How are planets built?

In the original solar system, the sun was surrounded by a disk-shaped cloud of dust and gas after it formed, 4.55 billion years ago. In this cloud, or "solar nebula," innumerable particles of dust condensed out of the gas and orbited the sun in nearly circular orbits. Adjacent particles underwent collisions at relatively low speed, in the same way that high speed race cars moving around a circular track might nudge into each other. Our program represents the motions of these particles at different distances from the sun, and tracks the results of collisions based on actual physical and mechanical properties. When we run the program with different starting conditions, we can actually see the innumerable small particles aggregate into smaller numbers of big bodies, eventually producing a system of a few planets. The program allows us to study conditions under which planets form.

Inside the solar nebula. This view shows the scene in the region of the Earth less than a million years after the sun formed. Small grains of dust are aggregating into "planetesimals." Planets grew by collisional aggregation of these objects.

Painting copyright William K. Hartmann.

Back to main page

Created on ... juillet 16, 2003