Emily Lakdawalla • Mar 03, 2009
A new moon for Saturn within the G ring
UPDATE: This new moon is now named Aegaeon.EDIT: Check out a correction posted on March 4: Cassini definitely could and may well get images of this newly discovered moon.
It's been a while since the last discovery of a moon at Saturn by Cassini; today comes a long-awaited announcement, the discovery of the parent body (perhaps just one of several) to Saturn's dusty G ring. It's long been suspected that there must be something responsible for the presence of that ring, but until now no one's been able to find the responsible moonlet. There's a good reason it was hard to find: they are guessing that the tiny thing is only about half a kilometer across, the size of Itokawa. It's provisionally named S/2008 S1, and its existence was announced today in the International Astronomical Union Circular #9023. My subscription to the IAUCs seems to have lapsed, so I don't know what other details are in the citation, unfortunately. Here's a set of photos:
S/2008 S1 may just be the easiest to find of a number of parent bodies that supply dusty material to the G ring. Methone, Anthe, and Pallene just have arcs, but the G ring extends all the way around the planet. So there could well be other objects, maybe just 100 meters or 50 meters across, orbiting in different positions within the G ring, all supplying the dust that keeps the G ring its dusty self. With this discovery, I think Cassini's beginning to venture into the murky terrain that separates "moons" from "ring particles."
What would S/2008 S1 look like up close? I don't know, but I can hazard some guesses. It's roughly the size of Itokawa, but I would think that it wouldn't look anything like Itokawa's bouldery and gravelly surface. S/2008 S1 orbits within an arc of dust of all sizes. The small moons of Saturn that orbit close to and within the rings that Cassini has photographed -- Atlas, for instance, or Pandora -- have odd football (American football, that is, or rugby ball, if you prefer) or saucer shapes, formed from the slow accretion and sliding of dust around their surfaces. I'd guess S/2008 S1 would look like that. Try to land on it, and your every motion would kick up puffs and clouds of dust, flying away on ballistic trajectories, to orbit Saturn in the "sky" around the little world. Weird.
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