10 Aug 2015

A paper by PSI’s Tom Prettyman says studies of materials on the surface of Vesta offer new evidence that the giant asteroid is the source of howardite, eucrite and diogenite (HED) basaltic meteorites, supporting current models of solar system evolution and terrestrial planet formation.
Prettyman and co-authors that included PSI’s Yuki Yamashita and Bob Reedy determined the globally averaged concentrations of radioactive elements potassium (K) and thorium (Th) on Vesta’s surface using data from the Gamma Ray and Neutron Detector (GRaND) instrument aboard NASA’s Dawn spacecraft.
“The K and Th content is important because together these elements provide constraints on the composition of materials from which Vesta was made and conditions in the early solar system,” Prettyman said. The K/Th ratio of Vesta is very similar to that of the HED meteorites and distinct from other basaltic meteorites, which strongly supports connection between Vesta and the HEDs.

Image:
Left An image of Vesta taken by NASA’s Dawn spacecraft.
Right From left, Gamma rays from the decay of radioelements K and Th are measured by Dawn's Gamma Ray and Neutron Detector (GRaND) in a low-altitude orbit around Vesta. The measured gamma ray spectrum contains peaks that can be analyzed to determine the concentration of these elements within Vesta's surface. The K/Th ratio of Vesta is similar to the HED meteorites (howardite). Vesta is depleted in K relative to Th and in comparison to the solar nebular (CI). The inner planets are also depleted in K, perhaps indicating that they grew initially from volatile-poor materials.