Ancient ice reveals tilting of Earth's moon
Using data from numerous missions,including the Lunar Reconnaissance Orbiter (LRO) and the Lunar Crater and Observation Sensing Satellite (LCROSS), researchers have gatheredevidence that the spin axis of Earth's moon actually shifted quitesubstantially in the body's ancient past. The researchers werelooking at how ice is deposited at the two poles, when the mirroreddistribution revealed the secret.
The Moon might have been a constantfixture in the night sky since the beginning of human history, butwe're almost constantly learning new things about it. Whether it'sanalysis of rocks brought home by Apollo 16 to shed light on the body's formation, or insights into where the Man in the Moon came from, we're still working to answer plenty of mysteries about Earth'slonely satellite.
The new study reveals a pretty hugerevelation about the Moon – that the exact same face hasn't alwaysbeen the one we see now, as the rotational axis actually shifted bysome five degrees around 3 billion years ago.
In areas of the moon that areperpetually bathed in shadow, it's possible you'll find ice. But if sunlight hits aregion, any ice deposits present will melt, meaning that the entire face ofthe moon as visible from Earth is ice-free. By looking at thedistribution of ice at the Moon's poles, scientists noticed somethingunexpected – that the positioning of ice deposits appeared to havechanged at some point in the body's history.
Using data collected by several NASAmissions – namely the LRO, LCROSS, Lunar Prospector, and theGravity Recovery and Interior Laboratory (GRAIL) – the researcherscarefully studied the lunar poles. It quickly became apparent thatthe two regions had more in common with one another than waspreviously thought, with concentrations of ice displaced from eachpole by the same distance, but in opposite directions, indicatingthat the body had shifted on its axis.
Such a huge shift would require asignificant redistribution of mass. Modelling how changes in thelunar interior could have caused such a change, the team came to theconclusion that the formation and evolution of the Procellarum regionon the lunar near-side, associated with high heat flow and ancientvolcanic activity, was responsible. The volume of radioactive material in the regionis thought to be sufficient to have heated the mantle, resulting in adensity change that in turn would have reoriented the entire moon.
"The new findings are a compellingview of the moon's dynamic past," said Dr Yvonne Pendleton of theSolar System Exploration Research Virtual Institute (SSERVI), whichsupported the research. "It is wonderful to see the results ofseveral missions pointing to these insights."
The results of the project arepublished in full in the journal Nature.