Moon and Saturn

StarDate: March 10, 2009

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Old Faithful is one of the most famous "hotheads" on the planet. Every hour to hour and a half or so, it blasts thousands of gallons of boiling water into the Wyoming sky.

But the geysers on one of the moons of Saturn make Old Faithful look like a squirt gun by comparison -- they can shoot water and ice hundreds of miles into space.

The moon is Enceladus. It's fairly small -- about three hundred miles in diameter -- and it's a long way out from Saturn. It's locked so that the same hemisphere always faces Saturn, just as the same hemisphere of our own moon always faces Earth.

But while our moon is alone, Enceladus has many sister moons. Some of them tug on it as they pass by, trying to force Enceladus to turn away from Saturn. This heats its interior, melting some of the water ice that coats the moon's surface.

This may form a "sea" that wraps around the entire southern hemisphere. Some of the water occasionally erupts into space from long cracks, known as tiger stripes. A geyser remains active until water freezes and plugs it up. After that, a new geyser forms somewhere else along the stripes.

The geysers blast enormous amounts of water into space -- enough to keep one of Saturn's outer rings constantly supplied with fresh ice.

Look for Saturn a little to the upper left of the Moon in early evening, and leading the Moon across the sky later on. It looks like a bright golden star.

Script by Damond Benningfield, Copyright 2009

For more skywatching tips, astronomy news, and much more, read StarDate magazine.

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