16
Growth and Differentiation of Planets
•Planet forms from homogeneous mix of material
•Planet heats up
–“Heat of formation”
(i.e. energy from gravity)
–Heat from radioactive decay of U, etc.
•Dense material (Fe) sinks to center
–Certain “siderophile” elements (like Ni)
–Other “lithophile” elements remain behind
•Homogeneous model too simple
–Final collisions can be big:
•Little planetesimals first form bigger ones, then bigger ones collide to form yet bigger ones
–Moon may be result of impact of Mars size body as Earth formed       (more later)
–First material to condense might separate out early
From our text:  Horizons by Seeds