The axis of the moon shifted three billion years ago, and ancient volcanoes may be to blame, a new study reports. This starling conclusion, on a body thought to be long-dead, was derived from an investigation of lunar ice.
Astronomers believe this ice may be left over from the same material that formed the oceans of the Earth.
The moon is largely dry and barren, but ice may be found in the dark recesses of craters near the poles. There, the frozen water is kept solid in the chilly shadows. However, a new study shows these deposits are off-kilter from the true axis, suggesting the pole on which our satellite orbits may have become tilted in the past. This idea is further supported by the idea that the offset is the same at each pole, tilted in opposite directions. The distance from the true poles to the ice caps is around 125 miles, or six degrees.
"This was such a surprising discovery. We tend to think that objects in the sky have always been the way we view them, but in this case the face that is so familiar to us — the Man on the Moon — changed," said Matthew Siegler of Southern Methodist University.
Researchers suggest that the shift may have taken place slowly around three billion years ago, over the course of approximately one billion years. As seen from the Earth, the man on the moon would have appeared to be turning his face upward, appearing more aloof over time.
A giant mass of molten material on one side of the moon may have shifted the internal balance of the moon's center of gravity, precipitating the change in axis.
The ice is seen through the detection of hydrogen, and the frozen deposits would quickly melt away when exposed to sunlight. As the axis shifted, much of the water once present on the moon likely escaped to space. Loss of illuminated ice to space makes the frozen caps a reliable marker to denote the north-south axis of our planetary companion.
A shift of the polar axis of a celestial body, known as polar wander, has been seen elsewhere in the solar system. The Earth has experienced the phenomenon, as have Mars and moons orbiting Jupiter and Saturn.
Investigation of the polar shift of the moon was profiled in the journal Nature.
