Primarily, we need to know how the moon formed in the first place. It was probably formed when a protoplanet had a serious collision with the Earth and part of it was drawn into orbit, forming Earth’s only moon. Due to radioactive decay and asteroid strikes that have hammered the moon over its existence, heat was generated in the core.
However, over time the moon has cooled and consequently ,shrunk. How? Well, just like when an apple goes bad, when heat stops being generated by the moon the mantle and crust compress, leaving in essence a ‘skin’ which is too large for the moon, and therefore it goes wrinkly.
We know this because of the existence of scarps. These are gigantic cliffs on the moon which can stretch for miles and miles. They have been captured on camera by NASA’s Lunar Reconnaissance Orbiter. The crust of the moon is a mere 50km thick and so when compression occurs within the faults, it leads to thrust faults which push layers of the crust above one another.
We can date the moon according to how many craters are on these scarps and how deep they are indicates how much it is shrinking by. Remarkably, the moon seems to have shrunk by 300 feet in the last billion years!
Keep your eyes peeled for my next post,