Why are planets circular??

[dominion]

Why are planets, (or why do they appear) circular?? Asteroids etc are not. i was always pants at physics, anyone know?

[Dagman]

Planets being larger than aseroids have greater gravity. this causes the material in a planet to move around (earthquakes/volcanic eruptions/weather) Through time, millions of years, the planet smooths out on it's surface always being drawn to the centre. It then resembles a ball. Themovements never stop. Hope this kinda helps.

[medico]

Planets aren't quite round...they are wider at the equator because as they spin, the centre is thrown slightly out so they are flatter at the poles. This is why you fly over greenland to go to the USA.

[Ewood27]

Drifting off topic, medico, but that's not why you go to the US via Greenland. It's the Great Circle route and the shortest way. Try stretching an elastic band between, say, London and Los Angeles on a globe instead of a flat map and you'll see what I mean.

[tartanwiz]

Since matter falls towards the centre of gravity at approximately the same rate, it is inevitable that planets will be spherical in shape.

[EssJay1]

Asteroids orbit the star without a massive rotational spin. Planets spin on their own axis, so like pizza bases being made (you know the way the flash pizza guys do?) planets form a circular shape. Then gravity and density come into it. Or something like that!