Very Recent Hydroclimatic Change on Mars?

Introduction: The geomorphology and geology of Mars, for at least the last 20 years [1], has presented a consistent, coherent picture of that planet as water-rich, such that aqueous activity has occurred, sporadically at least, on its surface throughout its history. The robustness of this conclusion is evidenced in its persistence , despite difficulties of reconciliation with geo-physical and geochemical theory [2], and numerous nonaqueous hypotheses [e.g., 3] applied to restricted subsets of the interrelated evidence for aqueous activity on Mars. More recently, the role of water on the Martian landscape has been confirmed by striking discoveries of (a) exceptionally young, water-related landforms [4, 5] interpreted as part of a whole assemblage of very recent, water-related activity [6], and (b) neutron and gamma-ray signatures of a near-surface zone of high water-ice abundance at high Martian latitudes [7]. What do these discoveries mean for past hydroclimatic change on Mars? Reconstructing the Past: There are two, somewhat conflicting strategies for specifying the boundary conditions necessary to explain the young aqueous landforms. Strategy U, a variant of uniformitarian principle , holds that present-day, exceedingly cold-dry Mars conditions are better (more simply, or parsimoniously) postulated as a basis for model simulations, rather than " speculations " about warmer, wetter past conditions. In terrestrial geology the uniformitarian principle has a long tradition of advocacy, and also one of scientifically counterproductive outcomes [8]. In contrast to Strategy U, Strategy C is less elegant in theory but more fruitful in historically demonstrable scientific success. It consists of colligation, coherence, and consilience. First one colligates all the evidence of the potential water-related landforms, as manifested in time and space. The most seasoned tool for this assembly , geological mapping, is used to demonstrate coherence of patterns. The fundamental questions to emerge from the revealed patterns are those of analogy and genesis [9]. If this entire assemblage of (apparently) water-related landforms, as manifested in time and spatial association (these being recognized by geological mapping), were to be observed on Earth, what would be the most productive hypotheses in regard to their origins? Finally, do the resulting hypotheses lead nowhere, or do subsequent discoveries line up in ways that make otherwise diverse theories converge in unified explanation, i.e., do we achieve consilience?