back to article Crack this mystery: Something rotated the ice shell around Jupiter's Europa millions of years ago, fracturing it

A new study of the ice shell encrusting Europa, Jupiter's sixth-closest moon, suggests it is free-floating and shifted 70 degrees after a major geologic event rotated the surface several millions of years ago. Astronomers at the Universities Space Research Association's Lunar and Planetary Institute; the University of Arizona …

  1. DS999

    That's what happens

    When you attempt a landing there.

    1. Mike Norrish NZ

      Re: That's what happens

      See, I love that I can click into these articles expecting a particular comment to have been made and almost *never* be disappointed! ;)

      1. 96percentchimp

        Re: That's what happens

        I'm disappointed for the same reasons. Can we assume that everyone here knows the obligatory SFF references?

        It's like bloody Groundhog Day.


        1. bigphil9009

          Re: That's what happens

          Did you get out of bed on the wrong side this morning? Lighten up :)

  2. Queeg

    My 2 Cents worth

    There's no impact scar, no smooth refrozen area.

    So nothing hit it and caused the shift but what about about a close pass of

    an extremely dense object.

    Dense enough to pull body off axis.

    If the surface is floating, with no contact with solid surface that might cause the shock fractures.

    I bow to any Astrophysicists in the house if I'm wrong.

    1. DS999

      Re: My 2 Cents worth

      Why would there be an impact scar on ice? It would melt and refreeze, leaving little or no trace visible on the surface.

      1. Queeg

        Re: My 2 Cents worth

        The cracks are still there, therefore any impact scar would also still be there.

        Showing as a relatively smooth area were the ice had refrozen.

      2. Pascal Monett Silver badge

        Re: leaving little or no trace visible on the surface

        Not sure of that. If we imagine a round-ish meteor punching a hole in the surface ice, the melt would clearly outline a circle and the interior would be noticeably smoother than the region around it.

        Might take a bit of time to spot, but I think it would be quite visible once you've found it.

        1. DS999

          Re: leaving little or no trace visible on the surface

          You're ignoring the massive amounts of melted ice that would be thrown up into orbit, and slowly settling over the entire moon.

          You might be able to find it from orbit if you check for gravitational anomalies...

    2. Timbo

      Re: My 2 Cents worth

      "So nothing hit it and caused the shift but what about about a close pass of an extremely dense object."

      Something large, heavy and dense.....something like Jupiter then ?

      (And yes I know it's a gas giant, but the part-solid, part-liquid core might be pretty dense).

  3. Chris Gray 1


    Well, that's what you get when you do sudden manoevering turns with the main body. Take it easy, or you'll break something, and then *they* will catch up quicker.

  4. HildyJ Silver badge


    So, given that Europa is an alien ship that moves by using an Alcubierre warp drive and maintains an ocean around it to protect it from radiation. They must have had to maneuver out of the way of a killer asteroid millions of years ago and that caused the axis to shift.

    Or not.

    Here's to the boffins who worked it out and to those working on the Europa Clipper. I just hope that with all the money being flung to get boots on the moon, we can still fling science to Europa.

  5. Jonathan Richards 1
    Thumb Up

    So many possibilities

    Maybe the ice-shell is almost free-floating, but pinned in place by high spots on the rocky interior... Or it was so pinned until relatively recently, when the pin points let go and the ice shell re-oriented itself to a minimum energy position. I can't begin to calculate the forces that would be unleashed - the entire moon would be some sort of precessing spherical gyroscope with viscous coupling between the ice shell and the rocky core, and the released energy would be dumped as heat, melting even more of the shell. Then there's the fact that humans are quite familiar with the mechanical properties of ice... at Earth planetary temperatures. Does anyone have values for the hardness and toughness of ice as cold as the surface of Europa? What do all those impurities do to those values? Can I have another go around at life and be a europologist, please?

    1. hoola Bronze badge

      Re: So many possibilities

      May be aliens have been dumping all the CO2 from their planet under the ice causing it to expand cracking the surface.

  6. bonkers

    Wingnut effect?

    Could it simply be that the ice shell grew thicker at the poles - as they are likely to be colder for a number of reasons - until the moment of inertia for north-to-south rotation was higher than for regular east-west rotation?

    At this point, an effect similar to the Wingnut effect or tennis raquet theorem came into play - forcing the system to rotate about the axis with the highest moment of inertia.

    Essentially the previous rotation becomes energetically unstable and the system "flips".

    The fact that it was a (large) 70 degree rotation might point to this, one would expect 90 degrees in a textbook situation.

    1. bonkers

      Re: Wingnut effect?

      By Jove, I think we might have cracked it :)

      Presumably, if it has happened once, then there is a good chance it has happened several times.

      The mechanism above would expect the now-equatorial polar accretions to melt, and new ones to form at the new poles.

      There should be evidence of successive shell-flips. Each one would knock some mountaintops flat, increasing the opportunity for the next.

    2. tfb Silver badge

      Re: Wingnut effect?

      That's a really clever idea. Europa is tidally-locked to Jupiter, so its poles will be orthogonal to its orbital plane. I am pretty sure the inclination of the whole system is small enough that it does indeed get much less light at the poles. It also has complicated resonances with the other Galilean moons which means it gets lots of tidal whacking which could easily be enough to trigger the ice sheet breaking loose if it already wants to.

      I wonder if the proper boffins have thought of this?

  7. aregross

    Atlas poo'd

  8. 89724102172714182892114I7551670349743096734346773478647892349863592355648544996312855148587659264921 Bronze badge

    > Crack this mystery

    It was moved by a gigantic and continuous (for a time) eruption into it's liquid ocean between crust and mantle - steam powered locomotion from beneath the ice by it's very and constantly active core

  9. JCitizen Bronze badge

    I wonder..

    if anyone has done a full orbital computer study of all the moons there, so that they could rule out any near miss or other local gravitational effects? Of course a large body plunging into the host planet could barely miss the moon, and no one would be the wiser, as all evidence was destroyed by the gas giant.

  10. Benchops

    Wrong planet I know, but...

    Suddenly the top began moving, rotating, unscrewing

  11. Timbo

    Arthur C. Clarke predicted it:

    All these worlds are yours except Europa. Attempt no landing there. !!

    1. Alister Silver badge

      Re: Arthur C. Clarke predicted it:

      18 hours too late.

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