About 4 billion years ago, something caused Jupiter and the other gas giant planets to shift in their orbits, shoving countless space rocks out of their positions in the asteroid belt. Tugged inward by the sun, these asteroids migrated toward Earth and the moon, ultimately bombarding our young planet and its satellite.
In a cataclysmic shower of destruction, Earth, Mars, Venus and Mercury suffered gigantic impact craters, though on our planet much of the evidence was lost to time and tectonics. The moon, however, still bears the scars of this period, known as the Late Heavy Bombardment or lunar cataclysm. And so does the giant asteroid known as Vesta.