Mars' North Polar Spiral Trough Migration Paths as Revealed Through 3D Radar Mapping

We present observations and maps of Mars' northern polar spiral trough migration paths (TMPs) as revealed through the 3D SHARAD (Shallow Radar) data volume, identify patterns of TMP morphology, and provide interpretations and implications of these TMPs on past climate. This data set provides additional spatial context over traditional 2D data as it allows for radargrams to be taken perpendicular to each trough strike, which minimizes distortion of migration paths due to oblique viewing geometry. Here, we present an expanded survey of trough migration and analysis of surface troughs across the north polar layered deposits. We corroborate many previous observations of trough migration such as: the general poleward and stratigraphically upward migration from the TMP initiation point; the broadly similar depth of trough initiation across the cap; regional variability in TMP morphology; and the presence of buried promontories. Our results support the presence of two generations of troughs, though we cannot confirm that the oldest generation originated deeper than ∼600 m beneath the current surface, as previously reported. Two generations of troughs suggest that climate conditions favorable for initiation of trough migration have occurred at least twice. Trough initiation occurring only in the upper ∼600 m suggests that troughs are relatively recent features in the polar cap, developing after the formation of ∼half the current cap height. The mapped TMPs provide insight into the consistency of Mars' climate during the accumulation of the past few hundred meters of ice by recording the boundary of erosion and accumulation of ice at the troughs.