Igneous and Aqueous Processes on Mars: Evidence from Measurements of K and Th by the Mars Odyssey Gamma Ray Spectrometer

We report preliminary measurements of the concentrations of K and Th on Mars. Concentrations of K and Th and the K/Th ratio vary across the surface. Concentrations are higher than in Martian meteorites, suggesting that most of the crust formed by partial melting of enriched mantle. The average Th concentration (1.1 ppm), if applicable to the entire crust, implies a maximum thickness of about 65 km. The variation in the K/Th ratio suggests that aqueous processes have affected the chemistry of the surface.