What philosophical doctrine was challenged by the discovery of Earth-like imperfections on the Moon?

Answer

The division between perfect celestial bodies and imperfect Earthly ones

Since Aristotle, celestial bodies were thought to be made of perfect *aether*, while Earth was composed of mutable elements. Finding mountains on the Moon suggested the heavens were not fundamentally different from our terrestrial sphere.

What philosophical doctrine was challenged by the discovery of Earth-like imperfections on the Moon?
discoveryGalileoastronomysurfaceMoon