Testing for flow in the north polar layered deposits of Mars using radar stratigraphy and a simple 3D ice-flow model

Abstract

The water‐ice‐rich north polar layered deposits (NPLD) of Mars play a key role in the Martian climate through an active exchange of water vapor with the atmosphere. Conditions are not currently amenable for flow of the NPLD; however, gross morphological evidence for past flow suggests the possibility of a warmer climate in the past. Here we present the first comparison of internal stratigraphy predicted by a flow model with that observed by an orbital radar sounder. We have analyzed radar data from Gemina Lingula, the southernmost tongue of the NPLD, acquired by the Shallow Radar on board NASA’s Mars Reconnaissance Orbiter. The data shows extensive internal reflections and several radar reflectors were mapped to create gridded surfaces of this part of the NPLD. All the mapped radar reflectors were smooth with no sudden dips towards the surface or the bedrock. The internal radar reflectors were then compared with modeled isochrones in two different areas of Gemina Lingula under the assumption of flow occurring. Results indicate that flow of ice is unlikely to have occurred between the main dome and Gemina Lingula. Furthermore, we found no evidence for the existence of a prior ablation zone in Gemina Lingula as predicted in another study.

Spiral trough diversity on the north pole of Mars, as seen by Shallow Radar (SHARAD)

“…Because of the discrepancies of internal stratigraphy predicted by ice flow models and those observed in both this study and that of Karlsson et al . [], we posit that there was no significant role for ice flow in the evolution of the troughs on the NPLD.…”

Water on Mars, With a Grain of Salt: Local Heat Anomalies Are Required for Basal Melting of Ice at the South Pole Today

“…A variety of geological processes and structures can contribute to geothermal heat flow (e.g., Rezvanbehbahani et al, 2017). This effect is not observed to be occurring in the polar layered deposits (Karlsson et al, 2011), nor is it predicted to occur except possibly at some margins (Sori et al, 2016). Models of Martian midlatitude glaciation similarly found that increases in geothermal heat flux were needed to achieve subglacial melting but also required strain heating of the ice due to internal deformation of flowing ice (Butcher et al, 2017).…”

Islands of ice on Mars and Pluto

“…It has been argued that the morphology of large portions of the NPLD resembles a flowing ice mass (Winebrenner et al, ), and some numerical modeling studies have predicted that viscous flow should be an important process in PLD evolution (Pathare & Paige, ). However, SHARAD data have revealed that the NPLD's internal stratigraphy is not consistent with ice flow, as observed radar reflectors do not exhibit dips toward the surface as predicted by flow models (Karlsson et al, ). A proposed solution to this inconsistency is that dust‐rich layers in both PLDs effectively break up the large ice mass into smaller portions, preventing interior viscous deformation of the stratigraphy (Smith, ).…”