The Water-Wheel IR (WIR): A Contact Survey Experiment for Water and Carbonates on Mars

Water and Carbonates on Mars: Minimum requirements for life include water and accessible carbon. Mars has both in its polar caps and atmosphere. Water (or water-equivalent hydrogen) is present at shallow depths (~10 – 20 cm) at latitudes ≥60° and is heterogeneously distributed in other parts of Mars [1]. Mars may have once had surface water that could plausibly have produced carbonate deposits [2-5]. Mars shows signs of hydrothermal activity [6-8] that may have affected soil composition [9, 10]. The Thermal Emission Spectrometer on the Mars Global Surveyor found large and small patches of hematite that may have been water-borne or water-derived [11, 12]. Current orbiting spacecraft (MGS & Odyssey) have not found massive carbonate deposits, however [13]. Shales and limestones, which we associate with moist and benign environments on Earth, are apparently not abundant on Mars. Both carbonate and organic carbon occur as alteration products in Martian meteorites of igneous origin [14]. One study of MGS-TES data suggests 2-5 wt% carbonates (mainly MgCO3) in surface dust, but found no concentrated source [15]. Carbonates and H2O/OH bearing minerals will be sought by the mini-TES and Mossbauer experiments on the Mars Exploration Rovers, one of which landed successfully on Mars on January 3. WIR – a Contact-Survey Experiment: The water-wheel IR experiment is designed to detect directly water in different forms (liquid, ice, or clathrates, structural H2O and OH, and water adsorbed on grain surfaces), carbonates, and under favorable conditions sulfates and C-H & N-H bonds in organic species. WIR will use an active near IR (2-6 μm) reflective spectrometer installed inside a well set into the middle wheel of a planetary rover. During rover travel, when the well is at nadir, the IR sources will irradiate soil disturbed by the front or rear wheel of the rover. Radiation reflected from the sample (mainly diffuse reflection) in the 2-6 μm spectral range will be collected and recorded. The measurement will not interfere with the normal activity of the rover. Information on the spatial distribution of the abovementioned phases will be obtained along the rover traverses. WIR is a Contact-Survey experiment. It will observe thousands small (~1 cm) patches of soil at near contact range. Examining a small area at a time enables observation of relatively sparse species that are concentrated in a given area, without the spectral background of major materials in a broader area in which the species is a minor or trace component. This minor or trace component. This enhances the probability of finding rare substances.