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Moons of Jupiter

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Moons of Jupiter

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

There are 67 confirmed moons of Jupiter.[1] This gives Jupiter the largest number 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% 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 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. 16 irregular satellites, discovered since 2003, have not yet been named.

Contents

  • Characteristics 1
  • Origin and evolution 2
  • Discovery 3
  • Naming 4
  • Groups 5
    • Regular satellites 5.1
    • Irregular satellites 5.2
  • List 6
  • Exploration by spacecraft 7
  • See also 8
  • Notes 9
  • References 10
  • External links 11

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]
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.

Simulations suggest that, while the disk had a relatively high mass at any given moment, over time a substantial fraction (several tenths 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

Jupiter and the Galilean moons through a 10" (25 cm) Meade LX200 telescope
The Galilean moons. From left to right, in order of increasing distance from Jupiter: Io, Europa, Ganymede, Callisto
The Galilean moons and their orbits around Jupiter

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 January 1610, he had sighted the four massive Galilean moons with his 30x magnification telescope, and published his results in March 1610.[9] Simon Marius had independently discovered them one day after Galileo, though he did not publish his book on the subject until 1614, and it is the names that Marius assigned that we now use: Ganymede, Callisto, Io, and Europa.[10] No additional satellites were discovered until E. E. Barnard observed Amalthea in 1892.[11] With the aid of telescopic photography, further discoveries followed quickly over the course of the twentieth century. Himalia was discovered in 1904,[12] Elara in 1905,[13] Pasiphaë in 1908,[14] Sinope in 1914,[15] Lysithea and Carme in 1938,[16] Ananke in 1951,[17] and Leda in 1974.[18] By the time Voyager space probes reached Jupiter around 1979, 13 moons had been discovered, not including Themisto, which had been observed in 1975,[19] 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.[20]

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.[21] 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 be captured asteroidal or perhaps cometary bodies, possibly fragmented into several pieces;[22] but very little is actually known about them. Since 2003, 16 additional moons have been discovered but not yet named,[23] 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

The Galilean moons of Jupiter (Io, Europa, Ganymede and Callisto) were named by Simon Marius soon after their discovery in 1610.[24] 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.[24] The names Io, Europa, Ganymede, and Callisto became popular in the 20th century, whereas the rest of the moons, usually numbered in Roman numerals V (5) through XII (12), remained unnamed.[25] By a popular though unofficial convention, Jupiter V, discovered in 1892, was given the name Amalthea, first used by the French astronomer Camille Flammarion.[21]

The other moons, in the majority of astronomical literature, were simply labeled by their Roman numeral (i.e. Jupiter IX) until the 1970s.[26] In 1975, the International Astronomical Union's (IAU) Task Group for Outer Solar System Nomenclature granted names to satellites V–XIII,[27] and provided for a formal naming process for future satellites to be discovered.[27] 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.[28] All of Jupiter's satellites from XXXIV (Euporie) are named after daughters of Jupiter or Zeus.[28]

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

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:

  • 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.[29] 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, whereas Amalthea and Thebe each maintain their own faint outer rings.[30][31]
  • Main group or Galilean moons: Io, Europa, Ganymede and Callisto. They are some of the largest objects in the Solar System outside the Sun and the eight planets in terms of mass and are larger than any known dwarf planet, Ganymede exceeding even the planet Mercury in diameter. They are respectively the fourth-, sixth-, first-, and third-largest natural satellites in the Solar System, containing approximately 99.997% 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 are 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.[32] Several are suspected of having subsurface oceans.

Irregular satellites

Jupiter's outer moons and their highly inclined orbits

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:[23][33][34]

  • Themisto[33] is the innermost irregular moon and not part of a known family.[23]
  • Carpo is the outermost prograde moon and not part of a known family.[23]
Retrograde satellites: inclinations (°) vs. eccentricities, with Carme's (orange) and Ananke's (yellow) groups identified
  • 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.[22]
  • 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.[22]
  • 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.[22] The colors also vary significantly, from red to grey, which might be the result of multiple collisions. Sinope, sometimes included in the Pasiphae group,[22] is red and, given the difference in inclination, it could have been captured independently;[33] Pasiphae and Sinope are also trapped in secular resonances with Jupiter.[35]
  • S/2003 J 2 is the outermost moon of Jupiter, and is not part of a known family.

List

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 four inner moons are much smaller, the fourth most massive being more than 7000 times more massive than the fifth-most. The irregular captured moons are shaded light gray when prograde and dark gray when retrograde.

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

(km)[36]
Orbital period
(d)[36][note 5]
Inclination
(°)[36]
Eccentr.
[23]
Discovery
year
[21]
Discoverer[21] Group
[note 6]
1 XVI Metis
60 × 40 × 34 ≈ 3.6 127690 +7h 4m 29s 0.06[37] 0.00002 1979 Synnott
(Voyager 1)
Inner
2 XV Adrastea
20 × 16 × 14 ≈ 0.2 128690 +7h 9m 30s 0.03[37] 0.0015 1979 Jewitt
(Voyager 2)
Inner
3 V Amalthea
250 × 146 × 128
(167±4.0)
208 181366 +11h 57m 23s 0.374[37] 0.0032 1892 Barnard Inner
4 XIV Thebe
116 × 98 × 84 ≈ 43 221889 +16h 11m 17s 1.076[37] 0.0175 1979 Synnott
(Voyager 1)
Inner
5 I Io
3660.0
× 3637.4
× 3630.6
8931900 421700 +1.7691 0.050[37] 0.0041 1610 Galilei Galilean
6 II Europa
3121.6 4800000 671034 +3.5512 0.471[37] 0.0094 1610 Galilei Galilean
7 III Ganymede
5262.4 14819000 1070412 +7.1546 0.204[37] 0.0011 1610 Galilei Galilean
8 IV Callisto
4820.6 10759000 1882709 +16.689 0.205[37] 0.0074 1610 Galilei Galilean
9 XVIII Themisto 8 0.069 7393216 +129.87 45.762 0.2115 1975/2000 Kowal & Roemer/
Sheppard et al.
Themisto
10 XIII Leda
16 0.6 11187781 +240.82 27.562 0.1673 1974 Kowal Himalia
11 VI Himalia
170 670 11451971 +250.23 30.486 0.1513 1904 Perrine Himalia
12 X Lysithea 36 6.3 11740560 +259.89 27.006 0.1322 1938 Nicholson Himalia
13 VII Elara
86 87 11778034 +257.62 29.691 0.1948 1905 Perrine Himalia
14 LIII Dia 4 0.0090 12570424 +287.93 27.584 0.2058 2001 Sheppard et al. Himalia?
15 XLVI Carpo 3 0.0045 17144873 +458.62 56.001 0.2735 2003 Sheppard et al. Carpo
16 S/2003 J 12 1 0.00015 17739539 −482.69 142.680 0.4449 2003 Sheppard et al. ?
17 XXXIV Euporie 2 0.0015 19088434 −538.78 144.694 0.0960 2002 Sheppard et al. Ananke
18 S/2003 J 3 2 0.0015 19621780 −561.52 146.363 0.2507 2003 Sheppard et al. Ananke
19 S/2003 J 18 2 0.0015 19812577 −569.73 147.401 0.1569 2003 Gladman et al. Ananke
20 S/2011 J 1 1 20155290 −582.22 162.8 0.2963 2011 Sheppard et al. ?
21 LII S/2010 J 2 1 20307150 −588.36 150.4 0.307 2010 Veillet Ananke?
22 XLII Thelxinoe 2 0.0015 20453753 −597.61 151.292 0.2684 2003 Sheppard et al. Ananke
23 XXXIII Euanthe 3 0.0045 20464854 −598.09 143.409 0.2000 2002 Sheppard et al. Ananke
24 XLV Helike 4 0.0090 20540266 −601.40 154.586 0.1374 2003 Sheppard et al. Ananke
25 XXXV Orthosie 2 0.0015 20567971 −602.62 142.366 0.2433 2002 Sheppard et al. Ananke
26 XXIV Iocaste 5 0.019 20722566 −609.43 147.248 0.2874 2001 Sheppard et al. Ananke
27 S/2003 J 16 2 0.0015 20743779 −610.36 150.769 0.3184 2003 Gladman et al. Ananke
28 XXVII Praxidike 7 0.043 20823948 −613.90 144.205 0.1840 2001 Sheppard et al. Ananke
29 XXII Harpalyke 4 0.012 21063814 −624.54 147.223 0.2440 2001 Sheppard et al. Ananke
30 XL Mneme 2 0.0015 21129786 −627.48 149.732 0.3169 2003 Gladman et al. Ananke
31 XXX Hermippe 4 0.0090 21182086 −629.81 151.242 0.2290 2002 Sheppard et al. Ananke?
32 XXIX Thyone 4 0.0090 21405570 −639.80 147.276 0.2525 2002 Sheppard et al. Ananke
33 XII Ananke Ananké.jpg 28 3.0 21454952 −640.38 151.564 0.3445 1951 Nicholson Ananke
34 L Herse 2 0.0015 22134306 −672.75 162.490 0.2379 2003 Gladman et al. Carme
35 XXXI Aitne 3 0.0045 22285161 −679.64 165.562 0.3927 2002 Sheppard et al. Carme
36 XXXVII Kale 2 0.0015 22409207 −685.32 165.378 0.2011 2002 Sheppard et al. Carme
37 XX Taygete 5 0.016 22438648 −686.67 164.890 0.3678 2001 Sheppard et al. Carme
38 S/2003 J 19 2 0.0015 22709061 −699.12 164.727 0.1961 2003 Gladman et al. Carme
39 XXI Chaldene 4 0.0075 22713444 −699.33 167.070 0.2916 2001 Sheppard et al. Carme
40 S/2003 J 15 2 0.0015 22720999 −699.68 141.812 0.0932 2003 Sheppard et al. Ananke?
41 S/2003 J 10 2 0.0015 22730813 −700.13 163.813 0.3438 2003 Sheppard et al. Carme?
42 S/2003 J 23 2 0.0015 22739654 −700.54 148.849 0.3930 2004 Sheppard et al. Pasiphae
43 XXV Erinome 3 0.0045 22986266 −711.96 163.737 0.2552 2001 Sheppard et al. Carme
44 XLI Aoede 4 0.0090 23044175 −714.66 160.482 0.6011 2003 Sheppard et al. Pasiphae
45 XLIV Kallichore 2 0.0015 23111823 −717.81 164.605 0.2041 2003 Sheppard et al. Carme?
46 XXIII Kalyke 5 0.019 23180773 −721.02 165.505 0.2139 2001 Sheppard et al. Carme
47 XI Carme 46 13 23197992 −763.95 165.047 0.2342 1938 Nicholson Carme
48 XVII Callirrhoe
9 0.087 23214986 −727.11 139.849 0.2582 2000 Spahr, Scotti Pasiphae
49 XXXII Eurydome 3 0.0045 23230858 −723.36 149.324 0.3769 2002 Sheppard et al. Pasiphae?
50 S/2011 J 2 1 23329710 −725.06 151.8 0.3867 2011 Sheppard et al. Pasiphae?
51 XXXVIII Pasithee 2 0.0015 23307318 −726.93 165.759 0.3288 2002 Sheppard et al. Carme
52 LI S/2010 J 1 2 23314335 −722.83 163.2 0.320 2010 Jacobson et al. Carme?
53 XLIX Kore 2 0.0015 23345093 −776.02 137.371 0.1951 2003 Sheppard et al. Pasiphae
54 XLVIII Cyllene 2 0.0015 23396269 −731.10 140.148 0.4115 2003 Sheppard et al. Pasiphae
55 XLVII Eukelade 4 0.0090 23483694 −735.20 163.996 0.2828 2003 Sheppard et al. Carme
56 S/2003 J 4 2 0.0015 23570790 −739.29 147.175 0.3003 2003 Sheppard et al. Pasiphae
57 VIII Pasiphae 60 30 23609042 −739.80 141.803 0.3743 1908 Melotte Pasiphae
58 XXXIX Hegemone 3 0.0045 23702511 −745.50 152.506 0.4077 2003 Sheppard et al. Pasiphae
59 XLIII Arche 3 0.0045 23717051 −746.19 164.587 0.1492 2002 Sheppard et al. Carme
60 XXVI Isonoe 4 0.0075 23800647 −750.13 165.127 0.1775 2001 Sheppard et al. Carme
61 S/2003 J 9 1 0.00015 23857808 −752.84 164.980 0.2761 2003 Sheppard et al. Carme
62 S/2003 J 5 4 0.0090 23973926 −758.34 165.549 0.3070 2003 Sheppard et al. Carme
63 IX Sinope 38 7.5 24057865 −739.33 153.778 0.2750 1914 Nicholson Pasiphae
64 XXXVI Sponde 2 0.0015 24252627 −771.60 154.372 0.4431 2002 Sheppard et al. Pasiphae
65 XXVIII Autonoe 4 0.0090 24264445 −772.17 151.058 0.3690 2002 Sheppard et al. Pasiphae
66 XIX Megaclite 5 0.021 24687239 −792.44 150.398 0.3077 2001 Sheppard et al. Pasiphae
67 S/2003 J 2 2 0.0015 30290846 −1077.02 153.521 0.1882 2003 Sheppard et al. ?

Exploration by spacecraft

See also

Notes

  1. ^ Jupiter Mass of 1.8986 × 1027 kg / Mass of Galilean moons 3.93 × 1023 kg=4,828
  2. ^ Order refers to the position among other moons with respect to their average distance from Jupiter.
  3. ^ Label refers to the Roman numeral attributed to each moon in order of their naming.
  4. ^ Diameters with multiple entries such as "60 × 40 × 34" reflect that the body is not a perfect spheroid and that each of its dimensions have been measured well enough.
  5. ^ Periods with negative values are retrograde.
  6. ^ "?" refers to group assignments that are not considered sure yet.

References

  1. ^ a b
  2. ^
  3. ^ a b c d e
  4. ^
  5. ^ a b
  6. ^
  7. ^
  8. ^
  9. ^
  10. ^
  11. ^
  12. ^
  13. ^
  14. ^
  15. ^
  16. ^
  17. ^
  18. ^
  19. ^
  20. ^
  21. ^ a b c d
  22. ^ a b c d e
  23. ^ a b c d e
  24. ^ a b
  25. ^
  26. ^
  27. ^ a b
  28. ^ a b
  29. ^
  30. ^
  31. ^
  32. ^
  33. ^ a b c d
  34. ^
  35. ^
  36. ^ a b c
  37. ^ a b c d e f g h

External links

  • Jupiter Satellite Data
  • Jupiter, and The Giant Planet Satellite and Moon Page
  • Simulation showing the position of Jupiter's Moon
  • Animated tour of Jupiter's Moons, University of South Wales
  • Jupiter's Moons by NASA's Solar System Exploration
  • "43 more moons orbiting Jupiter" article appeared in 2003 in the San Francisco Chronicle
  • Articles on the Jupiter System in Planetary Science Research Discoveries
  • An animation of the Jovian system of moons
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