A contrast in satellite topography: first, Saturn’s second largest moon, Rhea. Notice the shadows along the day-night terminator from a valley in the north, some hilly terrain just to the left and south of that, and the numerous craters.
As with earthbound astronomers looking at our own satellite, geologists appreciate less the full moon and more the partial phases in which altitude can be easily distinguished in landforms. Or in the case of Saturn’s moons, “iceforms,” as these satellites are a few hundred degrees colder than the Earth and their surfaces are mostly dirty ice.
Almost a billion miles from our sun, water freezes hard to a consistency of rock. One would find in the Saturn system a strange set of corollary forms: ice dust, ice sand (on Titan), icy regolith (like dirt), and on at least one moon, ice lava (otherwise known as water) sloshing around under the surface and spraying out to create a very different surface.
Left is a Cassini image taken above the south pole of Enceladus about five weeks ago. No rough valleys, mountains, or craters show, but a very different kind of icescape: wrinkles, smooth valleys, and plains devoid of the usual features we see on other Saturnian moons.
The geochemistry of ice must be a fascinating topic. Water is a very interesting substance. In liquid form, various other chemicals can dissolve in it. Then these freeze way out in Saturn’s neighborhood. How does that affect the strength of the resulting ice-rock? What chemical reactions can take place at these cold temperatures? What sort of strange formations would explorers find if they went exploring on the surface of these moons, or better yet, poked around in gullies and caves?
We’ll probably have to wait another several decades to know.