Also of note, LRO found bright spots not just on Shackleton's floor, an indication of highly reflective water ice, but also even brighter areas on the crater's walls, an unexpected and puzzling finding.
"We found that extremely interesting," Zuber said. "If the only explanation of what was in the crater was water ice then one would expect the ice to be concentrated in the coldest, darkest part of the crater, which would be the floor. So it suggests to us that there was some space weathering going on, with material sliding down the walls."
HOWSTUFFWORKS: Water on the Moon
One theory is that the moon may have periodic "moonquakes" from meteorite impacts or gravitational tugs by Earth which caused the crater walls to shake and shed their older material, revealing fresher, brighter soil.
Scientists also determined that the crater, which is believed to be more than 3 billion years old, is very well preserved, with its floor the same age as its rim. That suggests that very little has changed as far as what has been deposited at the bottom of the crater.
The research appears in this week's Nature.
Images: Top: False color image of Shackleton crater, located near the moon's south pole, was made with more than 5 million elevation measurements from NASA's Lunar Reconnaissance Orbiter's laser altimeter instrument (NASA/GSFC/SVS); Bottom: False-color elevation map of the crater. Blue areas are lowest; red and white are highest (NASA/Maria Zuber, et al Nature)