by neufer » Sat Apr 14, 2012 4:15 pm
Chris Peterson wrote:orin stepanek wrote:the smallest only a fraction of a kilometer across.
How large does a moon have to be to get counted? If you counted every rock and snow ball in Saturn's ring the number would be uncountable!
I'm guessing that there are a lot of then between the size of the smallest one listed and tapering down in size to the dust that form the rings.
If it's a body in orbit around a planet, it's a moon. Material in rings is sort of an exception to that. Otherwise, it could be thousands of kilometers across or it could be dust. Keep in mind that below a certain size, objects are likely to be in fairly unstable orbits, meaning that their tenure as "moons" will be quite short (like the occasional extra moons that Earth periodically acquires).
http://en.wikipedia.org/wiki/Natural_satellite wrote:
<<A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary.
There is not an established lower limit on what is considered a moon. Every body with an identified orbit, some as small as a kilometer across, has been identified as a moon, though objects a tenth that size within Saturn's rings, which have not been directly observed, have been called moonlets. Small asteroid moons, such as Dactyl, have also been called moonlets. The upper limit is also vague. Two orbiting bodies are sometimes described as a double body rather than primary and satellite. Asteroids such as 90 Antiope are considered double asteroids, but they have not forced a clear definition of what constitutes a moon. Some authors consider the Pluto-Charon system to be a double (dwarf) planet. The most common dividing line on what is considered a moon rests upon whether the barycentre is below the surface of the larger body, though this is somewhat arbitrary, as it relies on distance as well as relative mass.
Formally classified moons include 173 planetary satellites orbiting six of the eight planets, and seven orbiting three of the five IAU-listed dwarf planets. As of January 2012, over 200 minor planet moons have been discovered. There are 76 in the asteroid belt (5 with two satellites), 4 Jupiter trojans, 37 near-Earth objects and 9 Mars-crossers. There are also 76 known moons of trans-Neptunian objects.
Some 150 additional small bodies were observed within rings of Saturn, but they were not tracked long enough to establish orbits.>>
http://en.wikipedia.org/wiki/Moons_of_Saturn#Ring_moonlets wrote:
<<In 2006, four tiny moonlets were found in Cassini images of the A Ring. Before this discovery only two larger moons had been known within gaps in the A Ring: Pan and Daphnis. These are large enough to clear continuous gaps in the ring. In contrast, a moonlet is only massive enough to clear two small—about 10 km across—partial gaps in the immediate vicinity of the moonlet itself creating a structure shaped like an airplane propeller. The moonlets themselves are tiny, ranging from about 40 to 500 meters in diameter, and are too small to be seen directly. In 2007, the discovery of 150 more moonlets revealed that they (with the exception of two that have been seen outside the Encke gap) are confined to three narrow bands in the A Ring between 126,750 and 132,000 km from Saturn's center. Each band is about a thousand kilometers wide, which is less than 1% the width of Saturn's rings. This region is relatively free from the disturbances related to resonances with larger satellites, although other areas of the A Ring without disturbances are apparently free of moonlets. The moonlets were probably formed from the breakup of a larger satellite. It is estimated that the A Ring contains 7,000–8,000 propellers larger than 0.8 km in size and millions larger than 0.25 km.
During late July 2009, a moonlet was discovered in the B Ring, 480 km from the outer edge of the ring, by the shadow it cast. It is estimated to be 300 m in diameter. Unlike the A Ring moonlets, it does not induce a 'propeller' feature, probably due to the density of the B Ring.
Similar moonlets may reside in the F Ring. There, "jets" of material may be due to collisions, initiated by perturbations from the nearby small moon Prometheus, of these moonlets with the core of the F Ring. One of the largest F-Ring moonlets may be the as-yet unconfirmed object S/2004 S 6. The F Ring also contains transient "fans" which are thought to result from even smaller moonlets, about 1 km in diameter, orbiting near the F Ring core.>>
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http://en.wikipedia.org/wiki/Aegaeon_%28moon%29 wrote:
<<Aegaeon (Greek Αιγαίων), also Saturn LIII (provisional designation S/2008 S 1), is a natural satellite of Saturn. Its discovery was announced by Carolyn Porco of the Cassini Imaging Science Team on March 3, 2009, from observations taken on August 15, 2008.
Aegaeon orbits within the bright segment of Saturn's G Ring, and is probably a major source of the ring. Debris knocked off the moon forms a bright arc near the inner edge, which in turn spreads to form the rest of the ring. Aegaeon orbits in a 7:6 resonance with Mimas, which causes a ≈ 4-year oscillation of ≈ 4 km in its semi-major axis. Assuming it has the same albedo as Pallene, it is estimated to be half a kilometer in diameter. It orbits Saturn at an average distance of 167,500 km in 0.80812 days, at an inclination of 0.001° to Saturn's equator, with an eccentricity of 0.0002.
It is named after Ægæon, one of the hecatonchires. The Hecatonchires, or Hekatonkheires (Ἑκατόγχειρες) "Hundred-Handed Ones," Latinised Centimani), were figures in an archaic stage of Greek mythology, three giants of incredible strength and ferocity that surpassed that of all Titans whom they helped overthrow. Their name derives from the Greek ἑκατόν (hekaton; "hundred") and χείρ (kheir; "hand"), "each of them having a hundred hands and fifty heads." Hesiod's Theogony reports that the three Hekatonkheires became the guards of the gates of Tartarus.
According to Hesiod, the Hekatonkheires were children of Gaia (Earth) and Uranus (sky). Their names were Briareus (Βριάρεως) the Vigorous, also called Aigaion (Αἰγαίων), Latinised as Aegaeon, the "sea goat", Cottus (Κόττος) the Striker or the Furious, and Gyges (Γύγης) or Gyes (Γύης) the Big-Limbed. If some natural phenomena are symbolised by the Hekatoncheires then they may represent the gigantic forces of nature that appear in earthquakes and other convulsions or in the motion of sea waves.
Soon after they were born their father Uranus threw them into the depths of Tartarus because he saw them as hideous monsters.
In some versions Uranus saw how ugly the Hekatonkheires were at their birth and pushed them back into Gaia's womb, upsetting Gaia greatly, causing her great pain and setting into motion the overthrow of Uranus by Cronus (a.k.a, Saturn), who later imprisoned them in Tartarus. The Hekatonkheires remained there, guarded by the dragon Campe, until Zeus rescued them, advised by Gaia that they would serve as good allies against Cronus and the Titans. During the War of the Titans the Hekatonkheires threw rocks as big as mountains, one hundred at a time, at the Titans, overwhelming them.
Other accounts make Briareus or Aegaeon one of the assailants of Olympus, who, after his defeat, was buried under Mount Aetna. Briareus is mentioned in the Divine Comedy poem Inferno as one of the Giants in the Ninth Circle of Hell (Inferno XXXI.99). The giant is also mentioned in Cervantes' Don Quixote, in the famous episode of the windmills.>>
[quote="Chris Peterson"][quote="orin stepanek"][quote]the smallest only a fraction of a kilometer across. [/quote]
How large does a moon have to be to get counted? If you counted every rock and snow ball in Saturn's ring the number would be uncountable! :roll: I'm guessing that there are a lot of then between the size of the smallest one listed and tapering down in size to the dust that form the rings. :wink:[/quote]
If it's a body in orbit around a planet, it's a moon. Material in rings is sort of an exception to that. Otherwise, it could be thousands of kilometers across or it could be dust. Keep in mind that below a certain size, objects are likely to be in fairly unstable orbits, meaning that their tenure as "moons" will be quite short (like the occasional extra moons that Earth periodically acquires).[/quote][quote=" http://en.wikipedia.org/wiki/Natural_satellite"]
<<A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. [b][color=#4000FF]There is [u]not[/u] an established lower limit on what is considered a moon. [u]Every body with an identified orbit, some as small as a kilometer across, has been identified as a moon[/u], though objects a tenth that size within Saturn's rings, which have not been directly observed, have been called moonlets. Small asteroid moons, such as Dactyl, have also been called moonlets.[/color][/b] The upper limit is also vague. Two orbiting bodies are sometimes described as a double body rather than primary and satellite. Asteroids such as 90 Antiope are considered double asteroids, but they have not forced a clear definition of what constitutes a moon. Some authors consider the Pluto-Charon system to be a double (dwarf) planet. The most common dividing line on what is considered a moon rests upon whether the barycentre is below the surface of the larger body, though this is somewhat arbitrary, as it relies on distance as well as relative mass.
Formally classified moons include 173 planetary satellites orbiting six of the eight planets, and seven orbiting three of the five IAU-listed dwarf planets. As of January 2012, over 200 minor planet moons have been discovered. There are 76 in the asteroid belt (5 with two satellites), 4 Jupiter trojans, 37 near-Earth objects and 9 Mars-crossers. There are also 76 known moons of trans-Neptunian objects. [b][color=#FF0000]Some 150 additional small bodies were observed within rings of Saturn, but they were not tracked long enough to establish orbits.[/color][/b]>>[/quote][quote=" http://en.wikipedia.org/wiki/Moons_of_Saturn#Ring_moonlets"]
[float=right][img3="[b][color=#0000FF]Location of the first four moonlets detected in the A ring.[/color][/b]"]http://upload.wikimedia.org/wikipedia/commons/thumb/b/ba/First_moonlets_PIA07792.jpg/1280px-First_moonlets_PIA07792.jpg[/img3][/float]<<In 2006, four tiny moonlets were found in Cassini images of the A Ring. Before this discovery only two larger moons had been known within gaps in the A Ring: Pan and Daphnis. These are large enough to clear continuous gaps in the ring. In contrast, a moonlet is only massive enough to clear two small—about 10 km across—partial gaps in the immediate vicinity of the moonlet itself creating a structure shaped like an airplane propeller. The moonlets themselves are tiny, ranging from about 40 to 500 meters in diameter, and are too small to be seen directly. In 2007, the discovery of 150 more moonlets revealed that they (with the exception of two that have been seen outside the Encke gap) are confined to three narrow bands in the A Ring between 126,750 and 132,000 km from Saturn's center. Each band is about a thousand kilometers wide, which is less than 1% the width of Saturn's rings. This region is relatively free from the disturbances related to resonances with larger satellites, although other areas of the A Ring without disturbances are apparently free of moonlets. The moonlets were probably formed from the breakup of a larger satellite. It is estimated that the A Ring contains 7,000–8,000 propellers larger than 0.8 km in size and millions larger than 0.25 km.
During late July 2009, a moonlet was discovered in the B Ring, 480 km from the outer edge of the ring, by the shadow it cast. It is estimated to be 300 m in diameter. Unlike the A Ring moonlets, it does not induce a 'propeller' feature, probably due to the density of the B Ring.
Similar moonlets may reside in the F Ring. There, "jets" of material may be due to collisions, initiated by perturbations from the nearby small moon Prometheus, of these moonlets with the core of the F Ring. One of the largest F-Ring moonlets may be the as-yet unconfirmed object S/2004 S 6. The F Ring also contains transient "fans" which are thought to result from even smaller moonlets, about 1 km in diameter, orbiting near the F Ring core.>>[/quote].
[c][url=http://asterisk.apod.com/viewtopic.php?f=23&t=18918&p=118620#p118620][size=150]Dangerous Moonlet: Aegaeon (a.k.a., Briareus)[/size][/url][/c][quote=" http://en.wikipedia.org/wiki/Aegaeon_%28moon%29"]
[float=right][img3="[b][color=#0000FF]Three images of the bright arc of the G Ring with Aegaeon (a.k.a., Briareus) embedded within it, taken over the course of ten minutes[/color][/b]"]http://upload.wikimedia.org/wikipedia/commons/thumb/9/9a/Aegaeon_%282008_S1%29.jpg/800px-Aegaeon_%282008_S1%29.jpg[/img3][/float]<<Aegaeon (Greek Αιγαίων), also Saturn LIII (provisional designation S/2008 S 1), is a natural satellite of Saturn. Its discovery was announced by Carolyn Porco of the Cassini Imaging Science Team on March 3, 2009, from observations taken on August 15, 2008.
Aegaeon orbits within the bright segment of Saturn's G Ring, and is probably a major source of the ring. Debris knocked off the moon forms a bright arc near the inner edge, which in turn spreads to form the rest of the ring. Aegaeon orbits in a 7:6 resonance with Mimas, which causes a ≈ 4-year oscillation of ≈ 4 km in its semi-major axis. Assuming it has the same albedo as Pallene, it is estimated to be half a kilometer in diameter. It orbits Saturn at an average distance of 167,500 km in 0.80812 days, at an inclination of 0.001° to Saturn's equator, with an eccentricity of 0.0002.
It is named after Ægæon, one of the hecatonchires. The Hecatonchires, or Hekatonkheires (Ἑκατόγχειρες) "Hundred-Handed Ones," Latinised Centimani), were figures in an archaic stage of Greek mythology, three giants of incredible strength and ferocity that surpassed that of all Titans whom they helped overthrow. Their name derives from the Greek ἑκατόν (hekaton; "hundred") and χείρ (kheir; "hand"), "each of them having a hundred hands and fifty heads." Hesiod's Theogony reports that the three Hekatonkheires became the guards of the gates of Tartarus.
According to Hesiod, the Hekatonkheires were children of Gaia (Earth) and Uranus (sky). Their names were Briareus (Βριάρεως) the Vigorous, also called Aigaion (Αἰγαίων), Latinised as Aegaeon, the "sea goat", Cottus (Κόττος) the Striker or the Furious, and Gyges (Γύγης) or Gyes (Γύης) the Big-Limbed. If some natural phenomena are symbolised by the Hekatoncheires then they may represent the gigantic forces of nature that appear in earthquakes and other convulsions or in the motion of sea waves.
Soon after they were born their father Uranus threw them into the depths of Tartarus because he saw them as hideous monsters. [b][color=#FF0000]In some versions Uranus saw how ugly the Hekatonkheires were at their birth and pushed them back into Gaia's womb, upsetting Gaia greatly[/color][/b], causing her great pain and setting into motion the overthrow of Uranus by Cronus (a.k.a, Saturn), who later imprisoned them in Tartarus. The Hekatonkheires remained there, guarded by the dragon Campe, until Zeus rescued them, advised by Gaia that they would serve as good allies against Cronus and the Titans. During the War of the Titans the Hekatonkheires threw rocks as big as mountains, one hundred at a time, at the Titans, overwhelming them.
Other accounts make Briareus or Aegaeon one of the assailants of Olympus, who, after his defeat, was buried under Mount Aetna. Briareus is mentioned in the Divine Comedy poem Inferno as one of the Giants in the Ninth Circle of Hell (Inferno XXXI.99). The giant is also mentioned in Cervantes' Don Quixote, in the famous episode of the windmills.>>[/quote]