Quantitative morphology of rocks at the Mars Pathfinder landing site

Abstract

[1] We adapt and test a standard terrestrial technique of assessing morphology quantitatively for use with sites on Mars based on two-dimensional equations and particle outlines, whereby images of particles obtained remotely may yield dimensionless, numerical shape and roundness values consistent with previous knowledge of the lithology and sedimentary transport history. Our test site was the particle-rich Rock Garden at the Mars Pathfinder landing site, a location where the primary geologic processes and lithology have been determined by other means. A total of 575 particles were assessed in terms of size, sphericity, elongation, and roundness; qualitative roundness was determined for 460 particles. Particles are mostly pebble-to cobble-sized and have an average sphericity of 0.75, elongation of 0.63, and relative roundness of 0.083; 69% of particles are subangular or subrounded. Particle sphericity is unimodal, with a sizesphericity profile matching trends for terrestrial populations of similar lithology and elongations nearly identical to those for particles at Vikings 1 and 2. This matches the predictions for a site with the single overall lithology implied from other analyses. Roundness data indicate one or possibly two particle populations, representing the primary processes that likely affected particle roundness most strongly: impact and catastrophic flooding. Finally, we tested a hypothesis suggesting that darker, smaller, more angular particles comprise a population transported through impact cratering, while larger, less dark, more rounded particles are associated with catastrophic flood transport. The opposite result is seen: larger particles throughout the Rock Garden are more angular than smaller ones.

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

“…Schematic of the methods used for determining sphericity and roundness of particles, adapted from Riley [1941] and Dobkins and Folk [1970, derived from Wentworth , 1919]. The equations that utilize these variables are listed and described in the text, after Yingst et al [2007].…”

“…The limit for sphericity is less stringent, as it is the overall shape of the particle that is important. We chose a conservative limit of 20–30 pixels apparent diameter (8–12 mm) as the minimum size particle for which sphericity could be measured on the basis of previous similar work with Mars Pathfinder loose particles [ Yingst et al , 2007].…”

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

“…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 ., ]).…”

Rock size-frequency distribution analysis at the Chang’E-3 landing site

“…Rock populations on the surface of a planet can provide important geological information related to the planet's origin, the evolution of its crust, and the timing of critical events such as volcanism and meteorite bombardment (Garvin et al, 1981;Grant et al, 2006;Ouyang, 2005;Ward et al, 2005;Yingst et al, 2007). Analyzing and characterizing size-frequency distributions of rocks at planetary landing sites is important for understanding the geological history of the region and is also critical in identifying potential hazards in support of future landings and rover navigation (Golombek et al, 2003(Golombek et al, , 2008Golombek and Rapp, 1997).…”