PETER GOLDREICH, INSTITUTE FOR ADVANCED STUDY - PRINCETON

PRINCETON ASTRONOMY COLLOQUIUM - APRIL 5, 2005

ABSTRACT

Planet Formation

I shall briefly review modern scenarios for planet formation. The growth of the smallest gravitationally active bodies, planetesimals, is mired in controversy. Orderly growth by the merging of planetesimals is followed by runaway accretion in which a small fraction of the bodies grow much larger than all the others. When these big bodies are sparse enough, runaway growth gives way to oligarchic growth during which the big bodies grow in lockstep maintaining similar masses and uniformly spaced orbits. As oligarchs grow, their orbital spacing increases and their number decreases.

My focus will be on how oligarchy ends and what happens after it does. I will address three major questions regarding solar system planets.

• What determined their number?
• Why are their orbits nearly circular and coplanar?
• How long dd they take to form?

Answers to these will be given in terms of:

• Stability against large scale chaos.
• Dynamical friction by small bodies.
• The accretion rate at the geometrical cross section in the inner planet region and the ejection rate at the gravitationally enhanced cross section in the outer planet region.