how and why is the moon shrinking, and will moonquakes speed this up?
In: Planetary Science
Its mass is staying the same, but it’s not as dense as it could be. ILike a snowball, where you can keep packing it tighter and tighter, or a cup of loose granular material, where if you shake it and tap it, things get more dense and the level goes down.
That’s what the moon’s gravity combined with the gravitational effects of orbiting the earth and rotating around the sun with the earth is slowly doing over time.
I don’t know if quakes will speed it up, so much as they’re part of the whole process of the moon being a big ball of rocks and dust held together by the collective gravity of all the other rocks and dust. There is still a little room to settle, so it will continue to shrink a little, but most of its shrinking happened in its first 4 billion years, so the 150-200 feet it lost from its diameter over the last half billion years is just a tiny crawl compared to how quickly it compressed when it was still new and fluffy.
Moonquakes are a result of the shrinking, not a cause.
Big rocky planets with lots of heavy radioactive elements concentrated in their cores like Earth and Venus generate a considerable amount of heat from the radiodecay. Despite being billions of years old, their innards are still white hot.
Smaller planets and moons exhaust that supply and start to cool, and when things cool they contract.
The moon didn’t start with much of a core to begin with so it has cooled dramatically and shrunk considerably over the millennia. It’s still contracting today.
Mercury’s crust has a global “wrinkle” texture to it that’s likely a result of significant contraction after it formed and cooled down.
Latest Answers