| Jupiter's Natural Satellites |
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Information AboutJupiter's Natural Satellites |
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DISCOVERY OF THE MOONS '': Shown from left to right in order of increasing distance from Jupiter, Io is closest, followed by Europa , Ganymede , and Callisto .]] The first moons of Jupiter to be discovered were the large Galilean Moons , discovered by Galileo in 1610 . An earlier discovery by ancient Chinese astronomer Gan De may have occurred in 362 BC . Over the next four centuries after Galileo, nine smaller moons were discovered by ground-based Astronomer s. The Voyager 1 mission discovered three inner moons in 1979 , bringing the total then known to 16 (17 if one counted Themisto , which had been found but then lost in 1975 ). The total rested there until 1999 . Since then, researchers using sensitive ground-based detectors have recovered Themisto and found a further 46 tiny moons in long, Eccentric , generally Retrograde Orbit s. They average 3 kilometres in diameter, and the largest is barely 9 km across. All of these moons are thought to be captured Asteroid al or perhaps Comet ary bodies, possibly fragmented into several pieces, but very little is actually known about them. The total number of known moons of Jupiter now stands at 63, currently the most of any planet in the Solar System . Many additional tiny moons may exist that have not yet been discovered. The most recent discoveries On October 6 1999 , the Spacewatch project discovered an Asteroid , 1999 UX18. But it was soon realised that this was in fact a previously undiscovered moon of Jupiter, now called Callirrhoe . One year later, between November 23 and December 5 , 2000 , the team led by Scott S. Sheppard and David C. Jewitt of the University Of Hawaii began a systematic search for small irregular moons of Jupiter. The other members of the team included, at various times, Yanga R. Fernández , Eugene A. Magnier , Scott Dahm , Aaron Evans , Henry H. Hsieh , Karen J. Meech , John L. Tonry , David J. Tholen (all from the University of Hawaii), Jan Kleyna ( Cambridge University ), Brett J. Gladman ( University Of Toronto ), John J. Kavelaars ( Hertzberg Institute Of Astrophysics ), Jean-Marc Petit ( Observatoire De Besançon ) and Rhiannon Lynne Allen ( University Of Michigan / University Of British Columbia ). The team used the world's two largest (8.3 m diameter) and the Canada-France-Hawaii (3.6 m). The 2000 observations revealed ten new moons, putting the count at 28 (Themisto had been rediscovered at the beginning of 2000). The following year, on December 9 - 11 , 2001 , eleven other moons were discovered, bringing the total to 39. The year 2002 bore less fruit, netting only one moon, Arche . However, four months later, between February 5 and 9 , 2003 , 23 more moons were found, making for a complete sum of 63 moons. References:
TABLE OF KNOWN MOONS The Jovian moons are listed here by orbital period, from shortest to longest. Moons massive enough for their surfaces to have Collapsed into a Spheroid are highlighted in purple; these are the "Galilean Moons", which are comparable in size to Earth's moon. Irregular (captured) moons are indicated by light grey.
GROUPING THE MOONS The interior groups - The Four Inner Moons and the Galileans - seem natural. Themisto is isolated in space. The Himalia Group is "tight", spread over barely 1.4 Gm in Semi-major Axis and 1.6° in inclination (27.5 ± 0.8°). The Eccentricities vary between 0.11 and 0.25. Carpo and S/2003 J 12 are two other isolated cases, and so is S/2003 J 2 , the most exterior moon. What is left of the outer retrograde irregular satellites of Jupiter can be grouped into three families, based on shared orbital characteristics and bearing the name of the largest member in each case. These families are clumps in semi-major axis, but also in inclination and in eccentricity. In the two plots below, Carme's group is in orange and Ananke's in yellow. Carme's Group is obvious, centered on a = 23 404 Mm; i = 165.2±0.3° and e = 0.238–0.272. Only S/2003 J 10 seems somewhat apart, because of its great eccentricity. Ananke's Group is centered on a = 21 276 Mm; i = 149.0±0.5° and e = 0.216–0.244; but its borders are less definite. The eight core members ( S/2003 J 16 , Mneme , Euanthe , Orthosie , Harpalyke , Praxidike , Thyone , Thelxinoe , Ananke , Iocaste ) are well-clumped, but the attribution of the remaining eight members to the group is debatable to varying degrees. Pasiphaë's Group , finally, picks up the remainder, with the exception of the moons at the inner and outer limits of the groups ( S/2003 J 12 and S/2003 J 2 ); it is centered on a = 23 624 Mm; i = 151.4±6.9° and e = 0.156–0.432 (note the much larger spreads). If it is real, it must be ancient to explain the dispersion of its membership. NAMING NOTES Some , 38 Leda , 52 Europa , 85 Io , 113 Amalthea , 239 Adrastea . A couple of asteroids shared the names of Jovian moons until spelling differences were made permanent by the IAU. Those contrasting pairs are the moon Ganymede and the asteroid 1036 Ganymed ; and the moon Callisto and the asteroid 204 Kallisto . The moon Themisto purposely uses a name derived from the longer gentive form of the source of the name for asteroid 24 Themis . Note that the satellites discovered between 1904 and 1951 ( Himalia , Elara , Pasiphaë , Sinope , Lysithea , Carme and Ananke ) were not officially named until 1975 , 24 years after the last satellite was discovered. They were simply known by their Roman numeral designations (Jupiter VI through Jupiter XII). See Naming Of Natural Satellites . SEE ALSO
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