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Jupiter's natural satellites

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Jupiter's natural satellites

The planet Jupiter has 67 confirmed moons.[1] This gives it the largest retinue of moons with "reasonably secure" orbits of any planet in the Solar System.[2] The most massive of them, the four Galilean moons, were discovered in 1610 by Galileo Galilei and were the first objects found to orbit a body that was neither Earth nor the Sun. From the end of the 19th century, dozens of much smaller Jovian moons have been discovered and have received the names of lovers, conquests, or daughters of the Roman god Jupiter, or his Greek equivalent, Zeus. The Galilean moons are by far the largest and most massive objects in orbit around Jupiter, with the remaining 63 moons and the rings together comprising just 0.003 percent of the total orbiting mass.

Eight of Jupiter's moons 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 ellipsoidal in shape, due to having planetary mass, and so would be considered (dwarf) planets if they were in direct orbit about 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. There are 17 recently discovered irregular satellites that have not yet been named.


Characteristics

The moons' physical and orbital characteristics 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). Orbital shapes range from nearly perfectly circular to highly eccentric and inclined, and many revolve in the direction opposite to Jupiter's spin (retrograde motion). Orbital periods range from seven hours (taking less time than Jupiter does to spin around its axis), to some three thousand times more (almost three Earth years).

Origin and evolution

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.[3][4] They may be the remnants of a score of Galilean-mass satellites that formed early in Jupiter's history.[3][5]

Simulations suggest that, while the disk had a relatively low 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 processed through it. However, the disk mass of only 2% that of Jupiter is required to explain the existing satellites.[3] Thus there may have been several generations of Galilean-mass satellites in Jupiter's early history. Each generation of moons would have spiraled into Jupiter, due to drag from the disk, with new moons then forming from the new debris captured from the Solar nebula.[3] By the time the present (possibly fifth) generation formed, the disk had thinned out to the point that it no longer greatly interfered with the moons' orbits.[5] The current Galilean moons were still affected, falling into and being partially protected by an orbital resonance 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.[3]

The outer, irregular moons are thought to have originated from passing asteroids while the protolunar disk was still massive enough to absorb much of their momentum and thus capture them into orbit. Many broke up by the stresses of capture, or afterward by collisions with other small bodies, producing the families we see today.[6]

Discovery


The first claimed observation of one of Jupiter's moons is that of the Chinese astronomer Gan De around 364 BC.[7] However, the first certain observations of Jupiter's satellites were those of Galileo Galilei in 1609.[8] By March 1610, he had sighted the four massive Galilean moons with his 30x magnification telescope:[9] Ganymede, Callisto, Io, and Europa. No additional satellites were discovered until E. E. Barnard observed Amalthea in 1892.[10] With the aid of telescopic photography, further discoveries followed quickly over the course of the twentieth century. Himalia was discovered in 1904,[11] Elara in 1905,[12] Pasiphaë in 1908,[13] Sinope in 1914,[14] Lysithea and Carme in 1938,[15] Ananke in 1951,[16] and Leda in 1974.[17] By the time Voyager space probes reached Jupiter around 1979, 13 moons had been discovered; while Themisto was observed in 1975,[18] but due to insufficient initial observation data, it was lost until 2000. The Voyager missions discovered an additional three inner moons in 1979: Metis, Adrastea, and Thebe.[19]

For two decades no additional moons were discovered; but between October 1999 and February 2003, researchers using sensitive ground-based detectors found and later named another 34 moons, most of which were discovered by a team led by Scott S. Sheppard and David C. Jewitt.[20] These are tiny moons, in long, eccentric, generally retrograde orbits, and average of 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 be captured asteroidal or perhaps cometary bodies, possibly fragmented into several pieces,[21] but very little is actually known about them. A number of 17 additional moons have been discovered but not yet named since 2003,[22] bringing the total number of known moons of Jupiter to 67.[1] As of 2013, this is the most of any planet in the Solar System, but additional undiscovered, tiny moons may exist.

Naming

Main article: Naming of moons

The Galilean moons of Jupiter (Io, Europa, Ganymede and Callisto) were named by Simon Marius soon after their discovery in 1610.[23] 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.[23] The names Io, Europa, Ganymede, and Callisto became popular in the 20th century, while the rest of the moons, usually numbered in Roman numerals V (5) through XII (12), remained unnamed.[24] By a popular though unofficial convention, Jupiter V, discovered in 1892, was given the name Amalthea, first used by the French astronomer Camille Flammarion.[20]

The other moons, in the majority of astronomical literature, were simply labeled by their Roman numeral (i.e. Jupiter IX) until the 1970s.[25] In 1975, the International Astronomical Union's (IAU) Task Group for Outer Solar System Nomenclature granted names to satellites V–XIII,[26] and provided for a formal naming process for future satellites to be discovered.[26] The practice was to name newly discovered moons of Jupiter after lovers and favorites of the god Jupiter (Zeus), and since 2004, after their descendants also.[27] All of Jupiter's satellites from XXXIV (Euporie) are named after daughters of Jupiter or Zeus.[27]

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.

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, Adrastea, Amalthea, and Thebe. 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.[28] These moons, along with a number of as-yet-unseen inner moonlets, replenish and maintain Jupiter's faint ring system. Metis and Adrastea help to maintain Jupiter's main ring, while Amalthea and Thebe each maintain their own faint outer rings.[29][30]
  • Main group or Galilean moons: Io, Europa, Ganymede and Callisto. With radii that are larger than any of the dwarf planets, they are some of the largest objects in the Solar System outside the Sun and the eight planets in terms of mass, and Ganymede exceeds the planet Mercury in diameter. Respectively the fourth, sixth, first and third largest natural satellites in the Solar System, they contain almost 99.999% of the total mass in orbit around Jupiter. Jupiter is almost 5,000 times more massive than the Galilean moons.[note 1] The inner moons also participate in a 1:2:4 orbital resonance. Models suggest that they formed by slow accretion 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.[31]

Irregular satellites

Main article: Irregular satellite

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:[22][32][33]

  • Themisto[32] is the innermost irregular moon and not part of a known family.[22]
  • Carpo is the outermost prograde moon and not part of a known family.[22]


  • Retrograde satellites:
  • S/2003 J 12 and S/2011 J 1 are the innermost of the retrograde moons, and are not part of any known family.
  • The Carme group is spread over only 1.2 Gm in semi-major axis, 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 progenitor, possibly a Jupiter Trojan.[21]
  • The Ananke group 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.[21]
  • The Pasiphae group 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.[21] The colors also vary significantly, from red to grey, which might be the result of multiple collisions. Sinope, sometimes included in the Pasiphae group,[21] is red and, given the difference in inclination, it could have been captured independently;[32] Pasiphae and Sinope are also trapped in secular resonances with Jupiter.[34]
  • S/2003 J 2 is the outermost moon of Jupiter, and is not part of a known family.

Table

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 Earth's Moon. The four inner moons are much smaller. The irregular captured moons are shaded light gray when prograde and dark gray when retrograde.

Order
[note 2]
Label
[note 3]
Name
Pronunciation
(key)
Image Diameter
(km)[note 4]
Mass
(×1016 kg)
Semi-major
axis

(km)[35]
Orbital period
(d)[35][note 5]
Inclination
(°)[35]
Eccentr.
[22]
Discovery
year
[20]
Discoverer[20] Group
[note 6]
1 XVI Metis ˈmiːtɨs
60×40×34 ~3.6 127,690 +7h 4m 29s 0.06°[36] 0.000 02 1979 Synnott
(Voyager 1)
Inner
2 XV Adrastea ˌædrəˈstiːə
20×16×14 ~0.2 128,690 +7h 9m 30s 0.03°[36] 0.0015 1979 Jewitt
(Voyager 2)
Inner
3 V Amalthea ˌæməlˈθiːə
167 ± 4.0 km
250×146×128
208 181,366 +11h 57m 23s 0.374°[36] 0.0032 1892 Barnard Inner
4 XIV Thebe ˈθiːbiː
116×98×84 ~43 221,889 +16h 11m 17s 1.076°[36] 0.0175 1979 Synnott
(Voyager 1)
Inner
5 I Io ˈaɪ.oʊ
3,660.0
×3,637.4
×3,630.6
8,931,900 421,700 +1.769 1 0.050°[36] 0.0041 1610 Galilei Galilean
6 II Europa jʊˈroʊpə
3,121.6 4,800,000 671,034 +3.551 2 0.471°[36] 0.0094 1610 Galilei Galilean
7 III Ganymede ˈɡænɨmiːd
5,262.4 14,819,000 1,070,412 +7.154 6 0.204°[36] 0.0011 1610 Galilei Galilean
8 IV Callisto kəˈlɪstoʊ
4,820.6 10,759,000 1,882,709 +16.689 0.205°[36] 0.0074 1610 Galilei Galilean
9 XVIII Themisto θɨˈmɪstoʊ 8 0.069 7,393,216 +129.87 45.762° 0.2115 1975/2000 Kowal & Roemer/
Sheppard et al.
Themisto
10 XIII Leda ˈliːdə
50px
16 0.6 11,187,781 +240.82 27.562° 0.1673 1974 Kowal Himalia
11 VI Himalia haɪˈmeɪliə
170 670 11,451,971 +250.23 30.486° 0.1513 1904 Perrine Himalia
12 X Lysithea laɪˈsɪθiːə 36 6.3 11,740,560 +259.89 27.006° 0.1322 1938 Nicholson Himalia
13 VII Elara ˈɛlərə
86 87 11,778,034 +257.62 29.691° 0.1948 1905 Perrine Himalia
14 S/2000 J 11 4 0.009 0 12,570,424 +287.93 27.584° 0.2058 2001 Sheppard et al. Himalia?
15 XLVI Carpo ˈkɑrpoʊ 3 0.004 5 17,144,873 +458.62 56.001° 0.2735 2003 Sheppard et al. Carpo
16 S/2003 J 12 1 0.000 15 17,739,539 −482.69 142.680° 0.4449 2003 Sheppard et al. ?
17 XXXIV Euporie juːˈpɒrɨ.iː 2 0.001 5 19,088,434 −538.78 144.694° 0.0960 2002 Sheppard et al. Ananke
18 S/2003 J 3 2 0.001 5 19,621,780 −561.52 146.363° 0.2507 2003 Sheppard et al. Ananke
19 S/2003 J 18 2 0.001 5 19,812,577 −569.73 147.401° 0.1569 2003 Gladman et al. Ananke
20 S/2011 J 1 1 20,155,290 −582.22 162.8° 0.2963 2011 Sheppard et al. ?
21 S/2010 J 2 1 20,307,150 −588.36 150.4° 0.307 2010 Veillet Ananke?
22 XLII Thelxinoe θɛlkˈsɪnɵʊiː 2 0.001 5 20,453,753 −597.61 151.292° 0.2684 2003 Sheppard et al. Ananke
23 XXXIII Euanthe juːˈænθiː 3 0.004 5 20,464,854 −598.09 143.409° 0.2000 2002 Sheppard et al. Ananke
24 XLV Helike ˈhɛlɨkiː 4 0.009 0 20,540,266 −601.40 154.586° 0.1374 2003 Sheppard et al. Ananke
25 XXXV Orthosie ɔrˈθɒsɨ.iː 2 0.001 5 20,567,971 −602.62 142.366° 0.2433 2002 Sheppard et al. Ananke
26 XXIV Iocaste ˌaɪ.ɵˈkæstiː 5 0.019 20,722,566 −609.43 147.248° 0.2874 2001 Sheppard et al. Ananke
27 S/2003 J 16 2 0.001 5 20,743,779 −610.36 150.769° 0.3184 2003 Gladman et al. Ananke
28 XXVII Praxidike prækˈsɪdɨkiː 7 0.043 20,823,948 −613.90 144.205° 0.1840 2001 Sheppard et al. Ananke
29 XXII Harpalyke hɑrˈpælɨkiː 4 0.012 21,063,814 −624.54 147.223° 0.2440 2001 Sheppard et al. Ananke
30 XL Mneme ˈniːmiː 2 0.001 5 21,129,786 −627.48 149.732° 0.3169 2003 Gladman et al. Ananke
31 XXX Hermippe hərˈmɪpiː 4 0.009 0 21,182,086 −629.81 151.242° 0.2290 2002 Sheppard et al. Ananke?
32 XXIX Thyone θaɪˈoʊniː 4 0.009 0 21,405,570 −639.80 147.276° 0.2525 2002 Sheppard et al. Ananke
33 XII Ananke əˈnæŋkiː 28 3.0 21,454,952 −640.38 151.564° 0.3445 1951 Nicholson Ananke
34 L Herse ˈhɜrsiː 2 0.001 5 22,134,306 −672.75 162.490° 0.2379 2003 Gladman et al. Carme
35 XXXI Aitne ˈaɪtniː 3 0.004 5 22,285,161 −679.64 165.562° 0.3927 2002 Sheppard et al. Carme
36 XXXVII Kale ˈkeɪliː 2 0.001 5 22,409,207 −685.32 165.378° 0.2011 2002 Sheppard et al. Carme
37 XX Taygete teɪˈɪdʒɨtiː 5 0.016 22,438,648 −686.67 164.890° 0.3678 2001 Sheppard et al. Carme
38 S/2003 J 19 2 0.001 5 22,709,061 −699.12 164.727° 0.1961 2003 Gladman et al. Carme
39 XXI Chaldene kælˈdiːniː 4 0.007 5 22,713,444 −699.33 167.070° 0.2916 2001 Sheppard et al. Carme
40 S/2003 J 15 2 0.001 5 22,720,999 −699.68 141.812° 0.0932 2003 Sheppard et al. Ananke?
41 S/2003 J 10 2 0.001 5 22,730,813 −700.13 163.813° 0.3438 2003 Sheppard et al. Carme?
42 S/2003 J 23 2 0.001 5 22,739,654 −700.54 148.849° 0.3930 2004 Sheppard et al. Pasiphaë
43 XXV Erinome ɨˈrɪnɵmiː 3 0.004 5 22,986,266 −711.96 163.737° 0.2552 2001 Sheppard et al. Carme
44 XLI Aoede eɪˈiːdiː 4 0.009 0 23,044,175 −714.66 160.482° 0.6011 2003 Sheppard et al. Pasiphaë
45 XLIV Kallichore kəˈlɪkɵriː 2 0.001 5 23,111,823 −717.81 164.605° 0.2041 2003 Sheppard et al. Carme?
46 XXIII Kalyke ˈkælɨkiː 5 0.019 23,180,773 −721.02 165.505° 0.2139 2001 Sheppard et al. Carme
47 XI Carme ˈkɑrmiː 46 13 23,197,992 −763.95 165.047° 0.2342 1938 Nicholson Carme
48 XVII Callirrhoe kəˈlɪrɵʊiː
9 0.087 23,214,986 −727.11 139.849° 0.2582 2000 Spahr, Scotti Pasiphaë
49 XXXII Eurydome jʊˈrɪdəmiː 3 0.004 5 23,230,858 −723.36 149.324° 0.3769 2002 Sheppard et al. Pasiphaë?
50 S/2011 J 2 1 23,329,710 −725.06 151.8° 0.3867 2011 Sheppard et al. Pasiphaë?
51 XXXVIII Pasithee pəˈsɪθɨ.iː 2 0.001 5 23,307,318 −726.93 165.759° 0.3288 2002 Sheppard et al. Carme
52 S/2010 J 1 2 23,314,335 −722.83 163.2° 0.320 2010 Jacobson et al. Pasiphaë?
53 XLIX Kore ˈkɔəriː 2 0.001 5 23,345,093 −776.02 137.371° 0.1951 2003 Sheppard et al. Pasiphaë
54 XLVIII Cyllene sɨˈliːniː 2 0.001 5 23,396,269 −731.10 140.148° 0.4115 2003 Sheppard et al. Pasiphaë
55 XLVII Eukelade juːˈkɛlədiː 4 0.009 0 23,483,694 −735.20 163.996° 0.2828 2003 Sheppard et al. Carme
56 S/2003 J 4 2 0.001 5 23,570,790 −739.29 147.175° 0.3003 2003 Sheppard et al. Pasiphaë
57 VIII Pasiphaë pəˈsɪfeɪ.iː 60 30 23,609,042 −739.80 141.803° 0.3743 1908 Melotte Pasiphaë
58 XXXIX Hegemone hɨˈdʒɛməniː 3 0.004 5 23,702,511 −745.50 152.506° 0.4077 2003 Sheppard et al. Pasiphaë
59 XLIII Arche ˈɑrkiː 3 0.004 5 23,717,051 −746.19 164.587° 0.1492 2002 Sheppard et al. Carme
60 XXVI Isonoe aɪˈsɒnɵʊiː 4 0.007 5 23,800,647 −750.13 165.127° 0.1775 2001 Sheppard et al. Carme
61 S/2003 J 9 1 0.000 15 23,857,808 −752.84 164.980° 0.2761 2003 Sheppard et al. Carme
62 S/2003 J 5 4 0.009 0 23,973,926 −758.34 165.549° 0.3070 2003 Sheppard et al. Carme
63 IX Sinope sɨˈnoʊpiː 38 7.5 24,057,865 −739.33 153.778° 0.2750 1914 Nicholson Pasiphaë
64 XXXVI Sponde ˈspɒndiː 2 0.001 5 24,252,627 −771.60 154.372° 0.4431 2002 Sheppard et al. Pasiphaë
65 XXVIII Autonoe ɔːˈtɒnɵʊiː 4 0.009 0 24,264,445 −772.17 151.058° 0.3690 2002 Sheppard et al. Pasiphaë
66 XIX Megaclite ˌmɛɡəˈklaɪtiː 5 0.021 24,687,239 −792.44 150.398° 0.3077 2001 Sheppard et al. Pasiphaë
67 S/2003 J 2 2 0.001 5 30,290,846 −1077.02 153.521° 0.1882 2003 Sheppard et al. ?

See also

Notes

References

External links

  • Jupiter Satellite Data
  • Jupiter, and The Giant Planet Satellite and Moon Page
  • Simulation showing the position of Jupiter's Moon
  • , University of South Wales
  • NASA's Solar System Exploration
  • "San Francisco Chronicle
  • Planetary Science Research Discoveries
  • An animation of the Jovian system of moons

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