Abstract
Slope streaks have been frequently observed in the equatorial, low thermal inertia and dusty regions of Mars. The reason behind their formation remains unclear with proposed hypotheses for both dry and wet mechanisms. Here, we report an up-to-date distribution and morphometric investigation of Martian slope streaks. We find: (i) a remarkable coexistence of the slope streak distribution with the regions on Mars with high abundances of water-equivalent hydrogen, chlorine, and iron; (ii) favourable thermodynamic conditions for transient deliquescence and brine development in the slope streak regions; (iii) a significant concurrence of slope streak distribution with the regions of enhanced atmospheric water vapour concentration, thus suggestive of a present-day regolith-atmosphere water cycle; and (iv) terrain preferences and flow patterns supporting a wet mechanism for slope streaks. These results suggest a strong local regolith-atmosphere water coupling in the slope streak regions that leads to the formation of these fluidised features. Our conclusions can have profound astrobiological, habitability, environmental, and planetary protection implications.
Highlights
Exploration of Martian surface features is important to understand its landscape evolution, geochemistry, climatic shifts, and geological regimes[1]
Nearly the entire Martian terrain has been captured at an unprecedented high spatial resolution using the Mars Reconnaissance Orbiter (MRO) ConTeXt (CTX) imager and the High Resolution Imaging Science Experiment (HiRISE) camera[27]
We report the high spatial correlation (Fig. 1e) of the Slope Streak Regions (SSR) with the satellite-observed yearly water vapour column as a plausible indicator of the existence of a present-day regolith-atmosphere water vapour cycle in the SSR mediated by the mechanisms that cause the appearance and disappearance of the slope streak features
Summary
Exploration of Martian surface features is important to understand its landscape evolution, geochemistry, climatic shifts, and geological regimes[1]. (i) the groundwater discharge hypothesis faces strong criticism based on surface layer occurrence of the slope streaks and their inconsistency with the bedrock geology[13, 21]; (ii) transient aqueous flow mechanisms are not effectively supported by the observed lack of seasonality in the slope streak formation[23]; (iii) slope streaks can climb over small obstacles of 1–2 m21; and (iv) they initiate only over a slope threshold (∼20°), which argue against the possible involvement of wet processes[21] This ongoing debate on one of the most active surface manifestations on present-day Mars receives a new perspective through our study. We further correlate the distribution map of slope streaks with various physio-chemical parameters of the Martian regolith and atmosphere to characterise the slope streaks and understand their origin
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