Planets and Moons  ID: 5023

Lunar Polar Wander

The North and South Poles of the Moon haven't always been where they are today. Asteroid impacts both large and small, most of which occurred early in the Moon's history, have changed the Moon's mass distribution. After each impact, the Moon gradually rebalanced itself around its spin axis. This kind of rebalancing, in which a planet or moon reorients itself while the spin axis continues to point in the same direction in space, is called true polar wander.

In a study published in the Planetary Science Journal, David E. Smith, Vishnu Viswanathan, and their coauthors used maps of the Moon's topography and gravity, based on data gathered by NASA's LRO and GRAIL missions, to infer the evolution of the Moon's mass distribution and its effect on the location of the poles. They found that impacts have moved the poles almost 10 degrees in latitude – 300 kilometers or 190 miles – over the roughly 4.25 billion years since the cataclysmic event that created the South Pole-Aitken basin.

The visualization on this page shows the polar wander calculated by the computer simulation created for the study. As seen here, the South Pole arrives in roughly its present position relatively early in the Moon's history, raising the possibility that some of the water ice and other volatiles trapped in permanently shadowed regions near the South Pole may be up to 3.8 billion years old.

For More Information

NASA Study: Small Craters Add Up to Wandering Poles on the Moon

Visualization Credits

Ernie Wright (USRA): Lead Visualizer
Lonnie Shekhtman (ADNET Systems, Inc.): Lead Writer
Vishnu Viswanathan (University of Maryland Baltimore County): Lead Scientist
David Ladd (Advocates in Manpower Management, Inc.): Producer
Please give credit for this item to:
NASA's Scientific Visualization Studio

Science Paper:
The Contribution of Small Impact Craters to Lunar Polar Wander, David E. Smith et al 2022 Planet. Sci. J. 3 217

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LRO (Lunar Reconnaissance Orbiter)

Data Used:
LRO/LOLA/Digital Elevation Map also referred to as: DEM
JPL DE421 also referred to as: DE421
Ephemeris - NASA/JPL
Note: While we identify the data sets used in these visualizations, we do not store any further details nor the data sets themselves on our site.

This item is part of this series:
The Moon

SVS >> Moon
GCMD >> Earth Science >> Solid Earth >> Geodetics/Gravity >> Polar Motion
SVS >> Hyperwall
SVS >> Lunar Reconnaissance Orbiter
SVS >> Moon >> South Pole
SVS >> Solar System >> Moon >> Craters
NASA Science >> Planets and Moons
SVS >> Gravity Recovery and Interior Laboratory

GCMD keywords can be found on the Internet with the following citation: Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version