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Daily and seasonal processes shape hydrological activity and detectability of moisture in Antarctic, Mars-analog soils

Deutsch, Ariel N. and Levy, Joseph S. and Dickson, James L. and Head, James W. (2022) Daily and seasonal processes shape hydrological activity and detectability of moisture in Antarctic, Mars-analog soils. Icarus, 380 . Art. No. 114990. ISSN 0019-1035. doi:10.1016/j.icarus.2022.114990.

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Soil salt deliquescence and soil porewater solution growth are key processes that generate potentially habitable conditions in hyperarid environments on Earth and could form near-surface pore waters on Mars. However, direct detection of soils darkened by saline porewater solutions on Mars has proven difficult owing to the limited number of imaging opportunities over potential brine-bearing sites, the limited diel temporal coverage of orbital sensors, and the diversity of spectroscopic properties of potentially brine-bearing substrates that limits direct detection of hydrated mineral phases. Here, we explore how these observational limitations would affect the interpretation of highly dynamic soil salt patches observed in the McMurdo Dry Valleys, Antarctica. These salt patches show daily and seasonal albedo change, darkening and brightening over timescales of minutes. Fully darkened conditions occur at a median surface relative humidity of 67.9 ± 10.7%, while bright conditions occur at lower median surface relative humidity of 38.9 ± 14.5%, leading to the interpretation that the albedo changes are caused by soil salt deliquescence and brine droplet growth. These humidity thresholds and the daily hysteresis between deliquesced and effloresced conditions are consistent with the properties of sulfate and chloride salts found at the site, but occur on timescales much faster than those observed under laboratory conditions (minutes vs. hours–days). Darkened soil patch conditions are most common between 21:00 and 06:00 local time, and are not detected during 78% of afternoon imaging opportunities, suggesting that episodic, afternoon satellite imaging would not be effective in resolving rapid albedo changes on similar planetary landscapes such as Mars. Instead, synoptic, high-cadence imaging is a more suitable remote sensing tool for evaluating albedo changes driven by surface salt deliquescence and efflorescence.

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Head, James W.0000-0003-2013-560X
Additional Information:© 2022 Elsevier. Received 6 August 2021, Revised 18 January 2022, Accepted 8 March 2022, Available online 12 March 2022, Version of Record 16 March 2022. This work was supported in part by the National Science Foundation under grants OPP-1847067 and OPP-1343835 to JSL. Declaration of Competing Interest: None.
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Subject Keywords:Mars; Brines; Habitability; Microclimate; Antarctica
Record Number:CaltechAUTHORS:20220318-999066000
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Official Citation:Ariel N. Deutsch, Joseph S. Levy, James L. Dickson, James W. Head, Daily and seasonal processes shape hydrological activity and detectability of moisture in Antarctic, Mars-analog soils, Icarus, Volume 380, 2022, 114990, ISSN 0019-1035,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:113970
Deposited By: George Porter
Deposited On:21 Mar 2022 14:37
Last Modified:21 Mar 2022 14:37

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