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The Handlens Atlas: A Terrestrial Image Library of Microscale Structures as Analogues for Mars
On Earth, understanding the origin of a geologic material as the summed history of its constituent grains is a proven and powerful strategy to maximize the information that can be gleaned from limited samples. Multiple properties such as size, sorting, roundness, and texture may reveal clues to transport regime (e.g. fluvial, glacial, eolian), transport distance and diagenesis, eruptive patterns and processes, and differentiation of primary or recycled (by surface processes) grains. The ability to directly compare martian and terrestrial microscale textures and fabric elements is the first step in revealing those similarities diagnostic of various origin, transport and weathering regimes. However, terrestrial image atlases provide images either at the outcrop scale, or as processed microsamples (e.g. thin sections). A library of terrestrial analogue images at the handlens scale bridges this gap, providing a crucial resource for comparative studies.
We used a professional single lens reflex (SLR) digital camera with interchangeable lens capability and megapixel imaging. For most images, a 100mm f/2.8 macro lens was threaded into the lens adaptor and a twin-tube ring light was mounted on the extended lens. A tripod with a three-way head provided stability during high-resolution imaging. Formations of interest were imaged for context at outcrop scale, then features of interest were imaged at ~10 µm/pxl to mimic the resolution of current and future martian microscopic imagers. When possible, samples were taken of imaged formations for further analysis in the laboratory.
The handlens atlas currently contains nearly 1000 images, each accompanied by supporting documentation and description. The atlas is searchable by key textural terms or by type of formation.