Enceladus 土卫二(中英)

Enceladus is the eighth of Saturn's known satellites:
　　orbit:    238,020 km from Saturn
　　diameter: 498 km
　　mass:    7.30e19 kg
　　In Greek mythology Enceladus was a Titan who was defeated in battle and buried under Mount Etna by Athena.
　　Discovered in 1789 by Herschel.
　　Craters and smooth plains Enceladus has the highest albedo (>0.9) of any body in the solar system. Its surface is dominated by fresh, clean ice.
　　At least five different types of terrain have been identified on Enceladus. In addition to craters there are smooth plains and extensive linear cracks and ridges. At least some of the surface is relatively young, probably less than 100 million years.
　　This means that Enceladus must have been active until very recently (and perhaps is still active today). Perhaps some sort of "water volcanism" is at work.
　　Enceladus is much too small to be heated by the decay of radioactive material in its interior at present (the heat would have all dissipated long ago).
　　Cassini closeup view (looks like Europa?) Enceladus is locked in a 1:2 resonance with Dione (similar to the situation between Io and Europa). This may provide a heating mechanism but it is probably insufficient to melt water ice. Enceladus may therefore be composed of some low-melting point material rather than pure water.
　　Enceladus may be the source of the material in Saturn's tenuous E ring. And since the material cannot persist in the ring for more than a few thousand years, it may be due to very recent activity on Enceladus. Another possibility, though, is that the rings are maintained by high-velocity collisions between dust particles and the various moons.
　　Enceladus 是土星已知卫星中距其第八远的一颗：
　　公转轨道：距土星 238,020 千米
　　卫星直径：498 千米
　　质量：7.30e19 千克
　　在希腊神话中，Enceladus是一个巨人，他在战斗中战败后被雅典娜埋葬在Etna山下。
　　它由赫歇耳于1789年发现。
　　土卫二在太阳系诸多星体中具有较高的反照率 (>0.9)。它的表面有新鲜、干净的空气。
　　土卫二表面至少有五种地形已被确认。除了陨石坑外还有平缓的平原和沿直线延伸的裂缝与山脊。一些表面相对来说较年轻，可能小于1亿年。
　　这意味着土卫二最近可能非常活跃（可能至今都很活跃）。也可能有一些“水火山”依然动作。
　　土卫二太小，不能被内部衰退的放射性物质加热（热量可能在很久以前既已衰退完）。
　　土卫二与土卫四以1:2的固定共动关系运行（与木卫一和木卫二的情形相似）。这形成了供热机制，但这还不足以溶解冰。土卫二可能由一些低溶点的物质，如纯水组成。
　　土卫二可能是土星的稀薄的E光环中物质的供给源。另外由于这物质不可能在光环中存在数千年之久，它可能与土卫二最近的活跃有关。另外光环也有可能是由高速的不断碰撞的粒子与不同的卫星共同维系。