Fig. 3.
A schematic illustration of the timing and conditions of events following a giant impact. (A) t1, 0 y A hot (>4,000 K) gas- and dust-rich vapor envelope surrounds the proto-Earth within its Roche limit. At 4,000 K, >99.99% of the volatile species of molar mass 0.052 kg/mol have vth < 3.8 km/s, significantly lower than the 11.2 km/s vesc of Earth, preventing any volatile escape of Cr. (B) As the disk cools, the vapor disk rotates, settles, and spreads along the midplane, exceeding the Roche limit over a period of ∼100 y. (C) The material outside the Roche limit is able to condense and accrete to form the Moon. At this point, the temperature has fallen to 1,600–1,800 K, and the remaining gas particles have a Maxwell–Boltzmann distribution of velocities, 2–4% of which exceed the escape velocity of the Moon at a given time, which is calculated to occur at the Hill radius at 3 RE to be 1.56 km/s and are lost over the timescale of years.