CONICET | Buscador de Institutos y Recursos Humanos

Martian slope streaks are elongated down-slope, low-albedosurface features that currently form within sub-annual time scales in thehigh-albedo (?dusty?) regions of equatorial Mars. These km-scale streaks, whichcan persist up to several decades on the Martian surface, present one of themost enigmatic and dynamic suites of active surface features on present-dayMars. Two categories of explanations remain in debate regarding their nature:1) ?Dry? formation models, in which surface darkening is associated with masswasting processes, such as dust avalanches; and 2) ?Wet? formation models, inwhich surface darkening is associated with transient wetting of the surface byeither seepage of sub-surface brines or deliquescence of atmospheric moisture.Here, we report recently discovered dark slope streaks that occur in the highAtacama Desert in Chile and display a close geomorphic resemblance to theMartian streaks. Field examination of the Atacama slope streaks revealed thatthey formed through down-slope seepage of groundwater brines sourced from theSalar de Pedernales located 500 m away. Chemical and mineralogical analysesdemonstrate that salts deposited from the Pedernales brines combined withdetrital input from soils/dust are responsible for surface darkening in theAtacama case. Field-based spectral measurements in the 0.4-2.5 micronwavelength range compare to those obtained from orbit for the Martian slopestreaks. In addition, high-resolution topography derived from drone imageryrevealed that the Atacama streaks are rougher than their surroundings at thedecimeter-scale roughness of the entire hillslope they occur on. A similardistinction was previously established between Martian slope streaks and theirsurrounding slopes, although on Mars these roughness variations appear to occurat lower-range sub-centimeter scales. Our study of the unique Atacama slopestreaks may support ?wet? formation as a viable hypothesis for some of theMartian slope streaks.

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