Moving Around Saturn
 Saturn's moons Titan (background) and Rhea line up in this view from the Cassini spacecraft. Although they look close together, the two satellites were actually more than one million miles apart when the picture was shot. Cassini will fly about 3,500 miles from Rhea on the night of August 29, and about 2,000 miles from Titan just 30 hours later. Rhea, Saturn's second-largest moon, is a ball of ice and rock. Much larger Titan has a thick, cold atmosphere. Sunlight scattering through the atmosphere creates the bright ring effect in this image.[NASA/JPL/SSI]
Cassini's been orbiting the planet Saturn for more than three years. It's transmitted thousand of images and many other readings of the planet and its rings and moons.
Tomorrow, it'll pass outside the edge of the rings. Scientists don't expect any problems, but just in case, Cassini will use its big radio antenna to shield it from impacts with the small bits of ice or rock that make up the rings.
Tomorrow night, Cassini will fly past Rhea, Saturn's second-largest moon -- a cold, dead world that's taken a beating. We'll have more about that tomorrow.
And on Thursday night, the craft will fly past the largest moon, Titan. It's a lot more interesting than Rhea because it has a thick, cold atmosphere that may resemble that of the young Earth. Lakes of liquid methane dot its surface, and dunes of ice grains as tall as a 30-story building ripple across the landscape.
Among other things, Cassini will probe Titan's atmosphere by watching as a star disappears behind it -- Antares, the brightest star of Scorpius. The bright orange star is in view from Earth, too, low in the south at sunset, just below the brilliant planet Jupiter. Saturn is out of sight now, but thanks to Cassini, we can still keep an eye on the planet and its moons.
Script by Damond Benningfield, Copyright 2007
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