Saturn
This is the second biggest planet in our Solar system. In Roman mythology, Saturn is the god of agriculture. The associated Greek god, Cronus, was the son of Uranus and Gaia and the father of Zeus (Jupiter). Saturn is the root of the English word "Saturday."
Saturn has been known since prehistoric times. Galileo was the first to observe it with a telescope in 1610. He noted its odd appearance but was confused by it. Early observations of Saturn were complicated by the fact that the Earth passes through the plane of Saturn's rings every few years as Saturn moves in its orbit. A low resolution image of Saturn therefore changes drastically. It was not until 1659 that Christiaan Huygens correctly inferred the geometry of the rings. Saturn's rings remained unique in the known solar system until 1977 when very faint rings were discovered around Uranus (and shortly thereafter around Jupiter and Neptune).
In 1655 Huygens discovered the moon Titan and Cassini discovered four more later that century that he named the Sidera Lodoicea. Here's some of Saturn's important attributes:
| Distance from Sun: | |
|---|---|
| Mean: | 9.53 AU |
| Perihelion: | 1,352.55 x 106 km |
| Ahelion: | 1,514.50 x 106 km |
| Size: | |
| Volume: | 82,713 x 1010 km3 |
| Diameter: | 120,536 km |
| Mass: | 5.68 x 1026 kg |
| Motion: | |
| Year: | 29.4 E Years |
| Day: | 10.7 E Hours |
| Other: | |
| Density: | 687 kg per m3 |
| Surface Temperature: | -130°C or 97°K |
Saturn is visibly flattened (oblate) when viewed through a small telescope; its equatorial and polar diameters vary by almost 10% (120,536 km vs. 108,728 km). This is the result of its rapid rotation and fluid state. The other gas planets are also oblate, but not so much so. Saturn is the least dense of the planets; its specific gravity (0.7) is less than that of water.
Like Jupiter, Saturn is about 75% hydrogen and 25% helium with traces of water, methane, ammonia and "rock", similar to the composition of the primordial Solar Nebula from which the solar system was formed. Saturn's interior is similar to Jupiter's consisting of a rocky core, a liquid metallic hydrogen layer and a molecular hydrogen layer. Traces of various ices are also present.
Saturn's interior is hot (12000 K at the core) and Saturn radiates more energy into space than it receives from the Sun. Most of the extra energy is generated by the Kelvin-Helmholtz mechanism as in Jupiter. But this may not be sufficient to explain Saturn's luminosity; some additional mechanism may be at work, perhaps the "raining out" of helium deep in Saturn's interior.
Two prominent rings (A and B) and one faint ring (C) can be seen from the Earth. The gap between the A and B rings is known as the Cassini division. The much fainter gap in the outer part of the A ring is known as the Encke Division (but this is somewhat of a misnomer since it was very likely never seen by Encke). The Voyager pictures show four additional faint rings. Saturn's rings, unlike the rings of the other planets, are very bright (albedo 0.2 - 0.6). Click Here to see the rings.
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