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Astronomers Discover the First Ring Around a Moon

discovermagazine.com — Astronomers were recently shocked to find that Saturn's second-biggest moon, Rhea, is surrounded by a ring. So how did it get there? And what's keeping it there?

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  • v4veer, on 07/07/2008, -34/+1Hey mate...nice information sharing with us...keep posting

    Please add me to your friend list if you havn't yet so that i'll keep digging through your submissions...
    Happpy Diggin
  • ivan423, on 07/07/2008, -11/+3Earth has a ring of satellites, and space junk.
  • scooterbaga, on 07/08/2008, -2/+52...I'm going to make a WILD guess and say the answer to both those questions is gravity.
    • kaelyiesta, on 07/08/2008, -1/+7The question is more complicated than that. Differential equations describing the equilibrium stability of the bodies involved are very good at showing that even if you do get an orbit, its not always the case that it will be constant. This is the issue the article raises. Even slight perturbations can send an unstable system of bodies off their orbit and into decay.

      For example, the direction our moon revolves around the earth and the earth around our sun is not a stable equilibrium inherently. Only the fact that the moon is so close to the earth and in such a tight spin keeps the influence of the sun from causing too much change to the moons orbit. The same cannot be said of the math describing the ring around Rhea(or so the article claims implicitly, I don't know the numbers myself so I'm just taking their word for it), and thats why they are surprised they see a ring; It would only be temporary unless conditions were good enough to support a stable equilibrium, which for a moon is rare.
      • scooterbaga, on 07/09/2008, -0/+1But what force of nature pulled the matter there in the first place? I'm guessing it's the same force that causes it to orbit, regardless of it's stability...

        GRAVITY.

        The question they should be asking is, if the orbit is stable, why?
    • brunson, on 07/08/2008, -1/+5They're there because Jesus wanted them there. Asshats.
  • suckanucka, on 07/08/2008, -15/+5God put it there 13,600 years ago when he created the jewniverse.
  • bigmrpig, on 07/08/2008, -2/+23Pics or it didn't happen
  • Echomote, on 07/08/2008, -9/+4I'm going to take a guess before reading the article, that gravity is behind "keeping it there".
  • Chassit, on 07/08/2008, -2/+3The answer to those questions is simple: tidal effect (caused by gravity).
  • Depravo, on 07/08/2008, -7/+0Astronomers discover the first ring around a moon?

    Well what a surprise! Seriously, who were you expecting to discover it? A ***** binman?
  • NesloTterrag, on 07/08/2008, -7/+1Ring! Ring! around the Moon! you mean a Halo?!?!? call the Master Chief!!!
  • burjzyntski, on 07/08/2008, -5/+0four magic powers.
  • Kenzan, on 07/08/2008, -4/+4So how did it get there? And what's keeping it there?
    Um...the same debris from Saturn? and um...gravity FTW.
  • Amadeus2490, on 07/08/2008, -3/+1I guess the same thing that put on and is keeping the ring around Saturn, right?
  • mal1964, on 07/08/2008, -3/+13God put it there.
  • ryleyleckie, on 07/08/2008, -0/+4...let's all 'guess' the same thing
  • Nerdable, on 07/08/2008, -1/+5damn thetons
  • stretch611, on 07/08/2008, -0/+1Why is this surprising?

    Stars rotate around the center of our galaxy. Planets rotate around stars. Moons rotate around planets. Why is it so surprising to have debris rotating around a moon?
    • ezran, on 07/08/2008, -0/+2Because the moon is quite close to a planet...
  • kidwithsword, on 07/08/2008, -0/+2If the moon is significantly smaller than Saturn, then it makes sense that the astronomers were shocked. Logically, Saturn would pull any debris from the small moon toward itself since it has a greater gravitational pull.

    It has been a while since I have studied the behavior of physics and gravity in space, but the way I understand it, the moon must be made of an immensely dense material, a material much more dense than that which Saturn is composed of.
    • com2, on 07/09/2008, -0/+1That's what I was thinking too.
    • InsaneOni, on 07/09/2008, -0/+1gravitational force is a function of 1/R^2. If the ring is the right distance from the moon, the forces will be more or less equal.
  • chesscat, on 07/08/2008, -2/+8Bigger than the rings around Uranus?
    • str1fe, on 07/08/2008, -0/+12Oh, astronomers changed the name of that planet ages ago to kill that stupid pun once and for all.

      It's called Urectum now.
      • gdog05, on 07/08/2008, -1/+2I don't know if you want the Rhea anywhere near Uranus or Urectum.
    • com2, on 07/09/2008, -2/+1Sounds like you need to wash Uranus.
  • antipoet, on 07/08/2008, -0/+2I would like to be open minded enough to believe that we aren't the only race out there intelligent enough to completely fill up the geosynchronous orbit around their planet
  • ezran, on 07/08/2008, -1/+2I bet that the ring is not round, but more elliptical egg like shape...
  • theotherdude, on 07/08/2008, -0/+1“a ring system around a moon comes as a surprise because the parent planet’s gravity should destabilize any ring system that might form”

    It makes sense that they are surprised by this discovery because, logically, the force of gravity from the planet should be (and generally is) much, much stronger than the force of gravity from the moon. However, the force of gravity decreases exponentially with increased distance, so it does make sense that since the planet is so much farther away it's pull is not as strong as the moon's... at least at that close distance. Still, the astronomers obviously know this so I think that their surprise conveys that they know a little bit more about what is going on than we do.
  • oilcan, on 07/08/2008, -0/+1it's God testing our faith in Big Bang physics.
  • Cheeseburgers, on 07/08/2008, -0/+1that moon should try Wisk
  • leetneko, on 07/08/2008, -0/+1That's no moon. It's a space station.
    • snareguy17, on 07/08/2008, -1/+1That reminded me of Phantasy Star IV for the Genesis for some reason.
  • macbethslady, on 07/09/2008, -0/+0Cool...but how have these rings not been discovered sooner? Cosmically speaking, Saturn is close to us and well-studied.
  • linedrawing76, on 07/09/2008, -1/+0This is all very well and good, but what good is it spending all this time discovering new rings all over the place, when we have a jackpot of rings around Saturn, all waiting to be dipped in batter and deep fried? Let's eat those first, then look for more. Time's a wasting.
  • calenlas, on 07/09/2008, -0/+1Why bother with second-hand reporting when a more detailed article is available directly from NASA?

    http://www.nasa.gov/home/hqnews/2008/mar/HQ_08074_ ...
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