Adsorbed water and thin liquid films on Mars

Abstract

At present, bulk liquid water on the surface and near-subsurface of Mars does not exist due to the scarcity of condensed-and gas-phase water, pressure and temperature constraints. Given that the nuclei of soil and ice, that is, the soil solid and ice lattice. respectively, are coated with adsorbed and/or thin liquid films of water well below 273 K and the avai lability of water limits biological activity. we quantify lower a nd upper limits for the thickness of such adsorbed/water films on the surface of the Martian regolith and for subsurface ice. These limits were calculated based on experimental and theoretical data for pure water ice and water ice containing impurities, where water ice containing impurities exhibit thin liquid film enhancements, ranging from 3 to 90. Close to the cold limit ofwat~.::r stabil ity (i.e. 273 K), thin liquid film thicknesses at the surface of the Martian regolith is 0.06 nm (pure water icc) and ranges from 0.2 to 5 nm (water icc with impurities). An adsorbed water layer of 0.06 nm implies a dessicated surface as the thickness of one monolayer of water is 0.3 nm but represents 0.001-0.02% of the Martian atmospheric water vapour inventory. Taking into account the specific surface a rea (SSA) of surface-soil (i.e. top I mm of regolith and 0.06 nm adsorbed water layer), shows Martian surface-soil may contain interfac ial water that represents 6 66% of the upper-and lower-limit atmospheric water vapour inventory and almost four times and . 13°/.,, the lower-and upper-limit Martian atmospheric water vapour inventory. Similarly, taking the SSA of Martian soil, the top I mm or regolith at 5 nm thin liquid water thickness, yields 1.10 x I OIJ and 6.50 x I OIJ lit res of waters, respectively, 55-325 times larger than Mars' atmospheric water vapour inventory. %, respectively, of the Martian atmospheric water vapour inventory. Thin liquid film thicknesses on/in subsurface ice were investigated via two scenarios: (i) under the idealistic case where it is asswncd that the diurnal thermal wave is equal to the temperature of icc tens of centimetres below the surface, allowing for such icc to experience temperatures close to 273 K and (ii) under the, likely, realistic scenario where the diurnal thermal wave allows for the maximum subsurface ice temperature of 235 Kat I m depth between 30°N and 30°S. Scenario I yields thin liquid film thicknesses ranging from II to 90 nm: these amounts represent 4 x I 0 6 3.0 x I 0 7 litres of water. For pure water ice, Sce nario 2 reveals that the thickness of thin liquid films contained on/within Martian subsurface is less than 1.2 nm , several molecular layers thick. Conversely, via Lhc cfTect of impurities a t 235 K a llows for a thin liquid film thickness on/within subsurface icc of 0.5 nm , corresponding to 6.0 x I 0 4 litrcs of water. The existence of thin films on Mars is supported by data from the Mars Exploration Rovers (MERs) Spirit and Opportunity's Alpha Proton X-ray Spectrometer instrumentation. which have detected increased levels of brom...

New insights into martian atmospheric chemistry

“…At present, finding life on Mars may not be limited by essential life nutrients, such as water and nitrogen (Boxe et al, 2012a;Boxe et al, 2012b). It's atmosphere is comprised primarily of carbon dioxide (Owen, 1977), approximately ~ 95%, which is readily photolyzed by solar ultraviolet radiation below 205 nm to produce carbon monoxide (CO) , respectively, and a CO:O 2 ratio of 2:1, which is in contradiction to the observed mixing ratios (7.0 × 10 -4 for CO and 1.3 × 10 -3 for O 2 ) and ratio of 0.5 (Yung and Demore, 1999).…”

Possibility of H2O2 decomposition in thin liquid films on Mars

“…In this work we overviewed how liquid water, among them the most probable existing candidate: thin interfacial liquid water (Möhmann, 2004(Möhmann, , 2008Boxe et al, 2012;Kereszturi and RiveraValentin, 2012), could influence the stability, and possible decomposition of H 2 O 2 . Comparing the possible pathways, under the present conditions thermal driven decomposition might be too slow, and theoretical computations suggest the chemical ingredients in these thin liquid layers might play a stronger role on the decomposition process of H 2 O 2 than those temperature values, which are expected in the Amazonian period.…”

“…While the analysis of bulk melting point decreasing the effect of various salts has been extensively analyzed under simulated Martian conditions (Haberle et al, 2001a(Haberle et al, , 2001bBurt and Knauth, 2003;Zent et al, 1990), few detailed laboratory measurements have been realized about the role of solved salts on the thickness of interfacial liquid water below ice. Based on the estimation of Boxe et al (2012) the effect of solved impurities at 235 K produces thickness in liquid layers up to 0.5 nm, which is more than one monolayer, while based on Kossacki and Markiewicz (2010) calculations around 200 K under favorable conditions up to 3 monolayers of H 2 O molecule could exist. These calculations suggest more than one monolayer could be present under ideal case today, and there could be an even thicker liquid layer if one takes into account the different climatic conditions in the past.…”

“…Because of the changes in the orbital tilt of Mars (Mellon, 1999;Rubincam, 1990), water ice might have in the past different spatial and temporal distribution than today (Kanner et al, 2004;Haberle et al, 2003), and the solar insulation could also be modified (Yokohata et al, 2002) during this period. Our basic assumption is the conditions that are present today are characteristic for a substantial part of the Amazonian period (Golombek et al, 2006;Fastook et al, 2011), but occasionally more favorable conditions for the existence of liquid interfacial water might appear (Boxe et al, 2012;Burr et al, 2012;. Beside theoretical argumentation (Zent, 2006) the observed soluble materials (Kounaves et al, 2010;Kounaves et al, 2006) and salt distribution (Cull et al, 2010) at the Phoenix landing site is also compatible with the appearance of occasionally thicker water layer that could trigger chemical reactions.…”

“…Oxidants are also invoked as important players in the chemical processes on the Martian surface (Zent, 1998;Chevrier and Mathé, 2007;Davila et al, 2008). This oxidant could be decomposed in bulk (macroscopic) liquid water, but the current conditions on the Martian surface for the appearance of such bulk liquid are unfavorable, although there are models or observations (Boxe et al, 2012;Clow, 1987;Haberle et al, 2001aHaberle et al, , 2001bHecht, 2002;Rennó et al, 2009aRennó et al, , 2009bMöhlmann, 2004Möhlmann, , 2008Möhlmann and Kereszturi, 2010;Kossacki et al, 2004;Martinez et al, 2013) that suggest under special conditions it might be present ephemerally.…”