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Ananke (moon)
Encyclopedia
Ananke is a retrograde
irregular
satellite
of Jupiter
. It was discovered by Seth Barnes Nicholson
at Mount Wilson Observatory
in 1951 and is named after the mythological Ananke
, the personification of Necessity, and the mother of the Moirae
by Zeus
. The adjectival form of the name is Anankean.
Ananke did not receive its present name until 1975; before then, it was simply known as . It was sometimes called "Adrastea" between 1955 and 1975 (Adrastea
is now the name of another satellite of Jupiter).
Ananke gives its name to the Ananke group
, retrograde irregular moons which orbit Jupiter between 19.3 and 22.7 Gm, at inclinations of roughly 150°.
Ananke orbits Jupiter on a high eccentricity and high inclination retrograde orbit. Eight irregular satellites discovered since 2000 follow similar orbits. The orbital elements are as of January 2000. They are continuously changing due to Solar
and planetary perturbations. The diagram illustrates Ananke's orbit in relation to other retrograde irregular satellites of Jupiter. The eccentricity of selected orbits is represented by the yellow segments (extending from the pericentre
to the apocentre
). The outermost regular satellite Callisto
is located for reference.
Given these orbital elements and the physical characteristics known so far, Ananke is thought to be the largest remnant of an original break-up forming the Ananke group
.
, Ananke appears neutral to light-red (colour indices
B-V=0.90 V-R=0.38).
The infrared
spectrum is similar to P-type asteroid
s but with a possible indication of water.
Retrograde motion
Retrograde motion is motion in the direction opposite to the movement of something else, and is the contrary of direct or prograde motion. This motion can be the orbit of one body about another body or about some other point, or the rotation of a single body about its axis, or other phenomena such...
irregular
Irregular satellite
In astronomy, an irregular moon is a natural satellite following a distant, inclined, and often eccentric and retrograde orbit. They are believed to have been captured by their parent planet, unlike regular satellites, which form in situ....
satellite
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 Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
. It was discovered by Seth Barnes Nicholson
Seth Barnes Nicholson
Seth Barnes Nicholson was an American astronomer.Nicholson was born in Springfield, Illinois and was raised in rural Illinois...
at Mount Wilson Observatory
Mount Wilson Observatory
The Mount Wilson Observatory is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a 5,715 foot peak in the San Gabriel Mountains near Pasadena, northeast of Los Angeles...
in 1951 and is named after the mythological Ananke
Ananke (mythology)
In Greek mythology, Ananke, also spelled Anangke, Anance, or Anagke , was the personification of destiny, necessity and fate, depicted as holding a spindle. She marks the beginning of the cosmos, along with Chronos...
, the personification of Necessity, and the mother of the Moirae
Moirae
The Moirae, Moerae or Moirai , in Greek mythology, were the white-robed incarnations of destiny . Their number became fixed at three...
by Zeus
Zeus
In the ancient Greek religion, Zeus was the "Father of Gods and men" who ruled the Olympians of Mount Olympus as a father ruled the family. He was the god of sky and thunder in Greek mythology. His Roman counterpart is Jupiter and his Etruscan counterpart is Tinia.Zeus was the child of Cronus...
. The adjectival form of the name is Anankean.
Ananke did not receive its present name until 1975; before then, it was simply known as . It was sometimes called "Adrastea" between 1955 and 1975 (Adrastea
Adrastea (moon)
Adrastea , also known as ', is the second by distance, and the smallest of the four inner moons of Jupiter. It was discovered in Voyager 2 probe photographs taken in 1979, making it the first natural satellite to be discovered from images taken by an interplanetary spacecraft, rather than...
is now the name of another satellite of Jupiter).
Ananke gives its name to the Ananke group
Ananke group
The Ananke group is a group of retrograde irregular satellites of Jupiter that follow similar orbits to Ananke and are thought to have a common origin....
, retrograde irregular moons which orbit Jupiter between 19.3 and 22.7 Gm, at inclinations of roughly 150°.
Orbit
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
and planetary perturbations. The diagram illustrates Ananke's orbit in relation to other retrograde irregular satellites of Jupiter. The eccentricity of selected orbits is represented by the yellow segments (extending from the pericentre
Apsis
An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...
to the apocentre
Apsis
An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...
). The outermost regular satellite Callisto
Callisto (moon)
Callisto named after the Greek mythological figure of Callisto) is a moon of the planet Jupiter. It was discovered in 1610 by Galileo Galilei. It is the third-largest moon in the Solar System and the second largest in the Jovian system, after Ganymede. Callisto has about 99% the diameter of the...
is located for reference.
Given these orbital elements and the physical characteristics known so far, Ananke is thought to be the largest remnant of an original break-up forming the Ananke group
Ananke group
The Ananke group is a group of retrograde irregular satellites of Jupiter that follow similar orbits to Ananke and are thought to have a common origin....
.
Physical characteristics
In the visible spectrumElectromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
, Ananke appears neutral to light-red (colour indices
Color index
In astronomy, the color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature...
B-V=0.90 V-R=0.38).
The infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
spectrum is similar to P-type asteroid
P-type asteroid
P-type asteroids have low albedo and a featureless reddish electromagnetic spectrum. It has been suggested that they have a composition of organic rich silicates, carbon and anhydrous silicates, possibly with water ice in their interior...
s but with a possible indication of water.