Martian Slope Streaks Formed by Chlorate Salt Brines and Not Dry Dust Avalanchesby Tommy on 24/10/2012
Formation of recurring slope lineae by liquid brines on present-day Mars, Vincent F Chevrier and Edgard G Rivera-Valentin, Geophysical Research Letters, 5 October 2012
Recurring Slope Lineae (RSL) are small scale seasonal flow features identified by Mars Reconnaissance Orbiter that present several interesting characteristics such as an albedo contrast, seasonal dependence, and a strong preference for equator-facing slopes. All of these characteristics strongly suggest a thermally driven mechanism such as a liquid triggered or dominated flow. Here we investigate the possibility that these features are formed by melting of brines of various compositions via a combination of thermodynamic and kinetic numerical models. Results suggest that a solution with a freezing temperature of ~223 K can best reproduce the observed seasonality. Relatively high surface evaporation rates at the RSL locations make the flows quickly disappear over a single season. Our model reproduces well the seasonality of RSL and can explain the preference for equator-facing slopes suggesting that brine flows, and therefore liquids, are possible on a small time and space scale today on Mars. However, if the RSL are indeed formed by brines, it may indicate that a recharge mechanism is active in order to maintain a source of brine over even short geological timescales, which would have important implications for the martian water cycle.
Chlorate salts and solutions on Mars, Jennifer Hanley, Vincent F. Chevrier, Deanna J. Berget, Robert D. Adams, Geophysical Research Letters,
Chlorate (ClO3−) is an intermediate oxidation species between chloride (Cl−) and perchlorate (ClO4−), both of which were found at the landing site by the Wet Chemistry Lab (WCL). The chlorate ion is almost as stable as perchlorate, and appears to be associated with perchlorate in most terrestrial reservoirs (e.g. Atacama and Antarctica). It is possible that chlorate contributed to the ion sensor response on the WCL, yet was masked by the strong perchlorate signal. However, very little is known about chlorate salts and their effect on the stability of water. We performed evaporation rate experiments in our Mars simulation chamber, which enabled us to determine the activity of water for various concentrations. From this we constructed solubility diagrams for NaClO3, KClO3, Mg(ClO3)2 and Ca(ClO3)2, and determined the Pitzer parameters for each salt. Chlorate salt eutectic temperatures range from 270 K (KClO3) to 204 K (Mg(ClO3)2). Modeling the addition of chlorate to the initial WCL solutions shows that it precipitates in concentrations comparable to other common salts, such as gypsum and epsomite, and implies that chlorates may play an important role in the wet chemistry on Mars.