It seems intuitive that an opaque material should contain more stuff than a more translucent substance. For example, muddier water has more suspended particles of dirt in it than clearer water. Likewise, you might think that, in the rings of Saturn, more opaque areas contain a greater concentration of material than places where the rings seem more transparent.
But this intuition does not always apply, according to a recent study of the rings using data from NASA’s Cassini mission. In their analysis, scientists found surprisingly little correlation between how dense a ring might appear to be — in terms of its opacity and reflectiveness — and the amount of material it contains.