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Earth's Moon's Axis Shifted 3 Billion Years Ago

posted by martyb on Monday March 28 2016, @06:13PM   
from the rocket-fuel-prospectors-take-note dept.

jbWolf writes:

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)

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Original Submission

• Re:complicated stuff (Score: 0) by Anonymous Coward on Tuesday March 29 2016, @03:02AM

  by Anonymous Coward on Tuesday March 29 2016, @03:02AM (#324197)

  You've got the general idea. Here is the editor's summary:

  Matthew Siegler and co-authors show that the polar hydrogen deposits detected on the Moon by orbital neutron spectroscopy pose something of a mystery: the spatial distribution of hydrogen, which is thought to arise from the presence of water ice, does not match that expected from present-day lunar temperatures. The explanation may lie in the phenomenon known as 'true polar wander', in which a reference point on a solid body rotates with respect to its spin axis. Based on an analysis of polar deposit locations and of the lunar figure, the authors suggest that the shift occurred as a result of changes in the Moon's moment of inertia caused by a low-density thermal anomaly beneath the Procellarum region. Procellarum was most geologically active early in lunar history, which would imply that polar wander initiated billions of years ago and that a large portion of the measured polar hydrogen is ancient, recording early delivery of water to the inner Solar System.

  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.

  Parent