土卫十七1980

概述

土卫十七于1980年因旅行者1号探测飞船拍摄的照片而被发现，当时暂名为S/1980 S26。于1985年年底正式以希腊神话中的“潘多拉”（也可以称做潘朵拉）为卫星命名。同时，它亦被命名为土卫十七（Saturn XVII）。

土卫十七属土星环F环中的外守护卫星（outer shepherd satellite）（守护卫星是用引力维持环的规模的卫星）。它比附近的土卫十六（普罗米修斯）拥有更多的陨石坑，有两个陨石坑直径最少达30公里。

土卫十七的轨道看起来很混乱，此乃由于与土卫十六产生轨道共振。大约每隔6.2年，当土卫十七的拱点与土卫十六的远拱点成直线，两个卫星的距离于大约1400公里之内，这时候最能够观察到它们轨道的改变。此外，土卫十七亦与土卫一拥有3:2的轨道共振。

由于其较低密度及相对地高的反照率，土卫十七有可能是一个多缝隙的冰体。由于这方面的数据充满不确定因素，所以未能确定这说法是否属实。

Pandora is an inner satellite of Saturn. It was discovered in 1980 from photos taken by the Voyager 1 probe and was provisionally designated S/1980 S 26. In late 1985, it was officially named after Pandora from Greek mythology. It is also designated as Saturn XVII.

Pandora was thought to be an outer shepherd satellite of the F Ring. However, recent studies indicate that it does not play such a role, and that only Prometheus, the inner shepherd, contributes to the confinement of the narrow ring. It is more heavily cratered than nearby Prometheus and has at least two large craters 30 kilometres (19 mi) in diameter. The majority of craters on Pandora are shallow as a result of being filled with debris. Ridges and grooves are also present on the moon's surface.

The orbit of Pandora appears to be chaotic as a consequence of a series of four 118:121 mean-motion resonances with Prometheus. The most appreciable changes in their orbits occur approximately every 6.2 years, when the periapsis of Pandora lines up with the apoapsis of Prometheus and the moons approach to within about 1,400 kilometres (870 mi). Pandora also has a 3:2 mean-motion resonance with Mimas, and also a 21:19 mean-motion resonance with Epimetheus, but only while it is on the outer orbit relative to Janus. No such configuration with Janus exists.

Due to their gravitational interactions with the rings, Prometheus and Pandora are expected to crash into each other or Mimas in the next 20 million years.

From its very low density and relatively high albedo, it seems likely that Pandora is a very porous icy body. However, there is much uncertainty in these values, so this remains to be confirmed.