The Shape of the Solar System

Graphic - space1

The mass of the solar system is distributed in a disc, with the sun at its center. All the planets rotate in the same direction about the sun, and the orbits of almost all the planets lie in a single plane, the exception being Pluto, which has an orbit with a significant tilt. Why does the solar system have this structure?

The shape of the solar system is a result of conservation of angular momentum. The solar system formed from a large diffuse cloud of gas, left over from the remnants of a super nova. This initial gas cloud had a small angular velocity and hence a non-zero angular momentum. As the gas cloud collapsed under the influence of gravity the initial angular momentum was conserved, since there were no external forces acting on the embryonic solar system. Bodies began to orbit the center of mass, and collide with other orbiting bodies. Since collisions are most likely in the region where the orbits cross - the plane perpendicular to the angular momentum vector - the mass accumulated into a disc, and the s olar system as we know it evolved. Interestingly, 70% of the angular momentum of the solar system is in the rotation of the sun, most of the other 30% is stored in the rotation of Jupiter around its axis.