Seasonal low albedo streaks at the edge of the Martian south polar layered deposits

Abstract

Low Albedo Streaks (LAS) are narrow dark streaks observed at the edges of the South Polar Layered Deposits (SPLD) on Mars. We investigate the seasonal morphology, surface topography of LAS-rich areas using monochrome and multiband images from both the High Resolution Imaging Science Experiment (HiRISE) and the Color and Stereo Surface Imaging System (CaSSIS). We complement the image analysis with spectral data from the Compact Reconnassiance Imaging Spectrometer (CRISM). In addition, we analyze the thermal environment of LAS-rich areas with data from a Martian global climatological model. Our analysis suggests that streaks (i) originate from similar scarps and outcrops on the edge of layered structures at the end of local winter during different Martian years, (ii) lengthening in spring forming sinuous branches on terrain with rippled ridges, and (iii) eventually fade leaving distinguishable bright deposits within the streaked area. The surface topography analysis indicates that streaks advance on slopes between 4° and 34°, while the dust flows emanated from mass-wasting scars propagate on the slope steeper than 20°. Our spectral data analysis suggests that pyroxene- or basaltic-bearing materials are deposited on the surface mainly composed of dust by LAS. Thermal analysis indicates that LAS are active when the surface temperature rises from 145.5 K to 162 K, fading when the temperature increases suddenly and significantly. Finally, we evaluate several possible mechanisms to explain the formation of LAS. LAS might be formed by liquids, and such liquids might be brines. However, the presence of salts with lower eutectic temperatures seems to be necessary for the existence of brine on the Martian surface, and should be investigated at the target area in the future.