Complex Brines and Their Implications for Habitability.

Nilton O Renno,Jennifer Hanley,Germán Martínez,Erik Fischer

doi:10.3390/life11080847

Abstract

There is evidence that life on Earth originated in cold saline waters around scorching hydrothermal vents, and that similar conditions might exist or have existed on Mars, Europa, Ganymede, Enceladus, and other worlds. Could potentially habitable complex brines with extremely low freezing temperatures exist in the shallow subsurface of these frigid worlds? Earth, Mars, and carbonaceous chondrites have similar bulk elemental abundances, but while the Earth is depleted in the most volatile elements, the Icy Worlds of the outer solar system are expected to be rich in them. The cooling of ionic solutions containing substances that likely exist in the Icy Worlds could form complex brines with the lowest eutectic temperature possible for the compounds available in them. Indeed, here, we show observational and theoretical evidence that even elements present in trace amounts in nature are concentrated by freeze–thaw cycles, and therefore contribute significantly to the formation of brine reservoirs that remain liquid throughout the year in some of the coldest places on Earth. This is interesting because the eutectic temperature of water–ammonia solutions can be as low as ~160 K, and significant fractions of the mass of the Icy Worlds are estimated to be water substance and ammonia. Thus, briny solutions with eutectic temperature of at least ~160 K could have formed where, historically, temperature have oscillated above and below ~160 K. We conclude that complex brines must exist in the shallow subsurface of Mars and the Icy Worlds, and that liquid saline water should be present where ice has existed, the temperature is above ~160 K, and evaporation and sublimation have been inhibited.

Highlights

One of the top goals of NASA’s space science program is to use knowledge of the history of the Earth, and the life on it, as a guide for determining the processes and conditions that create and maintain habitable environments beyond Earth [1]
It follows from the discussion above those elements that exist in trace amounts on Earth, Mars, and the Icy Worlds such as lithium [75] can be concentrated by the precipitation of other compounds during the cooling of their aqueous solutions [10,11,45]
Since the process that forms complex brines appears to be ubiquitous in nature [11,46,69], complex brines must exist in the shallow subsurface of Mars and the Ice Worlds; liquid saline water should be present where ice has existed, the temperature is the lowest eutectic temperature possible, and sublimation and evaporation have been inhibited

Summary

Introduction

One of the top goals of NASA’s space science program is to use knowledge of the history of the Earth, and the life on it, as a guide for determining the processes and conditions that create and maintain habitable environments beyond Earth [1]. As an ionic solutionfound starts to ice and the chondrites least soluble compounds precipitate from elements infreeze, carbonaceous [20], at least in trace amou first, the brine withtogether the lowestwith possible temperature freezes This process use while this hypothesis oureutectic knowledge of the saltslast. Microbes could have adapted to higher salt concentrations than the terrestrial microorHeinz et al found that the yeast Debaryomyces hansenii is the most halotolerant miganisms we know because Martian microbes would have had a longer exposure to the croorganism discovered so far [60] They argue that it is possible that potential Martian briny environments occurring naturally on Mars but not on Earth. Vapor pressure at the triple point of water (~600 Pa) is below the present day atmospheric pressure at the lowest regions of Mars, such as the Phoenix, Curiosity, and

Freeze–ThawPerseverance

Low Temperature Brine Candidates

Findings

Discussion

Conclusions