2007-10-25 02:57:22 · 8 answers · asked by colin ? 1 in Science & Mathematics ➔ Astronomy & Space
By definition, a planet is a body with sufficient gravity to pull all its matter into a ball.
A sphere is the shape that has the SMALLEST surface area for the GREATEST volume.
2007-10-25 03:02:14 · answer #1 · answered by Anonymous · 4⤊ 0⤋
Any liquid object in free fall - that is with no over all force acting on it - will take up the most efficient shape to contain the volume of the liquid - smallest overall surface area for a given volume - which happens to be a sphere. For example - Round pellets for a shot gun used to be made by pouring molten lead through a seive from the top of a tower into water. The free falling droplets took up an approx spherical shape and then solidified.
2007-10-25 03:13:36 · answer #2 · answered by Anonymous · 1⤊ 0⤋
The lowest-energy shape a mass can assume is a sphere.
If you had, say, a square-ish planet, there'd be regions that are much further from the center of gravity, creating an area of potential energy (Like, big mountains here on Earth... they have landslides that eventually level them off).
Smaller bodies - like asteroids - don't have the gravitational pull to enforce a spherical shape... but large bodies - say, more than 500 miles in diameter - tend to 'equalize' themselves, trying to create a shape with few areas farther from the center of mass than others.
2007-10-25 04:37:28 · answer #3 · answered by quantumclaustrophobe 7 · 0⤊ 0⤋
Gravity pulls them into a sphere. Any large enough object, even if made of solid rock, cannot support itself in any other shape. Gravity causes landslides and such effects that will always try to pull any large object into a spherical shape.
2007-10-25 03:07:24 · answer #4 · answered by campbelp2002 7 · 1⤊ 0⤋
Planets rotate and revolve. The centrifugal force causes all matter contained within the planet to form a sphere. That is smaller circumference at the poles and largest at the equator. An asteroid, on the other hand may revolve around a sun or planet but it does not rotate, thus not forming into a sphere.
2007-10-25 03:08:39 · answer #5 · answered by Wine and Window Guy 4 · 0⤊ 4⤋
all planets and roughly round thats how gravity makes them
2007-10-25 03:05:48 · answer #6 · answered by washable mist 4 · 1⤊ 0⤋
Because gravity pulls it into a sphere.
2007-10-25 03:03:30 · answer #7 · answered by Sibbs . 4 · 1⤊ 0⤋
Because they are all (roughly) round.
2007-10-25 03:00:08 · answer #8 · answered by mark 7 · 4⤊ 0⤋