A hypothesis for undetectable flow at the polar layered deposits of Mars

Abstract

Since the discovery of thick ice deposits on the polar caps of Mars, scientists have proposed that they flow as glaciers or ice sheets, and simultaneously, others have suggested that erosional activity, primarily by wind, has been the main driver shaping them. This debate began in 1971, and following those original interpretations, numerous studies have suggested that the PLDs flow, up to 1 m per year at steep marginal scarps, and numerous subsequent studies have negated those interpretations. Further, each time a testable prediction has been made in support of flow, is has been falsified by observations. To date, no flow has been observed at the PLDs. This creates an enduring problem; according to conventional wisdom, the polar caps “should” be flowing, but they have not in any appreciable, measurable way. Here, I review the evidence for and against flow and offer and test four hypotheses to retard flow of the NPLD based. The first three hypotheses overpredict strain and fail to account for other observations. The fourth hypothesis, based on stratified layers of varying rheology, successfully explains why the polar ice has no measurable flow. Plain language summaryThe polar ice caps of Mars together comprise as much ice as the Greenland Ice Sheet on Earth. They reach 2–3 km thick and span >1000 km. On Earth, where ice is as many as 100° warmer, places with ice ~1 km thick flow at a measurable rate. However, at the poles of Mars, all predictions of a flowing ice sheet have been negated by observations – any flow would have to be so miniscule as to have no effect on the surface or be detectable in the stratigraphy. Mars does have abundant evidence of past flowing ice in the mid-latitudes, mostly as glaciers, and the poles have experienced temperatures warm enough for flow in the recent past, so explaining this lack of evidence for flow has eluded scientists. This manuscript proposes four ideas to inhibit flow and finds one based on stacking layers of alternating viscosity to successfully match observations. The more resistant layers act to reduce overall flow to an undetectable level.