Alteration processes in volcanic soils and identification of exobiologically important weathering products on Mars using remote sensing

Determining the mineralogy of the Martian surface material provides informa tion about the past and present environments on Mars which are an integral aspect of whether or not Mars was suitable for the origin of life. Mineral identification on Mars will most likely be achieved through visible-infrare d remote sensing in combination with other analyses on landed missions. The refore, understanding the visible and infrared spectral properties of terre strial samples formed via processes similar to those thought to have occurr ed on Mars is essential to this effort and will facilitate site selection f or future exobiology missions to Mars. Visible to infrared reflectance spec tra are presented here for the fine-grained fractions of altered tephra/lav a from the Haleakala summit basin on Maul, the Tarawera volcanic complex on the northern island of New Zealand, and the Greek Santorini island group. These samples exhibit a range of chemical and mineralogical compositions, w here the primary minerals typically include plagioclase, pyroxene, hematite , and magnetite. The kind and abundance of weathering products varied subst antially for these three sites due, in part, to the climate and weathering environment. The moist environments at Santorini and Tarawera are more cons istent with postulated past environments on Mars, while the dry climate at the top of Haleakala is more consistent with the current Martian environmen t. Weathering of these tephra is evaluated by assessing changes in the leac hable and immobile elements, and through detection of phyllosilicates and i ron oxide/oxyhydroxide minerals. Identifying regions on Mars where phyllosi licates and many kinds of iron oxides/oxyhydroxides are present would imply the presence of water during alteration of the surface material. Tephra sa mples altered in the vicinity of cinder cones and steam vents contain highe r abundances of phyllosilicates, iron oxides, and sulfates and may be inter esting sites for exobiology.