Planetary scientists examined NASA data concerning the moon's north and south poles. Hydrogen ice (hidden from the sun in craters), boils off when exposed to the sun. An odd offset of the ice from the moon's current north and south poles prompted a closer look at the data. Statistical analysis and modeling revealed the ice is offset at each pole by the same distance, but in exactly opposite directions. This precise opposition indicates the moon's axis—the imaginary pole that runs north to south through it's middle, and around which the moon rotates—shifted at least six degrees, likely over the course of 1 billion years starting 3 billion years ago. Ancient volcanic activity some 3.5 billion years ago probably melted a portion of the moon's mantle, causing it to bubble up toward its surface and causing an internal shift of the moon's mass.
The article can be found here.
Lunar true polar wander inferred from polar hydrogen (DOI: 10.1038/nature17166)
(Score: 1, Interesting) by Anonymous Coward on Monday March 28 2016, @07:02PM
I'm always confused when people talk about the axis of a planet shifting. Does it mean that the crust moved, or the entire planet? As far as I can see, in this case they're acting as if the crust is stuck to the interior, and it was a change in the interior that made the difference.
But for the Earth, when they say that some earthquake shifted the axis by whatever, I don't understand what they are talking about, since most of the Earth is in fact "liquid".
In any case, generally I would like them to explain a bit better what they mean by "axis of rotation". Obviously, as long as no interaction with outside objects is involved, the angular momentum of the planet is conserved.
(Score: 3, Informative) by Runaway1956 on Monday March 28 2016, @07:25PM
The article seems to indicate that volcanic activity caused some of the moon's mass to shift "off center". Shifting the mass caused the moon to kinda "wobble", thus changing it's axis by a few degrees, over the course of a billion years.
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(Score: 1, Touché) by Anonymous Coward on Monday March 28 2016, @07:28PM
pole that runs north to south through it's middle
thus changing it's axis
its!
(Score: 0) by Anonymous Coward on Monday March 28 2016, @08:59PM
Grammer? We don't need no stinking grammer.
(Score: 2) by dyingtolive on Monday March 28 2016, @09:26PM
steenkin'!
Don't blame me, I voted for moose wang!
(Score: 0) by Anonymous Coward on Tuesday March 29 2016, @03:02AM
You've got the general idea. Here is the editor's summary:
They found hydrogen, not at the pole, which would have come from water, but they found it in regions where water couldn't survive because it gets a lot of sunlight. They also found another deposit 180 degrees from the first. They argue that you'd see this if these regions were originally at the poles, where here when they say "poles", they mean the poles defined by the axis of rotation, so the axis of rotation must have shifted over time.
Angular momentum is conserved, but it will rotate about an axis that depends upon the distribution of mass inside. This paper says that due to molten stuff moving around, the mass distribution changed and the Moon settled on a new axis of rotation.
(Score: 0) by Anonymous Coward on Tuesday March 29 2016, @12:24AM
On earth 3 billion years ago, with the way the moon was rotating and causing the tides back then.
Whoa dude.