Ancient lunar ice has indicated that the moon's axis — the imaginary pole running north to south through the middle and around which the Earth's moon rotates — shifted by 6 degrees over a billion years, new research suggests. How have scientists discovered this rare event?
Southern Methodist University's Matthew Siegler and his team analyzed NASA's data revolving around lunar polar hydrogen, which is thought to take the form of ice concealed from the sun in craters that surround the south and north poles of the moon. These frozen-water deposits appeared to be off-kilter from the moon's true axis, which suggested that the pole on which Earth's satellite orbits may have previously tilted.
The theory is even more supported by the offset being the same at every pole, yet tilted in opposing directions.
This likely happened in a 1 billion-year span roughly 3 billion years ago, according to Siegler. The familiar view — the Man on the Moon — had changed, as heating in the interior of the moon led the face to move upward as the pole altered positions.
"It would be as if Earth's axis relocated from Antarctica to Australia," the planetary scientist adds, pinpointing how the Man on the Moon did turn his nose up at planet Earth as the pole moved.
And it doesn't happen very often. "True polar wander" or planetary mass shifting and resulting in it relocating on its axis rarely occurs, meaning the moon now is part of an "extremely exclusive club" along with Earth, Mars, Jupiter's moon Europa, and Saturn's moon Enceladus.
Planets assume their axis depending on their own mass, wherein light spots lean approaching the pole and heavier ones lean toward the equator. In the case of the moon, polar wander may have happened because of heavy volcanic activity, where there was a change in mass due to a huge, sole mantle "plume" shifting.
In simple terms, ancient volcanoes billions of years past melted part of the mantle and formed the black patches of ancient lava humans witness at night. Siegler pointed out that this massive piece of hot mantle was lighter than cold mantle found elsewhere.
The change in mass caused the moon's single crust region, known as Procellarum, and the whole moon to move.
After the relocation of the moon's axis and its slow movement over a billion-year span, the axis eventually shifted around half the distance between Dallas and Houston, or 125 miles.
Lunar ice may also hold the key to more mysteries in space, such as why there is water found on the moon as well as on Earth. Theory that around the solar system's formation believes that water could not have been present much closer to the sun than Jupiter.
With lunar ice correlating strongly with true polar wander, could it be that it is very ancient and actually a "time capsule" from the same source of the original water on Earth?
The findings were discussed in the journal Nature.