On the possibility of viscoelastic deformation of the large south polar craters and true polar wander on the asteroid Vesta

Abstract

The asteroid Vesta, located within the inner asteroid belt, is a differentiated body with a prominent rotational bulge. NASA's Dawn mission revealed the presence of two large, relatively shallow impact craters in the south polar region, one with a high-standing central peak. The shallowness and prominent central peak are reminiscent of large craters on some icy satellites that may have experienced strong topographic relaxation. The location of these basins near the south pole is also unusual and suggests true polar wander, which requires relaxation of the rotational bulge. Thus, we use the finite element method and a viscoelastic rheology to examine the feasibility of relaxation processes operating on Vesta. Given the plausible thermal state of Vesta by the decay of long-lived radioactive elements, we find that the lithosphere is not compliant enough to allow strong relaxation of the large south polar craters, and thus the peculiar morphology is possibly a product of the formation of these large basins at a planetary scale. Additionally, the asteroid has not been warm enough to permit the relaxation of the rotational bulge. Consequently, these craters both happened to form near the south pole, as unlikely as that is.