Saturn is surrounded by immense rings built of chunks of water ice, with a sprinkling of rocky material. The rings can reach a width of 185,000 miles (300,000 kilometers), and the particles can travel at thousands of miles per hour. Researchers have found that the rings' particles are loose and porous. When two particles collide, if they're moving slowly enough, they will merge into one — but if they're moving too quickly, they'll shatter. We can use this image to talk about mathematically how this simple behavior agrees with the strangely precise distribution of the particle's sizes.