Wikipedia:Today's featured article/July 20, 2006

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Enceladus is the sixth-largest moon of Saturn, discovered in 1789 by William Herschel. Until the two Voyager spacecraft and Pioneer 11 passed near it in the early 1980s, very little was known about this small moon, other than the presence of water ice on its surface. The Voyagers showed that Enceladus is only 500 kilometers in diameter and reflects almost 100% of the sunlight that strikes it. The Cassini orbiter performed several close flybys of Enceladus in 2005, revealing the moon's surface and environment in greater detail. In particular, the probe discovered a water-rich plume venting from the moon's south polar region. This discovery, along with the presence of escaping internal heat and very few, if any, impact craters in the south polar region, shows that Enceladus is geologically active today. Enceladus is one of only three outer solar system bodies where active eruptions have been observed. Analysis of the outgassing suggests that it originates from a body of sub-surface liquid water, which, along with the unique chemistry found in the plume, has fueled speculation that Enceladus may be important in the study of astrobiology. (More...)

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