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Mimas (moon)
Encyclopedia
Mimas is a moon
of Saturn
which was discovered in 1789 by William Herschel
. It is named after Mimas
, a son of Gaia
in Greek mythology
, and is also designated Saturn I.
By diameter (396 kilometers) the twentieth-largest moon in the Solar System
, Mimas is the smallest known astronomical body that is known to be rounded in shape due to self-gravitation.
William Herschel
on 17 September 1789. He recorded his discovery as follows: "The great light of my forty-foot telescope was so useful that on the 17th of September, 1789, I remarked the seventh satellite, then situated at its greatest western elongation."
s in Greek mythology
, Mimas
. The names of all seven then-known satellites of Saturn, including Mimas, were suggested by William Herschel's son John
in his 1847 publication Results of Astronomical Observations made at the Cape of Good Hope. He named them after Titans specifically because Saturn (the Roman equivalent of Kronos
in Greek mythology), was the leader of the Titans and ruler of the world for some time.
The adjectival form of Mimas is Mimantean or Mimantian, and this is accepted by the Cassini mission at JPL.
The low density of Mimas, 1.15 g/cm3, indicates that it is composed mostly of water ice with only a small amount of rock. Due to the tidal forces acting on it, the moon is not perfectly spherical; its longest axis is about 10% longer than the shortest. The ellipsoid shape of Mimas is especially noticeable in recent images from the Cassini probe.
Mimas' most distinctive feature is a colossal impact crater
130 kilometres (80.8 mi) across, named Herschel after the moon's discoverer. Herschel's diameter is almost a third of the moon's own diameter; its walls are approximately 5 kilometres (3.1 mi) high, parts of its floor measure 10 kilometres (6.2 mi) deep, and its central peak rises 6 kilometres (3.7 mi) above the crater floor. If there were a crater of an equivalent scale on Earth
it would be over 4000 kilometres (2,485.5 mi) in diameter, wider than Australia
. The impact that made this crater must have nearly shattered Mimas: fractures can be seen on the opposite side of Mimas that may have been created by shock waves from the impact travelling through the moon's body.
The Mimantean surface is saturated with smaller impact craters, but no others are anywhere near the size of Herschel. Although Mimas is heavily cratered, the cratering is not uniform. Most of the surface is covered with craters greater than 40 kilometres (24.9 mi) in diameter, but in the south polar region, craters greater than 20 kilometres (12.4 mi) are generally lacking.
Three types of geological features are officially recognized on Mimas: crater
s, chasmata (chasms) and catenae
(crater chains).
with Mimas. Mimas is responsible for clearing the material from the Cassini Division, the gap between Saturn's two widest rings, the A ring and B ring. Particles in the Huygens Gap at the inner edge of the Cassini division are in a 2:1 resonance
with Mimas. They orbit twice for each orbit of Mimas. The repeated pulls by Mimas on the Cassini division particles, always in the same direction in space, force them into new orbits outside the gap. The boundary between the C and B ring is in a 3:1 resonance with Mimas. Recently, the G ring was found to be in a 7:6 co-rotation eccentricity resonance with Mimas; the ring's inner edge is about 15000 kilometres (9,320.6 mi) inside Mimas' orbit.[citation needed]
Mimas is also in a 4:2 mean motion resonance with the larger moon Tethys
, and in a 2:3 resonance with the outer F ring shepherd
moonlet, Pandora
.
flew by Saturn in 1979, and its closest approach to Mimas was 104,263 km on September 1, 1979. Voyager 1
flew by in 1980, and Voyager 2
in 1981.
Mimas has been imaged several times by the Cassini orbiter, which entered into orbit around Saturn in 2004. A close flyby occurred on February 13, 2010, when Cassini passed by Mimas at 9500 km (5,903 mi).
, a fictional space station known from the film Star Wars Episode IV: A New Hope
, which is said to be roughly 140 kilometres in diameter. This resemblance stems from the fact that Herschel can appear in Mimas' northern hemisphere, much like the concave disc of the Death Star's "superlaser". This is purely coincidental, as the first film was made three years before the first close-up photographs of Mimas were taken.
In 2010, NASA revealed a temperature map of Mimas, using images obtained by Cassini. The warmest regions, which are along one edge of the moon, create a shape similar to the video game character Pac-Man
, with Herschel Crater assuming the role of an "edible dot" known from Pac-Man gameplay.
Natural satellite
A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....
of Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
which was discovered in 1789 by William Herschel
William Herschel
Sir Frederick William Herschel, KH, FRS, German: Friedrich Wilhelm Herschel was a German-born British astronomer, technical expert, and composer. Born in Hanover, Wilhelm first followed his father into the Military Band of Hanover, but emigrated to Britain at age 19...
. It is named after Mimas
Mimas (giant)
Mimas was one of the Gigantes of Greek mythology. Like the other giant sons of Gaia, Mimas had serpents for legs and was born fully armoured. Mimas was slain by Hephaestus during the war against the Olympians by a volley of molten iron.-References:...
, a son of Gaia
Gaia (mythology)
Gaia was the primordial Earth-goddess in ancient Greek religion. Gaia was the great mother of all: the heavenly gods and Titans were descended from her union with Uranus , the sea-gods from her union with Pontus , the Giants from her mating with Tartarus and mortal creatures were sprung or born...
in Greek mythology
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...
, and is also designated Saturn I.
By diameter (396 kilometers) the twentieth-largest moon in the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
, Mimas is the smallest known astronomical body that is known to be rounded in shape due to self-gravitation.
Discovery
Mimas was discovered by the astronomerAstronomer
An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...
William Herschel
William Herschel
Sir Frederick William Herschel, KH, FRS, German: Friedrich Wilhelm Herschel was a German-born British astronomer, technical expert, and composer. Born in Hanover, Wilhelm first followed his father into the Military Band of Hanover, but emigrated to Britain at age 19...
on 17 September 1789. He recorded his discovery as follows: "The great light of my forty-foot telescope was so useful that on the 17th of September, 1789, I remarked the seventh satellite, then situated at its greatest western elongation."
Name
Mimas is named after one of the TitanTitan (mythology)
In Greek mythology, the Titans were a race of powerful deities, descendants of Gaia and Uranus, that ruled during the legendary Golden Age....
s in Greek mythology
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...
, Mimas
Mimas (giant)
Mimas was one of the Gigantes of Greek mythology. Like the other giant sons of Gaia, Mimas had serpents for legs and was born fully armoured. Mimas was slain by Hephaestus during the war against the Olympians by a volley of molten iron.-References:...
. The names of all seven then-known satellites of Saturn, including Mimas, were suggested by William Herschel's son John
John Herschel
Sir John Frederick William Herschel, 1st Baronet KH, FRS ,was an English mathematician, astronomer, chemist, and experimental photographer/inventor, who in some years also did valuable botanical work...
in his 1847 publication Results of Astronomical Observations made at the Cape of Good Hope. He named them after Titans specifically because Saturn (the Roman equivalent of Kronos
Cronus
In Greek mythology, Cronus or Kronos was the leader and the youngest of the first generation of Titans, divine descendants of Gaia, the earth, and Uranus, the sky...
in Greek mythology), was the leader of the Titans and ruler of the world for some time.
The adjectival form of Mimas is Mimantean or Mimantian, and this is accepted by the Cassini mission at JPL.
Physical characteristics
Mimas' most distinctive feature is a colossal impact crater
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
130 kilometres (80.8 mi) across, named Herschel after the moon's discoverer. Herschel's diameter is almost a third of the moon's own diameter; its walls are approximately 5 kilometres (3.1 mi) high, parts of its floor measure 10 kilometres (6.2 mi) deep, and its central peak rises 6 kilometres (3.7 mi) above the crater floor. If there were a crater of an equivalent scale on Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
it would be over 4000 kilometres (2,485.5 mi) in diameter, wider than Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. The impact that made this crater must have nearly shattered Mimas: fractures can be seen on the opposite side of Mimas that may have been created by shock waves from the impact travelling through the moon's body.
The Mimantean surface is saturated with smaller impact craters, but no others are anywhere near the size of Herschel. Although Mimas is heavily cratered, the cratering is not uniform. Most of the surface is covered with craters greater than 40 kilometres (24.9 mi) in diameter, but in the south polar region, craters greater than 20 kilometres (12.4 mi) are generally lacking.
Three types of geological features are officially recognized on Mimas: crater
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
s, chasmata (chasms) and catenae
Crater chain
A crater chain is a line of craters along the surface of an astronomical body. The descriptor term for crater chains is catena , as specified by the International Astronomical Union's rules on planetary nomenclature....
(crater chains).
Orbital resonances
A number of features in Saturn's rings are related to resonancesOrbital resonance
In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of...
with Mimas. Mimas is responsible for clearing the material from the Cassini Division, the gap between Saturn's two widest rings, the A ring and B ring. Particles in the Huygens Gap at the inner edge of the Cassini division are in a 2:1 resonance
Orbital resonance
In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of...
with Mimas. They orbit twice for each orbit of Mimas. The repeated pulls by Mimas on the Cassini division particles, always in the same direction in space, force them into new orbits outside the gap. The boundary between the C and B ring is in a 3:1 resonance with Mimas. Recently, the G ring was found to be in a 7:6 co-rotation eccentricity resonance with Mimas; the ring's inner edge is about 15000 kilometres (9,320.6 mi) inside Mimas' orbit.[citation needed]
Mimas is also in a 4:2 mean motion resonance with the larger moon Tethys
Tethys (moon)
Tethys or Saturn III is a mid-sized moon of Saturn about across. It was discovered by G. D. Cassini in 1684 and is named after titan Tethys of Greek mythology. Tethys is pronounced |Odysseus]] is about 400 km in diameter, while the largest graben—Ithaca Chasma is about 100 km wide and...
, and in a 2:3 resonance with the outer F ring shepherd
Planetary ring
A planetary ring is a ring of cosmic dust and other small particles orbiting around a planet in a flat disc-shaped region.The most notable planetary rings known in Earth's solar system are those around Saturn, but the other three gas giants of the solar system possess ring systems of their...
moonlet, Pandora
Pandora (moon)
Pandora is an inner satellite of Saturn. It was discovered in 1980 from photos taken by the Voyager 1 probe, and was provisionally designated '. In late 1985 it was officially named after Pandora from Greek mythology. It is also designated as '.Pandora is the outer shepherd satellite of the F Ring...
.
Exploration
Pioneer 11Pioneer 11
Pioneer 11 is a 259-kilogram robotic space probe launched by NASA on April 6, 1973 to study the asteroid belt, the environment around Jupiter and Saturn, solar wind, cosmic rays, and eventually the far reaches of the solar system and heliosphere...
flew by Saturn in 1979, and its closest approach to Mimas was 104,263 km on September 1, 1979. Voyager 1
Voyager 1
The Voyager 1 spacecraft is a 722-kilogram space probe launched by NASA in 1977, to study the outer Solar System and eventually interstellar space. Operating for as of today , the spacecraft receives routine commands and transmits data back to the Deep Space Network. At a distance of as of...
flew by in 1980, and Voyager 2
Voyager 2
The Voyager 2 spacecraft is a 722-kilogram space probe launched by NASA on August 20, 1977 to study the outer Solar System and eventually interstellar space...
in 1981.
Mimas has been imaged several times by the Cassini orbiter, which entered into orbit around Saturn in 2004. A close flyby occurred on February 13, 2010, when Cassini passed by Mimas at 9500 km (5,903 mi).
Unusual resemblances
When seen from certain angles, Mimas closely resembles the Death StarDeath Star
The Death Star is a fictional moon-sized space station and superweapon appearing in the Star Wars movies and expanded universe. It is capable of destroying a planet with a single destructive super charged energy beam.-Origin and design:...
, a fictional space station known from the film Star Wars Episode IV: A New Hope
Star Wars Episode IV: A New Hope
Star Wars Episode IV: A New Hope, originally released as Star Wars, is a 1977 American epic space opera film, written and directed by George Lucas. It is the first of six films released in the Star Wars saga: two subsequent films complete the original trilogy, while a prequel trilogy completes the...
, which is said to be roughly 140 kilometres in diameter. This resemblance stems from the fact that Herschel can appear in Mimas' northern hemisphere, much like the concave disc of the Death Star's "superlaser". This is purely coincidental, as the first film was made three years before the first close-up photographs of Mimas were taken.
In 2010, NASA revealed a temperature map of Mimas, using images obtained by Cassini. The warmest regions, which are along one edge of the moon, create a shape similar to the video game character Pac-Man
Pac-Man
is an arcade game developed by Namco and licensed for distribution in the United States by Midway, first released in Japan on May 22, 1980. Immensely popular from its original release to the present day, Pac-Man is considered one of the classics of the medium, virtually synonymous with video games,...
, with Herschel Crater assuming the role of an "edible dot" known from Pac-Man gameplay.
In popular culture
- The Red DwarfRed DwarfRed Dwarf is a British comedy franchise which primarily comprises eight series of a television science fiction sitcom that aired on BBC Two between 1988 and 1999 and Dave from 2009–present. It gained cult following. It was created by Rob Grant and Doug Naylor, who also wrote the first six series...
novel Infinity Welcomes Careful Drivers is partially set on Mimas. Mimas is owned by the Spanish government, and is home to many bars and brothels, with a heavy organized-crime presence.
- "The First Duty" (1992), episode of Star Trek: The Next GenerationStar Trek: The Next GenerationStar Trek: The Next Generation is an American science fiction television series created by Gene Roddenberry as part of the Star Trek franchise. Roddenberry, Rick Berman, and Michael Piller served as executive producers at different times throughout the production...
. Mimas is the site of an evacuation station to which four StarfleetStarfleetIn the fictional universe of Star Trek, Starfleet or the Federation Starfleet is the deep-space exploratory, peacekeeping and military service maintained by the United Federation of Planets . It is the principal means by which the Federation conducts its exploration, defense, diplomacy and research...
cadets, including Wesley CrusherWesley CrusherWesley Crusher is a character in the television series Star Trek: The Next Generation. He is Beverly Crusher's son and is portrayed by actor Wil Wheaton, the character was a regular for the first four seasons. Afterwards, the character appeared sporadically. The character also appeared briefly in...
, transport after their vessels collide.
External links
- Cassini mission page – Mimas
- Mimas Profile at NASA's Solar System Exploration site
- The Planetary Society: Mimas
- Mimas page at The
NineEight Planets - Views of the Solar System – Mimas
- Cassini images of Mimas
- Images of Mimas at JPL's Planetary Photojournal
- Paul Schenk's Mimas blog entry and movie of Mimas's rotation on YouTube
- Mimas global and polar basemaps (February 2010) from Cassini images
- Mimas atlas (July 2010) from Cassini images
- Mimas nomenclature and Mimas map with feature names from the USGS planetary nomenclature page
- Figure "J" is Mimas transiting Saturn in 1979, imaged by Pioneer 11 from here
