Eutectic Brines on Mars: Origin and Possible Relation to Young Seepage Features

If the recently observed young gullies on Mars represent seeps or outflows of aqueous fluid, that fluid must be highly concentrated brine to be even moderately stable under current martian surface conditions. Such brines are to be expected in the megaregolith if an initial saline hydrosphere underwent evapoconcentration via water escape from the atmosphere, evolved into subsurface CaCl2-enriched brines by chemical interaction with mafic rocks, and then froze until eutectic compositions were reached. Although most such brines would tend to sink deep into the megaregolith, they could be preserved locally at relatively high elevations as aquifers (or frozen paleoaquifers) perched between ground ice and crystalline salts.