| The Columbia Encyclopedia, Sixth Edition. 2001-07. |
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| Rhea, in astronomy |
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| in astronomy, one of the named moons, or natural satellites, of Saturn. Also known as Saturn V (or S5), Rhea is 950 mi (1530 km) in diameter, orbits Saturn at a mean distance of 327,487 mi (527,040 km), and has equal orbital and rotational periods of 4.517 earth days. The second largest of Saturn’s moons, Rhea was discovered by the Italian-French astronomer Gian Domenico Cassini in 1672. Rhea’s density of 1.3 means that it is composed primarily of water ice, rocky material making up about a third of its mass. Its leading hemisphere is highly reflective and heavily cratered, strongly resembling the cratered highlands of the moon, although Rhea’s craters do not have high walls or a towering central peak; the trailing hemisphere is darker with bright wispy streaks and few impact craters. |
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| | | The Columbia Encyclopedia, Sixth Edition. Copyright © 2007 Columbia University Press. |
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