system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What would happen if an Earth sized planet crashed into another Earth sized planet? (Neither is inhabited)

Assuming that neither is inhabited would they collide and create a new planet or would they shatter? In the event that they formed a new planet how long would it take for it to become relatively round?
gpt
Astronomers believe almost that very thing happened to the young Earth before it had a moon: it was hit by a Mars-sized body, which obliterated both, and the modern Earth/Moon system was born out of the debris.

Such an event would have sterilized both bodies, if there had been anything living.