Seasonal H₂O and CO₂ ice cycles at the Mars Phoenix landing site: 1. Prelanding CRISM and HiRISE observations

Abstract

[1] The condensation, evolution, and sublimation of seasonal water and carbon dioxide ices were characterized at the Mars Phoenix landing site from Martian northern midsummer to midspring (L s ∼ 142°-L s ∼ 60°) for the year prior to the Phoenix landing on 25 May 2008. Ice relative abundances and grain sizes were estimated using data from the Compact Reconnaissance Imaging Spectrometer for Mars and High Resolution Imaging Science Experiment aboard Mars Reconnaissance Orbiter and a nonlinear mixing model. Water ice first appeared at the Phoenix landing site during the afternoon in late summer (L s ∼ 167°) as an optically thin layer on top of soil. CO 2 ice appeared after the fall equinox. By late winter (L s ∼ 344°), the site was covered by relatively pure CO 2 ice (∼30 cm thick), with a small amount of ∼100 mm diameter water ice and soil. As spring progressed, CO 2 ice grain sizes gradually decreased, a change interpreted to result from granulation during sublimation losses. The combined effect of CO 2 sublimation and decreasing H 2 O ice grain sizes allowed H 2 O ice to dominate spectra during the spring and significantly brightened the surface. CO 2 ice disappeared by early spring (L s ∼ 34°) and H 2 O ice by midspring (L s ∼ 59°). Spring defrosting was not uniform and occurred more rapidly over the centers of polygons and geomorphic units with relatively higher thermal inertia values.

Detection of oxygen isotopic anomaly in terrestrial atmospheric carbonates and its implications to Mars

“…The production of anomalous carbonates on Mars likely occurs via multiple pathways: (i) MIF (mass independently fractionated) CO 2 production in the atmosphere and its interaction with aqueous solutions to form mineral evaporites and (ii) surfical peroxide-mediated process involving interaction of O 3 and CO 2 with adsorbed water similar to the mechanisms suggested for terrestrial atmospheric carbonate formation. The combination of ground observations from the Mars Phoenix Lander and orbital data from the CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) and High Resolution Imaging Science Experiment indicated mixture of soil particles (∼100 μm) covered with CO 2 ice and water (4,59), an appropriate mixture for in situ carbonate formation. It is possible that heterogeneous chemical transformations may occur on aerosol particles during Martian dust events in the presence of water and ozone, as we observe in this work, providing an alternate route to carbonate formation.…”

“…The uptake of ozone at the hydrated calcite surface is a multistep process consisting of (i) gas phase diffusion of the O 3 molecules to the liquid interface, (ii) transfer across the interface, (iii) diffusion and reaction with water in the condensed phase, and (iv) diffusion out and desorption of the residual reaction products. Isotopically anomalous hydrogen peroxide formation via dissociation of O 3 (1a-1c) transfers the isotopic signature in the hydration layer, which in turn transfers the isotopic anomaly to the carbonates (2)(3)(4) …”

“…Central to the question of potential life on Mars is whether liquid water ever existed on the surface of Mars and, if so, under what climatic conditions (2). Apart from satellite observations of valleys and channels formed by aqueous activity, there are few quantitative measures (e.g., Thermal and Electrical Conductivity probe on Phoenix Lander; Compact Reconnaissance Imaging Spectrometer for Mars; High Energy Neutron Detector on board Mars Odyssey spacecraft) of significant amounts of liquid water at the surface of Mars today (3)(4)(5). Secondary minerals such as carbonates and sulfates record physicalchemical settings of the environment in which they are formed and geochemical relations between the atmosphere and the Martian surface (6).…”

Observations of the northern seasonal polar cap on Mars II: HiRISE photometric analysis of evolution of northern polar dunes in spring

“…Most of volatile deposition happens during dark winter season which makes it extremely hard to observe with passive remote sensing instruments. Some estimations of bulk proportions of H 2 O to CO 2 ices come from the earliest spring observations by spectrometers and are within 0.1 wt.% (Cull et al, 2010;Appere et al, 2011). This number however is expected to vary depending on the location inside the cap.…”

Concentrated perchlorate at the Mars Phoenix landing site: Evidence for thin film liquid water on Mars

“…An alternative redistribution mechanism involves seasonal ices. The Phoenix site is covered in early fall by an ∼90 micrometer layer of seasonal H 2 O ice, which is then topped in winter by a translucent slab of CO 2 ice that reaches ∼30 cm thick [Cull et al, 2010]. At the base of the translucent CO 2 slab, a solid greenhouse effect can increase the temperature at the ice-surface interface, a process that Kieffer et al [2000] proposed could be responsible for southern hemisphere "spider" features.…”