New discoveries of ice patches near the poles may indicate the moon’s axis had shifted eons ago, and the finding has scientists excited about the structure and evolution of the moon, according to a story on Christian Science Monitor.
Study lead author Matt Siegler, of the Planetary Science Institute in Tucson, Arizona, and Southern Methodist University in Dallas, said he and his colleagues analyzed measurements made by two spacecraft, NASA’s Lunar Prospector (LP), which orbited the moon from January 1998 until July 1999, and the Lunar Reconnaissance Orbiter (LRO), which is currently orbiting the moon.
The data revealed the presence of ice deposits, as expected at each pole, but large patches were also noted near each pole, offset at 5.5 degrees. The scientists noted if they connected the two spots with a straight line through the moon, it would resemble the body’s axis.
The team believes they have found an explanation for the ice patches, that being the rotational axis of the moon had shifted by 5.5 degrees, most likely due to internal distribution of lunar mass. Working with models, they estimate these ice patches were the moon’s actual poles about 3 billion years ago.
“Models are models,” commented Sigler, “so you can make the migration happen any time between 1.5-4.5 billion years ago depending on how you tweak parameters (such as the past rigidity of the lunar crust), but it most likely was around 3 billion years ago.”
The team estimates the lunar poles shifted about 125 miles over a period of about a billion years, at a rate of about an inch every 126 years.
The researchers also believe they know where the mass distribution shifted as well. Their findings point to a region on the near side of the moon, called the Procellarum KREEP Terrane (PKT), an area that was volcanically active ages ago. They believe the volcanoes heated the moon’s mantle, creating what they term a “low-density thermal anomaly” that caused the shift.
The ice would likely be very ancient, and could give scientists a better understanding of the origin of water on Earth. Siegler continued, “The ice may be a time capsule from the same source that supplied the original water to Earth. This is a record we don’t have on Earth. Earth has reworked itself so many times, there’s nothing that old left here. Ancient ice from the moon could provide answers to this deep mystery.”
The findings of the study were published in the journal Nature.