Moons of Jupiter

Last updated

A montage of Jupiter and its four largest moons (distance and sizes not to scale) Jupiter family.jpg
A montage of Jupiter and its four largest moons (distance and sizes not to scale)

There are 80 known moons of Jupiter, 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: Io; Europa; Ganymede; and Callisto, which were independently discovered in 1610 by Galileo Galilei and Simon Marius and were the first objects found to orbit a body that was neither Earth nor the Sun. 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 Jupiter or his Greek equivalent Zeus. The Galilean moons are by far the largest and most massive objects to orbit Jupiter, with the remaining 76 known moons and the rings together composing just 0.003% of the total orbiting mass.


Of Jupiter's moons, eight are regular satellites with prograde and nearly circular orbits that are not greatly inclined with respect to Jupiter's equatorial plane. The Galilean satellites are nearly spherical in shape due to their planetary mass, and so would be considered at least dwarf planets 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 whose prograde and retrograde orbits are much farther from Jupiter and have high inclinations and eccentricities. These moons were probably captured by Jupiter from solar orbits. Twenty-three of the irregular satellites have not yet been officially named.


The Galilean moons. From left to right, in order of increasing distance from Jupiter: Io; Europa; Ganymede; Callisto. The Galilean satellites (the four largest moons of Jupiter).tif
The Galilean moons. From left to right, in order of increasing distance from Jupiter: Io; Europa; Ganymede; Callisto.

The physical and orbital characteristics of the moons vary widely. The four Galileans are all over 3,100 kilometres (1,900 mi) in diameter; the largest Galilean, Ganymede, is the ninth largest object in the Solar System, after the Sun and seven of the planets, Ganymede being larger than Mercury. All other Jovian moons are less than 250 kilometres (160 mi) in diameter, with most barely exceeding 5 kilometres (3.1 mi). [note 1] Their orbital shapes range from nearly perfectly circular to highly eccentric and inclined, and many revolve in the direction opposite to Jupiter's rotation (retrograde motion). Orbital periods 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

The relative masses of the Jovian moons. Those smaller than Europa are not visible at this scale, and combined would only be visible at 100x magnification. Relative Masses of Jovian Satellites.png
The relative masses of the Jovian moons. Those smaller than Europa are not visible at this scale, and combined would only be visible at 100× magnification.

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. [1] [2] They may be the remnants of a score of Galilean-mass satellites that formed early in Jupiter's history. [1] [3]

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. [1] 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. [1] By the time the present (possibly fifth) generation formed, the disk had thinned so that it no longer greatly interfered with the moons' orbits. [3] The current Galilean moons were still affected, falling into and being partially protected by an orbital resonance with each other, which still exists for Io, Europa, and Ganymede. Ganymede's larger mass means that it would have migrated inward at a faster rate than Europa or Io. [1]

The outer, irregular moons are thought to have originated from captured asteroids, 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. [4]


Jupiter and the Galilean moons through a 25 cm (10 in) Meade LX200 telescope. Jupiter-moons.jpg
Jupiter and the Galilean moons through a 25 cm (10 in) Meade LX200 telescope.
The number of moons known for each of the four outer planets up to October 2019. Jupiter currently has 80 known satellites. Outer planet moons.svg
The number of moons known for each of the four outer planets up to October 2019. Jupiter currently has 80 known satellites.

Chinese historian Xi Zezong claimed that the earliest record of a Jovian moon (Ganymede or Callisto) was a note by Chinese astronomer Gan De of an observation around 364 BC regarding a "reddish star". [5] However, the first certain observations of Jupiter's satellites were those of Galileo Galilei in 1609. [6] By January 1610, he had sighted the four massive Galilean moons with his 20× magnification telescope, and he published his results in March 1610. [7]

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, Io, and Europa. [8] No additional satellites were discovered until E. E. Barnard observed Amalthea in 1892. [9]

With the aid of telescopic photography, further discoveries followed quickly over the course of the 20th century. Himalia was discovered in 1904, [10] Elara in 1905, [11] Pasiphae in 1908, [12] Sinope in 1914, [13] Lysithea and Carme in 1938, [14] Ananke in 1951, [15] and Leda in 1974. [16] By the time that the Voyager space probes reached Jupiter, around 1979, 13 moons had been discovered, not including Themisto, which had been observed in 1975, [17] but was lost until 2000 due to insufficient initial observation data. The Voyager spacecraft discovered an additional three inner moons in 1979: Metis, Adrastea, and Thebe. [18]

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. [19] These are tiny moons, in long, eccentric, generally retrograde orbits, and averaging 3 km (1.9 mi) in diameter, with the largest being just 9 km (5.6 mi) across. All of these moons are thought to have been captured asteroidal or perhaps comet bodies, possibly fragmented into several pieces. [20] [21]

By 2015, a total of 15 additional moons were discovered. [21] Two more were discovered in 2016 by the team led by Scott S. Sheppard at the Carnegie Institution for Science, bringing the total to 69. [22] On 17 July 2018, the International Astronomical Union confirmed that Sheppard's team had discovered ten more moons around Jupiter, bringing the total number to 79. [23] 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. [23]

In September 2020, researchers from the University of British Columbia identified 45 candidate moons from an analysis of archival images taken in 2010 by the Canada-France-Hawaii Telescope. [24] These candidates were mainly small and faint, down to a magnitude of 25.7 or over 800 m (0.50 mi) in diameter. From the number of candidate moons detected within a sky area of one square degree, the team extrapolated that the population of retrograde Jovian moons brighter than magnitude 25.7 is around 600, within a factor of 2. [25] 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. [24]


Galilean moons around Jupiter
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Jupiter *
Io *
Europa *
Ganymede *
Callisto Galilean moons around Jupiter.gif
Galilean moons around Jupiter   Jupiter ·  Io ·  Europa ·  Ganymede ·  Callisto
Orbits of Jupiter's inner moons within its rings PIA01627 Ringe.jpg
Orbits of Jupiter's inner moons within its rings

The Galilean moons of Jupiter (Io, Europa, Ganymede, and Callisto) were named by Simon Marius soon after their discovery in 1610. [26] 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. [26] The names Io, Europa, Ganymede, and Callisto became popular in the mid-20th century, [27] whereas the rest of the moons remained unnamed and were usually numbered in Roman numerals V (5) to XII (12). [28] [29] 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. [19] [30]

The other moons were simply labeled by their Roman numeral (e.g. Jupiter IX) in the majority of astronomical literature until the 1970s. [31] Several different suggestions were made for names of Jupiter's outer satellites, but none were universally accepted until 1975 when the International Astronomical Union's (IAU) Task Group for Outer Solar System Nomenclature granted names to satellites V–XIII, [32] and provided for a formal naming process for future satellites still to be discovered. [32] The practice was to name newly discovered moons of Jupiter after lovers and favorites of the god Jupiter (Zeus) and, since 2004, also after their descendants. [19] All of Jupiter's satellites from XXXIV (Euporie) onward are named after descendants of Jupiter or Zeus, [19] 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. [33] 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 magnitudes greater than 18 or diameters smaller than 1 km (0.62 mi). [34] Some of the most recently confirmed moons have not received names.

Some asteroids share the same names as moons of Jupiter: 9 Metis, 38 Leda, 52 Europa, 85 Io, 113 Amalthea, 239 Adrastea. Two more asteroids previously shared the names of Jovian moons until spelling differences were made permanent by the IAU: Ganymede and asteroid 1036 Ganymed; and Callisto and asteroid 204 Kallisto.


The orbits of Jupiter's irregular satellites, and how they cluster into groups: by semi-major axis (the horizontal axis in Gm); by orbital inclination (the vertical axis); and orbital eccentricity (the yellow lines). The relative sizes are indicated by the circles. TheIrregulars JUPITER.svg
The orbits of Jupiter's irregular satellites, and how they cluster into groups: by semi-major axis (the horizontal axis in Gm); by orbital inclination (the vertical axis); and orbital eccentricity (the yellow lines). The relative sizes are indicated by the circles.

Regular satellites

These have prograde and nearly circular orbits of low inclination and are split into two groups:

Irregular satellites

Orbits and positions of Jupiter's irregular satellites as of 1 January 2021. Prograde orbits are colored blue while retrograde orbits are colored red. Jupiter irregular moon orbits Jan 2021.png
Orbits and positions of Jupiter's irregular satellites as of 1 January 2021. Prograde orbits are colored blue while retrograde orbits are colored red.
Inclinations (deg) vs. eccentricities of Jupiter's irregular satellites, with the major groups identified. Data as of 2021. Jupiter moons e vs i.png
Inclinations (°) vs. eccentricities of Jupiter's irregular satellites, with the major groups identified. Data as of 2021.

The irregular satellites are substantially smaller objects with more distant and eccentric orbits. They form families with shared similarities in orbit (semi-major axis, inclination, eccentricity) 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: [42] [43] [44]


The moons of Jupiter are listed below by orbital period. Moons massive enough for their surfaces to have collapsed into a spheroid are highlighted in bold. These are the four Galilean moons, which are comparable in size to the Moon. 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, [46] therefore the epochs of all orbital elements listed are based on the Julian date of 2459200.5, or 17 December 2020. [47] As of 2021, S/2003 J 10 is the only moon of Jupiter considered lost due to its uncertain orbit. [48] 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. [46]

Inner moons

Galilean moons

Ungrouped moons

Himalia group

Ananke group

Carme group

Pasiphae group
[note 3]
[note 4]
PronunciationImage Abs.
Diameter (km) [note 5] Mass
(×1016 kg)
Semi-major axis
(km) [49]
Orbital period (d)
[49] [note 6]
(°) [49]
Discoverer [19] Group
[note 7]
1XVI Metis /ˈmtəs/
(+7h 10m 16s)
2.2260.00771979 Synnott
( Voyager 1 )
2XV Adrastea /ædrəˈstə/
(+7h 15m 21s)
2.2170.00631979 Jewitt
( Voyager 2 )
3V Amalthea /æməlˈθə/ [50]
Amalthea (moon).png
(+12h 01m 46s)
2.5650.00751892 Barnard Inner
4XIV Thebe /ˈθb/
(+16h 16m 02s)
(Voyager 1)
5I Io /ˈ/
Io highest resolution true color frame.jpg
8931900421700+1.76910.050 [51] 0.00411610 Galilei Galilean
6II Europa /jʊəˈrpə/ [52]
−1.43121.64799800671034+3.55120.471 [51] 0.00941610Galilei Galilean
7III Ganymede /ˈɡænəmd/ [53] [54]
Ganymede - Perijove 34 Composite.png
−2.15268.2148190001070412+7.15460.204 [51] 0.00111610Galilei Galilean
8IV Callisto /kəˈlɪst/
−1.24820.6107590001882709+16.6890.205 [51] 0.00741610Galilei Galilean
9XVIII Themisto /θəˈmɪst/
S 2000 J 1.jpg
12.990.0697405000+130.1844.5900.25141975/2000 Kowal & Roemer/
Sheppard et al.
10XIII Leda /ˈldə/
Leda WISE-W3.jpg
12.721.50.611196000+242.0227.6410.16481974 Kowal Himalia
11LXXI Ersa /ˈɜːrsə/
Ersa CFHT precovery 2003-02-24.png
15.930.004511348700+246.9931.0280.10432018Sheppard et al. Himalia
12LXV Pandia /pænˈdə/
Pandia CFHT precovery 2003-02-28.png
16.230.004511462300+250.7127.0230.20842017Sheppard et al. Himalia
13VI Himalia /hɪˈmliə/
Cassini-Huygens Image of Himalia.png
42011497400+251.8630.2140.15101904 Perrine Himalia
14X Lysithea /lˈsɪθiə/
Lysithea2.jpg Nicholson Himalia
15VII Elara /ˈɛlərə/
Elara - New Horizons.png
9.679.98711671600+257.6030.2160.20791905Perrine Himalia
16LIII Dia /ˈdə/
Dia-Jewitt-CFHT image-crop.png
16.340.00912304900+278.8527.4810.26062000Sheppard et al. Himalia
17XLVI Carpo /ˈkɑːrp/
Carpo CFHT 2003-02-25 annotated.gif
16.130.004517151800+458.9050.1380.49672003Sheppard et al.Carpo
18LXII Valetudo /væləˈtjd/
Valetudo CFHT precovery 2003-02-28 annotated.gif
17.010.0001518819000+527.4132.0330.20182016Sheppard et al.Valetudo
19XXXIV Euporie /ˈjpər/
16.320.001519593900−560.32147.8510.14022001Sheppard et al. Ananke
20LX Eupheme /jˈfm/
Eupheme CFHT 2003-02-25 annotated.gif
16.620.001520126300−583.31150.0420.41042003Sheppard et al. Ananke
21 LV S/2003 J 18
2003 J 18 CFHT recovery full.gif
16.520.001520348800−593.01142.7830.04652003Gladman et al. Ananke
22 LII S/2010 J 2
2010 J 2 CFHT discovery full.gif
17.310.0001520436700−596.86148.6970.34032010Veillet Ananke
23XLV Helike /ˈhɛlək/
Helike CFHT 2003-02-25 annotated.gif
16.040.00920479500−598.74155.0670.13312003Sheppard et al. Ananke
24  S/2003 J 16
2003 J 16 CFHT recovery full.gif
16.320.001520512500−600.18151.1630.33312003Gladman et al. Ananke
25  S/2003 J 2
2003 J 2 Gladman CFHT annotated.gif
16.720.001520554400−602.02149.2040.27772003Sheppard et al. Ananke
26XXXIII Euanthe /jˈænθ/
16.430.004520583300−603.29146.8080.10962001Sheppard et al. Ananke
27 LXVIII S/2017 J 716.620.001520600100−604.03146.7390.26262017Sheppard et al. Ananke
28XXX Hermippe /hərˈmɪp/
15.640.00920666200−606.94146.7530.19812001Sheppard et al. Ananke
29XXVII Praxidike /prækˈsɪdək/
14.970.04320682900−607.68149.6920.29592000Sheppard et al. Ananke
30XXIX Thyone /θˈn/
15.840.00920712800−609.00147.3280.17702001Sheppard et al. Ananke
31XLII Thelxinoe /θɛlkˈsɪn/ 16.320.001520893300−616.97146.9160.17092003Sheppard et al. Ananke
32 LXIV S/2017 J 3
2017 J 3 CFHT 2003-12-25 annotated.gif
16.520.001520976900−620.68147.9680.19072017Sheppard et al. Ananke
33XII Ananke /əˈnæŋk/
11.729.13.021042500−623.59148.6750.17471951Nicholson Ananke
34XL Mneme /ˈnm/
Mneme Discovery Image.jpg
16.320.001521064100−624.55151.0870.34282003 Gladman et al. Ananke
35 LIV S/2016 J 1
2016 J 1 CFHT 2003-02-26 annotated.gif
16.810.0001521154000−628.56143.8240.12942016Sheppard et al. Ananke
36XXXV Orthosie /ɔːrˈθz/
16.720.001521171000−629.31148.4880.48382001Sheppard et al. Ananke
37XXII Harpalyke /hɑːrˈpælək/
15.940.00921280200−634.19148.2980.16022000Sheppard et al. Ananke
38XXIV Iocaste /əˈkæst/
15.450.01921431800−640.98149.4240.32952000Sheppard et al. Ananke
39 LXX S/2017 J 916.130.004521492900−643.72155.7750.25242017Sheppard et al. Ananke
40  S/2003 J 12
2003 J 12 Gladman CFHT annotated.gif
17.010.0001521557700−646.64154.6900.36572003Sheppard et al. Ananke
41  S/2003 J 4
2003 J 4 Gladman CFHT annotated.gif
16.720.001522048600−668.85149.4010.49672003Sheppard et al. Pasiphae
42XXV Erinome /ɛˈrɪnəm/ (?)
16.030.004522354300−682.80164.8210.20522000Sheppard et al. Carme
43XXXI Aitne /ˈtn/
16.030.004522386500−684.28166.2380.31502001Sheppard et al. Carme
44L Herse /ˈhɜːrs/ 16.520.001522408800−685.30164.3470.18542003Gladman et al. Carme
45XX Taygete /tˈɪət/
15.550.01622433500−686.44163.2610.32572000Sheppard et al. Carme
46 LXIII S/2017 J 2
2017 J 2 CFHT 2003-02-26 annotated.gif
16.420.001522472900−688.25165.6760.38522017Sheppard et al. Carme
47 LXVII S/2017 J 616.420.001522543800−691.51155.1850.32262017Sheppard et al. Pasiphae
48XLVII Eukelade /jˈkɛləd/
Eukelade s2003j1movie arrow.gif
15.940.00922576700−693.02163.8220.27902003Sheppard et al. Carme
49XI Carme /ˈkɑːrm/
10.646.71322579900−693.17163.5350.22951938Nicholson Carme
50 LXI S/2003 J 1916.620.001522752500−701.13167.7380.29282003Gladman et al. Carme
51XXVI Isonoe /ˈsɒn/
16.040.00922776700−702.25162.8340.21592000Sheppard et al. Carme
52(lost) S/2003 J 10
2003 J 10 Gladman CFHT annotated.gif
16.820.001522896200−707.78163.4810.20662003Sheppard et al. Carme?
53XXVIII Autonoe /ɔːˈtɒn/
15.540.00922933400−709.51148.1450.42902001Sheppard et al. Pasiphae
54LVIII Philophrosyne /fɪləˈfrɒzən/ 16.720.001522939900−709.81147.9000.30132003Sheppard et al. Pasiphae
55XLVIII Cyllene /səˈln/ 16.320.001522965200−710.99150.0470.60792003Sheppard et al. Pasiphae
56XXXVIII Pasithee /ˈpæsəθ/
16.820.001522967800−711.11164.7270.20972001Sheppard et al. Carme
57 LI S/2010 J 1
2010 J 1 CFHT image.gif
16.420.001522986900−712.00164.5590.29372010Jacobson et al. Carme
58  S/2003 J 2416.630.004523088000−715.4162.1050.25452003Sheppard et al. Carme
59VIII Pasiphae /pəˈsɪf/
10.157.83023119300−718.16151.9980.43621908 Melotte Pasiphae
60XXXVI Sponde /ˈspɒnd/
16.720.001523146500−719.42144.5630.34552001Sheppard et al. Pasiphae
61 LXIX S/2017 J 8
2017 J 8 CFHT precovery full.gif
17.010.0001523173700−720.69166.0710.20392017Sheppard et al. Carme
62XXXII Eurydome /jʊəˈrɪdəm/
16.230.004523214500−722.59150.2890.29752001Sheppard et al. Pasiphae
63 LXVI S/2017 J 516.520.001523352500−729.05166.5550.24602017Sheppard et al. Carme
64XXIII Kalyke /ˈkælək/
Kalyke-Jewitt-CFHT-annotated.gif−730.21166.8990.26602000Sheppard et al. Carme
65XXXIX Hegemone /həˈɛmən/ 15.930.004523422300−732.32154.6750.33582003Sheppard et al. Pasiphae
66XXXVII Kale /ˈkl/
16.420.001523512200−736.54166.1770.28932001Sheppard et al. Carme
67XLIV Kallichore /kəˈlɪkər/ 16.420.001523552900−738.45167.7270.31832003Sheppard et al. Carme
68 LXXII S/2011 J 116.720.001523714400−746.06164.7990.31932011Sheppard et al. Carme
69 LIX S/2017 J 1
2016 J 1 CFHT 2003-02-26 annotated.gif
16.620.001523753600−747.91147.2530.45002017Sheppard et al. Pasiphae
70XXI Chaldene /kælˈdn/
16.040.00923848300−752.39162.7490.27052000Sheppard et al. Carme
71XLIII Arche /ˈɑːrk/
16.230.004523926500−756.09166.4080.23672002Sheppard et al. Carme
72LVII Eirene /ˈrn/ 15.840.00923934500−756.47162.7130.24132003Sheppard et al. Carme
73XLIX Kore /ˈkɔːr/
Kore s2003j14movie circled.gif
16.620.001523999700−759.56136.6280.23472003Sheppard et al. Pasiphae
74 LVI S/2011 J 216.810.0001524114700−765.03152.1250.17292011Sheppard et al. Pasiphae
75  S/2003 J 9
2003 J 9 Gladman CFHT annotated.gif
16.910.0001524168700−767.60166.3340.17022003Sheppard et al. Carme
76XIX Megaclite /ˌmɛɡəˈklt/
15.050.02124212300−769.68145.5740.31392000Sheppard et al. Pasiphae
77XLI Aoede /ˈd/ 15.640.00924283000−773.05151.9080.31312003Sheppard et al. Pasiphae
78  S/2003 J 23
16.620.001524678200−792.00146.1550.32082003Sheppard et al. Pasiphae
79XVII Callirrhoe /kəˈlɪr/
Callirrhoe - New Horizons.gif−792.69149.7920.35621999Scotti et al. Pasiphae
80IX Sinope /səˈnp/
11.1357.524864100−800.97158.5970.16691914Nicholson Pasiphae


The orbit and motion of the Galilean moons around Jupiter, as captured by JunoCam aboard the Juno spacecraft. Jupiter and the Galilean moons animation.gif
The orbit and motion of the Galilean moons around Jupiter, as captured by JunoCam aboard the Juno spacecraft.

The first spacecraft to visit Jupiter 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. [55] The Voyager 1 and Voyager 2 probes visited Jupiter in 1979, discovering the volcanic activity on Io and the presence of water ice on the surface of Europa. 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 spacecraft flew by Jupiter in 2007 and made improved measurements of its satellites' orbital parameters.

The Galileo 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.

Ganymede taken by Juno during its 34th perijove. Ganymede JunoGill 2217.jpg
Ganymede taken by Juno during its 34th perijove.

In 2016, the Juno spacecraft imaged the Galilean moons from above their orbital plane as it approached Jupiter orbit insertion, creating a time-lapse movie of their motion. [56]

See also


  1. For comparison, the area of a sphere with diameter 250 km is about the area of Senegal and comparable to the area of Belarus, Syria and Uruguay. The area of a sphere with a diameter of 5 km is about the area of Guernsey and somewhat more than the area of San Marino. (But note that these smaller moons are not spherical.)
  2. Jupiter Mass of 1.8986 × 1027 kg / Mass of Galilean moons 3.93 × 1023 kg = 4,828
  3. Order refers to the position among other moons with respect to their average distance from Jupiter.
  4. Label refers to the Roman numeral attributed to each moon in order of their naming.
  5. Diameters with multiple entries such as "60×40×34" reflect that the body is not a perfect spheroid and that each of its dimensions has been measured well enough.
  6. Periods with negative values are retrograde.
  7. "?" refers to group assignments that are not considered sure yet.

Related Research Articles

Galilean moons Four largest moons of Jupiter

The Galilean moons 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 in March 1610. They were the first objects found to orbit a planet other than the Earth.

Callisto (moon) Second largest Galilean moon of Jupiter and third largest in the solar system

Callisto, or Jupiter IV, is the second-largest moon of Jupiter, after Ganymede. It is the third-largest moon in the Solar System after Ganymede and Saturn's largest moon Titan, and the largest object in the Solar System that may not be properly differentiated. Callisto was discovered in 1610 by Galileo Galilei. At 4821 km in diameter, Callisto has about 99% the diameter of the planet Mercury but only about a third of its mass. It is the fourth Galilean moon of Jupiter by distance, with an orbital radius of about 1883000 km. It is not in an orbital resonance like the three other Galilean satellites—Io, Europa, and Ganymede—and is thus not appreciably tidally heated. Callisto's rotation is tidally locked to its orbit around Jupiter, so that the same hemisphere always faces inward. Because of this, there is a sub-Jovian point on Callisto's surface, from which Jupiter would appear to hang directly overhead. It is less affected by Jupiter's magnetosphere than the other inner satellites because of its more remote orbit, located just outside Jupiter's main radiation belt.

Amalthea (moon) Moon of Jupiter

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 Jupiter V. It is also the fifth largest moon of Jupiter, after the four Galilean Moons. Edward Emerson Barnard discovered the moon on 9 September 1892 and named it after Amalthea of Greek mythology. It was the last natural satellite to be discovered by direct visual observation; all later moons were discovered by photographic or digital imaging.

Natural satellite Astronomical body that orbits a planet

A natural satellite is in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small solar system body. While natural satellites are often colloquially referred to as moons, there is only the Moon of Earth.

Ganymede (moon) Largest moon of Jupiter and in the Solar System

Ganymede, a satellite of Jupiter, is the largest and most massive of the Solar System's moons. The ninth-largest object of the Solar System, it is the largest without a substantial atmosphere. It has a diameter of 5,268 km (3,273 mi), making it 26% larger than the planet Mercury by volume, although it is only 45% as massive. Possessing a metallic core, it has the lowest moment of inertia factor of any solid body in the Solar System and is the only moon known to have a magnetic field. Outward from Jupiter, it is the seventh satellite and the third of the Galilean moons, the first group of objects discovered orbiting another planet. Ganymede orbits Jupiter in roughly seven days and is in a 1:2:4 orbital resonance with the moons Europa and Io, respectively.

Thebe (moon) Moon of Jupiter

Thebe, also known as Jupiter XIV, is the fourth of Jupiter's moons by distance from the planet. It was discovered by Stephen P. Synnott in images from the Voyager 1 space probe taken on March 5, 1979, while making its flyby of Jupiter. In 1983, it was officially named after the mythological nymph Thebe.

Ananke (moon) Moon of Jupiter

Ananke is a retrograde irregular moon 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 Moirai (Fates) by Zeus. The adjectival form of the name is Anankean.

Pasiphae (moon) Moon of Jupiter

Pasiphae, formerly spelled Pasiphaë, is a retrograde irregular satellite of Jupiter. It was discovered in 1908 by Philibert Jacques Melotte and later named after the mythological Pasiphaë, wife of Minos and mother of the Minotaur from Greek legend.

Sinope (moon) Moon of Jupiter

Sinope is a retrograde irregular satellite of Jupiter discovered by Seth Barnes Nicholson at Lick Observatory in 1914, and is named after Sinope of Greek mythology.

The naming of moons has been the responsibility of the International Astronomical Union's committee for Planetary System Nomenclature since 1973. That committee is known today as the Working Group for Planetary System Nomenclature (WGPSN).

Himalia group

The Himalia group is a group of prograde irregular satellites of Jupiter that follow similar orbits to Himalia and are thought to have a common origin.

Solar eclipses on Jupiter When moons of Jupiter pass before the Sun

Solar eclipses on Jupiter occur when any of the natural satellites of Jupiter pass in front of the Sun as seen from the planet Jupiter.

Irregular moon Captured satellite following an irregular orbit

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 satellites, which formed in orbit around them. Irregular moons have a stable orbit, unlike temporary satellites which often have similarly irregular orbits but will eventually depart. The term does not refer to shape as Triton is a round moon, but is considered irregular due to its orbit.

Jupiters moons in fiction

Jupiter's extensive system of natural satellites – in particular the four large Galilean moons – has been a common science fiction setting.

The exploration of Jupiter has been conducted via close observations by automated spacecraft. It began with the arrival of Pioneer 10 into the Jovian system in 1973, and, as of 2016, has continued with eight further spacecraft missions. All of these missions were undertaken by the National Aeronautics and Space Administration (NASA), and all but two were flybys taking detailed observations without landing or entering orbit. These probes make Jupiter the most visited of the Solar System's outer planets as all missions to the outer Solar System have used Jupiter flybys. On 5 July 2016, spacecraft Juno arrived and entered the planet's orbit—the second craft ever to do so. Sending a craft to Jupiter is difficult, mostly due to large fuel requirements and the effects of the planet's harsh radiation environment.

Exploration of Io Overview of the exploration of Io, Jupiters innermost Galilean and third-largest moon

The exploration of Io, Jupiter's innermost Galilean and third-largest moon, began with its discovery in 1610 and continues today with Earth-based observations and visits by spacecraft to the Jupiter system. Italian astronomer Galileo Galilei was the first to record an observation of Io on January 8, 1610, though Simon Marius may have also observed Io at around the same time. During the 17th century, observations of Io and the other Galilean satellites helped with the measurement of longitude by map makers and surveyors, with validation of Kepler's Third Law of planetary motion, and with measurement of the speed of light. Based on ephemerides produced by astronomer Giovanni Cassini and others, Pierre-Simon Laplace created a mathematical theory to explain the resonant orbits of three of Jupiter's moons, Io, Europa, and Ganymede. This resonance was later found to have a profound effect on the geologies of these moons. Improved telescope technology in the late 19th and 20th centuries allowed astronomers to resolve large-scale surface features on Io as well as to estimate its diameter and mass.

Planetary-mass moon Moons comparable in size to small planets

A planetary-mass moon is a planetary-mass object that is also a natural satellite. They are large and ellipsoidal in shape. Two moons in the Solar System are larger than the planet Mercury : Ganymede and Titan, and seven are larger and more massive than the dwarf planet Pluto.

The following outline is provided as an overview of and topical guide to Jupiter:

Gan De is the tentative name for a proposed interplanetary mission by China to study the Jupiter system and its environs.


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