Question: Why is everything round? For example, the sun, the earth, the moon?

Iain Moal answered on 15 Jun 2010:

Hi Clark,
Its because of gravity. Tall things tend to fall down, or get eroded away. The most stable configuration of things on a planet is spherical. Even the mountains will eventually erode away. It not too bad though, because the tectonic plates will keep clashing into each other and forming new mountains, until the centre of the earth cools down into a solid and the planet no longer has enough energy to make new mountains. Then earth will erode to be as smooth and round as mars, whose core cooled down a long time ago.