A study that looked at billions of years of asteroid craters on the moon’s surface has concluded that the space rock is affecting so much that the poles moved.
Over the past 4.25 billion years, the Moon’s poles have “wandered” by 186 miles or 10 degrees in latitude.
The study could be important for , as NASA returns to the satellite with manned missions in the coming years.
Vishnu Viswanathan, a NASA Goddard scientist who led the study, “Based on the Moon’s cratering history, polar migration appears to have been moderate enough that water near the poles has remained in the shadows and had stable conditions over billions of years.”
A team based at NASA’s Goddard Space Flight Center in Greenbelt, Maryland used computer simulations to “erase” thousands of craters from the moon’s surface, as if turning back the clock 4.25 billion years to a time before the craters formed.
They found that the position of the moon’s north and south poles moved slightly during this time period.
Information about wandering poles can be useful for understanding the evolution of the Moon; specifically, the state of resources, such as water, on the surface.
Scientists have found frozen water in shadowy areas near the moon’s poles, but they don’t yet know how much there is.
If the Moon had drastically shifted the position of the poles towards a warmer, less shadowed area, such as the equator, some frozen water could have sublimated (changed from a solid state to a gaseous state) from the surface, with new water less time to accumulate on the new poles.
The phenomenon behind the shifting poles is known as True Polar Wander, and it’s what happens under the laws of physics to an object, in this case the moon, trying to stay in motion when faced with obstacles, such as changes in the way its mass distributed.
When the asteroid hits excavated mass and leaves depressions in the surface—or pockets of lower mass—the Moon reorients itself to bring these pockets toward the poles, while driving higher-mass regions equatorward via centrifugal force.
It’s the same force that acts on the dough when a pizza machine tosses and spins it in the air to stretch it out.
The researchers became interested in using gravity data to determine how far the moon’s poles have wandered after serving as deputy lead for NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission.
GRAIL mapped the Moon’s gravitational field in great detail before the mission ended in 2012.
David E. Smith, principal investigator for the Lunar Orbiter Laser Altimeter (LOLA), aboard NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft said: “If you look at the Moon with all these craters on it, you can see them in the gravity field data.
“I thought, ‘Why can’t I just take one of these craters and suck it out, remove the signature completely?'”
Viswanathan said his team is getting closer to figuring out the true rate of polar migration on the moon, but scientists still need to refine their estimate.
They plan to erase several small craters from the Moon and to remove other features, such as volcanic eruptions, that could have helped move the poles.
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