The moon just joined a very exclusive club right there with Earth, Mars, Saturn’s moon Enceladus, and Jupiter’s moon Europa. What’s the common trait? They’ve all experienced “true polar wander”, otherwise known as a shift in axis.
In a recent research paper published to journal Nature, scientists Matt Siegler and his team from Southern Methodist University, Dallas Planetary claim that the Moon shifted axis around 3.5 billion years ago probably due to very strong volcanoes. This volcanic activity would have released tremendous amounts of energy, resulting in heating up of the Moon’s surface. The team studied the data provided by NASA, and found that the hydrogen on the Moon’s surface could be in the form of ice, as it lie safely in craters at the poles away from sunlight.
Now here’s the interesting part. The team suspect that when the hydrogen was exposed to sunlight, it boiled up into space and this molten matter would have shifted the internal balance of the lunar gravity. Why is this interesting? Well, because the Moon’s poles are always shrouded by shadow never exposed to sunlight, and for the boiling to happen, the poles must have moved into sunlight. Furthermore, the axis usually followed the density of a planet; meaning the heavier part is usually the equator, and the lighter parts are the poles. So after this volcanic eruption the density of the lunar body would have changed, shifting the axis in the process.
The tell-tale indicator of shifted poles was the odd offset of ice from the Moon’s current poles. There approximately a 125 mile trace of ice from these poles, which means the poles shifted around 6° around 3 billion years ago. The shift might have even continued on a very slow pace for the next billion years.
The other shifts in celestial bodies that scientists know of including Earth’s and Mars’s. In Earth, the shift supposedly happened due to the changes in continental plates; however, in Mars, the scenario is a little similar to the Moon’s, as the shift was attributed to heavy volcanic activity, too.