Exploring the internal textures and physical properties of digitate sinter in hot springs: Implications for remote sampling on Mars

Hydrothermal silica deposits on the surface of Mars with textures analogous to terrestrial hot spring deposits are, arguably, one of the best potential targets in the search for evidence of life beyond Earth. Here we investigate terrestrial hot spring digitate silica structures (modern: El Tatio, Chile; Mars Pool at Rotokawa geothermal area, and Te Kopia thermal stream, New Zealand; 1.6–1.8 ka: Opal Mound, Utah, U.S.A.), which are texturally and mineralogically analogous to martian deposits in the Columbia Hills of Gusev crater, in order to elucidate how their physical properties vary with depositional environment, and to help guide future remote sampling endeavors. Micro-computed tomography allows visualization of the internal texture of geological materials through variations in porosity and relative density, and is demonstrated here as a key, non-invasive technique for investigating future returned planetary samples. Bulk porosity, associated with pore sizes greater than >1–2 μm, varies from 4.7 to 21.3% in the four studied terrestrial digitate sinter samples, representing a range of fluid pHs of formation. Moreover, density variations between laminae largely reflect a nano-scale porosity (