Today it's about black and white. There is one small but interesting satellite of Saturn - Iapetus. One hemisphere of Iapetus is black as pitch, and the other glistens like snow. It is still not known for sure why this icy block in space is so clearly divided into light and dark. However, that's not all - along the equator of Iapetus runs a series of unnaturally level mountain peaks called Iapetus Wall (height 13 km). There is a theory of its origin - Iapetus once had a ring in orbit, which fell to the surface of the satellite under the influence of gravity. There...