The formation of sulfate, nitrate and perchlorate salts in the martian atmosphere

Funding: 2011 NAI Director’s Discretionary Fund award titled ‘‘Perchlorate, Water, and Life’’, along with a NASA postdoctoral program award to work at the Virtual Planetary Laboratory.In extremely arid regions on Earth, such as the Atacama Desert, nitrate, sulfate and perchlorate salts form in the atmosphere and accumulate on the surface from dry deposition according to diagnostic evidence in their oxygen isotopes. Salts of similar oxyanions should have formed in the atmosphere of Mars because of comparable photochemical reactions. We use a 1-D photochemical model to calculate the deposition rates of sulfate, nitrogen oxyanions, and perchlorate from Mars' atmosphere, given a plausible range of volcanic fluxes of sulfur- and chlorine-containing gases in the past. To calculate integrated fluxes over time, we assume that throughout the last 3. byr (the Amazonian eon), the typical background atmosphere would have been similar to today's cold and dry environment. If the soil has been mixed by impact perturbations to a characteristic depth of ~2. m during this time, given a time-average volcanic flux 0.1% of the modern terrestrial volcanic flux, the model suggests that the soil would have accumulated 1.0-1.7. wt.% SO42- and 0.2-0.4. wt.% N in the form of pernitrate (peroxynitrate) or nitrate. The calculated sulfate concentration is consistent with in situ observations of soils from rovers and landers and orbital gamma ray spectroscopy. However, nitrates or pernitrates are yet to be detected. The modeled formation of perchlorate via purely gas-phase oxidation of volcanically-derived chlorine is insufficient by orders of magnitude to explain 0.4-0.6. wt.% ClO4- measured by NASA's Phoenix Lander. The far smaller amount of ozone in the martian atmosphere compared to the terrestrial atmosphere and the colder, drier conditions are the cause of lower rates of gas phase oxidation of chlorine volatiles to perchloric acid. Our calculations imply that non-gas-phase processes not included in the photochemical model, such as heterogeneous reactions, are likely important for the formation of perchlorate and are yet to be identified.Publisher PDFPeer reviewe

Consequences of Giant Impacts on Early Uranus for Rotation, Internal Structure, Debris, and Atmospheric Erosion

We perform a suite of smoothed particle hydrodynamics simulations to investigate in detail the results of a giant impact on the young Uranus. We study the internal structure, rotation rate, and atmospheric retention of the post-impact planet, as well as the composition of material ejected into orbit. Most of the material from the impactor's rocky core falls in to the core of the target. However, for higher angular momentum impacts, significant amounts become embedded anisotropically as lumps in the ice layer. Furthermore, most of the impactor's ice and energy is deposited in a hot, high-entropy shell at a radius of ~3 R ⊕. This could explain Uranus' observed lack of heat flow from the interior and be relevant for understanding its asymmetric magnetic field. We verify the results from the single previous study of lower resolution simulations that an impactor with a mass of at least 2 M ⊕ can produce sufficiently rapid rotation in the post-impact Uranus for a range of angular momenta. At least 90% of the atmosphere remains bound to the final planet after the collision, but over half can be ejected beyond the Roche radius by a 2 or 3 M ⊕ impactor. This atmospheric erosion peaks for intermediate impactor angular momenta (~3 × 1036 kg m2 s−1). Rock is more efficiently placed into orbit and made available for satellite formation by 2 M ⊕ impactors than 3 M ⊕ ones, because it requires tidal disruption that is suppressed by the more massive impactors

Topographic, spectral and thermal inertia analysis of interior layered deposits in Iani Chaos, Mars

We present an analysis of Interior Layered Deposits (ILDs) in Iani Chaos using visible, infrared, hyperspectral and topographic datasets acquired by instruments aboard NASA’s Mars Global Surveyor, Mars Odyssey, Mars Reconnaissance Orbiter and ESA’s Mars Express spacecraft. We focus on four main regions where ILDs outcrop in Iani Chaos. Deposits span a ∼2 km range of elevations and exhibit moderate to high albedos, layering at sub-decameter scales, thermal inertias of 300–800 J m−2 K−1 s−1/2 and a range of surface textures. Thermal inertia calculations use slope and azimuth corrections from High Resolution Stereo Camera (HRSC) topography. Spectral features in hyperspectral data acquired by NASA’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) suggest that gypsum (CaSO4·2H2O) and kieserite (MgSO4·H2O) are present in most deposits. We report absorptions typically exhibited by alunite (KAl3(SO4)2(OH)6) and jarosite View the MathML sourceKFe33+(OH)6(SO4)2 as well as a number of features that may be attributable to a wide range of mono- and polyhydrated sulphates and hydroxyl-sulphates bearing a number of cations, including Mg2+, Fe2+, Fe3+ and Ca2+. Spectral features similar to those of ammonium sulphates may also be present. Analysis of a HiRISE stereo DEM shows planar layering in some ILDs, favouring a sedimentary deposition origin. Stratigraphic mapping of hydration and sulphate spectral features in flat ILDs in central Iani Chaos suggest that specific elevation intervals in the stratigraphic column were subject to different levels of hydration, perhaps during episodes of water table elevation. This is consistent with formation models for ILDs and hydrological modelling. Geomorphic characteristics of deposits in northern and southern Iani Chaos suggest their relatively recent exhumation and significant erosion by aeolian processes. We conclude that any formation theory for ILDs in Iani Chaos should support mechanisms for different hydration states at different stratigraphic elevations and subsequent significant aeolian erosion, burial and re-exposure

A Pre-Landing Assessment of Regolith Properties at the InSight Landing Site

This article discusses relevant physical properties of the regolith at the Mars InSight landing site as understood prior to landing of the spacecraft. InSight will land in the northern lowland plains of Mars, close to the equator, where the regolith is estimated to be ≥3--5 m thick. These investigations of physical properties have relied on data collected from Mars orbital measurements, previously collected lander and rover data, results of studies of data and samples from Apollo lunar missions, laboratory measurements on regolith simulants, and theoretical studies. The investigations include changes in properties with depth and temperature. Mechanical properties investigated include density, grain-size distribution, cohesion, and angle of internal friction. Thermophysical properties include thermal inertia, surface emissivity and albedo, thermal conductivity and diffusivity, and specific heat. Regolith elastic properties not only include parameters that control seismic wave velocities in the immediate vicinity of the Insight lander but also coupling of the lander and other potential noise sources to the InSight broadband seismometer. The related properties include Poisson’s ratio, P- and S-wave velocities, Young’s modulus, and seismic attenuation. Finally, mass diffusivity was investigated to estimate gas movements in the regolith driven by atmospheric pressure changes. Physical properties presented here are all to some degree speculative. However, they form a basis for interpretation of the early data to be returned from the InSight mission.Additional co-authors: Nick Teanby and Sharon Keda

Meteorological measurement on the surface of Mars

SIGLEAvailable from British Library Document Supply Centre- DSC:D185295 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Ultraviolet radiation on the surface of Mars and the Beagle 2 UV sensor

In this paper a simple radiative transfer model for the transmission of UV to the surface of Mars is presented for the wavelength range 190–410 nm. The model accounts for the variable presence of dust aerosols in the martian atmosphere and its effects upon direct and diffuse irradiance. A range of situations is presented, including variations in orbital position, latitude, time of day, dust loading and ozone presence. High dust loading is seen to have an inverting effect on direct/diffuse transmission ratios, with a significant amount of illumination still being provided even at high optical depths typical of dust storms. Diffuse transmission is also observed as the primary component close to sunrise and sunset as expected. An ozone absorption feature is seen for high-latitude northern winter cases, offering limited shielding centred around 250 nm in the biologically damaging region of the UV spectrum. The use of the model is then discussed in the role of designing and developing the Beagle 2 UV sensor, an instrument to measure the surface UV flux between 200 and 400 nm and set to land on the surface of Mars in 2003. The model is used to determine flux levels and spectral regions of particular interest, leading to a detailed instrument design and specification

Hematitic concretions at Meridiani Planum, Mars: their growth timescale and possible relationship with iron sulfates

Using diffusion-based models for concretion growth, we calculate growth times of hematitic concretions that have been found in the Burns formation at Meridiani Planum, Mars, by NASA's Opportunity Mars Exploration Rover. Growth times of ~ 350–1900 terrestrial years are obtained for the observed size range of the concretions over a range of parameters representing likely diagenetic conditions and allowing for an iron source from diagenetic redistribution. This time scale is consistent with radiometric age constraints for the growth time of iron oxide concretions in sandy sediments of the acid-saline Lake Brown in Western Australia (< 3000 yr) reported elsewhere. We consider the source of the iron for Meridiani concretions by calculating the constraints on the supply of Fe3+ to growing concretions from the dissolution and oxidation rates of iron minerals on early Mars. Mass balance arguments suggest that acid dissolution of jarosite ((H3O,K)(Fe3+3(OH)6(SO4)2) and minor ferric sulfates is probably the most plausible dominant contributor to Fe3+ in the concretions. Ferrous iron released from melanterite (Fe2+SO4·7H2O) that is subsequently oxidized could also have been an important iron source if melanterite existed prior to diagenesis. Our conclusion that the iron is sourced from iron sulfates may explain the global observation from orbiters that grey crystalline hematite occurs in association with sulfate deposits