¹M.S.Fernanders et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114715]
¹Cooperative Institute for Research in Environmental Sciences and Department of Chemistry, University of Colorado, Boulder, CO, USA
Copyright Elsevier

Chlorine is ubiquitous on Mars, some of it in the form of oxy-chlorine salts. Chlorine-containing salts have been found at several landing sites, including that of Phoenix and Curiosity, in the form of perchlorates and chlorides. Several intermediate states also exist, of which chlorate is the most stable. While perchlorates have received much attention in the past few years, chlorate salts are much less studied. The ratio of perchlorate to chlorate on Mars is not well-defined but may be approximately 1:1. Chlorate salts have similar properties to perchlorates: high solubility, low eutectic temperatures, and likely low deliquescence relative humidities. Laboratory studies were performed to determine the ability of sodium and magnesium chlorate salts to take up water vapor at low temperatures (296 K to 237 K). These studies were performed using a Raman microscope equipped with an environmental chamber and a single particle optical levitator equipped with a Raman spectrometer. The deliquescence of sodium chlorate (NaClO3) was found to be temperature-dependent with the average relative humidity (RH) values ranging from 68% RH at 296 K to 80% RH at 237 K. Additionally, there was a slight deviation between experimental deliquescence values for this salt and those predicted by equilibrium thermodynamics. The observed efflorescence (recrystallization) of NaClO3 occurred at lower RH values ranging from 18% RH at 264 K to 24% RH at 249 K, demonstrating the hysteresis common to salt recrystallization. Several experiments were performed below the reported eutectic temperature of NaClO3 which resulted in supercooling of the brine and depositional ice nucleation. Based on the supercooling effects observed during our experiments, a revised metastable eutectic temperature of 237 K is suggested for NaClO3 compared to the previously reported value of 252 K. Two phases of magnesium chlorate (Mg(ClO3)2) were observed and exhibited different water uptake behavior. The most common form of Mg(ClO3)2 appeared to be a hydrated, amorphous phase, Mg(ClO3)2 • X H2O(a) that continuously took up water when the RH was increased. This water uptake behavior was even observed at very low humidity values, 5.0 (±1.9)% RH, with little temperature dependence. This detectable water persisted down to RH values close to 0%, averaging 0.5 (±0.6)% RH with no visible temperature dependence. The deliquescence relative humidity (DRH) of the hexahydrate, Mg(ClO3)2 • 6 H2O, was found to range from 50.9 (± 7.5)% at 227 K to 55.8 (± 6.6)% at 224 K and was consistent with thermodynamic calculations. Under conditions measured by the Remote Environmental Monitoring Station (REMS) instrument at Gale Crater and conditions modeled in the shallow subsurface, magnesium chlorate, if present, likely interacts with water vapor during some diurnal cycles.

^1,2M. K. McClure,¹C. Dominik,^3,4M. Kama
Astronomy & Astrophysics 642, L15 Link to Article [DOI https://doi.org/10.1051/0004-6361/202038912]
¹Anton Pannekoek Institute for Astronomy, Universiteit van Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
²Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
³Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁴Tartu Observatory, University of Tartu, Observatooriumi 1, Tõravere 61602, Estonia

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¹M. Agúndez,²J. I. Martínez,²P. L. de Andres,¹J. Cernicharo,²J. A. Martín-Gago
Astronomy & Astrophysics 637, A59 Link to Article [DOI https://doi.org/10.1051/0004-6361/202037496]
¹Instituto de Física Fundamental, CSIC, C/ Serrano 123, 28006 Madrid, Spain
²Instituto de Ciencia de Materiales de Madrid, CSIC, C/ Sor Juana Inés de la Cruz 3, 28049 Cantoblanco, Spain

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¹T.Kohout et al. (>10)
Astronomy & Astrophysics 639, A146 Link to Article [DOI https://doi.org/10.1051/0004-6361/202037593]
¹Department of Geosciences and Geography, University of Helsinki, Finland
²Institute of Geology, The Czech Academy of Sciences, Czech Republic

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¹William Goode,¹Sascha Kempf,^2,3Jürgen Schmidt
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.pss.2021.105343]
¹LASP, University of Colorado, Boulder, CO, USA
²Institute of Geological Sciences, Freie Universität, Berlin, Germany
³Space Physics and Astronomy Research Unit, University of Oulu, Finland
Copyright Elsevier

Europa and Ganymede are both likely to have subsurface oceans (Carr et al., 1998; Khurana et al., 1998; Kivelson et al., 2000). Young surface features may provide an opportunity to sample material from either a subsurface ocean or bodies of liquid water near the surface (McCord et al., 1999, 2001). Detailed compositional information is of large interest for understanding the evolution, oceanic chemistry, and habitability of these moons. To develop an altitude-dependent model for the detectability of ejecta particle composition originating from surface features of a given size, we simulate detections by a dust analyzer with the capability of measuring compositional makeup on board a spacecraft performing close flybys of Europa and Ganymede (Postberg et al., 2011). We determine the origin of simulated detections of ejecta by backtracking their trajectories to the surface using velocity distributions given in the ejecta cloud model by Krivov et al. (2003). Our model is useful for designing flybys with typical closest approach altitudes, such as the ones planned for NASA’s Europa Clipper mission, where we wish to accurately identify the composition of surface features using a dust analyzer.</sup2,3<>