Only one planet shines throughout the evening hours this month: Saturn, the second-largest planet in the solar system. It's halfway up the southwestern sky as night falls, and looks like a bright golden star. It sets after midnight.
The feature that sets Saturn apart from the other planets is its system of bright, beautiful rings. It consists of thousands of individual rings that are made of small bits of dust and ice. The whole system spans a quarter-million miles -- the distance from Earth to the Moon -- but is generally no more than a few dozen feet thick.
Close-up observations show that the rings are constantly changing. Material clumps together and breaks apart. Electric fields levitate small dust grains above the rings, creating dark "spokes." One of Saturn's large moons, Enceladus, squirts out geysers of water and ice that add fresh material to one of the outer rings. And collisions between moons and smaller chunks of material can blast out ice and rock that add to the other rings.
Small moons create gravitational ripples that look like the wake of a boat. And some of the smallest moons -- up to about a half-mile across -- create twisted wakes that look like spinning propellers. The Cassini spacecraft has photographed many of these, and some of them have lasted for more than a year -- twisting their way across Saturn's constantly changing rings.
We'll talk about a partial ring that may be brand new tomorrow.
Script by Damond Benningfield, Copyright 2011
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