In American astronomer Alastair G. W. Cameron 's hypothesis from 1962 and 1963, the protosun, with a mass of about 1–2 Suns and a diameter of around 100,000 AU, was gravitationally unstable, collapsed, and broke into smaller subunits. The magnetic field was around 1/100,000 gauss. During the collapse, the magnetic lines of force were twisted. The collapse was fast and occurred due to the dissociation of hydrogen molecules, followed by the ionization of hydrogen and the double ionization of helium. Angular momentum led to rotational instability, which produced a Laplacean disk. At this stage, radiation removed excess energy, the disk would cool over a relatively short period of about 1 million years, and the condensation into what Whipple calls cometismals took place. Aggregation of these cometismals produced giant planets, which in turn produced disks during their formation, which evolved into lunar systems. The formation of terrestrial planets, comets, and asteroids involved disintegration, heating, melting, and solidification. Cameron also formulated the giant-impact hypothesis for the origin of the Moon.