Using MARSIS signal attenuation to assess the presence of South Polar Layered Deposit subglacial brines.

Knowledge of the physical and thermal properties of the South Polar Layer Deposits (SPLD) is key to constrain the source of bright basal reflections at Ultimi Scopuli detected by the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) radar sounder. Here we present a detailed analysis of attenuation, based on data acquired by MARSIS at 3, 4, and 5 MHz. We show that attenuation is frequency dependent, and that its behavior is consistent throughout the entire region. This suggests that the SPLD are compositionally homogeneous at Ultimi Scopuli, and our results are consistent with dust contents of 5 to 12%. Using these values as input, and plausible estimates of surface temperature and heat flux, we inferred basal temperatures around 200 K: these are consistent with perchlorate brines within liquid vein networks as the source of the reflections. Furthermore, extrapolation of the attenuation to higher frequencies explains why SHARAD (Shallow Radar) has thus far not detected basal reflections within the SPLD at Ultimi Scopuli.

Constraining the Potential Liquid Water Environment at Gale Crater, Mars.

The Mars Science Laboratory (MSL) Rover Environmental Monitoring Station (REMS) has now made continuous in situ meteorological measurements for several Martian years at Gale crater, Mars. Of importance in the search for liquid formation are REMS' measurements of ground temperature and in-air measurements of temperature and relative humidity, which is with respect to ice. Such data can constrain the surface and subsurface stability of brines. Here we use updated calibrations to REMS data and consistent relative humidity comparisons (i.e., with respect to liquid versus with respect to ice) to investigate the potential formation of surface and subsurface liquids throughout MSL's traverse. We specifically study the potential for the deliquescence of calcium perchlorate. Our data analysis suggests that surface brine formation is not favored within the first 1648 sols as there are only two times (sols 1232 and 1311) when humidity-temperature conditions were within error consistent with a liquid phase. On the other hand, modeling of the subsurface environment would support brine production in the shallow subsurface. Indeed, we find that the shallow subsurface for terrains with low thermal inertia (Γ â‰² 300 J m-2 K-1 s-1/2) may be occasionally favorable to brine formation through deliquescence. Terrains with Γ â‰² 175 J m-2 K-1 s-1/2 and albedos of ≳0.25 are the most apt to subsurface brine formation. Should brines form, they would occur around Ls 100°. Their predicted properties would not meet the Special nor Uncertain Region requirements, as such they would not be potential habitable environments to life as we know it.

Solute-solvent halogen bonding during adsorption on silver nanostructures.

We offer here evidence for halogen bonding induced by silver nanoparticles (SNPs) in a multilayer containing 4-iodobenzoate ion (4IBI) and CCl(4). SERS experiments show in the monolayer that CCl(4) does not adsorb and 4-iodobenzoic acid (4IBA) adsorbs as 4IBI. SEIRA experiments reveal that 4IBI forms in the multilayer during deposition from CCl(4) on SNPs. Further infrared experiments on clean BaF(2) prove that 4IBI formation caused by underlying SNPs was necessary for CCl(4) inclusion in a 4IBI multilayer. Several potential scenarios involving intermolecular attraction between CCl(4) and 4IBI are proposed to explain the results. Although halogen bonding involving solvents has been theoretically and experimentally demonstrated in solution phase chemistry, in bulk crystals, and at the monolayer level, here it is shown that halogen bonding interactions can also be significant in multilayer films. Results from this work will likely impact a range of applications across diverse fields where halogen bonding in thin films and nucleation chemistry are important.