Plates, spinning, fixed crater origins on Vesta

Vesta, one of the largest bodies in the asteroid belt, has long occupied human imagination – from Roman mythology to 20th century science fiction. 

The protoplanet's Divalia Fossae, massive surface troughs comparable in size to the Grand Canyon, encircle two-thirds of Vesta's equator. Rather than erosion, these deep basins were the result of large meteorite impacts that changed the asteroid’s gravitational field which, in turn, affected both the spin axis and rate of tectonic plate movement on Vesta.

A new study led by University of Georgia geologists present several geologic constraints that support a tectonic origin of the troughs due to the adjustment of Vesta’s spin axis to a geoid changed by large impacts. 

The best fit to Vesta’s gravitational field corresponds to a spin axis reorientation of 3° that, when coupled with despinning, induces a stress state that predicts Divalia Fossae’s established location, fracture type, and orientation. These insights underline the importance of tectonic processes in the early evolution of protoplanets.

"We have been studying the geology of Vesta in detail for several years now and found several pieces of evidence for rotational changes in the asteroid. We put the pieces together and came up with a scenario that explained all our observations," said Christian Klimczak, associate professor in the Franklin College of Arts and Sciences department of geology and co-author on the new study. "To test it, we teamed up with Dr. Matsuyama from the University of Arizona, who models the rotational dynamics of planetary bodies. His modeling was able to produce predictions that matched our observations really well."

The study was published in Science Advances June 25.

Image: Geologic map of Vesta (Mollweide projection) via NASA/JPL