The Preservation of Organics and Brines in Low-Temperature Aqueous Glasses
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Workshop on the Habitability of Icy Worlds (2014) 4015.pdf THE PRESERVATION OF ORGANICS AND BRINES IN LOW-TEMPERATURE AQUEOUS GLASSES. J. D. Toner1, D. C. Catling1, and B. Light2 1University of Washington, Dept. Earth & Space Sciences, Seattle, WA 98195, USA, 2Polar Science Center, Ap- plied Physics Laboratory, University of Washington, Seattle, Washington, USA. (e-mail: [email protected]) Introduction: We have investigated supercooling ous chemistry of the source brines and any putative and vitrification in aqueous salt solutions during slow organics/life in a pristine state. cooling (~0.2 K min–1) experiments1. Remarkably, we The preservation of orgamics. Organic molecules find that slowly cooled Ca(ClO4)2 and Mg(ClO4)2 solu- within vitrified brines would be preserved without de- tions do not crystallize during cooling, but harden into formation; in contrast, crystallization deforms cellular a glass (i.e. vitrify) near –120°C, even when mixed structures6. Glasses are also optically clear, which with soil. Vitrification occurs when the viscosity of a might facilitate the identification of organisms by fu- cooled solution increases to ~1013 poise, at which point ture robotic missions (Fig. 2). the liquid structure becomes literally ‘frozen’ in place2. The preservation of brines. Aqueous glasses form Low-temperature glasses are astrobiologically signifi- from a parent liquid. As a result, the presence of cant because vitrification is a widely used technique to glassy brines on the surface of an icy planet would preserve organisms in a prinstine state, such that they indicate the aqueous history. Furthermore, glasses remain viable after rewarming3. Here, we explore the would preserve the aqueous chemistry in an uncrystal- possibility that brines preserved as low-temperature lized state, so that the chemical composition of glasses glasses are useful for studying the aqueous chemistry directly reflects the parent brine composition. and habitability of icy worlds. References: [1] Toner et al. Icarus, in revision. Experimental Supercooling Measured in Aque- [2] Angel & Sare (1970), J. Chem. Phys., 52, 1058. ous Electrolyte Solutions: We studied supercool- [3] MacFarlane (1987), Cryobiology, 24, 181-195. ing/vitrification in concentrated MgSO4, MgCl2, CaCl2, [4] Schubertet al. (2010), Space Sci. Rev., 153, 447- NaCl, NaClO4, Mg(ClO4)2, and Ca(ClO4)2 solutions by 484. [5] Sohl et al. (2010), Space Sci. Rev., 153, 485- slowly cooling solutions in a large polystyrene insulat- 510. [6] Han & Bischof (2004), Cryobiology, 48, 8-21. ing block with a central cavity for holding the salt so- lutions. After adding a salt solution in a plastic bag to 20 eutectic melting the cavity, we cooled the insulating block using liquid 0 nitrogen and monitored the temperature of the salt so- C) -20 crystallization ° lution over time with a Platinum Resistance Thermom- -40 Teu CaCl2 -60 eter. Through inspection of the resulting temperature Teu Ca(ClO4)2 profile, we identify the precipitation and melting of -80 -100 solid phases by the heat of crystallization/dissolution. Ca(ClO ) glass transition -120 4 2 Salt solutions that vitrify are easily distinguished Temperature ( 4 m CaCl₂ -140 from crystallizing solutions by the lack of temperature 4 m Ca(ClO₄)₂ -160 excursions from crystallization/melting (Fig. 1). Visu- 0 5 10 15 ally, vitrified solutions appear identical to liquid solu- Time (hours) tions and are distinct from opaque crystallized solu- Fig. 1. Temperatures measured during cooling and tions (Fig. 2); however, vitrified solutions do not flow. warming of 4 m CaCl2 and Ca(ClO4)2 solutions, indi- In our slow cooling experiments, only Ca(ClO4)2 and cating crystallization in the CaCl2 solution, but none in Mg(ClO4)2 solutions vitrify; however, any brine will the Ca(ClO4)2 solution. 2 vitrify given a high cooling rate . Low-Temperature Glasses on Icy Worlds: Sev- eral icy bodies in the solar system are thought to con- tain subsurface oceans4,5. Due to the low temperatures on the surfaces of the outer icy planets, subsurface brines exposed to the surface by convection of ice or cryovolcanism would freeze rapidly, leading to vitrifi- cation. If such exhumation processes occur, then Fig. 2. (A) A clear, translucent, vitrified solution of 4 glasses originating from subsurface oceans should be m Ca(ClO ) . (B) a solution of 1.65 MgSO cooled to found on planetary surfaces and in ejecta from cry- 4 2 4 a eutectic solid. ovolcanism. These glasses would preserve the aque-.