The case against vast glaciation in Valles Marineris, Mars

Abstract

The Valles Marineris of Mars form the largest system of interconnected canyons in the Solar System, where morphological, mineralogical, and structural evidence of widespread glaciation has been recently reported. However, neither precipitation models nor global water budgets can account for such a colossal fill, and the hypothesis has thus far remained unchallenged by additional scrutiny. Here, we present the first thorough case against a Valles Marineris glaciation by describing new evidence that precludes the existence of a glacier. Most crucially, we review High Resolution Imaging Science Experiment (HiRISE) images of chaos terrain in Candor Chasma — previously interpreted as remnant glacial ice — and identify layered, boulder-rich scarps bearing no similarity to scarps of massive ice in Promethei Terra or the North Polar Layered Deposits. We also find no significant differences in the structure, morphology, and composition of chaos terrain in Candor and the Chryse Planitia region, which suggests Candor's Chaos, like Chryse's, is fractured highland terrain. We also review several other key supports for the glacial hypothesis, including the coincidence of an apparent glacial trimline with the water-bearing mineral jarosite, and the apparent presence of glacial features including kettle holes and sandur plains. These too are found to have more plausible explanations with non-glacial origins including tectonic reorganisation, groundwater sapping, and chaotic fracturing. We conclude that the Valles Marineris glacial hypothesis is inconsistent with both observed morphology and our understanding of the ancient Martian climate, and we find no evidence to support its existence.