This drawing shows possibilities for the mantle of Europa.
Click on image for full size
So, these studies suggest there might be two possibilities with regard to these observations. The first is that an ocean exists and explains all the features we have examined. Such an ocean would have to be roughly near the surface (found at no more than 500 km below the surface). Even so, since the surface of Europa is about ~50 degrees Kelvin (-150 C, -300 F) and the warm water about 300 degrees K (0 C, 32 F), then the crust and lithosphere which is over the ocean (shown here for the Earth) must be able to support such a large temperature difference.
Possibilities for Europa are shown in this picture. If the crust and lithosphere are not too thick, light from the sun will likely shine through this layer into the ocean beneath. On Earth, we know that there are life forms which can exist under conditions such as these.
The second possiblity is that there is no ocean and these observations are the result of the presence of processes in warm soft ice wherein, if there is melting, it takes place only in localized areas, or in a partial melt form.
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