How Many Moons Does Jupiter Have? Learn the Surprising Truth

Satellites of Jupiter
Jupiter is quite the crowd-puller as far as satellites are concerned. With 50 named satellites and counting, the giant planet has only just begun revealing its secrets.
ESA Orders Some JUICE for Jupiter
The European Space Agency (ESA) will launch JUICE (JUpiter ICy moons Explorer) in 2022 to explore Jupiter's moons - Europa, Callisto and Ganymede for habitability, as future targets for space colonization.
Jupiter has a record 67 satellites, of which only fifty are named till date, rest of the 17 being provisional moons - yet to be named after a Greek mythical character, as is the tradition. Jupiter is the largest of all Jovian planets (gaseous planets) and also the largest in our solar system. Its mass is almost one thousandth of the Sun (0.0009546 Solar Mass), that is 317.83 times Earth Mass or 1.8981 x 1027 Kg. With such an enormous amount of mass concentrated within, the gravitational pull of Jupiter is phenomenal. No small object can escape the gravitational tug of the planet within its domain of influence. That may be the reason why Jupiter has the largest number of satellites orbiting it. Most of them may be captured asteroids. Let me introduce you to the many moons imprisoned by the gas giant's gravity for eternity.
Moons of Jupiter
The 67 satellites include four Galilean Moons that are the largest of all. About 99.997% of the orbiting mass around Jupiter is concentrated in the four large Galilean moons, while the rest (0.003%) is distributed among the rings and smaller satellites. Here is a short introduction to every one of the known satellites of Jupiter. (Note: +/- indicate prograde/retrograde motion)
Ganymede
Diameter- 5,262.4 Km
Mass- 14.819 x 1022 Kg
Semi-Major Axis- 1,070,412 Km
Orbital Period
(In Earth Days) +7.1546 days
Inclination- 0.204°
Eccentricity- 0.0011
Year of Discovery- 1610, Padua
Discoverer- Galileo Galilei
Group- Galilean
Callisto
Diameter- 4,820.6 Km
Mass- 10.759 x 1022 Kg
Semi-Major Axis- 1,882,709 Km
Orbital Period
(In Earth Days) +16.689 days
Inclination- 0.205°
Eccentricity- 0.0074
Year of Discovery- 1610, Padua
Discoverer- Galileo Galilei
Group- Galilean
Io
Mean Diameter- 3642 Km
Mass- 8.9319 x 1022 Kg
Semi-Major Axis- 421,700 Km
Orbital Period
(In Earth Days) +1.7691 days
Inclination- 0.050°
Eccentricity- 0.0041
Year of Discovery- 1610, Padua
Discoverer- Galileo Galilei
Group- Galilean
Europa
Mean Diameter- 3,121.6 Km
Mass- 4.8 x 1022 Kg
Semi-Major Axis- 671,034 Km
Orbital Period
(In Earth Days) +3.5512 days
Inclination- 0.471°
Eccentricity- 0.0094
Year of Discovery- 1610, Padua
Discoverer- Galileo Galilei
Group- Galilean
Amalthea
Mean Diameter- 167 Km
Mass- 2.08 x 1018 Kg
Semi-Major Axis- 181,366 Km
Orbital Period
(In Earth Days) +11h 57m 23s
Inclination- 0.374°
Eccentricity- 0.0032
Year of Discovery- 1892, Lick Observatory
San Jose California
Discoverer- E. E. Barnard
Group- Inner
Himalia
Diameter- 170 Km
Mass- 6.7 x 1018 Kg
Semi-Major Axis- 11,451,971
Orbital Period
(In Earth Days) +250.23 days
Inclination- 30.486°
Eccentricity- 0.1513
Year of Discovery- 1904, Lick Observatory
San Jose California
Discoverer- Charles Dillon Perrine
Group- Himalia
Thebe
Diameter- 116×98×84 Km
Mass- 4.3 x 1017 Kg
Semi-Major Axis- 221,889 Km
Orbital Period
(In Earth Days) +16h 11m 17s
Inclination- 1.076°
Eccentricity- 0.0175
Year of Discovery- 1979
Voyager 1
Flyby
Discoverer- Stephen P. Synnott
Group- Inner
Elara
Diameter- 86 Km
Mass- 8.7 x 1017 Kg
Semi-Major Axis- 11,778,034 Km
Orbital Period
(In Earth Days) +257.62 days
Inclination- 29.691°
Eccentricity- 0.1948
Year of Discovery- 1905, Lick Observatory
San Jose
California
Discoverer- Charles Dillon Perrine
Group- Himalia
Pasiphaë
Diameter- 60 Km
Mass- 3 x 1017 Kg
Semi-Major Axis- 23,609,042 Km
Orbital Period
(In Earth Days) −739.80 days
Inclination- 141.803°
Eccentricity- 0.3743
Year of Discovery- 1908, Royal Greenwich Observatory
Discoverer- P. J. Melotte
Group- Pasiphaë
Metis
Diameter- 60×40×34 Km
Mass- 3.6 x 1016 Kg
Semi-Major
Axis 127,690 Km
Orbital Period
(In Earth Days) +7h 4m 29s
Inclination- 0.06°
Eccentricity- 0.00002
Year of Discovery- 1979
Voyager 1 Flyby
Discoverer- Stephen P. Synnott
Group- Inner
Carme
Diameter- 46 Km
Mass- 1.3 x 1017 Km
Semi-Major Axis- 23,197,992 Km
Orbital Period
(In Earth Days) −763.95 days
Inclination- 165.047°
Eccentricity- 0.2342
Year of Discovery- 1938, Mount Wilson Observatory
Los Angeles County, California
Discoverer- S. B. Nicholson
Group- Carme
Sinope
Diameter- 38 Km
Mass- 7.5 x 1016 Km
Semi-Major Axis- 24,057,865 Km
Orbital Period
(In Earth Days) −739.33 Days
Inclination- 153.778°
Eccentricity- 0.2750
Year of Discovery- 1914, Mount Wilson Observatory
Los Angeles County, California
Discoverer- S. B. Nicholson
Group- Pasiphaë
Lysithea
Diameter- 36 Km
Mass- 6.3 x 1016 Kg
Semi-Major Axis- 11,740,560 Km
Orbital Period
(In Earth Days) +259.89 Days
Inclination- 27.006°
Eccentricity- 0.1322
Year of Discovery- 1938, Mount Wilson Observatory
Los Angeles County, California
Discoverer- S.B. Nicholson
Group- Himalia
Ananke
Diameter- 28 Km
Mass- 3.0 x 1016 Kg
Semi-Major Axis- 21,454,952 Km
Orbital Period
(In Earth Days) −640.38 days
Inclination- 151.564°
Eccentricity- 0.3445
Year of Discovery- 1951, Mount Wilson Observatory
Los Angeles County, California
Discoverer- S.B. Nicholson
Group- Ananke
Adrastea
Diameter- 20×16×14 Km
Mass- 0.2 x 1016 Kg
Semi-Major
Axis 128,690 Km
Orbital Period
(In Earth Days) +7h 9m 30s
Inclination- 0.03°
Eccentricity- 0.0015
Year of Discovery- 1979
Voyager 2
Flyby
Discoverer- D.C. Jewitt
Group- Inner
Leda
Diameter- 16 Km
Mass- 0.6 x 1016 Kg
Semi-Major Axis- 11,187,781 Km
Orbital Period
(In Earth Days) +240.82 days
Inclination- 27.562°
Eccentricity- 0.1673
Year of Discovery- 1974, Mount Palomar Observatory, California
Discoverer- Charles T. Kowal
Group- Himalia
Callirrhoe
Diameter- 9 Km
Mass- 0.087 x 1016 Kg
Semi-Major Axis- 23,214,986 Km
Orbital Period
(In Earth Days) −727.11 days
Inclination- 139.849°
Eccentricity- 0.2582
Year of Discovery- 2000, Spacewatch
Kitt Peak National Observatory
Discoverer- Spahr, Scotti
Group- Pasiphaë
Themisto
Diameter- 8 Km
Mass- 0.069 x 1016
Semi-Major Axis- 7,393,216 Km
Orbital Period
(In Earth Days) +129.87 days
Inclination- 45.762°
Eccentricity- 0.2115
Year of Discovery- 1975/
2000
Discoverer- Kowal & Roemer/
Sheppard, Jewitt et.al
Group- Thermisto
Praxidike
Diameter- 7 Km
Mass- 0.043 x 1016 Kg
Semi-Major Axis- 20,823,948 Km
Orbital Period
(In Earth Days) −613.90 days
Inclination- 144.205°
Eccentricity- 0.1840
Year of Discovery- 2000, University of Hawaii
Discoverer- Scott S. Sheppard et al.
Group- Ananke
Iocaste
Diameter- 5 Km
Mass- 0.019 x 1016 Kg
Semi-Major Axis- 20,722,566 Km
Orbital Period
(In Earth Days) −609.43 days
Inclination- 147.248°
Eccentricity- 0.2874
Year of Discovery- 2001, University of Hawaii
Discoverer- Scott. S. Sheppard et al.
Group- Ananke
Taygete
Diameter- 5 Km
Mass- 1.6 x 1014 Kg
Semi-Major Axis- 22,438,648 Km
Orbital Period
(In Earth Days) −686.67 days
Inclination- 164.890°
Eccentricity- 0.3678
Year of Discovery- 2001, University of Hawaii
Discoverer- Scott.S. Sheppard et al.
Group- Carme
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Kalyke
Diameter- 5 Km
Mass- 1.9 x 1014 Kg
Semi-Major Axis- 23,180,773 Km
Orbital Period
(In Earth Days) −721.02
Inclination- 165.505°
Eccentricity- 0.2139
Year of Discovery- 2001, University of Hawaii
Discoverer- Scott.S. Sheppard et al.
Group- Carme
Megaclite
Diameter- 5 Km
Mass- 0.021 x 1016 Kg
Semi-Major Axis- 24,687,239 Km
Orbital Period
(In Earth Days) −792.44 days
Inclination- 150.398°
Eccentricity- 0.3077
Year of Discovery- 2001, University of Hawaii
Discoverer- Scott.S. Sheppard et al.
Group- Pasiphaë
S/2000 J 11
Diameter- 4 Km
Mass- 9 x 1013 Kg
Semi-Major Axis- 12,570,424
Orbital Period
(In Earth Days) +287.93 days
Inclination- 27.584°
Eccentricity- 0.2058
Year of Discovery- 2001, University of Hawaii
Discoverer- Scott.S. Sheppard et al.
Group- Himalia
Helike
Diameter- 4 Km
Mass- 9 x 1013 Kg
Semi-Major Axis- 20,540,266 Km
Orbital Period
(In Earth Days) −601.40 days
Inclination- 154.586°
Eccentricity- 0.1374
Year of Discovery- 2003
Discoverer- Scott.S. Sheppard et al.
Group- Ananke
Harpalyke
Diameter- 4 Km
Mass- 0.012 x 1016 Kg
Semi-Major Axis- 21,063,814 Km
Orbital Period
(In Earth Days) −624.54 days
Inclination- 147.223°
Eccentricity- 0.2440
Year of Discovery- 2001, University of Hawaii
Discoverer- Scott.S. Sheppard
Group- Ananke
Hermippe
Diameter- 4 Km
Mass- 9 x 1013 Kg
Semi-Major Axis- 21,182,086 Km
Orbital Period
(In Earth Days) −629.81
Inclination- 151.242°
Eccentricity- 0.2290
Year of Discovery- 2002, University of Hawaii
Discoverer- Scott.S. Sheppard et al.
Group- Ananke
Thyone
Diameter- 4 Km
Mass- 9 x 1013 Kg
Semi-Major Axis- 21,405,570 Km
Orbital Period
(In Earth Days) −639.8 days
Inclination- 147.276°
Eccentricity- 0.2525
Year of Discovery- 2002, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Ananke
Chaldene
Diameter- 4 Km
Mass- 7 x 1013 Kg
Semi-Major Axis- 22,713,444 Km
Orbital Period
(In Earth Days) −699.33
Inclination- 167.07°
Eccentricity- 0.2916
Year of Discovery- 2001, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Carme
Aoede
Diameter- 4 Km
Mass- 9 x 1013 Kg
Semi-Major Axis- 23,044,175 Km
Orbital Period
(In Earth Days) −714.66 days
Inclination- 160.482°
Eccentricity- 0.6011
Year of Discovery- 2003 Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Pasiphaë
Eukelade
Diameter- 4 Km
Mass- 9 x 1013 Kg
Semi-Major Axis- 23,483,694 Km
Orbital Period
(In Earth Days) −735.20 days
Inclination- 163.996°
Eccentricity- 0.2828
Year of Discovery- 2003, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Carme
Isonoe
Diameter- 4 Km
Mass- 7.5 x 1013 Kg
Semi-Major Axis- 23,800,647 Km
Orbital Period
(In Earth Days) −750.13 days
Inclination- 165.127°
Eccentricity- 0.1775
Year of Discovery- 2001, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Carme
S/2003 J 5
Diameter- 4 Km
Mass- 9 x 1013 Kg
Semi-Major Axis- 23,973,926 Km
Orbital Period
(In Earth Days) −758.34 days
Inclination- 165.549°
Eccentricity- 0.307
Year of Discovery- 2003, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Carme
Autonoe
Diameter- 4 Km
Mass- 9 x 1013 Kg
Semi-Major Axis- 24,264,445 Km
Orbital Period
(In Earth Days) −772.17 days
Inclination- 151.058°
Eccentricity- 0.3690
Year of Discovery- 2002, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Pasiphaë
Carpo
Diameter- 3 Km
Mass- 4.5 x 1013 Kg
Semi-Major Axis- 17,144,873 Km
Orbital Period
(In Earth Days) +458.62 days
Inclination- 56.001°
Eccentricity- 0.2735
Year of Discovery- 2003, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Carpo
Euanthe
Diameter- 3 Km
Mass- 4.5 x 1013 Km
Semi-Major Axis- 20,464,854 Km
Orbital Period
(In Earth Days) −598.09 days
Inclination- 143.409°
Eccentricity- 0.2
Year of Discovery- 2002, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Ananke
Aitne
Diameter- 3 Km
Mass- 4.5 x 1013 Kg
Semi-Major Axis- 22,285,161 Km
Orbital Period
(In Earth Days) −679.64 days
Inclination- 165.562°
Eccentricity- 0.3927
Year of Discovery- 2002, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Carme
Erinome
Diameter- 3 Km
Mass- 4.5 x 1013 Kg
Semi-Major Axis- 22,986,266 Km
Orbital Period
(In Earth Days) −711.96 days
Inclination- 163.737°
Eccentricity- 0.2552
Year of Discovery- 2001, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Carme
Eurydome
Diameter- 3 Km
Mass- 4.5 x 1013 Kg
Semi-Major Axis- 23,230,858 Km
Orbital Period
(In Earth Days) −723.36 days
Inclination- 149.324°
Eccentricity- 0.3769
Year of Discovery- 2002, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Pasiphaë
Hegemone
Diameter- 3 Km
Mass- 4.5 x 1013 Kg
Semi-Major Axis- 23,702,511 Km
Orbital Period
(In Earth Days) −745.5 days
Inclination- 152.506°
Eccentricity- 0.4077
Year of Discovery- 2003, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Pasiphaë
Arche
Diameter- 3 Km
Mass- 4.5 x 1013 Kg
Semi-Major Axis- 23,717,051 Km
Orbital Period
(In Earth Days) −746.19 days
Inclination- 164.587°
Eccentricity- 0.1492
Year of Discovery- 2002, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Carme
Euporie
Diameter- 2 Km
Mass- 1.5 x 1013 Kg
Semi-Major Axis- 19,088,434 Km
Orbital Period
(In Earth Days) −538.78 days
Inclination- 144.694°
Eccentricity- 0.0960
Year of Discovery- 2002, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Ananke
S/2003 J 3
Diameter- 2 Km
Mass- 1.5 x 1013 Kg
Semi-Major Axis- 19,621,780 Km
Orbital Period
(In Earth Days) −561.52 days
Inclination- 146.363°
Eccentricity- 0.2507
Year of Discovery- 2003, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Ananke
S/2003 J 18
Diameter- 2 Km
Mass- 1.5 x 1013 Kg
Semi-Major Axis- 19,812,577 Km
Orbital Period
(In Earth Days) −569.73 days
Inclination- 147.401°
Eccentricity- 0.1569
Year of Discovery- 2003, Mauna Kea, Hawaii
Discoverer- Brett J. Gladman et al.
Group- Ananke
Thelxinoe
Diameter- 2 Km
Mass- 1.5 x 1013 Kg
Semi-Major Axis- 20,453,753 Km
Orbital Period
(In Earth Days) −597.61 days
Inclination- 151.292°
Eccentricity- 0.2684
Year of Discovery- 2003, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Ananke
Orthosie
Diameter- 2 Km
Mass- 1.5 x 1013 Kg
Semi-Major Axis- 20,567,971 Km
Orbital Period
(In Earth Days) −602.62 days
Inclination- 142.366°
Eccentricity- 0.2433
Year of Discovery- 2002
Discoverer- Scott.S. Sheppard et al.
Group- Ananke
S/2003 J 16
Diameter- 2 Km
Mass- 1.5 x 1013 Kg
Semi-Major Axis- 20,743,779 Km
Orbital Period
(In Earth Days) −610.36 days
Inclination- 150.769°
Eccentricity- 0.3184
Year of Discovery- 2003, Mauna Kea, Hawaii
Discoverer- Brett J. Gladman et al.
Group- Ananke
Mneme
Diameter- 2 Km
Mass- 1.5 x 1013 Kg
Semi-Major Axis- 21,129,786 Km
Orbital Period
(In Earth Days) −627.48 Days
Inclination- 149.732°
Eccentricity- 0.3169
Year of Discovery- 2003, Mauna Kea, Hawaii
Discoverer- Brett.J. Gladman et al.
Group- Ananke
Herse
Diameter- 2 Km
Mass- 1.5 x 1013 Kg
Semi-Major Axis- 22,134,306 Km
Orbital Period
(In Earth Days) −672.75 days
Inclination- 162.490°
Eccentricity- 0.2379
Year of Discovery- 2003, Mauna Kea, Hawaii
Discoverer- Brett. J.Gladman et al.
Group- Carme
S/2003 J 19
Diameter- 2 Km
Mass- 1.5 x 1013 Kg
Semi-Major Axis- 22,709,061 Km
Orbital Period
(In Earth Days) −699.12 days
Inclination- 164.727°
Eccentricity- 0.1961
Year of Discovery- 2003, Mauna Kea, Hawaii
Discoverer- Brett.J. Gladman et al.
Group- Carme
S/2003 J 15
Diameter- 2 Km
Mass- 1.5 x 1013 Kg
Semi-Major Axis- 22,720,999 Km
Orbital Period
(In Earth Days) −699.68 days
Inclination- 141.812°
Eccentricity- 0.0932
Year of Discovery- 2003
Discoverer- Scott.S. Sheppard et al.
Group- Ananke
S/2003 J 10
Diameter- 2 Km
Mass- 1.5 x 1013 Kg
Semi-Major Axis- 22,730,813 Km
Orbital Period
(In Earth Days) −700.13 days
Inclination- 163.813°
Eccentricity- 0.3438
Year of Discovery- 2003, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Carme
S/2003 J 23
Diameter- 2 Km
Mass- 1.5 x 1013 Kg
Semi-Major Axis- 22,739,654 Km
Orbital Period
(In Earth Days) −700.54 days
Inclination- 148.849°
Eccentricity- 0.393
Year of Discovery- 2004, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Pasiphaë
Kallichore
Diameter- 2 Km
Mass- 1.5 x 1013 Kg
Semi-Major Axis- 23,111,823 Km
Orbital Period
(In Earth Days) −717.81 days
Inclination- 164.605°
Eccentricity- 0.2041
Year of Discovery- 2003, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Carme
S/2010 J 1
Diameter- 2 Km
Mass- --
Semi-Major Axis- 23,314,335 Km
Orbital Period
(In Earth Days) −722.83 days
Inclination- 163.2°
Eccentricity- 0.32
Year of Discovery- 2010, Palomar Observatory
Discoverer- Jacobson et al.
Group- Pasiphaë
S/2003 J 4
Diameter- 2 Km
Mass- 1.5 x 1013 Kg
Semi-Major Axis- 23,570,790 Km
Orbital Period
(In Earth Days) −739.29 days
Inclination- 147.175°
Eccentricity- 0.3003
Year of Discovery- 2003, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Pasiphaë
Sponde
Diameter- 2 Km
Mass- 1.5 x 1013 Kg
Semi-Major Axis- 24,252,627 Km
Orbital Period
(In Earth Days) −771.60 days
Inclination- 154.372°
Eccentricity- 0.4431
Year of Discovery- 2002, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Pasiphaë
S/2003 J 2
Diameter- 2 Km
Mass- 1.5 x 1013 Kg
Semi-Major Axis- 30,290,846 Km
Orbital Period
(In Earth Days) −1077.02
Inclination- 153.521°
Eccentricity- 0.1882
Year of Discovery- 2003, Hawaii University
Discoverer- Scott.S. Sheppard et al.
S/2003 J 12
Diameter- 1 Km
Mass- 1.5 x 1013 Kg
Semi-Major Axis- 17,739,539 Km
Orbital Period
(In Earth Days) −482.69 days
Inclination- 142.680°
Eccentricity- 0.4449
Year of Discovery- 2003, Hawaii University
Discoverer- Scott.S. Sheppard et al.
S/2011 J 1
Diameter- 1 Km
Mass- --
Semi-Major Axis- 20,155,290 Km
Orbital Period
(In Earth Days) −582.22 days
Inclination- 162.8°
Eccentricity- 0.2963
Year of Discovery- 2011, Hawaii University
Discoverer- Scott.S. Sheppard et al.
S/2010 J 2
Diameter- 1 Km
Mass- --
Semi-Major Axis- 20,307,150
Orbital Period
(In Earth Days) −588.36 days
Inclination- 150.4°
Eccentricity- 0.307
Year of Discovery- 2010, Mauna Kea, Hawaii
Discoverer- Christian Veillet
Group- Ananke
Pasithee
Diameter- 2 Km
Mass- 1.5 x 1013 Kg
Semi-Major Axis- 23,307,318
Orbital Period
(In Earth Days) −726.93 days
Inclination- 165.759°
Eccentricity- 0.3288
Year of Discovery- 2002, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Carme
Cyllene
Diameter- 2 Km
Mass- 1.5 x 1013 Kg
Semi-Major Axis- 23,396,269 Km
Orbital Period
(In Earth Days) −731.10 days
Inclination- 140.148°
Eccentricity- 0.4115
Year of Discovery- 2003, Hawaii University
Discoverer- Scott.S. Sheppard et al.
Group- Carme
S/2003 J 9
Diameter- 1 Km
Mass- 1.5 x 1012 Kg
Semi-Major Axis- 23,857,808 Km
Orbital Period
(In Earth Days) −752.84 days
Inclination- 164.98°
Eccentricity- 0.2761
Year of Discovery- 2003
Discoverer- Scott.S. Sheppard et al.
Group- Carme
Among these satellites, some have not been named yet and are therefore known by an alphanumeric code. Some of them have even gone missing after first detection. It is believed that Jupiter might have had many more satellites in the past, which have now been destroyed to form the thin ring that surrounds it.

Eight of these satellites are regular and have prograde motion (they orbit in the same direction as the planet rotates). The rest display retrograde motion. By regular, we mean that these planets have orbits close to Jupiter and have a low inclination with respect to Jupiter's equatorial radius. These may be Jupiter's satellites that formed in situ, along with the planet, while the rest might be captured satellites. The rest of the 59 satellites are irregular, in the sense that they have retrograde (orbit in the opposite direction of Jupiter's rotation) and prograde orbits of very high eccentricity and pronounced inclination from Jupiter's equatorial plane. While the largest four of the satellites were discovered by one of the pioneers of modern astronomy, Galileo Galilei in 1610, the rest were discovered much later with terrestrial telescopes and space probes.

The largest of all 66 moons is Ganymede, with a diameter of 3,270 miles - a satellite is larger than Mercury. The rest of the three Galilean moons have a diameter of more than 1,900 miles. All these four satellites are spheroidal in shape, largely because of the high tidal gravitational pull of Jupiter. Besides these big four satellites, the rest are less than 160 miles in diameter, with majority of them having a diameter around 1 to 3 miles.

Most of these moons have been captured by the planet. Future space exploration initiatives will be aimed at studying the Galilean moon Europa, which has been found to have conditions favorable for emergence of life. In fact, it may already be harboring life. Jupiter's family of moons may have many more secrets waiting to be revealed. Someday, one of them may become an outpost for space explorers as humanity takes the leap from the cradle of planet Earth to spread throughout the solar system and eventually the galaxy.
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