Moon and Saturn

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One of the most impressive mountain ranges on Earth runs down the center of the Atlantic Ocean. It's called the Mid-Atlantic Ridge, and it's thousands of miles long. The mountains build up as two plates of Earth's crust pull apart, allowing molten rock to bubble up from below.

A similar process is taking place on one of the moons of Saturn. Instead of hot rock, though, it's driven by liquid water.

At first glance, Enceladus doesn't sound all that interesting -- it's a ball of ice and rock that's only a few hundred miles in diameter.

But a close look at its south pole shows some of the most interesting terrain in the solar system. The region is marked by narrow, parallel grooves that resemble the stripes of a tiger. The stripes are hundreds of degrees warmer than the surrounding landscape. And they're venting liquid water into space -- plumes that feed one of Saturn's outer rings with fresh ice.

The Cassini spacecraft has flown past Enceladus several times. The repeat visits show that the tiger stripes are sliding apart from each other, with fresh ice welling up from below to fill in the edges -- just as magma fills in the gaps in the Mid-Atlantic Ridge. That gives Enceladus one of the most dynamic surfaces in the solar system.

Saturn follows the Moon across the sky this evening. Saturn looks like a bright golden star a little to the upper left of the Moon at nightfall. The true star Regulus is to the right of the Moon.

Script by Damond Benningfield, Copyright 2009

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