Saturn

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[1].

Photograph of Saturn.

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[3], and first identified by Dutch natural philosopher Christiaan Huygens[4], who discovered Saturn's moon Titan in 1655[5].

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[6].

Photograph of Saturn, showing its infrared ring.

Saturn's infrared ring. Image credit: NASA/JPL-Caltech/Keck/Public domain.

Planets in the Solar system, sizes are approximately to scale. Jupiter is the largest planet, followed by Saturn.

The planets, sizes approximately to scale. Image credit: Dave Jarvis/CC-SA.

2. Moons

2.1 Titan

Saturn has 62 moons, and the largest of these is Titan[7]. Titan is the second largest moon in the Solar System, after Jupiter's Ganymede, and it's about the same size as Mercury[8].

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[10], 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[11], 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[12].

Photograph of Titan.

Titan, a flattened view from the Huygens probe at three altitudes. Image credit: ESA/NASA/JPL/University of Arizona/Public domain.

Painting of people in rowboats on the surface of Titan, Saturn is setting in the background.

Artist's impression of people on Titan. Image credit: NASA/JPL/Public domain.

Artist's impression of Titan.

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[13]. It's covered in frozen water, and frequently erupts in geysers that can extend for up to 1500 km[14].

Cassini found evidence of liquid water on Enceladus in 2006[15], and in 2015, Cassini found evidence of a global ocean beneath Enceladus' surface[16], which "could contain environments suitable for living organisms”[17].

Photograph of Epimetheus and Titan.

Saturn's moons, Epimetheus and Titan, behind Saturn's rings (Titan is the larger planet). Image credit: NASA/JPL/Space Science Institute/Public domain.

Photograph showing plumes of water on Enceladus.

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

NASA's Pioneer 11 passed within 20,000 km of Saturn in 1979. NASA's Voyager 1 came within 124,000 km in 1980, and Voyager 2 came within about 700,000 km of Saturn in 1981.

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.

The Cassini spacecraft has made flybys of many of Saturn's moons, including Phoebe, Iapetus, Mimas, Tethys, Hyperion, Dione, Rhea, and Enceladus.

Cassini is currently still in operation, and a timeline of mission highlights is shown below.

Timeline of the Cassini mission.

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.

4. References

  1. NASA, 'Planetary Fact Sheet', last accessed 15-02-16.

  2. (a, b) NASA, 'Saturn: In Depth', last accessed 15-02-16.

  3. The Galileo Project, 'Saturn', last accessed 15-02-16.

  4. Huygens, C., 1659, 'The System of Saturn', Adriaan Vlacq/The Hague.

  5. Huygens, C., 1656, 'New Observation of a Moon of Saturn', The Hague.

  6. NASA, 'Giant Ring Discovered Around Saturn', last accessed 15-02-16.

  7. NASA, 'Saturn: Moons', last accessed 15-02-16.

  8. NASA, 'Solar System Small Worlds Fact Sheet', last accessed 15-02-16.

  9. (a, b) NASA, 'Titan: Saturn's Largest Moon', last accessed 15-02-16.

  10. Iess, L., et al, 2012, 'The tides of Titan', Science, 337, pp.457-459.

  11. NASA, 'Liquid Sea on Saturn's Titan', last accessed 15-02-16.

  12. NASA, 'Cassini Finds Lakes on Titan's Arctic Region', last accessed 15-02-16.

  13. NASA, 'Moons - Enceladus', last accessed 15-02-16.

  14. NASA, 'Enceladus: In Depth', last accessed 15-02-16.

  15. NASA, 'NASA's Cassini Discovers Potential Liquid Water on Enceladus', last accessed 15-02-16.

  16. NASA, 'Cassini Finds Global Ocean in Saturn's Moon Enceladus', last accessed 15-02-16.

  17. NASA, 'Spacecraft Data Suggest Saturn Moon's Ocean May Harbor Hydrothermal Activity', last accessed 15-02-16.

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