Like commuters on a freeway, planets and moons face the constant threat of collision -- not with each other, but with the countless comets and asteroids that litter the solar system. A collision between Earth and an asteroid may have wiped out the dinosaurs, for example.
A moon orbiting the planet Neptune may have suffered an even more traumatic collision -- one that blasted the moon to bits. All that's left of it is a lumpy ring around Neptune.
Neptune actually has several rings. Unlike the brilliant rings of Saturn, though, they're darker than chimney soot. They consist of small particles of rock and ice.
The most interesting is called the Adams ring. It's the farthest from the planet itself, and it consists of several clumps of material connected by a thin band of dust.
It's possible that the ring formed when a comet slammed into a small, rocky moon. The collision pulverized the moon, and the debris spread out to form a ring.
Although the gravity of Neptune and one of its moons are pulling on this material, it's slowly coming together into larger clumps. In a few millennia, the ring may coalesce to form a moon -- a moon reborn from the ashes of its own demise.
Neptune is putting on its best showing of the year. It lines up opposite the Sun, so it rises around sunset and remains visible all night. It's brightest for the year, too. Even so, you need a telescope to see it, in the constellation Aquarius.
More about Neptune tomorrow.
Script by Damond Benningfield, Copyright 2011