and Pandora, exert detectable effects on the ring, there are several unusual features that make the ring puzzling. There is mounting evidence from Cassini occultation data of a population of small (<1km) moons orbiting near the ring. Furthermore, Cassini images show that large (~500km) distortions in the ring are consistent with the effect of large (~10km) objects in ring-crossing orbits. There are also smaller (~50km) distortions in the core of the ring consistent with embedded satellites (radius <1km) on orbits perturbed by Prometheus. The proposed research will undertake a complete survey of Cassini images of the F ring in order to (i) identify and improve the orbits of the large objects so that their interactions with the ring can be understood, (ii) identify and track the smaller objects to build up a picture of the population distribution and (iii) search for unusual features of the ring that suggest the existence of more embedded objects and explain the dynamical processes associated with them. Over the timescale of the grant Cassini will witness the closest approach between the F ring and the moon Prometheus when we expect the distortions in the ring to be at a maximum. An extended mission will mean that we will have 6 years of observations of the F ring. This will give us the opportunity to study and understand all the dynamical processes that affect the ring and thereby give us a unqiue insight into the more general problems of ring-satellite and protoplanet-disk interactions.