REMOTE SENSING OF THE MINERALOGY OF MARS (Invited Presentation)

More than two decades of visible, near-infrared, and mid-infrared multispectral imaging, point spectroscopy, imaging spectroscopy, and other observations from orbiters, landers, and rovers have revolutionized our understanding of the mineralogy of the Martian surface. In addition, the remote sensing mineral insights have been significantly augmented by major advances in our understanding of the mineralogy of the planet's crust and mantle as gleaned from Martian meteorites.

Fundamentally, Mars is divided into bright-toned regions and dark-toned regions. Based on orbital remote sensing data, the mineralogy of the dark-toned regions is primarily basaltic, dominated by plagioclase and pyroxene but also containing variable abundances of olivine, oxides, and other phases. The typical basaltic composition of dark-toned rocks as observed by in situ rover measurements confirms the orbital interpretations; however, evidence for both more and less silicic and alkalic basaltic compositions has also been found in both individual rock samples as well as in the diversity of Mars meteorite compositions. The mineralogy of the bright-toned regions has been more difficult to assess, but is dominated by a globally-distributed fine-grained dust component with spectral properties dominated by nanophase ferric oxides. The nanophase materials appear to be a coating or rind covering individual (microns to sub-micron size) dust particles that themselves appear to be fundamentally basaltic.

High-resolution orbital remote sensing has enabled discoveries of localized mineralogic diversity that point to a much more complicated story than just "basalt" and "dust", however. For example, ultramafic, dacitic, and even granitic compositions have now been identified in places, as have spatially-coherent deposits of phyllosilicates, sulfates, silica, carbonates, chlorides, and crystalline iron oxides, many of which occur within spectacular layered sedimentary deposits and/or exciting and diagnostic landforms like ancient deltas, lake beds, and putative hot springs deposits. Like Earth, Mars has had a rich and interesting geologic history, and understanding the details of the planet's mineralogy is playing a major role in reconstructing that history.