2007-09-22 09:41:23 · 3 answers · asked by bert 1 in Science & Mathematics ➔ Astronomy & Space
Mainly because they have had several billion years to work it out. Over time the planets have found orbits where their mutual gravitational attraction does not cause major disruption. What minor changes in orbit do occur tend to be canceled out by other perturbations, so over the long term the planets stay where they are.
2007-09-22 10:46:53 · answer #1 · answered by injanier 7 · 0⤊ 0⤋
According to General Relativity theory the presence of a large quantity of matter is able to bend space around it resulting in a universe curved by matter and energy. Planets are held in orbit not by gravitational attraction as was postulated by newton, but are merely following the shortest possible path through space curved by the immense gravity of the sun, hence they are able to move through space indefinately, without ever loosing energy.
2007-09-22 17:43:36 · answer #2 · answered by Mandél M 3 · 0⤊ 0⤋
Because gravity is proportional to 1/r^2. Combining that with Newton's Laws of Motion, you can show that all orbits are conic sections. Thus all bound orbits are circles or ellipses. It doesn't work out that way if the force of gravity is proportional to anything else wrt r. Orbits with any other force law are unstable.
2007-09-22 16:56:50 · answer #3 · answered by ZikZak 6 · 0⤊ 0⤋