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The Moon used to "spin on a different axis" that was subject to "polar wander," a new study into the satellite's early history has said.
The Planetary Science Institute study, published in Nature, highlights two regions full of hydrogen deposits near the Moon's two poles. This, it says, suggests the presence of ice -- ice that only would have survived if it had remained in permanent shadow. "If the orientation of the Moon has changed, then the locations of the shadowed regions will also have changed," the researchers write.
The poles "wandered", according to the team, because of volcanic activity in the area, which would have warmed. It also would have made them less dense, causing the "wandering" of the axes. "The Moon has a single region of the crust where radioactive elements ended up as the Moon was forming," said Matthew Siegler, lead author of the study. "This radioactive crust acted like an oven broiler heating the mantle below."
"This giant blob of hot mantle was lighter than cold mantle elsewhere, causing the whole Moon to move."
The shift probably happened over three billion years ago, the team say, and would have meant the Moon showed a completely different face. Overall, the Moon shifted around six degrees over one billion years. Only a few other planetary bodies have been said to shift their axes -- Earth and Mars, as well as two moons of Saturn and Jupiter. "The same face of the Moon has not always pointed towards Earth," said Siegler. "As the axis moved, so did the face of the Man in the Moon. He sort of turned his nose up at the Earth." "These findings may open the door to further discoveries on the interior evolution of the Moon, as well as the origin of water on the Moon and early Earth," he said.
This article was originally published by WIRED UK
