Figure 2 – The final distribution of material after two successive impacts. The color corresponds to the depth the material originated from before the two impacts. Left: Southern hemisphere (location of the two impacts). The surface is filled with material from 60-100 km deep. Right: Northern hemisphere. The surface is dominated by material from only 20 km deep.

Figure 3 – A few of the different models of the interior composition that were tested. Left: Model of the interior composition, Right: Final distribution of material on the surface. All three of these models predict some olivine-rich mantle material (blue) in the southern hemisphere.

Asteroid Excavation: Probing the interior of Vesta through major impacts

Title: The structure of the asteroid 4 Vesta as revealed by models of planet-scale collisions
Authors: M. Jutzi, E. Asphaug, P. Gillet, J.-A. Barrat, & W. Benz
First Author’s Institution: Physics Institute, Space Research and Planetary Sciences, Center for Habitability, University of Bern


Though all asteroids are pockmarked by numerous collisions, the southern hemisphere of the asteroid Vesta has been completely pummeled by two major impacts – dredging up material from deep below the surface. Jutzi et al. have created new 3D impact models that predict how the impact ejecta are distributed over the surface of Vesta. By comparing model predictions to the observations from the Dawn spacecraft, they can directly probe the material from the interior of the asteroid that has ended up on the surface. The problem: the measurements don’t detect the material they expected from a layered, differentiated body like Vesta was expected to be.


Vesta is one of the largest bodies in the asteroid belt, second in mass behind Ceres, and third in size behind Pallas. Vesta does not have the spherical shape you would expect from an object of its mass because of the enormous impact basin in the southern hemisphere. The Dawn spacecraft, which orbited Vesta for over a year, discovered that the impact basin was actually two overlapping impact basins, named Veneneia (older impact) and Rheasilvia (younger, fresher impact).

Read more: Asteroid Excavation: Probing the interior of Vesta through major impacts | astrobites.

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