Gas surface density Σ in the (x, y) plane for a very short segment (t = 2605 to 2610 P_orb at 5.2 au) of the CaseIII_nominal simulation, showing approximately one long-period orbit during which a three-body interaction occurs, and results in a merger event. The y-coordinates are differentfor individual panels, but the overall range is always 4 au. The Sun is located at (0,0). The positions of the embryos areindicated by their Hill spheres (circles) and heliocentric distances (labels, in au units). The motion is in an anti-clockwise direction.