Object: Europa's subsurface ocean
Interesting property: Intense turbulence
As moons go, Europa is doing pretty well in the looks department. While other wrinkled and pockmarked planetary bodies look their age, Jupiter's moon, despite being billions of years old, is one of the smoothest objects in our solar system.
However, this moon is far from flawless. Europa is suspected to have a perpetually dark, liquid water ocean enclosed beneath a thick shell of water ice – around 40 per cent of which is covered with long, dark scratches and scars.
The prospect of liquid water places Europa near the top of the list of places in our solar system that might host alien life. However, it is hard to know what's actually going on in the sub-surface ocean. Does it teem with alien microbes – perhaps even bigger creatures – or is it a vast, inky, sterile wasteland?
The only window we have on the ocean is its icy surface, so scientists try to read its criss-cross scars for clues. But whether this so-called chaos terrain can tell us about what's going on underneath such a thick layer of ice is hotly disputed.
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