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Current Projects
Current Projects
The Habitability of Mars analog low-temperature brines in the Dry Valleys, Antarctica
The Habitability of Mars analog low-temperature brines in the Dry Valleys, Antarctica
Sletten, R. S.; Toner, J. D.; Catling, D. C.; Liu, L.; Ming, D.; Gillespie, A.; Mushkin, A.
Abstract: The exploration of Mars is motivated in large part by the possibility that Mars may have harbored life early in its history or may have extant life in the subsurface. Because water is an essential ingredient for life, research on the processes that form liquid water is critical for understanding the habitability of Mars. To investigate the possible formation of near-surface liquid water on Mars, we are using a combination of (1) field research on shallow groundwater features in a Mars analog environment, the McMurdo Dry Valleys (MDV), and (2) theoretical modeling of brine and vapor transport in permafrost soils. The field work component of this proposal is investigating the chemical, mineralogical, and isotopic composition of wide-spread shallow groundwaters in the MDV and soils associated with these features. To complement our field work, we are developing and applying a novel thermal-reactive-transport model using data collected from the field to constrain the model inputs and ground-truth the model outputs. At the conclusion of our research, we will have rigorously tested if mechanisms of groundwater formation in the MDV can produce wide-spread shallow groundwaters on Mars, and what the properties of putative Martian groundwaters would be.
A key goal of this project is to explain the formation of Recurring Slope Lineae (RSL) on Mars:
- Dark, narrow lineations on sunward facing slopes.
- Lengthen downslope during the Martian spring, and then fade during the autumn and winter.
- Reappear annually.
RSL are most likely caused by flowing liquid water. If true, then Mars is the only other solar system body, outside of Earth, where liquid water has been observed flowing on the surface. To understand how RSL form on Mars, and what their chemical composition is, we are investigating how similar features in the MDV form during the 2017/2018 Antarctic field season.
The MDVs are extremely cold and dry, and are the best analog we have on Earth for conditions on Mars. So by studying surface processes in the MDV, we can better understand what could be happening on Mars. A key target for our investigation in the MDVs is Don Juan Pond, the saltiest body of water on Earth. The unusual chemistry of Don Juan Pond causes it to spontaneously suck water from the atmosphere and prevents the pond from freezing until below -50°C. RSL-like features also form above Don Juan Pond.
RSL in Palikir Crater, Mars.
RSL-like features above Don Juan Pond. Images are from Head et al. 2007.
View of Don Juan Pond (R. S. Sletten).
[Toner et al. 2017] The geochemistry of Don Juan Pond; Evidence for a deep groundwater flow system in Wright Valley, Antarctica.pdfKing, 2019, AbSciCon.pdfLin, 2019, AbSciCon.pdfGoldschmidt 2017.pdfShumway, 2019, AbSciCon.pdfThe Habitability of Cold Aqueous Salt Solutions on Icy Worlds
The Habitability of Cold Aqueous Salt Solutions on Icy Worlds
Catling, D. C.; Toner, J. D.
Abstract: Salty water is important for understanding the potential for liquid water to form on icy worlds and whether such environments are suitable for life. Salty solutions can form potentially habitable environments by depressing the freezing point of water down to temperatures typical of Mars’ surface or the interiors of Europa or Enceladus. Crystalline salts are also sensitive indicators of the processes by which they formed (freezing or evaporation) and environmental conditions such as pH, temperature, pressure, and salinity. The study of solutions and salt assemblages on icy worlds requires an understanding of the low-temperature properties of salt solutions and the different conditions under which crystalline salts form. Currently, experimental data on low-temperature salt systems are generally lacking, which makes it impossible to study salt solutions as a function of temperature and pressure. To address these issues, we are working to: (1) measure various properties in salt solutions, (2) build new computer models using this data, and (3) apply these models to understanding solutions and crystalline salts on icy worlds. Our goal is to evaluate the potential habitability of low-temperature solutions and what crystalline salt assemblages tell us about environmental conditions, which addresses fundamental questions about habitability.
Important solution properties that we are measuring in the laboratory include:
- Heat Capacity: This property measures how much heat is needed to raise the temperature of a sample. It is one of the most basic properties of substances, and is useful because it determines the temperature dependence of solution chemistry. We are measuring this property using a state-of-the-art TA Q2000, liquid-nitrogen-cooled Differential Scanning Calorimeter (DSC) that we acquired using Royalty Research Funds from the University of Washington.
- Solubility: This measures how much salt can be dissolved in water, which is poorly known for some salts found on Mars. We are measuring this using several novel, self-built devices.
- Water Activity: Water activity, a difficult concept for newcomers to understand, measures how much water in a solution is free vs. bound up in salts. It is one of the most basic measures for determining if life can survive in a given solution; life cannot survive in low water activity solutions. We are measuring this property using a novel experimental apparatus (called an 'isopiestic' apparatus).
Several experimental set-ups that we are using to measure solution properties, and representative graphs of those properties. Left: Our TA Q2000 DSC. Center: A device for measuring solubility. Right: The isopiestic device used for measuring water activity.
A major product of this research is a new geochemical model for salt solutions covering concentrations up to the saturation limit and temperatures down to <200 K (-73°C). We wanted this model to be easily usable by researchers, so we developed the model in PHREEQC, probably the most widely used (and user-friendly) geochemical modeling software available. Our model is now distributed with the regular PHREEQC package as the 'ColdChem.dat' database, and will be regularly updated in the future. Below are some resources to get started with PHREEQC:
- The PHREEQC homepage
- Download PHREEQC
- Users guide (includes various examples)
[Toner and Catling 2017] A Low-Temperature Aqueous Thermodynamic Model for the Na–K–Ca–Mg–Cl–SO4 System Incorporating New Experimental Heat Capacities in Na2SO4, K2SO4, and MgSO4 S.pdf[Toner and Catling 2017] A Low-Temperature Thermodynamic Model for the Na-K-Ca-Mg-Cl System Incorporating New Experimental Heat Capacities in KCl, MgCl2, and CaCl2 Solutions.pdf[Toner et al. 2015] A revised Pitzer model for low-temperature soluble salt assemblages at the Phoenix site, Mars.pdfLPSC2014 Poster.pdf[Toner and Catling 2018] Chlorate brines on Mars; Implications for the occurrence of liquid water and deliquescence.pdf[Toner et al. 2015] Modeling salt precipitation from brines on Mars.pdf[Toner and Catling 2016] Water activities of NaClO4, Ca(ClO4)2, and Mg(ClO4)2 brines from experimental heat capacities.pdfLPSC2015 Poster.pdfPast Projects
Past Projects
Salts and Soils on Mars: Analysis of Phoenix Aqueous Chemistry in the Context of Previous Lander Data
Salts and Soils on Mars: Analysis of Phoenix Aqueous Chemistry in the Context of Previous Lander Data
Catling, D. C.; Light, B.; Giles, M.; Toner, J. D. (postdoc)
Abstract: Key issues for Mars exploration concern the origin of aqueous alteration materials and what they mean for the evolution and habitability of Mars. We propose to use data analysis and modeling to constrain the salt chemistry of the soil measured by Phoenix in the context of soil chemistry measured by the Viking Landers (VLs), Mars Pathfinder (MPF) and the two Mars Exploration Rovers (MERs). The major questions we seek to address are: (1) What is the quantitative composition of salts at the Phoenix site? (2) Is this consistent with the composition of soils at other lander sites? (3) What does the composition of salts indicate about the origin of the soil? (4) Assuming Phoenix soils went through past aqueous processing and evaporation or freezing, what salts would be expected, what is their chemical and physical expression, and can we identify these in lander data?
Key results from this project include :
- The salt chemistry of Mars: We reanalyzed and revised data from Wet Chemistry Laboratory (WCL) experiment on the Mars Phoenix Lander. The WCL experiment measured the salt composition of Martian soils by adding water and analyzing what salts dissolved into solution using an array of sensors. Our analysis provides better estimates of the measured solution composition, as well as improved uncertainty estimates.
- Supercool solutions: Salt solutions on Mars will supercool i.e. cool as a liquid to below the point where theoretical models predict they should freeze solid. For perchlorate salts believed to be on Mars, supercooling is extreme. These salts will cool down to -120°C, at which point they form a glass-like substance. This would greatly extend the possible condition for liquid water on Mars. In addition, glasses preserve organics in a pristine state and life can survive in the glass state.
[Toner et al. 2014] Soluble salts at the Phoenix Lander site, Mars; A reanalysis of the Wet Chemistry Laboratory data.pdf[Toner et al. 2014] The formation of supercooled brines, viscous liquids, and low-temperature perchlorate glasses in aqueous solutions relevant to Mars.pdfLPSC2013 Poster.pdfAGU2013 Poster.pdfReport abuse