Search for Chemical and Mechanical Weathering Processes on Mars, 15-R8135

Principal Investigators
Victoria E. Hamilton
Nathaniel E. Putzig

Inclusive Dates:  01/19/10 – 05/19/10

Background - Sediments are the geologic descendants of bedrock outcrops, formed by the mechanical and/or chemical breakdown of their parent rocks. Whether the breakdown has occurred primarily by mechanical and/or chemical processes may be deduced in part by comparing the mineralogy of the sediments to the mineralogy of their presumed parent outcrops. Sedimentary materials on Mars generally have been assumed to be the product of largely mechanical erosion, and thus have been interpreted as primary igneous compositions. The primary objective of this effort was to conduct a pilot study into whether or not there may be correlations between the effective particle sizes and mineralogies of geologic materials on Mars that would support a hypothesis suggesting chemical weathering could be a significant contributor to the breakdown of large rocky outcrops into sediments.

Approach - The project team examined available thermal inertia (a proxy for particle size) data sets and performed proof-of-concept analyses comparing Martian thermal inertia data to mineral abundances and spectral parameters indicative of hydrated minerals to show what kinds of correlations there are, and illustrate the usefulness of global- and local-scale studies. For example, the thermal inertia of Martian surface materials was compared to the modeled abundances of a silicate mineral called olivine (with the abundances having been derived previously from thermal infrared spectra acquired from orbit). Olivine is a mineral that is widely assumed to alter and/or dissolve readily in the presence of water, so its presence or absence could be an indicator of the degree of alteration experienced by surface materials. A positive correlation between thermal inertia and olivine abundance would indicate that rockier, more massive materials contain more olivine than finer sediments, suggesting that as rocks are broken down into fines, olivine is being removed, presumably by chemical alteration in the presence of water.

Accomplishments - Initial analysis shows that there is no global correlation between physical properties and mineralogies at spatial resolutions of ~3 x 6 km. This result is interpreted as indicating that either there is no correlation (refuting the hypothesis), or that this resolution may be too coarse to discern such a correlation (a likely condition). SwRI researchers identified an anomaly in one of the published data sets (thermal inertia) that was used for the analysis. Although the anomaly doesn't appear to have affected the results, the internal funding received under this project has allowed the researchers to investigate the source of the anomaly in cooperation with the researchers who wrote the original model code and produced the data sets. SwRI is working on a correction and hopes to regenerate the thermal inertia data in corrected form for dissemination to the Mars science community. A full-scale study has been proposed to NASA's Mars Data Analysis Program using data from this project as proof-of-concept.

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