This simulation of the impact that formed the Earth-Moon pair was developed by Robin Canup (Southwest Research Institute) and Erik Asphaug (University of California, Santa Cruz) in 2001. In the simulation, the smaller body impacting Earth is the size of Mars. It strikes Earth obliquely, speeding its rotation. (By the end of the simulation, Earth has a 5-hour day.)
In the collision’s aftermath, most of the impactor ends up accreting into Earth. But part of it flies off in a cloud of debris that orbits the planet. From this cloud will come the Moon.
The simulation uses color to track the temperature of the impactors and the fragments — redder colors are hotter. (Other simulations track changes in chemical content and the degree to which each body’s material intermixes with the other.)
The time span covered in the simulation is about 24 hours. We are looking down on the equatorial plane of impact.
- Moon-forming impact (2966kB)