That's what happens
When you attempt a landing there.
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 …
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.
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.
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.
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.
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?
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.
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.
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?
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.
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