Since the Discovery of Perchlorate (Clo4 –) Salts [18] in the Martian
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Ninth International Conference on Mars 2019 (LPI Contrib. No. 2089) 6271.pdf A NEW MARS CHAMBER AND SALT KINETICS MODEL TO BETTER UNDERSTAND MARTIAN SURFACE WATER UPTAKE. K. M. Primm1, D. E. Stillman1, and T. I. Michaels2, 1Dept. of Space Studies, Southwest Research Institute, 1050 Walnut St. #300, Boulder, CO 80302, USA ([email protected]). 2SETI Institute, 189 Bernardo Ave Suite 200, Mountain View, CA 94043. Introduction: Since the discovery of perchlorate In addition to our chamber experiments, we are de- – (ClO4 ) salts [18] in the martian regolith, the search for veloping a salt kinetics model to better model the mi- liquid brines has become more tangible. This discovery gration of H2O via salt deliquescence and freezing. has led to several findings that liquid brines might be Mars Chamber: We commissioned a custom-built possible on the surface of Mars today due to either Mars chamber (Fig. 1) that is able to: control tempera- deliquescence (salts absorbing water vapor, transition- ture via a LN2 cold plate with temperature-controlled ing to a saturated liquid solution) or the freezing point heaters within the cold plate, humidify CO2 flow con- depression of the salt (melting occurring when the salt trolled by Alicat mass flow controllers, monitor the is in contact with water ice) [1-4]. Possible detections relative humidity with a Vaisala DMT 152 dew point of liquid water on Mars have been hypothesized to transmitter, and hold the chamber pressure at Mars occur below the Southern Polar Layer Deposits values with a Welch vacuum pump. This Mars cham- (SPLD) in the form of a subglacial lake [5-6] and with- ber allows us to place our three-electrode sample hold- in Recurring Slope Lineae (RSL) [7]. However, these er [e.g., 16,17] onto the cold plate to simultaneously detections remain controversial [8-10]. measure the electrical properties, temperature, pres- There are only a few experimental chambers that sure, and relative humidity within the chamber. can replicate the atmospheric pressure, composition and temperature of Mars. However, each of them found different answers to the possibility of liquid water on Mars today [11-14]. Three have the capability to take Raman spectra (with varying resolutions) of the sample while under martian conditions, while the other one utilizes cameras and a balance to measure mass differ- ences. While Raman spectroscopy is a powerful tool to determine the phase of water in your sample, if the resolution of the instrument or if the sample size is greater than the laser beam penetration depth, ambigui- ty in your measurements is more likely. Thus, we de- signed a new Mars chamber that can measure the elec- trical properties of Mars regolith analogs under martian conditions, similar to [15]. Figure 1. Inside view of our Mars chamber. The elec- Electrical properties of materials are represented by trical leads are connected to the Solartron 1260A Im- the real part of the relative dielectric permittivity that pedance Analyzer and Solartron 1296A Dielectric In- represents charge storage in bound charges, and whose terface. The Vaisala DMT152 dew point transmitter is imaginary part represents energy loss. Briefly, the not shown because it is screwed into the lid of the dielectric permittivity drastically changes when liquid chamber. water is present (e.g., salt hydrate =4.5, while liquid water ~80). Through this measurement, we are able Model Methods: We are currently working on a to unambiguously determine if liquid water is within model that will be able to simulate the migration of our sample. H2O throughout a martian sol which will include the To help better understand if liquid solutions are water uptake contributions of magnesium perchlorate possible via deliquescence, there is an experiment within regolith. This simulation was performed using onboard the ExoMars rover (Rosalind Franklin), the MarsFlo [e.g., 21] integrated with the Mars Atmos- Brine Observation Transition to Liquid Experiment pheric Regional Modeling System (MRAMS: [22]). (BOTTLE), that will expose Mars-relevant salts to the The MarsFlo component proficiently simulates three- atmosphere of Mars and measure the electrical proper- phase (liquid, ice, vapor) H2O migration and thermal ties. Our research will help to better understand the evolution in porous media, while the MRAMS compo- results from this experiment. nent provides realistic surface boundary conditions as functions of time-of-day, season, and latitude. Ninth International Conference on Mars 2019 (LPI Contrib. No. 2089) 6271.pdf We modeled the water activity (Awi, initial) and temperature is >Teu and the initial RH is >DRH temperature at Palikir crater (41.6S, 202.3E) (Fig. 2). (hours 8 to 11 and 20 to 24) the brine vol% is much Our model requires the following initial inputs: salt lower than when the initial RH is <ERH. While initial wt%, salt mass, RH, temperature, total volume. In-situ water activities are >0.61 (minimum for terrestrial data suggest a perchlorate (for this study, Mg(ClO4)2) life), deliquescence reduces the water activity below wt% of ~0.5–1 [18-19]. We used neutron spectrometer this value. Furthermore, at high temperatures when data to estimate the amount of water to use in the mod- brine vol% is maximum, water activities are at a min- el at Palikir Crater; the water-equivalent wt% was imum. found to be ~4.3 [20]. The RH and temperature time- Future Directions: Our chamber is set up, and we series are taken from MarsFlo/MRAMS model output. are measuring the relative humidity, temperature, and pressure while simultaneously measuring the electri- cal properties of the sample. However, we are work- ing on how to better control the humidity and will present these data at the conference. Figure 2. Modeled diurnal profile of water activity and temperature vs local time at Palikir Crater (3cm depth and Ls=274). DRH and ERH are the deliques- cence relative humidity and the efflorescence relative humidity, respectively. Teu is the eutectic temperature of Mg(ClO4)2. Figure 3. Vol% of brine (blue) and ice (white) Results: The resulting final water activity, Awf, is throughout the sol in Fig. 2. All anhydrous salt and calculated using chemical modeling to manipulate the hydrate vol% are zero. temperature and water activity output by MarsFlo/ References: [1] Gough et al. (2011) EPSL, 312, MRAMS to show how Mg(ClO4)2 can affect these 371-377. [2] Toner et al. (2014) Icarus, 233, 36-47. [3] profiles. This chemical modeling will eventually be Nuding et al. (2014) Icarus, 243, 420-428. [4] Primm performed within our version of MarsFlo (to be called et al. (2017) GCA, 212, 211-220. [5] Orosei et al. MarsFloSalt thereafter). We calculate this change in (2018) Science, 361, 490-493. [6] Sori and Bramson water activity by assuming water vapor will deli- (2019) GRL, doi: 10.1029/2018GL080985, 1-10. [7] quesce or effloresce (D/E) if the initial RH is above Ojha et al. (2015) Nat. Geosci., doi: the DRH (Deliquescence Relative Humidity) or be- 10.1038/NGEO2546, 1-4. [8] Dundas et al. (2017) low the ERH (Efflorescence Relative Humidity), re- Nat. Geosci., 10, 903-907. [9] Leask et al. (2018) GRL, spectively. We then find the vol% of brine, salt hy- 45, 180-189. [10]Vincendon et al. (2019) Icarus, 325, th drate (Mg(ClO4)2•6H2O), ice, and/or anhydrous salt 115-127. [11] Slank et al. (2019) 50 LPSC Abstract (Fig. 3). The sol starts with a mixtures of ice and 1473. [12] Nikolakakos and Whiteway (2015) GCA, brine because temperatures are >Teu. When the tem- 42, 7899-7906. [13] Fischer et al. ( 2016) Astrobio., perature increases (8-17 hrs) the brine vol% is con- 16, 937-948. [14] Primm et al. (2018) JGR: Planets, tinuously increasing, while the ice vol% is decreasing. 123, 2076-2088. [15] Heinz et al. (2016) GRL, 43, The brine vol% peaks with temperature when RH/ 4880-4884. [16] Stillman et al. (2010) JPC B, water activity is at its lowest because the temperature 114,6065-6073 [17] Stillman et al. (2013) JGR: Earth increase affects the brine volume more (via melting) Surface, 1, 1-16. [18] Hecht et al. (2009) Icarus, 233, than the amount of water vapor within the pore space 36-47. [19] Glavin et al. (2013) JGR:Planets, 118, of the regolith that is D/E. 1955–1973.[20] Feldman et al. (2002) Science, 297, Conclusion: Here we combine temperature, RH, 75-78. [21] Painter (2011) Comput. Geosci., 15, 69-85. and D/E modeling to determine the amount of brine, [22] Michaels and Rafkin (2008) JGR, 113, ice, hydrate, and anhydrous salt produced during a sol doi:10.1029/2007JE003013. on present-day Mars. We find that even when the .