Contribution of Mars Odyssey GRS and Mars Reconnaissance Orbiter CRISM at Elysium Planitia: A case of mistaken identity

Two recent Icarus papers on the geology of Marsʹ Elysium plain (Diez et al. 2009 [Icarus 200, 19–29] and Jaeger et al. 2010 [Icarus 205, 230–243]) raise the issue of what gamma ray, neutron, and visible-infrared spectral observations (GRS-NS, CRISM11GRS-NS: Gamma-Ray and Neutron Spectrometers, onboard Mars Odyssey. CRISM: Compact Reconnaissance Imaging Spectrometer for Mars, onboard Mars Reconnaissance Orbiter. n geologically. This question is important because spectrometric data are readily accepted as supporting evidence of a particular geology (e.g., flood-volcanism on Mars). However, chemical composition is not a proxy for lithology.