NASA's Cassini has been in orbit around Saturn for six years now and has just produced images of snowball-like formations. The larger of Saturn's two moons, Prometheus, is orbiting around Saturn's F ring clumping icy particles into giant space snowballs as it swings by the planet.

The particles reside right at the equilibrium point between the tidal force and self-gravity of Saturn, which is why they are able to form. The so-called space snowballs are dense enough to have their own "self-gravity" and thus will continue to grow unless they are broken apart by another force.