Images from NASA's Lunar Reconnaissance Orbiter indicate that we are seeing less Moon than our ancestors did. Where's all this Moon going?
Many of us have come home from the grocery store with bags full of produce and hearts full of optimism. We unload the firm vegetables and luscious fruits, so full of wholesome vitamins that they're nearly bursting out of their skins. They'll taste delicious. Tomorrow. Or the day after that. Or maybe when we're not so tired.
And inevitably, when we returned to the fridge with enough will to cook something that doesn't have cheese injected into the crust, the produce we once knew is gone. In its place are withered lumps. The fruits and vegetables have dried, shrinking down, and let their skin fold in itself.
Similar folds have been spotted all over the Moon — on the Moon, these are called "lobate scarps." In fruits and vegetables, creases appear because they lose water. Cells filled with water have pushed against the skin of the vegetable, keeping it taut. The Moon wasn't filled with water, but it did have a hot core. That core exerted pressure on the outer layers of rock, pushing them out and away. As the core cools, the pressure it put on the outer layers of rock lessens. The pull of gravity remains the same. Without the counteracting force of pressure due to heat, the outer layers of the moon get pulled inward, and the moon shrinks.
Up until these scars were seen, the story was "the core shrunk." After noting their placement, and comparing their features to lunar features created at known times, astronomers have begun to think that the Moon, thought to be geologically stable, is shrinking. This isn't something to be alarmed by. The Moon, over the past billion years, has only shrunk down about one hundred meters. Still, it's exciting for those who thought that internal change on the Moon was over.
Via Physics World.