Discovery News: The Late Heavy Bombardment (LHB) was a period nearly 4 billion years ago in which the inner region of the solar system was flooded with asteroids. Evidence of the period is visible via impact craters on the Moon and other bodies that don't experience erosion or other resurfacing processes. Yet strangely, the large asteroid Vesta doesn't show evidence of impacts old enough to have occurred during the LHB. A new model by Simona Pirani of Lund Observatory in Sweden and colleagues suggests that the evidence has been overwritten by subsequent impacts. Pirani says Vesta is large enough that a significant portion of ejecta from impacts likely would have fallen back to the asteroid's surface and masked previous impacts. Seismic effects also could have contributed to the resurfacing.
