Thermally altered palagonitic tephra: a spectral and process analog to the soil and dust of Mars

We studied six palagonitic soil samples (PH-1 through PH-6) which were collected at 30cm intervals from a lava slab on Mauna Kea, Hawaii. The samples present an alteration sequence caused by heating during emplacement of molten lava over a preexisting tephra cone. They are both spectral and weathering/alteration process analogs to the Martian surface. Techniques employed included visible and near-IR spectroscopy, Mossbauer spectroscopy, and magnetic analysis. The reflectivity specta of samples PH-2 through PH-4 are similar to spectra of palagonites reported by other workers to be good Mars visible to near-IR spectral analogs. The reflectivity spectrum of PH-1 is an even better spectra analog to Mars in that it exhibits absorption features indicative of both nanophase and crystalline ferric oxides (similar to several new Martian telescopic data sets). Our sampling site may also be a process analog for Mars, in that heating episodes by volcanism and/or impact cratering could produce crystalline ferric oxides from poorly crystalline palagonitic material. -from Authors