Age constraints 1. This is the plane of the sun's equator. This includes most moons and rotations. The terrestrials have small orbits, short years, warm temperatures, small size, small mass, high density, made of metallic rocks not hydrogen-rich ices, slow spins, no rings, few moons. Pluto is partly in both groups.
Huge tides rip blobs of gas from both stars.
This makes the cloud shape flatter, becoming a dusty opaque disk. Sun lights up and blows away excess gas.