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Moons of the Solar System
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Moons of the Solar System |
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All the planetary moons in our solar system are shown here at their correct relative size and true color. Their diversity of size and appearance is testament to the unique and fascinating geologic history that each of these bodies has undergone. Two of the moons are larger than the planet Mercury, and eight of them are larger than Pluto. Earth's Moon is the fifth largest of the set, with a diameter of 3476 kilometers (2160 miles). Most of the moons are thought to have formed from a disk of debris left over from formation of the planet they orbit. However Triton, Neptune's largest moon, and several of the smallest moons, including the moons of Mars, are thought to be captured planetesimals that formed elsewhere in the solar system. Earth's Moon is thought to have formed from the debris ejected from a roughly Mars-sized object colliding with the early Earth, perhaps a unique event in the history of the solar system. The moons are organized on the diagram by the planet they orbit (top to bottom with increasing distance from the Sun) and their position relative to the planet (left to right with increasing distance from the planet). Below is a listing of the names of all the moons and the planets they orbit. Most moons are named for mythological characters associated with the character the planet is named for. While most of the planets are named for Roman characters (with the exceptions of Pluto and Uranus), most of the moon have names from Greek mythology. For example, Phobos and Deimos are the sons of Ares, the Greek version of Mars. Jupiter?s moons are all named for lovers and other close associates of Zeus (Jupiter). Saturn?s moons are named for Titans, the race that included Cronos (Saturn), Zeus? father. Neptune?s moons are named for mythological characters associated with water, and Charon was the ferryman of the dead who brought people to Pluto?s realm. By tradition, the discoverer of a moon gets to name it (now subject to approval by the International Astronomical Union). The son of the discoverer of the first two moons of Uranus (Sir William Herschel) decided to name Uranus? moons not for mythological characters, but instead for the king and queen of fairies in Shakespear?s A Midsummer Night?s Dream . This began a tradition whereby all uranian satellites are named for fairy characters in English drama. To read more about the names of the planets and their satellites, go to the U.S. Geological Survey?s nomenclature guide at http://wwwflag.wr.usgs.gov/USGSFlag/Space/nomen/append7.html . *Earth* Moon *Mars * Phobos, Deimos *Jupiter* Metis, Adrastea, Amalthea, Thebe, Io, Europa, Ganymede, Callisto, Leda, Himalia, Lysithea, Elara, Ananke, Carme, Pasiphae, Sinope *Saturn * Pan, Atlas, Prometheus, Pandora, Epimetheus, Janus, Mimas, Enceladus, Tethys, Calypso, Telesto, Dione, Helene, Rhea, Titan, Hyperion, Iapetus, Phoebe *Uranus * Cordelia, Ophelia, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Belinda, Puck, Miranda,, Ariel, Umbriel, Titania, Oberon *Neptune* Naiad, Thalassa, Despina, Galatea, Larissa, Proteus, Triton, Nereid *Pluto * Charon *Image Credit*: Image processing by Tim Parker (Jet Propulsion Laboratory) and Paul Schenk and Robert Herrick (Lunar and Planetary Institute), based on NASA images. |
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Ancient Craters on Saturn's
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Ancient Craters on Saturn's Rhea |
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Saturn's ragged moon Rhea has one of the oldest surfaces known. Estimated as changing little in the past billion years, Rhea [ http://en.wikipedia.org/wiki/Rhea_%28moon%29 ] shows craters [ http://en.wikipedia.org/wiki/Impact_crater ] so old they no longer appear round ? their edges have become compromised by more recent cratering. Like Earth's Moon [ http://antwrp.gsfc.nasa.gov/apod/ap051113.html ], Rhea's rotation is locked on Saturn, and the above image [ http://photojournal.jpl.nasa.gov/catalog/PIA08173 ] shows part of Rhea's surface [ http://antwrp.gsfc.nasa.gov/apod/ap051213.html ] that always faces Saturn. Rhea's leading surface is more highly cratered than its trailing surface. Rhea [ http://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search?rhea ] is composed mostly of water-ice but is thought to have a small rocky core. The above image [ http://photojournal.jpl.nasa.gov/catalog/PIA08173 ] was taken by the robot Cassini spacecraft [ http://www.esa.int/esaMI/Cassini-Huygens/SEM9D2HHZTD_0.html ] now orbiting Saturn. Cassini swooped past Rhea two months ago and captured the above image from about 100,000 kilometers away. Rhea [ http://www.nineplanets.org/rhea.html ] spans 1,500 kilometers making it Saturn's second largest moon after Titan [ http://antwrp.gsfc.nasa.gov/apod/ap060215.html ]. Several surface features on Rhea [ http://antwrp.gsfc.nasa.gov/apod/ap050215.html ] remain unexplained including large light patch [ http://antwrp.gsfc.nasa.gov/apod/ap050530.html ]es. |
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Rhea: Saturn's Second Larges
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Rhea: Saturn's Second Largest Moon |
| Explanation |
Rhea [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/rhea.html ] is the second largest moon of Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap950705.html ], behind Titan [ http://antwrp.gsfc.nasa.gov/apod/ap950923.html ], and the largest without an atmosphere. It is composed mostly of water ice, but has a small rocky core. Rhea [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/rhea.html ]'s rotation and orbit are locked together (just like Earth's Moon) so that one side always faces Saturn. A consequence of this is that one side always leads the other. Rhea's leading surface is much more heavily cratered than its trailing surface. The above photograph was taken with the Voyager 1 spacecraft in 1980. |
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Rhea: Saturn's Second Larges
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Rhea: Saturn's Second Largest Moon |
| Explanation |
Rhea [ http://www.nineplanets.org/rhea.html ] is the second largest moon of Saturn [ http://pds.jpl.nasa.gov/planets/choices/saturn1.htm ], behind Titan [ http://www.nineplanets.org/titan.html ], and the largest without an atmosphere. It is composed mostly of water ice, but has a small rocky core. Rhea [ http://www.solarviews.com/eng/rhea.htm ]'s rotation and orbit are locked together (just like Earth's Moon [ http://antwrp.gsfc.nasa.gov/apod/ap010218.html ]) so that one side always faces Saturn. A consequence of this is that one side always leads the other. Rhea's leading surface is much more heavily cratered than its trailing surface. The above photograph [ http://www.solarviews.com/cap/sat/rhea2.htm ] was taken with the Voyager 1 spacecraft [ http://voyager.jpl.nasa.gov/spacecraft/index.html ] in 1980. NASA's Cassini spacecraft [ http://saturn.jpl.nasa.gov/spacecraft/ ] is currently on route to Saturn and will arrive in 2004. |
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Saturn's Moon Rhea from Cass
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Saturn's Moon Rhea from Cassini |
| Explanation |
Each moon of Saturn seems to come with its own mystery [ http://antwrp.gsfc.nasa.gov/apod/ap050201.html ]. Rhea, Saturn's second largest moon behind Titan [ http://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search?titan ], shows unusual wisps, visible above as light colored streaks. Higher resolution images of similar wisps on Dione indicate that they might be made of long braided fractures. Rhea [ http://www.nineplanets.org/rhea.html ] is composed mostly of water ice [ http://www.mtu.edu/carnival/2005/statues.html ], but likely has a small rocky core [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003PEPI..136..201A ]. Rhea's rotation and orbit are locked together, just like Earth's Moon [ http://antwrp.gsfc.nasa.gov/apod/ap040829.html ], so that one side always faces Saturn [ http://en.wikipedia.org/wiki/Saturn_%28planet%29 ]. A consequence of this is that one side always leads the other. Rhea [ http://antwrp.gsfc.nasa.gov/apod/ap030608.html ]'s leading surface is much more heavily cratered [ http://antwrp.gsfc.nasa.gov/apod/ap990711.html ] than the trailing surface, pictured above. The above image [ http://photojournal.jpl.nasa.gov/catalog/PIA06578 ] in natural color was taken last month by the Cassini robot spacecraft [ http://saturn.jpl.nasa.gov/overview/mission.cfm ] in orbit around Saturn. |
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Rhea: Saturn's Second Larges
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Rhea: Saturn's Second Largest Moon |
| Explanation |
Rhea [ http://www.seds.org/nineplanets/nineplanets/rhea.html ] is the second largest moon of Saturn [ http://pds.jpl.nasa.gov/planets/welcome/saturn.htm ], behind Titan [ http://www.seds.org/nineplanets/nineplanets/titan.html ], and the largest without an atmosphere. It is composed mostly of water ice, but has a small rocky core. Rhea [ http://www.solarviews.com/eng/rhea.htm ]'s rotation and orbit are locked together (just like Earth's Moon [ http://antwrp.gsfc.nasa.gov/apod/ap991108.html ]) so that one side always faces Saturn. A consequence of this is that one side always leads the other. Rhea [ http://cass.jsc.nasa.gov/pub/research/outerp/rhea.html ]'s leading surface is much more heavily cratered than its trailing surface. The above photograph [ http://www.solarviews.com/cap/sat/rhea2.htm ] was taken with the Voyager [ http://antwrp.gsfc.nasa.gov/apod/ap960629.html ] 1 spacecraft in 1980. |
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