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Cassini Returns More Images of Saturn Moon, Rhea


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--- Quote ---Cassini Returns More Images of Saturn Moon, Rhea

 The joint NASA/European Space Agency probe Cassini recently flew by the Saturn moon Rhea and took a small group of images from 28,000 miles away. The pictures are of an ice covered surface pockmarked with craters, according to Space.Com
The images taken are from the side of Rhea that faces away from Saturn and contain a number of impact basins, such as Mamaldi that is 300 miles across and Tirawa that is 220 miles across.
Facts about Rhea

According to the page NASA maintains on Rhea, it is the second largest moon of Saturn, after Titan.
It has a diameter of 949 miles.

It orbits Saturn at a distance of 327,490 miles.

Rhea orbits Saturn every four and a half days.

Its surface temperature ranges from -174 degrees Celsius in sunlit areas and ranging down to -220 degrees Celsius.
It is comprised on three quarter water ice and one quarter rock.

Rhea is more heavily cratered than some other icy moons of Saturn, such as Dione. Scientists speculate that the moon suffered more asteroid bombardment than her closer sisters. Another theory suggests that moons like Dione, with greater internal heat than Rhea, seeped liquid water up to the surface that smoothed out its craters before refreezing.
Because of its distance from Saturn, there is less tidal attraction between Rhea and its parent planet. As a result, there is less tidal caused heating on Rhea than on closer moons such as Dione. However Rhea still maintains one side facing toward Saturn and the other facing away/
The moon was discovered by the Italian astronomer Giovanni Cassini, after whom the Cassini probe has been named. Rhea was subsequently named after the ancient Greek titan who was the mother of many of the Olympian gods, including Zeus.
What has Cassini discovered about Rhea so far?

Voyager images taken decades before had shown a series of "whispy" features on Rhea's surface, ranging from tens to hundreds of kilometers long, cutting through plains and craters alike. Cassini's images of the features showed them to be canyons created by subsidence of darker, rockier material exposing the more pure ice below it.
Measurements by Cassini also suggest that Rhea is not an ice planet with a rocky core, but rather a body with a mixture of ice and rock evenly distributed. Rhea has a very tenuous atmosphere, comprised of oxygen and carbon dioxide. The oxygen is thought to have been created by charged particles in Saturn's magnetosphere hitting the icy surface. Scientists are puzzled at the origin of the carbon dioxide.
The next close approach of Rhea by Cassini is scheduled for early March, 2013.

Mark R. Whittington is the author of Children of Apollo and The Last Moonwalker. He has written on space subjects for a variety of periodicals, including The Houston Chronicle, The Washington Post, USA Today, the L.A. Times, and The Weekly Standard.
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