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Evidence for a subsurface ocean on Europa.

机译：欧罗巴地下海洋的证据。

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Ground-based spectroscopy of Jupiter's moon Europa, combined with gravity data, suggests that the satellite has an icy crust roughly 150 km thick and a rocky interior. In addition, images obtained by the Voyager spacecraft revealed that Europa's surface is crossed by numerous intersecting ridges and dark bands (called lineae) and is sparsely cratered, indicating that the terrain is probably significantly younger than that of Ganymede and Callisto. It has been suggested that Europa's thin outer ice shell might be separated from the moon's silicate interior by a liquid water layer, delayed or prevented from freezing by tidal heating; in this model, the lineae could be explained by repetitive tidal deformation of the outer ice shell. However, observational confirmation of a subsurface ocean was largely frustrated by the low resolution (>2 km per pixel) of the Voyager images. Here we present high-resolution (54 m per pixel) Galileo spacecraft images of Europa, in which we find evidence for mobile 'icebergs'. The detailed morphology of the terrain strongly supports the presence of liquid water at shallow depths below the surface, either today or at some time in the past. Moreover, lower-resolution observations of much larger regions suggest that the phenomena reported here are widespread.
机译：木星月球欧罗巴的地面光谱，结合重力数据，表明该卫星的冰壳约150公里厚，内部岩石多变。此外，旅行者号飞船获得的图像显示，欧罗巴的表面被众多相交的山脊和暗带（称为线状植物）穿过，并且坑坑洼地，这表明该地貌可能比木卫三和卡利斯托的地貌年轻得多。有人提出欧罗巴的薄冰壳可能被液态水层与月球的硅酸盐内部隔开，但由于潮汐加热而延迟或阻止了冻结；在该模型中，线状现象可以通过外部冰壳的反复潮汐变形来解释。但是，航海者图像的低分辨率（每像素> 2 km）极大地挫败了对地下海洋的观测确认。在这里，我们展示了欧罗巴的高分辨率（每像素54 m）伽利略号航天器图像，在其中我们找到了移动“冰山”的证据。地形的详细形态有力地支持了今天或过去某个时间在地表以下较浅深度的液态水的存在。此外，对更大区域的低分辨率观测表明，这里报道的现象十分普遍。

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