1. Characteristics ↑
Saturn is the sixth closest planet to the Sun and the second largest planet in the Solar System, after Jupiter. It takes over 10,000 days to orbit the Sun, this is almost 30 years, and one day on Saturn is just under 11 hours long.
Saturn. Image credit: NASA/JPL-Caltech/Space Science Institute/G. Ugarkovic/Public domain.
Saturn is visible from the Earth, like Mercury, Venus, Mars, and Jupiter, and like them, it is also named after a Roman god, the god of agriculture[2a]. The rings of Saturn were first observed by Italian natural philosopher Galileo Galilei, and first identified by Dutch natural philosopher Christiaan Huygens, who discovered Saturn's moon Titan in 1655.
Saturn is almost entirely composed of hydrogen, with some helium, and trace amounts of other elements. It has a small core of rock and frozen water, surrounded by liquid hydrogen and helium. Saturn's rings are mostly composed of frozen water, but also contain rock and dust[2b]. A much larger ring was discovered using NASA's Spitzer Space Telescope in 2009. This is made of dust and is visible in infrared.
Saturn's infrared ring. Image credit: NASA/JPL-Caltech/Keck/Public domain.
2. Moons ↑
2.1 Titan ↑
Titan is the only moon in the Solar System to possess a significant atmosphere, and this is mostly composed of nitrogen, with some methane and ethane clouds[9a]. Titan is also thought to have an ocean of liquid water beneath its surface, like Jupiter's moons Ganymede, Callisto, and Europa.
In 2005, the ESA's Huygens probe found evidence of frozen water on Titan's surface, and radar images showed that Titan has coastlines, islands, sand dunes, and mountains[9b]. In 2006, NASA, ESA, and ASI's Cassini spacecraft found evidence of hydrocarbon lakes, the only surface liquid ever discovered outside of Earth.
Titan, a flattened view from the Huygens probe at three altitudes. Image credit: ESA/NASA/JPL/University of Arizona/Public domain.
Artist's impression of people on Titan. Image credit: NASA/JPL/Public domain.
Artist's impression of Titan showing hydrocarbon lakes. Image credit: ESA/ATG medialab/Public domain.
2.2 Enceladus ↑
Enceladus is one of the brightest objects in the Solar System, despite being only about 500 km in diameter. It's covered in frozen water, and frequently erupts in geysers that can extend for up to 1500 km.
Cassini found evidence of liquid water on Enceladus in 2006, and in 2015, Cassini found evidence of a global ocean beneath Enceladus' surface, which "could contain environments suitable for living organisms”.
Saturn's moons, Epimetheus and Titan, behind Saturn's rings (Titan is the larger planet). Image credit: NASA/JPL/Space Science Institute/Public domain.
Plumes of water on Enceladus, a mosaic of images taken from the Cassini spacecraft in 2009. Image credit: NASA/JPL/Space Science Institute/Public domain.
3. Missions to Saturn ↑
The Cassini spacecraft was launched in 1997, and became the first spacecraft to enter into orbit around Saturn in 2004. The Huygens probe separated from Cassini later that year, and landed on Titan in 2005.
Cassini is currently still in operation, and a timeline of mission highlights is shown below.
Cassini Mission Timeline. Image credit: NASA/ESA/ASI/Public domain.
The ESA and NASA were considering sending a new probe to land on Titan as part of the Titan Saturn System Mission. However, this has been postponed and currently has no launch date.