back to article Boffins puzzled over impossibly fast ice avalanches on Saturn's moon

Planetary boffins have spotted that Saturn's other moon, the walnut-shaped Iapetus, is home to spectacular ice avalanches that flow across the surface of the rock. A ridge around Iapetus' equator makes it look like a walnut The walnut in the sky. Credit:NASA/JPL/SSI The ridge of 20km-high mountains, twice the height of …


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  1. Richard Wharram

    It's something black with dimensions of 1, 4 and 9 relatively.

  2. TenDollarMan


    ... that's no moon!

  3. TeeCee Gold badge

    I can't look at pictures of Iapetus......

    ......without feeling an uncontrollable urge to split it open and find out what the plastic toy inside is.

  4. Miek

    "The researchers think that it may be sheer speed that cuts the friction for the ice, in the same way that major faults can slip off each other during an earthquake – resulting in \"localized frictional heating in [the] ice rubble\"."

    A bit like how Skis and Snowboards work. The friction melts ice directly beneath the board/skis allowing the rider to accelerate as the surface now has reduced friction.

    1. Jellied Eel Silver badge


      Is it water ice, or frozen gas? If it's gas, then maybe the rubble's playing air hockey. H/T to The Forever War and it's description of the hazards of going hot-foot across frozen gas fields.

    2. Anonymous Coward
      Anonymous Coward

      re: A bit like how Skis and Snowboards work

      I've heard that said of ice skates, where the pressure beneath the blades is quite high, but not of skis.

    3. Crisp

      I thought that the ice melting under skates/skis theory had been investigated and rejected.

      1. Don Jefe

        @ Crisp

        Having done a bit of skiing I can attest to the fact that nothing has melted. It's still frozen water no matter how many times you fall on it/ski over it.

        Also common sense should tell people that if every time skis passed over something and it melted (even a little bit) then the slopes at Vail and Cerro Bayo would have grooves/rails on them.

        1. Anonymous Coward
          Anonymous Coward

          Re: @ Crisp

          Not melting in bulk but quasi-melting on the surface. So no, it has next to nothing to do with the melting point of water vs. pressure but still a lot to do with different phases of water. (And one should be careful whenever dealing with "common sense".)

      2. Grikath


        Actually, the answers in that blog state that the surface effect melt *does* happen. The original post simply confuses bulk melt with the surface effect seen in the use of ice skates.

        In fact, speedskating rings use additives in the water to actually increase this effect, which in combination with an "ideal temperature" makes the ice that much more slippery.

        (Unfortunately not so much to prevent abrasions and friction burns if you hit the ice on your bum at 30+km/h.... /sadface)

        Something similar, although more complex happens with skis and snowboards, which despite their large surface area in reality only have minimal contact with the snow surface as they compress the snow irregularly (releasing as you can expect..heat) which creates an irregular wafer-thin ice/slush sheet at the points of contact which near-instantly refreezes as soon as the pressure is lifted.

        Demonstration of this compression melting-refreezing effect in snow is demonstrated yearly wherever kids meet fresh snow and start pelting innocent and not-so-innocent bystanders with devices called "snowballs".

        Mine's the one with the season ticket for the local ice ring.

  5. Purlieu

    Not natural

    Am I the only one who thinks that the line round the middle just doesn't look natural.

    Like it's some sort of "message" left by some visiting beings ?

    1. Rich 2 Silver badge

      Re: Not natural

      No, you're not.

      If you dig about, you'll also find pics of some odd and massive structures on Iapetus that defy any sort of known natural explanation. The oddest thing about anything like this though is that NASA seem to almost deliberately ignore it (not just on Iapetus, of course, but on the moon and on Mars); if they saw these things on Earth they'd be sending a team to go and investigate on the double.

      1. Anonymous Coward
        Anonymous Coward

        Re: Not natural

        No, don't be so silly. It's plain and simply an effect from the gravity of it's orbit (or the orbit of other close moons).

        Either it's a direct bulge from the tidal forces pulling on the center, or the bulge is from the gravity squashing it's top and bottom together.

        Well, unless it was created in a large impact. I think that's the other theory behind it. It could actually be a crater ring, if you scale a crater up to half the size of a moon, that's what it looks like.

    2. Ru

      Re: Not natural

      some sort of "message"

      Its a pretty atrocious sort of message, if that's what it is. If any alien visitors could sculpt a moon on that scale, they'd be quite capable of creating structures that woudl be far harder to mistake for a very unusual but entirely natural formation. Regular geometric shapes covering the entire surface spring to mind.

      No; creating a big weird mountain range is about as useful and plausible a means of communicating as abducting rednecks from the middle of nowhere and performing proctology upon them.

      1. Anonymous Coward
        Anonymous Coward

        Re: a pretty atrocious sort of message

        like, prepare to die, puny earthlings...?

    3. hplasm

      Re: Not natural

      "I've run the message thru the ICU- Mother doesn't think it's a message- she thinks it's a warning.-

      Something about Instant Mash..."

    4. Mussie (Ed)

      Re: Not natural

      I think that's just the light reflecting off your tin foil hat mate

  6. Anonymous Coward

    Low gravity?

    Surely its just down to the ultra low gravity whereby for a lot of the time the rubble is simply floating over the surface in a very gentle parabola? The only time it'll lose energy is on the rare occasions it touches the ground.

    1. Ru

      Re: Low gravity?

      This sort of slump would be much more easily spotted and understood; its a factor of local gravity and original height of the material and everything else is just elementary physics.

      Long runout slides have a far longer length-to-original-height ratio than can be easily explained. Lets give the landslide experts a little credit and assume they've done the absolute bare minimum undergrad-level due diligence here.

      1. Anonymous Coward

        Re: Low gravity?

        "Lets give the landslide experts a little credit "

        Just because someone is an expert at something on earth doesn't make them an expert elsewhere. Unless they're dumped all the variables in a computer model and run it then they won't have a clue. The telling line in the article is "So any theory of long runout landslides on Earth must also work for avalanches on Iapetus.".

        Why should it? As we've found out already atmospheric models based on ones written for the earth are pretty useless at predicting or understanding the behaviour of atmospheres on other planets such as jupiter or venus or titan so I fail to see why this would be any different.

        1. Ru

          Re: Low gravity?

          The underlying problem here is that you are assuming that everyone is stupid. This sort of charming anti-intellectualism is pretty much standard on the Reg, so you're not alone.

          I posit you know less about landslides and less about geology, less about orography and less about the whole mess that is geomorphology than the people involved in this study. So why should anything you have to say on this matter hold any weight?

          Couple of points to ponder... 1. the movement of large boulders are part of a landslide is primarily influenced by gravity; air resistance is negligible. 2. long runout slides have been seen on the moon, on mars and on venus. They all exhibit pretty similar behaviours. This suggests the underlying phenomenon is atmosphere composition and pressure independant. This also demonstrates this is not a new or unusual phenomenon, and the people involved have done this before.

          When geologists start making broad sweeping dismissals of trolling techniques, then you might have something useful to add to the discussion. Til then, though? Not so much.

          1. Anonymous Coward

            Re: Low gravity?

            "The underlying problem here is that you are assuming that everyone is stupid. This sort of charming anti-intellectualism is pretty much standard on the Reg, so you're not alone."

            Ah bless, an attempt at combining bon homie with a dose of patronising. I've seen better frankly.

            "posit you know less about landslides and less about geology, less about orography and less about the whole mess that is geomorphology than the people involved in this study. So why should anything you have to say on this matter hold any weight?"

            Umm, perhaps because this is also not a geological issue - its one of physics which is something I do know about. Where the rocks came from and their composition - other than how it relates to friction or perhaps fracturing of the rocks during the slide - is irrelevant.

            "then you might have something useful to add to the discussion. Til then, though? Not so much."

            Right back at you pal.

  7. Steve Knox

    So any theory of long runout landslides on Earth must also work for avalanches on Iapetus.

    This is a common logical fallacy. Two events with similar appearances "must" have the same explanation, even though they occur in very different environments with very different materials. It's actually quite possible that the long runout landslides and the ice avalanches are extended by entirely different factors. It's just not appealing to our human sensibilities, which tend to push us towards a single unifying explanation for everything.

  8. Nya


    Panic! Panic! Panic! Global warming causes avalanches on Saturn's moon!

    1. Michael Dunn

      Re: Panic!

      Yeah, you got there before me!

  9. Denarius
    Thumb Up

    odd out there

    Amazing how much happens on what were once considered to be cold unchanging places. Nitrogen geysers, water geysers, ice volcanoes, and at Jupiter, moons with real hot volcanoes. How much is missed because of the distance ? And now that a 4 earth mass (blue whale equivalent unknown :-) planet is postulated beyond Sedna there maybe much more to find in the icy parts of the solar system. About time nuclear powered plasma drives were built.

    1. Don Jefe

      Re: odd out there

      Does a plasma drive require nuclear? It was my understanding plasma could be generated with any massive power source. What we need is a matter/anit-matter drive.

      1. Crisp

        Re: odd out there

        Have you tried holding a handful of antihydrogen?

        Gamma rays and exotic particles everywhere. It's a total mess.

  10. Anonymous Coward
    Anonymous Coward

    That's no moon.

    Now that I've got that over a done with, carry on.

  11. Anonymous Coward
    Anonymous Coward

    Give all the collected data to Lewis Page

    I'm sure he can make up something wild, speculatory and insubstantial that bears no relevance to the information they provide based purely on how he feels about Saturn.

  12. Anonymous Coward
    Anonymous Coward

    This is clear evidence of man-made global warming!

    We must reduce our energy usage, increase taxation and hope that this gives us sufficient time to figure out if this is real or just a problem with our models and data collection.

  13. Alister

    I don't get this

    The scientists studying Iapetus said:

    "They give us examples of giant landslides in ice, instead of rock, with a different gravity, and no atmosphere. So any theory of long runout landslides on Earth must also work for avalanches on Iapetus."

    Why? If the starting conditions and environment are completely different, why should what happens on Iapetus bear any relevance to what happens on Earth?

  14. lawndart


    My immediate thought was "just like a pyroclastic flow running over water."

    Possibly the thermal difference in the falling material and the ground layer is enough to create a vapour between the two thick enough for the avalanche to ride on?

    1. Martin Budden Silver badge

      Re: says

      I also immediately thought about pyroclastic flows: even over land "the rocks flow on for 20 or 30 times farther than the first fall, sometimes even managing to surge uphill" - to quote the article about Iapetus.

  15. Dropper

    Moon Food

    I figure it must be because this moon is made out of Phili cream cheese rather than the more usual cheddar. Has anyone thought to consult the Iapetus Soup Dragon?

  16. Charlie van Becelaere

    Other Moon?

    Saturn has at least 62 moons, 53 of which have formal names ... and that's just the ones of which Wikipedia is aware!

  17. Martin Budden Silver badge


    Er no Ms Parnell, they may well be very fast but but we know for sure they are not impossibly fast.... because then their speed would be *cough* impossible and they wouldn't have happened the way they did. Have you, by any chance, ever used the expression "I literally died"?

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