Saturn has a new moon

[dragon]

Damn we just keep finding new stuff all the time. Saturn has over 5 dozen moon, thats a lot of moons.

PASADENA, Calif. – Scientists have found a new moon hidden in one of Saturn's dazzling outer rings. The international Cassini spacecraft spotted the moon, which measures about a third of a mile wide. The discovery was announced Tuesday in a notice by the International Astronomical Union.

Researchers have long puzzled over the formation of Saturn's G ring, one of the planet's more mysterious arcs. They now think the G ring was likely formed from icy debris that scattered when meteorites crash into the newfound moon.

Scientists confirmed the moon's existence last summer after analyzing images from Cassini. Saturn has over five dozen moons

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new moon

[wautd]

Well it's only a third of a mile wide. I wouldn't be suprised if they found more moons of this size hidden in its rings.

[Dooey Jo]

A third of a mile? Isn't there some kind of limit for when something ceases to be a moon and becomes an orbiting piece of rock?

[DaveJB]

I don't believe there is. IIRC though most smaller objects don't have stable orbits and will enter the planet's atmosphere sooner or later, making it largely a moot point.

[Ziggy Stardust]

Here is what NASA is saying.

Why must this moonlet necessarily be the source of the G ring? Astronomy.com has a good explanation for how it might be the source, but is it not just as possible that the ring came first, and the minimoon is a slowly accumulating mass of the matter in the ring (or maybe a meteor that got caught by gravity and ended up in the ring)? I know some people on these boards may know more about astronomy than I, so maybe they can answer this question.

[starslayer]

Here is what NASA is saying.

Why must this moonlet necessarily be the source of the G ring? Astronomy.com has a good explanation for how it might be the source, but is it not just as possible that the ring came first, and the minimoon is a slowly accumulating mass of the matter in the ring (or maybe a meteor that got caught by gravity and ended up in the ring)? I know some people on these boards may know more about astronomy than I, so maybe they can answer this question.

Saturn's rings are unstable, and, as such, must have something to continuously provide dust to them, or else they would be gone by now (they've probably existed for most of the Solar System's history). There aren't enough random dust particles floating around out there to build the rings through dust capture, and such a process wouldn't form rings anyway. Therefore, something must be present to provide the dust for the rings (must of it is literally dust grain sized particles). This object fulfills that criterion, as it is big enough to have been shedding dust all this time. Ergo, it is almost certainly the source of the ring.

This moon is also not a recent capture/formation from a collision event, either. It's orbit is far, far too circular for that. The momentum shift due to a collision, or the dynamics of a gravitational capture would make the orbit extremely elliptical, and probably severely inclined to Saturn's equator. Since this object has both a nearly circular orbit, and orbits in the plane of Saturn's equator, it almost certainly formed at around the same time Saturn did, thus again making the most likely candidate for the G ring creator. Accretion within the rings is also not much of a factor, because the gravitational interactions between the extant moons and Saturn itself tend to keep the ring material relatively spread out, and moving in similar orbits, preventing large scale collisions.

In any case, the rings are not very massive, the G ring especially so (it isn't very bright, and thus has less stuff in it). They are only a few tens of meters thick in most places, and are not very dense. Which makes it all the more amazing that they are visible in even the most basic of amateur telescopes and binoculars (yes, I have seen them in 10x50's). The other outer planets' ring systems are generally very faint, though they do exist.

[Darth Yoshi]

They're unstable? How does that work? Do the gravitational forces from Jupiter slow down the rings or something? This is the first I've heard of it.

[starslayer]

Upon further research, I can find no evidence that they are unstable in their present configuration, so I was wrong about that. They would be unstable if it weren't for the many shepherd moons within and around them; if the moons weren't there, they would diffuse away from Saturn due to solar radiation pressure and interactions with Saturn's magnetosphere, and be gone within about 100 millions years after their formation. The innermost rings might have been propelled into Saturn itself due to drag caused by plasma trapped in Saturn's magnetosphere.

As it stands, these sorts of instabilities are responsible for the very diffuse state of the G ring. As dust comes off of S/2008 S1, it initially settles into the bright arc surrounding the moonlet. Solar radiation and reflected radiation from Saturn push the dust into higher orbits, causing it to spread out into the expanse of the main ring. It would escape after a while if not for Mimas, which keeps it all in place as the G ring.