Planet Formation

Planets are usually born from a collection of dust that is left over from the formation of a star (which becomes the sun for the planets). The dust is called the accretion disc of the star and it is rotating around the star fast enough to avoid being pulled into the star by gravity. This is an attempt to animate the very long term evolution of planets from this dust in a process called gravitational collapse. Of course the dust particles have mutual gravitational attraction to each other so they may tend to stick together when they come into contact. These inelastic collisions do NOT conserve translational kinetic energy and therefore result in heating of the newly formed mass. This heat would be a big problem because a hot body usually evaporates some of its mass and therefore the mass gain would be canceled. However over long periods of time the heat will be radiated away into outer space via the Stefan-Boltzmann law of black body emmission. The process of planet formation is that the larger masses, because of their larger gravity attraction, sweep out the smaller remaining masses as they travel in approximately the same orbits. This is called gravitational instability. A learner selectable fraction of the collisions between masses can be chosen to be totally inelastic meaning that only momentum, not kinetic energy, is conserved. The internal energy of a mass that is formed is color coded and can be seen by the color bar at the right. The radius of a formed mass is proportional to the cube root of the mass. Also, there are sliders for the fractional variance of position and speed of particles in the accretion disc. The initial positions of the dust masses can be chosen to either be random or regimented using radio buttons. The nominal angular rotation rate, omega, and radius, r, at which the particles are positioned is given by the simple equation
r^3=G*Msun/omega^2
where G is the gravity constant and Msun is the mass of the star. After a planet forms into a mass which is 5% of the total mass of the accretion disc, its orbit is plotted. These can change precipitously when more mass is added. The interested learner should read the following link: Recipes for planet formation