Mass vs. semimajor axis evolution of the embryos in a simulation that produced a giant planet core. Horizontal displacement represents orbital migration, either inward or out-ward. Each vertical shift represents a collision. The three most massive planets are colored in red, green and blue. Each empty circle represents a collision, and each filled circle represents a surviving planet at its final position. Here the most massive embryo (in red) migrated outward to become a giant planet core.