Rock abrasion features in the Columbia Hills, Mars

Abstract

Wind‐abraded rocks (ventifacts) observed along the Mars Exploration Rover (MER) Spirit traverse in the Columbia Hills reveal evidence for complex wind flow patterns. Multiple superposed sets of eolian bed forms are evident in rover images and more broadly in High Resolution Imaging Science Experiment (HiRISE) image coverage. Formative wind directions inferred from ventifacts are more consistent with smaller, second‐order (T2) eolian ridges rather than larger, first‐order (T1) ridges. This suggests that the direction of recent highest‐energy saltation may more commonly be aligned with the higher‐order textures on bed form surfaces, perhaps because of bed form–modified (secondary) airflow around T1 ridges. Additionally, the lack of ventifacts with formative wind directions consistent with T1 ridges may indicate that either the ventifact textures consistent with T1 ridge orientations have been overprinted by abrasion commensurate with T2 ridges or, alternatively, the rocks were emplaced subsequent to the formation and stabilization of T1 bed forms. In both cases, T1 ridges appear fairly immobile and may provide less sand from winds blowing perpendicular to their ridge crests compared to winds consistent with T2 orientation.