Ence.odt



Enceladus‏‎

This article is about the moon of Saturn.

For the mythological giant, see Enceladus (mythology). For the Union ship, see USS Enceladus (AK-80)



Physical characteristics

Dimensions 513.2 × 502.8 × 496.6 km [3][6]

Mean radius

252.1±0.2 km [3][6] (0.0395 Earths, 0.1451 Moons)

Mass (1.08022±0.00101)×1020 kg [3][7] (1.8×10−5 Earths)

Mean density

1.609±0.005 g/cm³ [3][6]

Surface gravity

0.114 m/s² (0.0113 g)

Escape velocity

0.239 km/s (860.4 km/h) [3]

<p style="margin-bottom:0cm">Rotation period

<p style="margin-bottom:0cm">synchronous

<p style="margin-bottom:0cm">Axial tilt

<p style="margin-bottom:0cm">zero

<p style="margin-bottom:0cm">Albedo 1.375±0.008 (geometric) or 0.99 (Bond) [8]

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<p style="margin-bottom:0cm">Enceladus is the sixth-largest moon of Saturn. It was discovered in 1789 by William Herschel,[14][15][16] but little was known about Enceladus until the two Voyager spacecraft passed near it in the early 1980s.[17] The Voyagers showed that the diameter of Enceladus is only 500 kilometers (310 mi),[3] about a tenth of that of Saturn's largest moon, Titan, and that it reflects almost all the sunlight that strikes it. Voyager 1 found that Enceladus orbits in the densest part of Saturn's diffuse E ring, indicating a possible association between the two. Voyager 2 revealed that, despite Enceladus's small size, it has a wide range of surfaces ranging from old, heavily cratered regions to young, tectonically deformed terrains that formed as recently as 100 million years ago.

<p style="margin-bottom:0cm">In 2005, the Cassini spacecraft started multiple close flybys of Enceladus, revealing its surface and environment in greater detail. In particular, Cassini discovered a water-rich plume venting from Enceladus's south polar region. Cryovolcanoes near the south pole shoot geyser-like jets of water vapor, other volatiles, and solid material including sodium chloride crystals and ice particles into space, totaling approximately 200 kilograms (440 lb) per second.[17][18][19] Over 100 geysers have been identified.[20] Some of the water vapor falls back as "snow" and the rest escapes. This discovery revealed the mechanism by which Enceladus has released most of the material making up Saturn's E ring.[21]

<p style="margin-bottom:0cm">These observations, along with the finding of escaping internal heat and very few (if any) impact craters in the south polar region, show that Enceladus is geologically active today. Moons in the extensive satellite systems of gas giants often become trapped in orbital resonances that lead to forced libration or orbital eccentricity. Enceladus is in such a resonance with Saturn's fourth largest moon, Dione; proximity to Saturn leads to tidal heating of Enceladus's interior, offering a possible explanation for the activity. In 2014, NASA reported that evidence for a large south polar subsurface ocean of liquid water within Enceladus with a thickness of around 10 km had been found by Cassini.[22][23][24]

<p style="margin-bottom:0cm">Cassini has provided strong evidence that Enceladus has an ocean with an energy source, nutrients and organic molecules, making Enceladus one of the best places for the study of potentially habitable environments for extraterrestrial life.[25][26] By contrast, the water thought to be on Jupiter's moon Europa is locked under a very thick layer of surface ice, though recent evidence may show that Europa also erupts water plumes.[27]