International Year of Astronomy - Saturn, Jewel of the Solar System
Named for the Roman god of agriculture and harvest, Saturn is the sixth planet from the Sun and arguably the most famous celestial icon thanks to its magnificent set of rings. Saturn’s equatorial diameter is 9.4 times that of Earth, and is mainly composed of light elements—hydrogen, helium, and some ices—and a small, rocky core. The rings are composed of silica rock, iron oxide, and ice particles ranging in size from specks of dust to the size of a small car. Curiously, Saturn’s average density is less than that of water. Due to its rapid rotation (about 10.5 hours) and fluid state, Saturn’s diameter at the equator is about 10% greater than its diameter between the poles. The planet is about ten times more distant from the Sun than Earth is, and it completes an orbit around the Sun every 30 years.
Saturn’s iconic rings were first observed in 1610 by Galileo Galilei, who, due to the limited resolution of his telescope, mistakenly noted that the planet had “ears.” Forty-five years later, Christiaan Huygens, using a telescope far superior to Galileo’s, became the first person to suggest that Saturn was surrounded by rings. Saturn has at least 56 natural satellites, with Titan, the largest, being the only moon in the Solar System with a dense atmosphere.
To date, the most spectacular views and most valuable data about the ringed world and its satellites have been obtained by the Cassini-Huygens mission. Developed under international cooperation, Cassini entered into orbit around Saturn on July 1, 2004. The spacecraft completed two Titan flybys before releasing the probe Huygens on December 25, 2004. Huygens descended onto the surface of Titan on January 14, 2005, and sent back a flood of data during its atmospheric descent and after its landing.