Massive impacts show asteroid has deep crust

Artist's impression of the huge impact that deformed the protoplanetary asteroid Vesta, leaving the large impact basin we see today.

Martin Jutzi

A new study shows that the asteroid 4 Vesta may have a different internal structure than previously thought. Vesta, the second largest body in the asteroid belt after the dwarf planet Ceres, is notable for two gigantic craters, so big that they partly overlap despite being on opposite poles of the asteroid.

The first, chronologically speaking, is called Venenia (Named for a priestess of the goddess Vesta in Roman mythology), the result of an impact some 2 billion years ago. The crater is 395 kilometers in diameter, but only penetrated about 25 kilometers deep into the surface of Vesta. And then there’s Rheasilvia. Also named for a priestess of Vesta, Rheasilvia is a whopping 505 km in diameter (Vesta is only 525km in diameter), and the rim of the crater is also one of the tallest mountains in the solar system. Rheasilvia was probably created about one billion years ago, and it obliterated part of Venenia where the two overlap.

The impact penetrated so deep that it’s thought to reach down through the asteroid’s crust to its mantle. The new study, however, shows that, while it did reach about 60-100 km, it did not penetrate to the mantle, suggesting the mantle begins deeper than previously thought.