Dysnomia (moon)

Dysnomia (moon)

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Dysnomia, officially Eris I Dysnomia, is the only known moon
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 the dwarf planet
Dwarf planet
A dwarf planet, as defined by the International Astronomical Union , is a celestial body orbiting the Sun that is massive enough to be spherical as a result of its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite...

 Eris
Eris (dwarf planet)
Eris, formal designation 136199 Eris, is the most massive known dwarf planet in the Solar System and the ninth most massive body known to orbit the Sun directly...

 (the most-massive known dwarf planet
Dwarf planet
A dwarf planet, as defined by the International Astronomical Union , is a celestial body orbiting the Sun that is massive enough to be spherical as a result of its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite...

 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...

). It was discovered in 2005 by Mike Brown
Michael E. Brown
Michael E. Brown has been a professor of planetary astronomy at the California Institute of Technology since 2003....

 and the laser guide star adaptive optics team at the W. M. Keck Observatory, and carried the provisional designation of until officially named Dysnomia (from the Ancient Greek word meaning "lawlessness") after the daughter
Dysnomia (mythology)
Dysnomia , imagined by Hesiod among the daughters of "abhorred Eris" , is the daemon of "lawlessness", who shares her nature with Atë ; she makes rare appearances among other personifications in poetical contexts that are marginal to Greek mythology but become central to Greek philosophy: see...

 of the Greek goddess Eris
Eris (mythology)
Eris is the Greek goddess of strife and discord, her name being translated into Latin as Discordia. Her Greek opposite is Harmonia, whose Latin counterpart is Concordia. Homer equated her with the war-goddess Enyo, whose Roman counterpart is Bellona...

.

Discovery


During 2005, the adaptive optics
Adaptive optics
Adaptive optics is a technology used to improve the performance of optical systems by reducing the effect of wavefront distortions. It is used in astronomical telescopes and laser communication systems to remove the effects of atmospheric distortion, and in retinal imaging systems to reduce the...

 team at the Keck telescopes
Keck telescopes
The W. M. Keck Observatory is a two-telescope astronomical observatory at an elevation of near the summit of Mauna Kea in Hawai'i. The primary mirrors of each of the two telescopes are in diameter, making them the second largest optical telescopes in the world, slightly behind the Gran Telescopio...

 in Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...

 carried out observations of the four brightest Kuiper belt
Kuiper belt
The Kuiper belt , sometimes called the Edgeworth–Kuiper belt, is a region of the Solar System beyond the planets extending from the orbit of Neptune to approximately 50 AU from the Sun. It is similar to the asteroid belt, although it is far larger—20 times as wide and 20 to 200 times as massive...

 objects (Pluto
Pluto
Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...

, , , and ), using the newly commissioned laser guide star
Laser guide star
Laser guide stars are a form of artificial star created for use in astronomical adaptive optics imaging.Adaptive optics systems require a wavefront reference source in order to correct atmospheric distortion of light...

 adaptive optics system. Observations taken on 10 September revealed a moon
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....

 in orbit around Eris, provisionally designated . In keeping with the Xena
Xena
Xena is a fictional character from Robert Tapert's Xena: Warrior Princess franchise. She first appeared in the 1995–1999 television series Hercules: The Legendary Journeys, before going on to appear in Xena: Warrior Princess TV show and subsequent comic book of the same name...

nickname that was already in use for Eris, the moon was nicknamed "Gabrielle
Gabrielle (Xena)
Gabrielle is a fictional character played by Renée O'Connor in Xena: Warrior Princess. She is referred to by fans as the Battling Bard of Potidaea. Her trademark weapons are the Amazon fighting staff and later, the sais...

" by its discoverers, after the television warrior princess' sidekick.

Properties


Dysnomia was found 4.43 magnitudes fainter than Eris, and its diameter is estimated to be between 350 and 490 km, though Mike Brown claims that it is 500 times fainter and between 100 and 250 km in diameter. Combining Keck and Hubble observations, the satellite was used to constrain the mass of Eris, and orbital parameters were estimated. Its orbital period is calculated to be 15.774±0.002 d
Day
A day is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean that portion of the full day during which a location is illuminated by the light of the sun...

. These observations indicate that Dysnomia has a circular orbit around Eris, with a radius of This suggests that the mass of Eris is approximately 1.27 times that of Pluto.

Formation


Astronomers now know that three of the four brightest Kuiper belt objects (KBOs) have satellites. Among the fainter members of the belt only about 10% are known to have satellites. This is believed to imply that collisions between large KBOs have been frequent in the past. Impacts between bodies of the order of 1000 km across would throw off large amounts of material which would coalesce into a moon. A similar mechanism is believed to have led to the formation of Earth's own Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

 when the 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...

 was struck by a giant impactor
Giant impact hypothesis
The giant impact hypothesis states that the Moon was created out of the debris left over from a collision between the young Earth and a Mars-sized body. The colliding body is sometimes called Theia for the mythical Greek Titan who was the mother of Selene, the goddess of the moon.The giant impact...

 early in the history of 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...

.

Name


Mike Brown, the moon's discoverer, chose the name Dysnomia due to a number of resonances it possessed for him. Dysnomia, the daughter of Eris, fits the general historically established pattern of naming moons after lesser gods associated with the primary (hence, Jupiter's largest moons are named after lovers of Jupiter, while Saturn's are named after his fellow Titans). Also, the English translation of "Dysnomia", "lawlessness", echoes Lucy Lawless
Lucy Lawless
Lucy Lawless, MNZM is a New Zealander actress and singer best known for playing the title character of the internationally successful television series Xena: Warrior Princess....

, the actress famous for starring in Xena: Warrior Princess
Xena: Warrior Princess
Xena: Warrior Princess is an American–New Zealand supernatural fantasy adventure series that aired in syndication from September 4, 1995 until June 18, 2001....

on television. Before receiving their official names, Eris and Dysnomia were known informally as "Xena
Xena
Xena is a fictional character from Robert Tapert's Xena: Warrior Princess franchise. She first appeared in the 1995–1999 television series Hercules: The Legendary Journeys, before going on to appear in Xena: Warrior Princess TV show and subsequent comic book of the same name...

" and "Gabrielle
Gabrielle (Xena)
Gabrielle is a fictional character played by Renée O'Connor in Xena: Warrior Princess. She is referred to by fans as the Battling Bard of Potidaea. Her trademark weapons are the Amazon fighting staff and later, the sais...

" respectively (Gabrielle being Xena's sidekick), and Brown decided to retain that connection.

Brown also notes that Pluto owes its name in part to its first two letters, which form the initials of Percival Lowell
Percival Lowell
Percival Lawrence Lowell was a businessman, author, mathematician, and astronomer who fueled speculation that there were canals on Mars, founded the Lowell Observatory in Flagstaff, Arizona, and formed the beginning of the effort that led to the discovery of Pluto 14 years after his death...

, the founder of the observatory where its discoverer, Clyde Tombaugh
Clyde Tombaugh
Clyde William Tombaugh was an American astronomer. Although he is best known for discovering the dwarf planet Pluto in 1930, the first object to be discovered in what would later be identified as the Kuiper Belt, Tombaugh also discovered many asteroids; he also called for serious scientific...

, was working, and the person who inspired the search for "Planet X
Planet X
Following the discovery of the planet Neptune in 1846, there was considerable speculation that another planet might exist beyond its orbit. The search began in the mid-19th century but culminated at the start of the 20th with Percival Lowell's quest for Planet X...

". James Christy, who discovered Charon
Charon (moon)
Charon is the largest satellite of the dwarf planet Pluto. It was discovered in 1978 at the United States Naval Observatory Flagstaff Station. Following the 2005 discovery of two other natural satellites of Pluto , Charon may also be referred to as Pluto I...

, followed the principle established with Pluto
Pluto
Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...

by choosing a name which shared its first four letters with his wife's name, Charlene. "Dysnomia", similarly, has the same first letter as Brown's wife, Diane, and Brown uses the nickname "Dy" /ˈdaɪ/ for the moon, which he pronounces the same as his wife's nickname, Di. Because of this, Brown pronounces the full name daɪsˈnoʊmiə, with a long "y".

In addition, both Eris and Dysnomia, representing aspects of chaos, reflect the effect their existence had in the disputation on the definition of a planet (and specifically on the status of Pluto and Ceres), and the debate that followed.