木星的卫星木卫一全是岩石，其密度为每立方厘米3.5克。
Jupiter's moon Io, whose density is 3.5 grams per cubic centimetre, is all rock.
在这张照片的顶部，木卫一的表面上升起了一道大约140千米高的青烟，它从名为Pillan Patera的火山口喷发而出。
At the image top, over Io's limb, a bluish plume rises about 140 kilometers above the surface of a volcanic caldera known as Pillan Patera.
木星轨道左侧最远的是木卫四，然后是木卫二和木卫一，独自在右侧的是木卫三。
Farthest from Jupiter is Callisto, with Europa and Io all left of the planet's disk, while Ganymede stands alone at the right.
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