Moon and Saturn

StarDate: May 22, 2010

You are missing some Flash content that should appear here! Perhaps your browser cannot display it, or maybe it did not initialize correctly.

audio/mpeg icon

The region around the south pole of one of the moons of Saturn is like Yellowstone National Park on steroids. When the Cassini spacecraft flew past this region late last year, it photographed more than 30 geysers spewing water into space.

The moon is Enceladus. It's about 300 miles in diameter, and it's completely coated in ice. The ice reflects almost all of the sunlight that strikes Enceladus, so the little moon's surface is almost pure white -- and quite cold.

The interior should be cold, too -- Enceladus should be frozen solid. But it's not. Instead, there appear to be pockets of liquid water just below the surface around the south pole. Long, narrow fissures known as "tiger stripes" slice through the ice atop this water. The stripes are hundreds of degrees warmer than the rest of the moon's surface.

And that's where the water erupts into space. It's actually geysers of water vapor mixed with particles of ice. Some of this material falls back to the surface, repaving it with fresh ice. But some of it is moving so fast that it escapes Enceladus and adds fresh material to one of Saturn's rings.

Some of the geysers have been going since Cassini first flew past Enceladus several years ago -- blasting water away from this warm-on-the-inside, cold-on-the-outside moon.

Saturn appears near our own Moon tonight. They're high in the south at sunset, with Saturn above the Moon. It looks like a bright golden star.

Script by Damond Benningfield, Copyright 2010

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

The one constant in the Universe: StarDate magazine


©2015 The University of Texas McDonald Observatory