John Baez has written up a short history of some of Earth’s disasters. These include the Big Splat, also known as the formation of the Moon, the Heavy Bombardment, the Oxygen Catastrophe, and Snowball Earth.
In 2004, the astrophysicist Robin Canup, at the Southwest Research Institute in Texas, published some remarkable computer simulations of the Big Splat. To get a moon like ours to form — instead of one too rich in iron, or too small, or wrong in other respects — she had to choose the right initial conditions. She found it best to assume Theia is slightly more massive than Mars: between 10% and 15% of the Earth’s mass. It should also start out moving slowly towards the Earth, and strike the Earth at a glancing angle.
The result is a very bad day. Theia hits the Earth and shears off a large chunk, forming a trail of shattered, molten or vaporized rock that arcs off into space. Within an hour, half the Earth’s surface is red-hot, and the trail of debris stretches almost 4 Earth radii into space. After 3 to 5 hours, the iron core of Theia and most of the the debris comes crashing back down. The Earth’s entire crust and outer mantle melts. At this point, a quarter of Theia has actuallyvaporized!
Someone needs to send this to Bill O’Reilly.
Mars has two moons. Both are probably captured asteroids. Saturn has 62 moons, the last one being discovered in 2009.
Science – It Works.