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Saturn's Moon Iapetus Has A 'Belt'

Posted by timothy on from the it's-a-peach dept.

Believe writes "In another unexpected find by Cassini-Huygens, Saturn's moon Iapetus shows a bulging waistline. According to the story, the dark side of the moon is almost perfectly bisected by a tall, narrow ridge that runs for 1300 km (808 mi) and rises up to 20 km (12 mi) high. This height is amazing in such a small moon; it rivals Olympus Mons on Mars which is a body 5 times its size."

48 of 245 comments (clear)

  1. deathstar? by Phil246 · · Score: 2, Interesting

    with that ridge on this pic : http://saturn.jpl.nasa.gov/multimedia/images/image -details.cfm?imageID=1270 it REALLY has a passing resemblance to a death star.
    did anyone else notice this?

    1. Re:deathstar? by CdXiminez · · Score: 2

      Years ago, Saturn's moon Mimas was identified as a Death Star.

    2. Re:deathstar? by IPFreely · · Score: 3, Funny
      The Death Star had other features that this moon presently lacks.

      Oh come on. Give it a break. It was built a long time ago in a galaxy far, far away. It has a lot of miles and a lot of years on it. I think it looks good for its age.

      When 4 billion years you become, look as good you will not.

      --
      There is nothing so silly as other peoples traditions, and nothing so sacred as our own.
  2. So do I... by Black+Parrot · · Score: 5, Funny

    ...but you don't see it on the front page of Slashdot.

    --
    Sheesh, evil *and* a jerk. -- Jade
  3. Re:rotation ? by Chicane-UK · · Score: 3, Informative

    I think the belt is a physical feature on the moons surface - not a floating belt of debris, rock, etc.

    --
    "Hey! Unless this is a nude love-in, get the hell off my property!!"
  4. NASA... by Quaoar · · Score: 3, Funny

    That's no moon.

    --
    I'll form my OWN solar system! With blackjack! And hookers!
    1. Re:NASA... by hamsterspeed · · Score: 2, Funny

      That's no moon.

      It's a SPACE STATION!

      I have a very bad feeling about this...

      --
      pants
  5. Arthur C Clarke by panurge · · Score: 2, Interesting

    ...I think it was had a story about a planet with a wall round the middle. (A long time ago now.) If there's any chance this wall has similar properties, we need to get a robot down there to take a look at it.

    --
    Panurge has posted for the last time. Thanks for the positive moderations.
    1. Re:Arthur C Clarke by petterbergman · · Score: 4, Informative

      There is a short-story by Clarke about a universe that contains only one sun and one planet, the universe is about as big as the planets orbit. The planet is constantly showing the same face toward the sun, it has a day-side, very hot, and anight side, very cold. Humans live around the equator where the temperature is right.

      In the book the universe actually ends somewhere around the north pole(dark side) of the planet and a long time ago humans built a great wall to hide the end of the universe... great short-story.

    2. Re:Arthur C Clarke by kalidasa · · Score: 2, Informative

      The book 2010 was written as a sequel to the movie, not to the book. There are some things in the book from the book 2001 ("My god, it's full of stars!" wasn't in the movie - yes,I've checked a dozen times), but it discards Saturn and re-sets everything to Jupiter. The reason Jupiter was used in the movie? They couldn't get a convincing enough Saturn, and decided that by eliminating the ring by depicting Jupiter instead they'd simplify the FX issues.

  6. Lucas be praised! by duffahtolla · · Score: 4, Funny

    This cant be coincidence..

    1. Re:Lucas be praised! by dolphin558 · · Score: 2, Informative

      Another source of inspiration.

  7. Why surprising? by Velox_SwiftFox · · Score: 2, Insightful

    Why is it surprising that tall mountain ridges are found on small (relative to planets) moons, where there may be little weather and low gravity to cause their erosion?

    1. Re:Why surprising? by pe1rxq · · Score: 4, Interesting

      It is surprising in the way these mountains are on the moon's equator and form a nice belt.
      That there is little erosion isn't a surprise, but the mountains origin is far more interesting.
      On earth mountains are all results of our molten core (plate tektonics and vulcanoes). There must be some process that created this moutain belt.

      Jeroen

      --
      Secure messaging: http://quickmsg.vreeken.net/
    2. Re:Why surprising? by HuguesT · · Score: 5, Interesting

      For several reasons:

      On Earth mountains are caused by plate tectonics, i.e. disconnected area of crust floating on magma that run into each other, but such mechanism are impossible on small bodies because they cool too fast, i.e their crust quickly become too thick and form a single fused objet.

      Of course mountains can also be volcanoes, but similarly this implies magma that can rise to the surface, i.e a crust that is not too thick.

      The exception are moons close enough to their parent body so that internal heat can be sustained by tidal effects. This is the case on Io, for example.

      However there can only be tidal effects if the moon is rotating around itself at a different rate as it revolves around its parent body. For Iapetus, just like our moon, the two rates are the same and they always present the same face to their parent. This implies only minimal tidal effects due to the eccentricity of the orbit.

      Of course the mountain/volcano may have been formed a very long time ago when the moon wasn't as cool as it is now, probably this is the case for mount Olympus on Mars, however there is erosion on most planetary bodies even without atmosphere or low gravity, caused by the myriad of asteroid impact they sustain.

      One remaining option is impact by a large asteroid. We now have to come up with a reasonable impact scenario that can produce a feature similar to the one seen on Iapetus, which is indeed very strange.

    3. Re:Why surprising? by Vo0k · · Score: 4, Interesting

      I have two theories...

      Less possible:
      What I'd look for are two large craters of similar size and same age (can be estimated by amount of erosion from later meteorites), placed on opposite sides of the moon, shifted from the surface of the intersection by similar distance in opposite directions. Strong enough hit could have just split the moon it two...

      More possible:
      The moon had its own ring, just like Saturn has. But the ring's rotation was slowed down by Saturn's gravity (the same way our Moon's rotation got stopped by Earth) and the ring was pulled by the moon's gravity down, on the surface, depositing all the material straight below its orbit.

      --
      Anagram("United States of America") == "Dine out, taste a Mac, fries"
    4. Re:Why surprising? by rhennigan · · Score: 2, Insightful

      I'm willing to bet there used to be a ring around the moon, that eventually fell out of orbit, piling up in a neat row around the equator. Then again, IANAKP (Knowledgable Person), so feel free to suggest why this might not be possible.

    5. Re:Why surprising? by LeninZhiv · · Score: 2, Funny

      One remaining option is impact by a large asteroid. We now have to come up with a reasonable impact scenario that can produce a feature similar to the one seen on Iapetus, which is indeed very strange.

      Easy: two big asteroids struck the moon simultaneously on both poles!

    6. Re:Why surprising? by Vo0k · · Score: 2, Interesting

      Tidal lock doesn't necessarily mean that the revolution of Iapetus is in the plane of the ring or Saturn's rotation (or is it so? I can't locate its ephemeris).
      Actually Iapteus could orbit opposite to Saturn's location and perpendicular to the ring, it doesn't matter. What only matters is so its orbit axis was parell to its rotation axis when it had a normal daily cycle yet (no tilt), and paralell to its ring axis. (so tidal lock was changing speed, not direction of rotation). Nowadays when it's stopped it's impossible to tell.

      Its gravitation field is not significant enough to trap a larger number of small bodies as Saturn does.

      Sure it wouldn't if it was somewhere in open space. But in Saturn's ring it has enough debris nearby to catch them. Much lower strength but way more material to catch. And weak gravity isn't that much of a problem as most of the ring material travels at similar speed, very slowly, so obtaining a "high orbit" for a random piece of rock moving only slightly faster or slightly slower than the moon is really easy.

      As they decend onto the surface, it'd make a crater, not mountains.
      So they do. Great most of them. Only some that get onto its orbit get to create the ridge. They can keep orbiting for millenia (and get stabilized on the equatorial orbit from any randomness where they got) before they finally slowed down by gravity fall to the surface, and as Iapteus has no atmosphere, they can orbit an inch over the surface and still won't fall unless they hit something (horizontally), and rapidly losing speed fall somewhere more or less on vector of their orbit. You get a crater from a really powerful hit from straight above, when a fast moving body (be it accelerated by gravity or just floating through space at high speed) hits the surface. Not from a satellite of atmosphere-less planet, hitting the surface horizontally.

      --
      Anagram("United States of America") == "Dine out, taste a Mac, fries"
  8. Re:rotation ? by Iron+Sun · · Score: 2, Informative

    I'm not sure I understand your question. But in case it helps, Iapetus is tidally locked to Saturn. This means that like our moon it always shows the same face to the parent planet, as it completes one rotation on its axis in the same time it takes to orbit the planet.

    The newfound ridge stretches the entire width of the dark hemisphere, meaning the one facing forward in Iapetus' orbital sweep around Saturn (and is thus half visible, half on the 'far side' from Saturn's perspective.)

  9. Re:rotation ? by fbform · · Score: 2, Interesting

    It's a ridge on the planet surface, not a ring.

    But I don't see why it is "amazing in such a small moon". Aren't larger irregularities to be expected with smaller bodies? For instance, the Mariana-Everest difference is about 19 km, so Earth's crust can be described crudely as "R0 +/- 9.5 km". Olympus Mons on Mars is at 26 km above surrounding ground. Comets are not even spherical - the "peaks" are as big as the rest of the "planet". So why is Iapetus's ridge considered surprising? I'm more interested in the ridge being *only* as tall as Olympus Mons, which is on a planet 5 times the size of Iapetus.

    --
    Time flies like an arrow. Fruit flies like a banana.
  10. Re:it's obvious by Velox_SwiftFox · · Score: 3, Funny

    I think it is the remains of the ancient circum-Iapetus particle accelerator.

  11. The expanded midsection is because... by halcyon1234 · · Score: 4, Funny
    ... it ate too many MARS BARS

    Ahhhahahah! hahahaha! hahahaha...ooooo, just shoot me now.

    --
    UTF-8: There and Back Again
  12. nerds rejoyce by helioquake · · Score: 2, Funny

    Oh my, thousands of nerds will come out and rejoyce over this pic.

    Screw science tag; it's Star Wars, baby!

    [Literally, I expect to see little scientific discourse on this thread...so sad.]

  13. Thanks by scum-e-bag · · Score: 3, Interesting

    Thanks.

    Stories like this make slashdot cool.

    --
    Does it go on forever?
  14. Kim Stanley Robinson's A Short, Sharp Shock by boa13 · · Score: 2, Interesting

    Coincidences are weird, sometimes.

    Kim Stanley Robinson is well known for his hard sci-fi Mars trilogy (Red Mars, Green Mars, Blue Mars). He has also written a small and memorable fantasy book, A Short, Sharp Shock, which takes place on a strange world covered by sea, almost perfectly bisected by a tall, narrow ridge that seems to run all around the world (but maybe only for 1300 km?) and that sometimes almost reaches the sea, sometimes climbs up to great heights (20 km maybe?).

    Just a coincidence, of course, but it's funny that a man who loves space in general and planets in particular would use an existing but at the time unknown geological feature as the basis of a fantasy book.

  15. I think I speak for many when I say... by solios · · Score: 3, Funny

    o_O.

    It's a giant space WALNUT. :O

    1. Re:I think I speak for many when I say... by Ed_1024 · · Score: 2, Funny

      No, it's made of chocolate. The ridge is where the two halves of the mould met.

  16. The Wall Around the World by AYeomans · · Score: 2, Informative

    See the story The Wall Around the World written in 1953 by Theodore R. Cogswell. And look out for the Dark Man!
    (The Wall separated the technologists from the magicians.)

    --
    Andrew Yeomans
  17. Re:It's all about justification by Dano+Watt · · Score: 2, Funny

    It cost me $1 to buy a cheeseburger this afternoon, and to my knowledge no person was killed in the process. So I guess with your logic, the government should spend billions on cheeseburgers. Well, I wouldn't mind.

  18. I'm a product designer by I7D · · Score: 4, Funny

    And that is definitely a parting line, just an artifact of the mold.

    --
    Neil is that you? Yeah yeah, it's me... Neil...
    1. Re:I'm a product designer by Anonymous Coward · · Score: 3, Funny

      Quite true. It was a budget moon so it is bound to have some minor issues.

      Sincerely,
      Magrathea planetary wharf

  19. Size confusion by Spy+Handler · · Score: 5, Interesting
    "This height is amazing in such a small moon; it rivals Olympus Mons on Mars which is a body 5 times its size."

    Article submitter didn't take Astronomy 101 apparently. Small planetoids tend to have more prominent geological features than larger planets because stronger gravity pulls everything together harder and flattens things out. For instance, Olympus Mons on Mars is much higher than any mountain on Earth precisely because Earth has stronger gravity.

    1. Re:Size confusion by ralphh · · Score: 2, Interesting

      The submitter is rephrasing the JPL news release, which a implied a similar awe. In part: "No other moon in the solar system has such a striking geological feature. In places, the ridge is comprised of mountains. In height, they rival Olympus Mons on Mars, approximately three times the height of Mt. Everest, which is surprising for such a small body as Iapetus. Mars is nearly five times the size of Iapetus."

      --
      "A worthy cause has never been harmed by the truth" - Gandhi
    2. Re:Size confusion by SsShane · · Score: 2, Informative

      Also, Mars has a much thicker crust than Earth. Our mountains literally sink into the mantle when they reach a certain mass.

  20. It's not a ridge, it's a seam... by matt_wilts · · Score: 2, Funny

    ..like a Russian Doll, open it up & there's another moon inside!

  21. Re: Peace on Earth by Lem by TeknoHog · · Score: 2, Informative
    Stanislaw Lem had a story about a two-coloured planet with a line intersecting it in the middle, with two countries permanently at cold war :)

    It was our Moon, with Earth countries having a telepresence war. One of the best Lem books IMHO.

    --
    Escher was the first MC and Giger invented the HR department.
  22. The Iapetusian Wall by TintinX · · Score: 2, Funny

    This is a remnant from the Iapetusian Cold War, when the folk from the northern hemisphere were separated from those in the southern.
    Be grateful that Cassini-Huygens' lens isn't more powerful or you might have been able to make out David Hasselhoff standing on it singing a song about freedom.

  23. Amazing? Why? by slavemowgli · · Score: 3, Interesting

    his height is amazing in such a small moon

    Why? There is a limit on which heights are possible for a given celestial body (planets etc., that is, I'm not counting in stars here), and that limit is actually higher for a smaller body (for example, a volcano the size (height) of Olympus Mons wouldn't even theoretically be possible on earth).

    --
    quidquid latine dictum sit altum videtur.
  24. Wrong turn by LS · · Score: 2, Funny

    Looks like Bugs Bunny definitely took a wrong turn at Albuquerque...

    LS

    --
    There is a fine line between being a cultivated citizen and being someone else's crop. - A. J. Patrick Liszkie
  25. Kim Stanley Robinson by TuataraShoes · · Score: 2, Informative

    Having just read the very fine Red Mars by Kim Stanley Robinson, he describes the spectacular collapse of a space elevator causing a ring that went almost twice around the equator of Mars.

    Actually, the space elevator was actually one of Arthur C Clarke's ideas

    The structure of the ring is a bit different from this one, but the location (along the equator) is the link.

    --
    Surely in vain the net is spread in the sight of any bird -- Proverbs 1:17
    1. Re:Kim Stanley Robinson by kalidasa · · Score: 2, Informative

      Actually, Clarke himself attributes the space elevator to Tsiolkovsky. On this one, Wikipedia has it right.

  26. Sensible non-death-star explanation by adeyadey · · Score: 3, Insightful

    Many of the smaller moons/asteroids are barely spherical, and having been hit so often, barely held together by gravity. given the size of the impact crater, it is possible this moon was nearly torn apart by that impact, and the belt is a relic of that event.

    Some of the smaller moons & asteroids out there are more like piles of rubble held together by gravity than solid bodies - thus the headaches in what to do if one were ever found to be on collision course with earth, since an attempt to move it of course would merely fragment the body..

    --
    "You lied to me! There is a Swansea!"
  27. I know! It's.... by emilng · · Score: 2, Funny


    a giant mold line.
    Since we're all wildly speculating anyway.

  28. Second thoughts: I *know* what it looks like... by whitroth · · Score: 2, Interesting

    Anyone read Kim Stanley Robinson's [Red/Green/Blue] Mars?

    Reminds me of the *big* space elevator cable that fell. If that caused lava flows/vulcanism in a line....

    mark

  29. Chinese secret space program uncovered .... by constantnormal · · Score: 2, Funny

    ... Great Wall of Iapetus imaged by Western surveillance satellite.

    Film at 11

  30. Re:Nut by Dysan2k · · Score: 3, Funny

    I, for one, welcome our new giant, spacefaring squirrel overlords.

    --
    -What have you contributed lately?
  31. Iapetus' Belt - Proposed Explanations by wildsurf · · Score: 2, Funny

    10. The moon was actually injection-molded.
    9. The hill is the remains of an ancient alien rail-gun launcher.
    8. Iapetus, in a fit of sibling jealousy, has attempted to grow its own rings.
    7. Percival Lowell accidentally based his sketches on the wrong planet.
    6. This is the planet from Kim Stanley Robinson's "A Short, Sharp Shock", without the oceans.
    5. The moon was tectonically separated aeons ago from Vallis Marineris.
    4. This is the solar system's frenulum.
    3. Ringworld deorbited here.
    2. Not much, just loosening its belt after the holidays.

    and..

    1. That's No Moon...

    --
    Weeks of coding saves hours of planning.