Rhea is the second moon of Saturn by the size after Titan.
It was discovered in 1672 by Giovanni Domenico Cassini. Rhea was glanced through for the first time to Travel 1 in November, 1980. The Cassini probe is crossed in November 26th, 2005, in 500 km above its surface. Rhea is an ice-cold body of weak density (1240 kg / m3), indicating that the moon consists of a rocky nucleus counting only for a third of the mass of Rhea, the rest being mainly some ice-cold water.
The temperature on the surface of Rhea is of-174°C in the sun, and of-200°C in-220°C in the shadow. In synchronous rotation around Saturn, Rhea always presents the same hemisphere to Saturn.
The space probe Cassini presents us here the "back" face of Rhea.
The hemisphere before is strongly cratered and uniformly clearly. As Callisto, craters lack structures in the marked relief presents on the Moon and the Mercury. The back hemisphere presents a network of clear trails on a dark bottom, and few craters. These trails could be the matter ejected by volcanoes of ice while Rhea was still liquid under the surface.
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|Semi major axis||527 100 km|
|Orbital period ||4.518212 d|
(to Saturn's equator)
|Mean diameter||1527.6 km|
|Discovery date||23 December 1672|
|Discovery by||Jean-Dominique Cassini|
|Density||1 236 kg/m3|
|Escape velocity||0.635 km/s|
|temperature||53 K à 99 K|
-174°C à -220°C
Image: Image taken with the telephoto lens of the probe Cassini on January 17th, 2007 at a distance about 597000 kilometers of Rhea. Resolution is 4 kilometers by pixel.
In the Greek mythology, Rhea, Rheia or Rhee was Titanide, a girl of Ouranos ( the Sky) and Gaia the Earth), sister and woman of the Titan Cronos, and the mother of the gods Hestia, Demeter, Hera, Hades, Poseidon and Zeus.
With its 1 528 kilometers in diameters, Rhea appears here as a quite small grey and ice-cold object which contrasts with colors pastel of the huge planet, the Saturn.
Let us imagine ourselves the sight of Saturn since Rhea.
Rhea is 1528 km in diameter and Saturn 120 536 km in diameter. Rhea is situated in 527 100 km of Saturn, what is very close for this small object.
Let us come back to Earth and let us imagine that we have a celestial body also near and while keeping the same proportions it would mean observing in the sky a gigantic object 100 times as big as the Moon what would hide an enormous part of the sky.
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Image: This image taken by means of the red, green and blue filters was combined to produce this sight in natural color. The pictures were realized with the camera wide-angle lens of the space probe Cassini on February 4th, 2007 at a distance of 1,2 million kilometers of Saturn and at 679 000 kilometers of Rhea. The resolution is 68 kilometers by pixel on Saturn and about 40 kilometers by pixel on Rhea. This sight is taken since the side not lit by rings in approximately 3 degrees over their plan and their shadow is visible on the upper right of the image.