The planet Mars has been associated with its namesake god of war for millennia, but its own past may have been more violent than was previously imagined. A new study suggests that Mars was once hit by an asteroid so large that it melted nearly half of the planet’s surface.

Researchers came to this conclusion while studying a strange feature known as the Martian hemispheric dichotomy—a dramatic drop in surface elevation and crustal thickness that occurs near Mars’ equator. In the northern hemisphere the land’s elevation is on average about 5.5 kilometers lower and the crust is around 26 kilometers thinner.

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