Earth's moon, Saturn's Titan, Jupiter's Callisto, or Jupiter's Ganymede?

地球的星，土星的土六，星的四，星的Ganymede?

They're called Ganymede, Callisto, and Europa.

这几个分别叫三、四和二。

The next biggest moon is Callisto, at 4800 km in diameter.

第二大星四（卡斯托），直径约4800公里。

That means the surface is very old, maybe as old as Callisto itself.

这意味着它的表面非常古老，可能和四同岁。

Callisto orbits Jupiter farthest out of the four biggies, almost two million km away.

在四个大行星，四的公转轨道离星最远，约达200万千米。

The four largest moons, Io, Europa, Ganymede, and Callisto, are large enough to be seen from Earth with a telescope.

从地球上就可以用望远镜看到最大的四颗星，一，二，三，四。

Juice will investigate three of the so-called Galilean moons-Callisto, Europa and Ganymede, all of which are thought to have subsurface oceans.

“果汁”探测器将调查三颗所谓的伽略星——四、二和三，这三颗星都被认为拥有地下海洋。

" Jupiter's biggest moon is Ganymede, not Callisto, " she said, pointing over Ron's shoulder at a line in his Astronomy essay, " and it's lo that's got the volcanoes."

“星最大的星三，不四，”她从罗恩身后指着他那篇天文学论文的一行文字说道，“有火山的应该一。”