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Prometheus Caught Stealing From Saturn's Rings
merryprankster writes "Saturn's Moon Prometheus is living up to the reputation of
its Greek namesake. New Scientist is reporting that the latest images from the Cassini probe show the moon "stealing"
material for Saturn's F-ring. Evidence of this had been seen by Cassini in the past in the form of "streamers" and
gravitation wobbles within the rings but more fantastic images have now caught
the thief in the act."
Except that the last time Prometheus stole something, didn't he get chained to a rock with an eagle ripping out his liver?
Some people never learn...
In Xanadu did Kubla Khan
A stately pleasure dome decree
What, Mars's moons? No. They're big enough to be moons.
A moonlet is of order 10 km is diameter, typically. Actually, I don't think we've actually seen any to date. (Well, not conclusively.) In reality, the term is sort of slang anyway. Either you're a moon or you aren't. (Ring particles, dust, etc. are too small to be moons. Bigger, natural things orbiting planets... moons.)
Eccentricity isn't a player in moon-ness. It can tell you something about the origin of the moon in question (a large eccentricity, along with a high inclination and a retrograde orbit, is symptomatic of a captured body), but the distinction is bascially: does the object orbit a planet and is it bigger than some minimum size. (Probably in the region of kilometers or tens of kilometers. Opinions will vary about where to draw the line.)
Here's the original image from NASA's collection of raw images. A related image is here.
I figure by 2030 or so my 6-digit UID will be something to brag about.