Saturn

Cassini Spacecraft's view of Saturn in 2009 Credit: NASA Solar System

Saturn is the sixth planet from the Sun and the most distant that can be seen with the naked eye. Saturn is the second largest planet and is best known for its fabulous ring system that was first observed in 1610 by the astronomer Galileo Galilei. Like Jupiter, Saturn is a gas giant and is composed of similar gasses including hydrogen, helium and methane.

Equatorial Diameter: 120,536 km

Polar Diameter: 108,728 km

Moons: 62 (Titan, Enceladus, Iapetus & Rhea)

Rings: 30+ (7 Groups)

Orbit Distance: 1,426,666,422 km (9.54 AU)

Orbit Period: 10,756 days (29.5 years)

Effective Temperature: -178 °C

Saturn can be seen with the naked eye. It is the fifth brightest object in the solar system and is also easily studied through binoculars or a small telescope. Saturn is the flattest planet. Its polar diameter is 90% of its equatorial diameter, this is due to its low density and fast rotation. Saturn turns on its axis once every 10 hours and 34 minutes giving it the second-shortest day of any of the solar system’s planets. Saturn orbits the Sun once every 29.4 Earth years. Its slow movement against the backdrop of stars earned it the nickname of “Lubadsagush” from the ancient Assyrians. The name means “oldest of the old”. Saturn’s upper atmosphere is divided into bands of clouds. The top layers are mostly ammonia ice. Below them, the clouds are largely water ice. Below are layers of cold hydrogen and sulfur ice mixtures. Saturn’s atmosphere is composed primarily of hydrogen (96%) and helium (3%) with traces of other substances like methane, ammonia, acetylene, ethane, propane and phosphine. Winds in the upper atmosphere can reach speeds of 500 metres a second, these combined with heat rising from within the planet’s interior cause yellow and gold bands.

Saturn is made mostly of hydrogen. It exists in layers that get denser farther into the planet. Eventually, deep inside, the hydrogen becomes metallic. At the core lies a hot interior.

Saturn has 150 moons and smaller moonlets. All are frozen worlds. The largest moons are Titan and Rhea. Enceladus appears to have an ocean below its frozen surface.

Significant Dates:

• 700 BCE: The oldest written records documenting Saturn are attributed to the Assyrians, described the ringed planet as a sparkle in the night and named it "Star of Ninib."
• 400 BCE: Ancient Greek astronomers named what they thought was a wandering star in honor of Kronos, the god of agriculture. The Romans later change the name to Saturn, their god of agriculture.
• July 1610: Galileo Galilei spots Saturn's rings through a telescope, but mistakes them for a "triple planet."
• 1655: Christiaan Huygens discovers Saturn's rings and its largest moon, Titan.
• 1675: Italian-born astronomer Jean-Dominique Cassini discovered a "division" between what are now called the A and B rings.
• 1 Sep 1979: Pioneer 11 was the first spacecraft to reach Saturn. Among Pioneer 11's many discoveries are Saturn's F ring and a new moon.
• 1979 and 1981: In its 1979 flyby of Saturn, Voyager 1 reveals the intricate structure of the ring system, consisting of thousands of bands. Flying even close to Saturn in 1981, Voyager 2 provided more detailed images and documents the thinness of some of the rings.
• 1 Jul 2004: NASA's Cassini spacecraft becomes the first to orbit Saturn, beginning a decade-long mission that revealed many secrets and surprises about Saturn and its system of rings and moons.
• 14 Jan 2005: The European Space Agency's Huygens probe is the first spacecraft to make a soft landing on the surface of another planet's moon - Saturn's giant moon Titan. The probe provided a detailed study Titan's atmosphere during a 2 hour and 27 minute descent and relayed data and images from Titan's muddy surface for another hour and 10 minutes.
• 17 Sep 2006: Scientists discover a new ring. The new ring coincides with the orbits of Saturn's moons Janus and Epimetheus. Images obtained during the longest solar occultation of Cassini's four-year mission revealed the ring. During a solar occultation, the sun passes directly behind Saturn causing the rings to be brilliantly backlit. Usually, an occultation lasts only about an hour, but in this instance it lasted 12 hours.

Credit: Karl Tate/Space.com

Reference: Karl Tate/spacedotcom/Nasa Solar System