Janus is the sixth of Saturn¹'s known satellites:

　　orbit:    151,472 km from Saturn

　　diameter: 178 km (196 x 192 x 150)

　　mass:     2.01e18 kg

　　Janus was the god of gates and doorways², depicted³ with two faces looking in opposite directions; also the root of the English word "January".

　　Discovered by the French astronomer⁴ Audouin Dollfus in 1966.

　　Dollfus is credited with the discovery of Janus but it's not really certain whether the object he saw was Janus or Epimetheus and his observations led to a spurious orbit. (Walker discovered it independently but his telegram arrived a few hours after Dollfus'.) Larson and Fountain determined⁵ in 1978 that there are in fact two moons at about 151000 km from Saturn. This was confirmed in 1980 by Voyager 1.

　　Janus and Epimetheus are "co-orbital". The orbital radii⁶ of Janus and Epimetheus differ by only 50 km, less than the diameter of either. Their orbital velocities⁷ are thus very nearly equal and the lower, faster one slowly overtakes the other. As they approach each other they exchange a bit of momentum⁸ the end result of which is to boost the lower one into a higher orbit and to drop the higher one to a lower orbit. They thus exchange places. The exchange takes place about once every four years. The orbital data given here is as of the time of the Voyager encounters.

　　Janus is extensively cratered⁹ with several craters¹⁰ larger than 30 km but few linear features. Its surface appears to be older than Prometheus' but younger than Pandora's.

　　Janus 是土星已知卫星中距其第六近的一颗：

　　公转轨道：距土星 151,472 千米

　　卫星直径：178 千米（196×192×50）

　　质量：2.01e18 千克

　　杰纳斯是门与门口的神，他被描绘成在相反方向拥有两张脸。它也是英语单词“January（一月）”的词根。

　　它是在1966年被法国天文学家Audouin Dollfus发现的。

　　Dollfus被公认为发现了土卫十，但这不能肯定。他看到的物体是土卫十还是土卫十一不能确定，而且他的观察进入了一个错误的轨道。（步行者号独立发现了它，但是它的电报比Dollfus的晚到几个小时）Larson和Fountain在1978年认定事实上在土星上空大约151000千米处有两颗卫星。这在1980年被旅行者1号证实了。

　　土卫十和土卫十一是“双星”，两者公转轨道相关仅50千米，连它们任何一个的半径都不到。它们的轨道运行速度近似相等。低的、快的那一颗会慢慢地赶上另一颗，当他们相互靠近时，他们交换一些动量。这样最后导致低的一颗升到一个高的轨道，而高的一颗降低到低的轨道上。他们就这样交换位置。

　　这种转变每四年发生一次，这里所给出的轨道数据是当年旅行者号测得的。

　　土卫十被广泛地认为拥有大于30千米的环形山（陨石坑），但少有直线相貌。它的表面看上去比土卫十六的古老，但比土卫十七的年轻。