The Violent Birth of the Moon

In the beginning, about 4.6 billion years ago, all was chaos within a cloud of gas left over from a previous generation of stars. There was nothing but molecules of dust and gas, swirling around in the void. The star stuff drew closer together, and then something happened.

The material started to collapse under its own gravity. The sun ignited. Let there be light, one creation tale says. Winds howled outward from the infant sun, much more powerfully than the charged particles that stream through the solar wind now, and the gales pushed the remaining dust and gas around. The roiling mix eventually separated into clumps, which grew into larger piles, and eventually became the planets.

There were more than the eight we have today. Some of the sun’s original planets were probably consigned to oblivion. Gravitational interactions caused planets and planetesimals (planet embryos, basically) to like billiard balls, and some likely exited the solar system, doomed to silently sail among the stars.