Since it arrived at Saturn almost four years ago, the Cassini spacecraft has staged some terrific encounters. It's skimmed past Saturn's rings, mapped the lake-covered surface of the moon Titan, and watched storms at Saturn's poles that are as big as planets.
But if all goes well, Cassini's most impressive encounter yet may come tomorrow. The craft is scheduled to fly just a few miles above the south pole of the moon Enceladus. Scientists are particularly excited about the low pass because at that altitude, Cassini may fly through plumes of water that are jetting out from below the moon's icy crust.
Cassini spotted the plumes a couple of years ago. They came as quite a surprise, because Enceladus is bitterly cold -- its surface temperature is around 330 degrees below zero Fahrenheit.
Cassini also found that the moon's surface is cracked. Long parallel grooves form "tiger stripes" around the south pole. And that's where the water's coming from. Something is heating the layers just below the surface, melting some of the ice and cracking the crust. The warm water squirts into space and freezes. Some of these little drops of ice escape Enceladus and form one of Saturn's rings.
There was some concern that bits of ice could hit Cassini and damage the craft. But scientists decided that the odds are against such a collision, and the scientific rewards -- not to mention the view -- are worth the risk.
More about Enceladus tomorrow.
Script by Damond Benningfield, Copyright 2008
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