Morphology and texture of particles along the Spirit rover traverse from sol 450 to sol 745

Abstract

[1] We quantified and classified the shape, roundness, size, and texture of 935 loose surface particles along the Spirit rover traverse from sols 450-745 to assess origin, transport, and other alteration mechanisms that altered particles during and after formation. Variation in particle morphologic parameters along traverse is consistent with crossing mapped geologic unit boundaries. Texture is divided into four types: vesicular, smooth and flat-faceted, rough and flat-faceted, and very rough. Sphericity and roundness are intermediate and low, respectively, comparable to particles moved by high-energy transport or to crushed particles. This indicates intermittent, high-energy emplacement or modification of a single lithology, rather than systematic, continuous low-energy abrasion or wear over time. Comparison with particle morphology at other Mars landing sites is consistent with the hypothesis that no secondary systematic transport or wide-scale chemical alteration was active at a significant enough level to alter macromorphology. In particular, particle morphology at the Mars Pathfinder site shows stronger evidence of abrasion than along the Spirit traverse, suggesting Mars Pathfinder particles have undergone abrasion processes that particles in this study area have not. Additionally, morphology indices have correlation coefficients near zero, indicating that a fluvial transport mechanism is likely not responsible for morphology. Morphology and texture are instead related to origin and composition rather than subsequent modification. Morphology and texture support a volcanic origin, possibly without modification, but most likely altered primarily by ballistic impact, implying that the Spirit landing site and traverse may be utilized in the future as a standard site for characterization of impact-derived morphology.

Characteristics of pebble‐ and cobble‐sized clasts along the Curiosity rover traverse from Bradbury Landing to Rocknest

“…The size of a single clast, for example, may be ascertained to within 10–20% given a long axis that is at least 4–5 pixels in length (~1 mm long‐axis in M‐100 images); however, a substantial coating of unconsolidated “dust,” as is observed on a number of clasts, increases the practical limit for determination of size to ~10–20 pixels long axis. Similarly, characteristics such as shape and sphericity depend on resolving the smallest “lobe” or protuberance of a clast, and roundness requires even more detailed knowledge of the outline of a clast—5–10 pixels per edge or corner, translating to at least 100 pixels (~21 mm in M‐100 images) long axis for angular clasts [ Yingst et al ., ]. For more qualitatively assessed characteristics such as surface texture and color, the resolution required to make a reasonable analysis depends to a certain extent on the clast itself; varicolored clasts would require greater resolution to make an accurate assessment of individual components, for example.…”

“…These are comparable in roundness to that observed for the Mars Pathfinder site, the Spirit traverse, and from distal alluvial fan facies in the Atacama Desert, Earth. While the Spirit and Pathfinder sites show the sharp peak at subangular values that is common for a population subjected to high‐energy emplacement and little subsequent wear [ Yingst et al ., , ], the rounded pebble population at Gale Crater shows a flattened profile in Figure , which has as its maximum subrounded and rounded values. Based on this comparison, the most rounded clast populations at Gale Crater are more similar to terrestrial fluvial deposits than other Martian landing sites.…”

“…Some porphyritic‐type clasts are found in groups of similar clasts. Although relatively rare (or perhaps not always easy to resolve), these clasts differ substantially from those observed at other rover sites on Mars [e.g., Garvin et al ., ; Yingst et al ., , ; Wiens et al ., ].…”

“…Fluvial processes have been invoked only for the MPF site, and only for boulders, which have higher sphericity and are subrounded and imbricated. For clast sizes larger than ~21 mm, the percentage of clasts assessed as very angular to sub angular at the Curiosity site is nearly identical to that of other sites on Mars: 64%, compared to 62% (MER Spirit [ Yingst et al ., ]), 62% (MPF [ Yingst et al ., ]), 64% (V1), and 76% (V2 [ Garvin et al ., ]).…”

Image analysis algorithm for detection and measurement of Martian sand grains

“…The estimation of shape and size of Martian grains has been done manually in a number of publications (Weitz et al 2006;Jerolmack et al 2006;Yingst et al 2008;Sullivan et al 2008;Minitti et al 2013;Yingst et al 2013). Manual methods, however, are very time-consuming, tedious, and are not practical as the number of images steadily increases.…”