Moon and Saturn

StarDate: February 1, 2010

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Like a bully with a bad attitude, one of the moons of Saturn may be blowing smoke in the face of one of its siblings. That gives the sister moon a two-faced appearance: one hemisphere is brighter than new-fallen snow, while the other is darker than charcoal.

Spitzer Space Telescope discovered a wide belt of gas and dust around Saturn last year. The belt is millions of miles beyond Saturn's visible rings.

The material in this belt may come from Phoebe, a rocky outer moon. Collisions with comets and asteroids blast particles of rock off of Phoebe's surface and into space.

The sister moon is Iapetus. Its orbit around Saturn carries it through the belt of debris, which orbits in the opposite direction. The same side of Iapetus always faces forward as it orbits the giant planet. So as it flies through the belt, it sweeps up some of the ring particles, forming the dark coating. These particles warm up the ice below them, causing it to vaporize and escape into space, exposing even more dark material below.

The dark belt is so broad and thin that it's invisible to optical telescopes. It shows up only in infrared wavelengths -- the wavelengths studied by Spitzer.

Saturn itself is visible to the eye, and this is a good night to look for it. It's to the lower left of the Moon as they rise in late evening, and to the upper left of the Moon at first light. We'll have more about Saturn and the Moon tomorrow.

Script by Damond Benningfield, Copyright 2009

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

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