![Jupiter family](https://upload.wikimedia.org/wikipedia/commons/8/82/Jupiter_family.png)
There are 82 known
moons
A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body (or sometimes another natural satellite). Natural satellites are often colloquially referred to as ''moons'' ...
of
Jupiter
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
, not counting a number of
moonlets likely shed from the inner moons. All together, they form a
satellite system which is called the Jovian system. The most massive of the moons are the four
Galilean moons
The Galilean moons (), or Galilean satellites, are the four largest moons of Jupiter: Io, Europa, Ganymede, and Callisto. They were first seen by Galileo Galilei in December 1609 or January 1610, and recognized by him as satellites of Jupiter ...
:
Io,
Europa
Europa may refer to:
Places
* Europe
* Europa (Roman province), a province within the Diocese of Thrace
* Europa (Seville Metro), Seville, Spain; a station on the Seville Metro
* Europa City, Paris, France; a planned development
* Europa Cliff ...
,
Ganymede, and
Callisto Callisto most commonly refers to:
*Callisto (mythology), a nymph
*Callisto (moon), a moon of Jupiter
Callisto may also refer to:
Art and entertainment
*''Callisto series'', a sequence of novels by Lin Carter
*''Callisto'', a novel by Torsten Kro ...
, which were independently discovered in 1610 by
Galileo Galilei
Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He was ...
and
Simon Marius
Simon Marius ( latinized form of Simon Mayr; 10 January 1573 – 5 January 1625) was a German astronomer. He was born in Gunzenhausen, near Nuremberg, but spent most of his life in the city of Ansbach. He is most known for being among the first ...
and were
the first objects found to
orbit
In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...
a body that was neither
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
nor the
Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
. Much more recently, beginning in 1892, dozens of far smaller Jovian moons have been detected and have received the names of lovers (or other sexual partners) or daughters of the
Roman god
Roman mythology is the body of myths of ancient Rome as represented in the literature and visual arts of the Romans. One of a wide variety of genres of Roman folklore, ''Roman mythology'' may also refer to the modern study of these representat ...
Jupiter
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
or his
Greek equivalent Zeus
Zeus or , , ; grc, Δῐός, ''Diós'', label=Genitive case, genitive Aeolic Greek, Boeotian Aeolic and Doric Greek#Laconian, Laconian grc-dor, Δεύς, Deús ; grc, Δέος, ''Déos'', label=Genitive case, genitive el, Δίας, ''D ...
. The Galilean moons are by far the largest and most massive objects to orbit Jupiter, with the remaining 78 known moons and
the rings
''The Rings'' is a 1985 Iranian horror mystery film written by director Mohsen Makhmalbaf and directed by Mohammad Reza Honarmand. It tells the story of a reporter investigating the sudden, inexplicable deaths of a growing number of people who h ...
together composing just 0.003% of the total orbiting mass.
Of
Jupiter
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
's moons, eight are
regular satellites with
prograde and nearly circular orbits that are not greatly
inclined
Incline, inclined, inclining, or inclination may refer to:
*Grade (slope), the tilt, steepness, or angle from horizontal of a topographic feature (hillside, meadow, etc.) or constructed element (road, railway, field, etc.)
*Slope, the tilt, steepn ...
with respect to Jupiter's equatorial plane. The Galilean satellites are nearly spherical in shape due to their
planetary mass
In astronomy, planetary mass is a measure of the mass of a planet-like astronomical object. Within the Solar System, planets are usually measured in the astronomical system of units, where the unit of mass is the solar mass (), the mass of the Sun ...
, and so would be considered at least
dwarf planet
A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to p ...
s if they were in direct orbit around the Sun. The other four regular satellites are much smaller and closer to Jupiter; these serve as sources of the dust that makes up Jupiter's rings. The remainder of Jupiter's moons are
irregular satellites
In astronomy, an irregular moon, irregular satellite or irregular natural satellite is a natural satellite following a distant, inclined, and often eccentric and retrograde orbit. They have been captured by their parent planet, unlike regular sat ...
whose prograde and
retrograde orbit
Retrograde motion in astronomy is, in general, orbital or rotational motion of an object in the direction opposite the rotation of its primary, that is, the central object (right figure). It may also describe other motions such as precession or ...
s are much farther from Jupiter and have high
inclinations
Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object.
For a satellite orbiting the Earth ...
and
eccentricities. These moons were probably captured by Jupiter from solar orbits. Twenty-three of the irregular satellites have not yet been officially named.
Characteristics
The physical and orbital characteristics of the moons vary widely. The four Galileans are all over in diameter; the largest Galilean,
Ganymede, is the ninth
largest object in the
Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
, after the Sun and seven of the
planet
A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...
s, Ganymede being larger than
Mercury
Mercury commonly refers to:
* Mercury (planet), the nearest planet to the Sun
* Mercury (element), a metallic chemical element with the symbol Hg
* Mercury (mythology), a Roman god
Mercury or The Mercury may also refer to:
Companies
* Merc ...
. All other Jovian moons are less than in diameter, with most barely exceeding .
[For comparison, the area of a sphere with diameter 250 km is about the area of ]Senegal
Senegal,; Wolof: ''Senegaal''; Pulaar: 𞤅𞤫𞤲𞤫𞤺𞤢𞥄𞤤𞤭 (Senegaali); Arabic: السنغال ''As-Sinighal'') officially the Republic of Senegal,; Wolof: ''Réewum Senegaal''; Pulaar : 𞤈𞤫𞤲𞤣𞤢𞥄𞤲𞤣𞤭 ...
and comparable to the area of Belarus
Belarus,, , ; alternatively and formerly known as Byelorussia (from Russian ). officially the Republic of Belarus,; rus, Республика Беларусь, Respublika Belarus. is a landlocked country in Eastern Europe. It is bordered by R ...
, Syria
Syria ( ar, سُورِيَا or سُورِيَة, translit=Sūriyā), officially the Syrian Arab Republic ( ar, الجمهورية العربية السورية, al-Jumhūrīyah al-ʻArabīyah as-Sūrīyah), is a Western Asian country loc ...
and Uruguay
Uruguay (; ), officially the Oriental Republic of Uruguay ( es, República Oriental del Uruguay), is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast; while bordering ...
. The area of a sphere with a diameter of 5 km is about the area of Guernsey
Guernsey (; Guernésiais: ''Guernési''; french: Guernesey) is an island in the English Channel off the coast of Normandy that is part of the Bailiwick of Guernsey, a British Crown Dependency.
It is the second largest of the Channel Islands ...
and somewhat more than the area of San Marino
San Marino (, ), officially the Republic of San Marino ( it, Repubblica di San Marino; ), also known as the Most Serene Republic of San Marino ( it, Serenissima Repubblica di San Marino, links=no), is the fifth-smallest country in the world an ...
. (But note that these smaller moons are not spherical.) Their
orbital shapes range from nearly perfectly circular to highly
eccentric
Eccentricity or eccentric may refer to:
* Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal"
Mathematics, science and technology Mathematics
* Off-center, in geometry
* Eccentricity (graph theory) of a v ...
and
inclined
Incline, inclined, inclining, or inclination may refer to:
*Grade (slope), the tilt, steepness, or angle from horizontal of a topographic feature (hillside, meadow, etc.) or constructed element (road, railway, field, etc.)
*Slope, the tilt, steepn ...
, and many revolve in the direction opposite to Jupiter's rotation (
retrograde motion
Retrograde motion in astronomy is, in general, orbital or rotational motion of an object in the direction opposite the rotation of its primary, that is, the central object (right figure). It may also describe other motions such as precession or ...
).
Orbital period
The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...
s range from seven hours (taking less time than Jupiter does to rotate around its axis), to some three thousand times more (almost three Earth years).
Origin and evolution
![Relative Masses of Jovian Satellites](https://upload.wikimedia.org/wikipedia/commons/e/ec/Relative_Masses_of_Jovian_Satellites.png)
Jupiter's regular satellites are believed to have formed from a circumplanetary disk, a ring of accreting gas and solid debris analogous to a
protoplanetary disk
A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may also be considered an accretion disk for the star itself, be ...
.
They may be the remnants of a score of Galilean-mass satellites that formed early in Jupiter's history.
Simulations suggest that, while the disk had a relatively high mass at any given moment, over time a substantial fraction (several tens of a percent) of the mass of Jupiter captured from the solar nebula was passed through it. However, only 2% of the proto-disk mass of Jupiter is required to explain the existing satellites.
[ Thus, several generations of Galilean-mass satellites may have been in Jupiter's early history. Each generation of moons might have spiraled into Jupiter, because of drag from the disk, with new moons then forming from the new debris captured from the solar nebula.][ By the time the present (possibly fifth) generation formed, the disk had thinned so that it no longer greatly interfered with the moons' orbits.] The current Galilean moons were still affected, falling into and being partially protected by an orbital resonance
In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relationsh ...
with each other, which still exists for Io, Europa
Europa may refer to:
Places
* Europe
* Europa (Roman province), a province within the Diocese of Thrace
* Europa (Seville Metro), Seville, Spain; a station on the Seville Metro
* Europa City, Paris, France; a planned development
* Europa Cliff ...
, and Ganymede: they are in a 1:2:4 resonance. Ganymede's larger mass means that it would have migrated inward at a faster rate than Europa or Io.[ Tidal dissipation in the Jovian system is still ongoing and ]Callisto Callisto most commonly refers to:
*Callisto (mythology), a nymph
*Callisto (moon), a moon of Jupiter
Callisto may also refer to:
Art and entertainment
*''Callisto series'', a sequence of novels by Lin Carter
*''Callisto'', a novel by Torsten Kro ...
will likely be captured into the resonance in about 1.5 billion years, creating a 1:2:4:8 chain.
The outer, irregular moons are thought to have originated from captured asteroid
An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere.
...
s, whereas the protolunar disk was still massive enough to absorb much of their momentum and thus capture them into orbit. Many are believed to have broken up by mechanical stresses during capture, or afterward by collisions with other small bodies, producing the moons we see today.
Discovery
Chinese historian Xi Zezong
Xi Zezong (June 6, 1927, Yuanqu, Shanxi – December 27, 2008, Beijing) was a Chinese astronomer, historian, and translator. He was a member of the Chinese Academy of Sciences, and an awardee of the Astronomy Prize.
He identified a possible r ...
claimed that the earliest record of a Jovian moon (Ganymede or Callisto) was a note by Chinese astronomer Gan De
Gan De (; fl. 4th century BC), also known as the Lord Gan (Gan Gong), was an ancient Chinese astronomer and astrologer born in the State of Qi. Along with Shi Shen, he is believed to be the first in history known by name to compile a star catalo ...
of an observation around 364 BC regarding a "reddish star". However, the first certain observations of Jupiter's satellites were those of Galileo Galilei
Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He was ...
in 1609. By January 1610, he had sighted the four massive Galilean moons
The Galilean moons (), or Galilean satellites, are the four largest moons of Jupiter: Io, Europa, Ganymede, and Callisto. They were first seen by Galileo Galilei in December 1609 or January 1610, and recognized by him as satellites of Jupiter ...
with his 20× magnification
Magnification is the process of enlarging the apparent size, not physical size, of something. This enlargement is quantified by a calculated number also called "magnification". When this number is less than one, it refers to a reduction in siz ...
telescope
A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to observe ...
, and he published his results in March 1610.
Simon Marius had independently discovered the moons one day after Galileo, although he did not publish his book on the subject until 1614. Even so, the names Marius assigned are used today: Ganymede, Callisto Callisto most commonly refers to:
*Callisto (mythology), a nymph
*Callisto (moon), a moon of Jupiter
Callisto may also refer to:
Art and entertainment
*''Callisto series'', a sequence of novels by Lin Carter
*''Callisto'', a novel by Torsten Kro ...
, Io, and Europa
Europa may refer to:
Places
* Europe
* Europa (Roman province), a province within the Diocese of Thrace
* Europa (Seville Metro), Seville, Spain; a station on the Seville Metro
* Europa City, Paris, France; a planned development
* Europa Cliff ...
. No additional satellites were discovered until E. E. Barnard
Edward Emerson Barnard (December 16, 1857 – February 6, 1923) was an American astronomer. He was commonly known as E. E. Barnard, and was recognized as a gifted observational astronomer. He is best known for his discovery of the high proper mo ...
observed Amalthea in 1892.
With the aid of telescopic photography, further discoveries followed quickly over the course of the 20th century. Himalia was discovered in 1904, Elara in 1905, Pasiphae in 1908, Sinope in 1914, Lysithea and Carme in 1938, Ananke
In ancient Greek religion, Ananke (; grc, Ἀνάγκη), from the common noun , "force, constraint, necessity") is the personification of inevitability, compulsion and necessity. She is customarily depicted as holding a spindle. One of the ...
in 1951, and Leda
Leda may refer to:
Mythology
* Leda (mythology), queen of Sparta and mother of Helen of Troy in Greek mythology
Places
* Leda, Western Australia, a suburb of Perth, Western Australia
* Leda makeshift settlement, Bangladesh, a refugee camp ...
in 1974.
By the time that the Voyager space probes reached Jupiter, around 1979, 13 moons had been discovered, not including Themisto
In Greek mythology, Themisto (; Ancient Greek: Θεμιστώ) was a Thessalin princess as the daughter of King Hypseus of LapithsApollodorus, 1.9.2 and the naiad Chlidanope. Her name is derived from the Ancient Greek word: "θεμιστος" wh ...
, which had been observed in 1975, but was lost until 2000 due to insufficient initial observation data. The Voyager spacecraft discovered an additional three inner moons in 1979: Metis
Metis or Métis may refer to:
Ethnic groups
* Métis, recognized Indigenous communities in Canada and America whose distinct culture and language emerged after early intermarriage between First Nations peoples and early European settlers, prima ...
, Adrastea, and Thebe
Thebe may refer to:
* Any of several female characters in Greek mythology - see List of mythological figures named Thebe
* Thebe (moon), a moon of Jupiter
* Thebe (currency), 1/100 of a Botswana pula
* Thebe, an Amazons, Amazon
* Thebe, alternate ...
.
No additional moons were discovered for two decades, but between October 1999 and February 2003, researchers found another 34 moons using sensitive ground-based detectors. These are tiny moons, in long, eccentric
Eccentricity or eccentric may refer to:
* Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal"
Mathematics, science and technology Mathematics
* Off-center, in geometry
* Eccentricity (graph theory) of a v ...
, generally retrograde orbit
Retrograde motion in astronomy is, in general, orbital or rotational motion of an object in the direction opposite the rotation of its primary, that is, the central object (right figure). It may also describe other motions such as precession or ...
s, and averaging in diameter, with the largest being just across. All of these moons are thought to have been captured asteroid
An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere.
...
al or perhaps comet
A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ar ...
bodies, possibly fragmented into several pieces.
By 2015, a total of 15 additional moons were discovered. Two more were discovered in 2017 by the team led by Scott S. Sheppard
Scott Sander Sheppard (born 1977) is an American astronomer and a discoverer of numerous moons, comets and minor planets in the outer Solar System.
He is an astronomer in the Department of Terrestrial Magnetism at the Carnegie Institution for Scie ...
at the Carnegie Institution for Science
The Carnegie Institution of Washington (the organization's legal name), known also for public purposes as the Carnegie Institution for Science (CIS), is an organization in the United States established to fund and perform scientific research. Th ...
, bringing the total to 69. On 17 July 2018, the International Astronomical Union
The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...
confirmed that Sheppard's team had discovered ten more moons around Jupiter, bringing the total number to 79. Among these is Valetudo, which has a prograde orbit, but crosses paths with several moons that have retrograde orbits, making an eventual collision—at some point on a billions-of-years timescale—likely.
In September 2020, researchers from the University of British Columbia
The University of British Columbia (UBC) is a public university, public research university with campuses near Vancouver and in Kelowna, British Columbia. Established in 1908, it is British Columbia's oldest university. The university ranks a ...
identified 45 candidate moons from an analysis of archival images taken in 2010 by the Canada-France-Hawaii Telescope. These candidates were mainly small and faint, down to a magnitude of 25.7 or over in diameter. From the number of candidate moons detected within a sky area of one square degree
__NOTOC__
A square degree (deg2) is a non- SI unit measure of solid angle. Other denotations include ''sq. deg.'' and (°)2. Just as degrees are used to measure parts of a circle, square degrees are used to measure parts of a sphere. Analogous to ...
, the team extrapolated that the population of retrograde Jovian moons brighter than magnitude 25.7 is around 600, within a factor of 2. Although the team considers their characterised candidates to be likely moons of Jupiter, they all remain unconfirmed due to their insufficient observation data for determining reliable orbits for each of them.
Naming
The Galilean moons of Jupiter ( Io, Europa
Europa may refer to:
Places
* Europe
* Europa (Roman province), a province within the Diocese of Thrace
* Europa (Seville Metro), Seville, Spain; a station on the Seville Metro
* Europa City, Paris, France; a planned development
* Europa Cliff ...
, Ganymede, and Callisto Callisto most commonly refers to:
*Callisto (mythology), a nymph
*Callisto (moon), a moon of Jupiter
Callisto may also refer to:
Art and entertainment
*''Callisto series'', a sequence of novels by Lin Carter
*''Callisto'', a novel by Torsten Kro ...
) were named by Simon Marius
Simon Marius ( latinized form of Simon Mayr; 10 January 1573 – 5 January 1625) was a German astronomer. He was born in Gunzenhausen, near Nuremberg, but spent most of his life in the city of Ansbach. He is most known for being among the first ...
soon after their discovery in 1610. However, these names fell out of favor until the 20th century. The astronomical literature instead simply referred to "Jupiter I", "Jupiter II", etc., or "the first satellite of Jupiter", "Jupiter's second satellite", and so on. The names Io, Europa, Ganymede, and Callisto became popular in the mid-20th century, whereas the rest of the moons remained unnamed and were usually numbered in Roman numerals V (5) to XII (12). Jupiter V was discovered in 1892 and given the name '' Amalthea'' by a popular though unofficial convention, a name first used by French astronomer Camille Flammarion
Nicolas Camille Flammarion FRAS (; 26 February 1842 – 3 June 1925) was a French astronomer and author. He was a prolific author of more than fifty titles, including popular science works about astronomy, several notable early science fiction ...
.
The other moons were simply labeled by their Roman numeral (e.g. Jupiter IX) in the majority of astronomical literature until the 1970s. Several different suggestions were made for names of Jupiter's outer satellites, but none were universally accepted until 1975 when the International Astronomical Union
The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...
's (IAU) Task Group for Outer Solar System Nomenclature granted names to satellites V–XIII, and provided for a formal naming process for future satellites still to be discovered. The practice was to name newly discovered moons of Jupiter after lovers and favorites of the god Jupiter
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
(Zeus
Zeus or , , ; grc, Δῐός, ''Diós'', label=Genitive case, genitive Aeolic Greek, Boeotian Aeolic and Doric Greek#Laconian, Laconian grc-dor, Δεύς, Deús ; grc, Δέος, ''Déos'', label=Genitive case, genitive el, Δίας, ''D ...
) and, since 2004, also after their descendants.[Gazetteer of Planetary Nomenclature](_blank)
Planet and Satellite Names and Discoverers ''International Astronomical Union (IAU)'' All of Jupiter's satellites from XXXIV (Euporie
In Greek mythology, Euporie or Euporia is the goddess of abundance. She is one of the third generation of Horae.
Sources
* Gaius Julius Hyginus, ''Fabulae
Gaius Julius Hyginus (; 64 BC – AD 17) was a Latin author, a pupil of the scholar ...
) onward are named after descendants of Jupiter or Zeus,[ except LIII ( Dia), named after a lover of Jupiter. Names ending with "a" or "o" are used for prograde irregular satellites (the latter for highly inclined satellites), and names ending with "e" are used for retrograde irregulars. With the discovery of smaller, kilometre-sized moons around Jupiter, the IAU has established an additional convention to limit the naming of small moons with ]absolute magnitude
Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse Logarithmic scale, logarithmic Magnitude (astronomy), astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent mag ...
s greater than 18 or diameters smaller than . Some of the most recently confirmed moons have not received names.
Some asteroid
An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere.
...
s share the same names as moons of Jupiter: 9 Metis
Metis ( minor planet designation: 9 Metis) is one of the larger main-belt asteroids. It is composed of silicates and metallic nickel-iron, and may be the core remnant of a large asteroid that was destroyed by an ancient collision. Metis is es ...
, 38 Leda
Leda ( minor planet designation: 38 Leda) is a large, dark main-belt asteroid that was discovered by French astronomer J. Chacornac on January 12, 1856, and named after Leda, the mother of Helen of Troy in Greek mythology. In the Tholen clas ...
, 52 Europa
Europa ( minor planet designation: 52 Europa) is the 6th-largest asteroid in the asteroid belt, having a diameter of over 300 km, though it is not correspondingly massive. It is not round but is shaped like an ellipsoid of approximately ...
, 85 Io
Io (minor planet designation: 85 Io is carbonaceous asteroid from the central region of the asteroid belt, approximately 170 kilometers in diameter. It is an identified Eunomian interloper.
Discovery and naming
It was discovered by C. H. F ...
, 113 Amalthea
113 Amalthea () is a stony Florian asteroid and binary system from the inner regions of the asteroid belt, approximately in diameter. It was discovered on 12 March 1871, by German astronomer Robert Luther at the Bilk Observatory in Düsseldorf, ...
, 239 Adrastea
Adrastea (minor planet designation: 239 Adrastea) is a main belt asteroid. It was discovered by Johann Palisa on 18 August 1884 in Vienna, and was named after the Greek nymph Adrasteia. This asteroid is orbiting the Sun at a distance of with a ...
. Two more asteroids previously shared the names of Jovian moons until spelling differences were made permanent by the IAU: Ganymede and asteroid 1036 Ganymed
1036 Ganymed, provisional designation ', is a stony asteroid on a highly eccentric orbit, classified as a near-Earth object of the Amor group. It was discovered by German astronomer Walter Baade at the Bergedorf Observatory in Hamburg on 23 Oct ...
; and Callisto Callisto most commonly refers to:
*Callisto (mythology), a nymph
*Callisto (moon), a moon of Jupiter
Callisto may also refer to:
Art and entertainment
*''Callisto series'', a sequence of novels by Lin Carter
*''Callisto'', a novel by Torsten Kro ...
and asteroid 204 Kallisto
Kallisto ( minor planet designation: 204 Kallisto) is a fairly typical, although sizeable Main belt asteroid. It is classified as an S-type asteroid. Like other asteroids of its type, it is light in colour. It was discovered by Johann Palisa on ...
.
Groups
Regular satellites
These have prograde and nearly circular orbits of low inclination and are split into two groups:
*''Inner satellites'' or ''Amalthea group'': Metis
Metis or Métis may refer to:
Ethnic groups
* Métis, recognized Indigenous communities in Canada and America whose distinct culture and language emerged after early intermarriage between First Nations peoples and early European settlers, prima ...
, Adrastea, Amalthea, and Thebe
Thebe may refer to:
* Any of several female characters in Greek mythology - see List of mythological figures named Thebe
* Thebe (moon), a moon of Jupiter
* Thebe (currency), 1/100 of a Botswana pula
* Thebe, an Amazons, Amazon
* Thebe, alternate ...
. These orbit very close to Jupiter; the innermost two orbit in less than a Jovian day. The latter two are respectively the fifth and seventh largest moons in the Jovian system. Observations suggest that at least the largest member, Amalthea, did not form on its present orbit, but farther from the planet, or that it is a captured Solar System body. These moons, along with a number of seen and as-yet-unseen inner moonlets (see Amalthea moonlets
Amalthea is a moon of Jupiter. It has the third closest orbit around Jupiter among known moons and was the fifth moon of Jupiter to be discovered, so it is also known as . It is also the fifth largest moon of Jupiter, after the four Galilean ...
), replenish and maintain Jupiter's faint ring system
A ring system is a disc or ring, orbiting an astronomical object, that is composed of solid material such as dust and moonlets, and is a common component of satellite systems around giant planets. A ring system around a planet is also known as ...
. Metis and Adrastea help to maintain Jupiter's main ring, whereas Amalthea and Thebe each maintain their own faint outer rings.
*''Main group'' or ''Galilean moons
The Galilean moons (), or Galilean satellites, are the four largest moons of Jupiter: Io, Europa, Ganymede, and Callisto. They were first seen by Galileo Galilei in December 1609 or January 1610, and recognized by him as satellites of Jupiter ...
'': Io, Europa
Europa may refer to:
Places
* Europe
* Europa (Roman province), a province within the Diocese of Thrace
* Europa (Seville Metro), Seville, Spain; a station on the Seville Metro
* Europa City, Paris, France; a planned development
* Europa Cliff ...
, Ganymede and Callisto Callisto most commonly refers to:
*Callisto (mythology), a nymph
*Callisto (moon), a moon of Jupiter
Callisto may also refer to:
Art and entertainment
*''Callisto series'', a sequence of novels by Lin Carter
*''Callisto'', a novel by Torsten Kro ...
. They are some of the largest objects in the Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
outside the Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
and the eight planets in terms of mass, larger than any known dwarf planet
A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to p ...
. Ganymede exceeds (and Callisto nearly equals) even the planet Mercury
Mercury commonly refers to:
* Mercury (planet), the nearest planet to the Sun
* Mercury (element), a metallic chemical element with the symbol Hg
* Mercury (mythology), a Roman god
Mercury or The Mercury may also refer to:
Companies
* Merc ...
in diameter, though they are less massive. They are respectively the fourth-, sixth-, first-, and third-largest natural satellite
A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body (or sometimes another natural satellite). Natural satellites are often colloquially referred to as ''moons'' ...
s in the Solar System, containing approximately 99.997% of the total mass in orbit around Jupiter, while Jupiter is almost 5,000 times more massive than the Galilean moons. The inner moons are in a 1:2:4 orbital resonance
In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relationsh ...
. Models suggest that they formed by slow accretion
Accretion may refer to:
Science
* Accretion (astrophysics), the formation of planets and other bodies by collection of material through gravity
* Accretion (meteorology), the process by which water vapor in clouds forms water droplets around nucl ...
in the low-density Jovian subnebula—a disc of the gas and dust that existed around Jupiter after its formation—which lasted up to 10 million years in the case of Callisto. Europa, Ganymede, and Callisto are suspected of having subsurface water oceans, and Io may have a subsurface magma
Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...
ocean.
Irregular satellites
The irregular satellites are substantially smaller objects with more distant and eccentric orbits. They form families with shared similarities in orbit (semi-major axis
In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the long ...
, inclination
Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object ...
, eccentricity
Eccentricity or eccentric may refer to:
* Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal"
Mathematics, science and technology Mathematics
* Off-center, in geometry
* Eccentricity (graph theory) of a v ...
) and composition; it is believed that these are at least partially collisional families that were created when larger (but still small) parent bodies were shattered by impacts from asteroids captured by Jupiter's gravitational field. These families bear the names of their largest members. The identification of satellite families is tentative, but the following are typically listed:
* Prograde satellites:
**Themisto
In Greek mythology, Themisto (; Ancient Greek: Θεμιστώ) was a Thessalin princess as the daughter of King Hypseus of LapithsApollodorus, 1.9.2 and the naiad Chlidanope. Her name is derived from the Ancient Greek word: "θεμιστος" wh ...
is the innermost irregular moon and is not part of a known family.[
**The Himalia group is spread over barely 1.4 Gm in semi-major axes, 1.6° in inclination (27.5 ± 0.8°), and eccentricities between 0.11 and 0.25. It has been suggested that the group could be a remnant of the break-up of an asteroid from the ]asteroid belt
The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, called ...
.[
** Carpo is another prograde moon and is not part of a known family. It has the highest inclination of all of the prograde moons.][
** Valetudo is the outermost prograde moon and is not part of a known family. Its prograde orbit crosses paths with several moons that have retrograde orbits and may in the future collide with them.]
* Retrograde satellites:
**The Carme group
The Carme group is a group of retrograde and direct motion, retrograde irregular satellites of Jupiter that follow similar orbits to Carme (moon), Carme and are thought to have a common origin.
Their semi-major axis, semi-major axes (distances f ...
is spread over only 1.2 Gm in semi-major axis
In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the long ...
, 1.6° in inclination (165.7 ± 0.8°), and eccentricities between 0.23 and 0.27. It is very homogeneous in color (light red) and is believed to have originated from a D-type asteroid
D-type asteroids have a very low albedo and a featureless reddish Asteroid spectral types, spectrum. It has been suggested that they have a composition of organic-rich silicates, carbon and anhydrous silicates, possibly with water ice in their inte ...
progenitor, possibly a Jupiter trojan
The Jupiter trojans, commonly called trojan asteroids or simply trojans, are a large group of asteroids that share the planet Jupiter's orbit around the Sun. Relative to Jupiter, each trojan librates around one of Jupiter's stable Lagrange poin ...
.
**The 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.
Their semi-major axes (distances from Jupiter) range between 19.3 and 22.7 Gm, their orbital ...
has a relatively wider spread than the previous groups, over 2.4 Gm in semi-major axis, 8.1° in inclination (between 145.7° and 154.8°), and eccentricities between 0.02 and 0.28. Most of the members appear gray, and are believed to have formed from the breakup of a captured asteroid.[
**The ]Pasiphae group The Pasiphae group is a group of retrograde irregular satellites of Jupiter that follow similar orbits to Pasiphae and are thought to have a common origin.
Their semi-major axes (distances from Jupiter) range between 22.8 and 24.1 million km (th ...
is quite dispersed, with a spread over 1.3 Gm, inclinations between 144.5° and 158.3°, and eccentricities between 0.25 and 0.43.[ The colors also vary significantly, from red to grey, which might be the result of multiple collisions. Sinope, sometimes included in the Pasiphae group,][ is red and, given the difference in inclination, it could have been captured independently;] Pasiphae and Sinope are also trapped in secular resonance A secular resonance is a type of orbital resonance between two bodies with synchronized precessional frequencies. In celestial mechanics, secular refers to the long-term motion of a system, and resonance is periods or frequencies being a simple nu ...
s with Jupiter.
List
The moons of Jupiter are listed below by orbital period. Moons massive enough for their surfaces to have collapsed into a spheroid
A spheroid, also known as an ellipsoid of revolution or rotational ellipsoid, is a quadric surface obtained by rotating an ellipse about one of its principal axes; in other words, an ellipsoid with two equal semi-diameters. A spheroid has cir ...
are highlighted in bold. These are the four Galilean moons
The Galilean moons (), or Galilean satellites, are the four largest moons of Jupiter: Io, Europa, Ganymede, and Callisto. They were first seen by Galileo Galilei in December 1609 or January 1610, and recognized by him as satellites of Jupiter ...
, which are comparable in size to the Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
. The other moons are much smaller, with the least massive Galilean moon being more than 7,000 times more massive than the most massive of the other moons. The irregular captured moons are shaded light gray when prograde and dark gray when retrograde. The orbits and mean distances of the irregular moons are strongly variable over short timescales due to frequent planetary and solar perturbations, therefore the listed orbital elements of all irregular moons are averaged over a 400-year numerical integration
In analysis, numerical integration comprises a broad family of algorithms for calculating the numerical value of a definite integral, and by extension, the term is also sometimes used to describe the numerical solution of differential equations ...
. Their orbital elements are all based on the epoch
In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured.
The moment of epoch is usually decided by ...
of 1 January 2000.[ Note: Orbital elements of regular satellites are with respect to the ]Laplace plane The Laplace plane or Laplacian plane of a planetary satellite, named after its discoverer Pierre-Simon Laplace (1749–1827), is a mean or reference plane about whose axis the instantaneous orbital plane of that satellite precesses.
Laplace's ...
, while orbital elements of irregular satellites are with respect to the ecliptic
The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic again ...
. Orbital periods of irregular satellites may not be consistent with their semi-major axes due to perturbations. A number of other moons have only been observed for a year or two, but have decent enough orbits to be easily measurable at present.
Exploration
Nine spacecraft have visited Jupiter. The first were '' Pioneer 10'' in 1973, and '' Pioneer 11'' a year later, taking low-resolution images of the four Galilean moons and returning data on their atmospheres and radiation belts. The ''Voyager 1
''Voyager 1'' is a space probe launched by NASA on September 5, 1977, as part of the Voyager program to study the outer Solar System and interstellar space beyond the Sun's heliosphere. Launched 16 days after its twin ''Voyager 2'', ''Voyag ...
'' and ''Voyager 2
''Voyager 2'' is a space probe launched by NASA on August 20, 1977, to study the outer planets and interstellar space beyond the Sun's heliosphere. As a part of the Voyager program, it was launched 16 days before its twin, ''Voyager 1'', on a ...
'' probes visited Jupiter in 1979, discovering the volcanic activity on Io and the presence of water ice
Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaq ...
on the surface of Europa
Europa may refer to:
Places
* Europe
* Europa (Roman province), a province within the Diocese of Thrace
* Europa (Seville Metro), Seville, Spain; a station on the Seville Metro
* Europa City, Paris, France; a planned development
* Europa Cliff ...
. ''Ulysses
Ulysses is one form of the Roman name for Odysseus, a hero in ancient Greek literature.
Ulysses may also refer to:
People
* Ulysses (given name), including a list of people with this name
Places in the United States
* Ulysses, Kansas
* Ulysse ...
'' further studied Jupiter's magnetosphere in 1992 and then again in 2000.
The ''Galileo
Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He was ...
'' spacecraft was the first to enter orbit around Jupiter, arriving in 1995 and studying it until 2003. During this period, ''Galileo'' gathered a large amount of information about the Jovian system, making close approaches to all of the Galilean moons and finding evidence for thin atmospheres on three of them, as well as the possibility of liquid water beneath the surfaces of Europa, Ganymede, and Callisto. It also discovered a magnetic field around Ganymede.
Then the '' Cassini'' probe to Saturn flew by Jupiter in 2000 and collected data on interactions of the Galilean moons with Jupiter's extended atmosphere. The ''New Horizons
''New Horizons'' is an Interplanetary spaceflight, interplanetary space probe that was launched as a part of NASA's New Frontiers program. Engineered by the Johns Hopkins University Applied Physics Laboratory (APL) and the Southwest Research ...
'' spacecraft flew by Jupiter in 2007 and made improved measurements of its satellites' orbital parameters.
In 2016, the ''Juno
Juno commonly refers to:
*Juno (mythology), the Roman goddess of marriage and queen of the gods
*Juno (film), ''Juno'' (film), 2007
Juno may also refer to:
Arts, entertainment and media Fictional characters
*Juno, in the film ''Jenny, Juno''
*Ju ...
'' spacecraft imaged the Galilean moons from above their orbital plane as it approached Jupiter orbit insertion, creating a time-lapse movie of their motion.Juno Approach Movie of Jupiter and the Galilean Moons
NASA, July 2016
See also
* Jupiter's moons in fiction
Jupiter, the largest planet in the Solar System, has appeared in works of fiction across several centuries. The way the planet has been depicted has evolved as more has become known about its composition; it was initially portrayed as being entir ...
* Satellite system (astronomy)
A satellite system is a set of gravitationally bound objects in orbit around a planetary mass object (incl. sub-brown dwarfs and rogue planets) or minor planet, or its barycenter. Generally speaking, it is a set of natural satellites (moons), al ...
Notes
References
External links
* Scott S. Sheppard
Scott Sander Sheppard (born 1977) is an American astronomer and a discoverer of numerous moons, comets and minor planets in the outer Solar System.
He is an astronomer in the Department of Terrestrial Magnetism at the Carnegie Institution for Scie ...
Moons of Jupiter
* Scott S. Sheppard
The Jupiter Satellite and Moon Page
Jupiter Moons
b
NASA's Solar System Exploration
i
* Tilmann Denk
Outer Moons of Jupiter
{{DEFAULTSORT:Moons Of Jupiter
Lists of moons