Validation of martian meteorological data assimilation for MGS/TES using radio occultation measurements

We describe an assimilation of thermal profiles below about 40 km altitude and total dust opacities into a general circulation model (GCM) of the martian atmosphere. The data were provided by the Thermal Emission Spectrometer (TES) on board the Mars Global Surveyor (MGS) spacecraft. The results of the assimilation are verified against an independent source of contemporaneous data represented by radio occultation measurements with an ultra-stable radio oscillator, also aboard MGS. This paper describes a comparison between temperature profiles retrieved by the radio occultation experiments and the corresponding profiles given by both an independent, carefully tuned GCM simulation and by an assimilation of TES observations performed over the period of time from middle, northern summer in martian year 24, corresponding to May 1999, until late, northern spring in martian year 27, corresponding to August 2004. This study shows that the assimilation of TES measurements improves the overall agreement between radio occultation observations and the GCM analysis, in particular below 20 km altitude, where the radio occultation measurements are known to be most accurate. Discrepancies still remain, mostly during the global dust storm of year 2001 and at latitudes around 60° N in northern winter-early spring. These are the periods of time and locations, however, for which discrepancies between TES and radio occultation profiles are also shown to be the largest. Finally, a further direct validation is performed, comparing stationary waves at selected latitudes and time of year. Apart from biases at high latitudes in winter time, data assimilation is able to represent the correct wave behaviour, which is one major objective for martian assimilation.     

Water-ice clouds and dust in the north polar region of Mars using MGS TES data

Water-ice and dust optical depths in Mars’ north polar region are mapped as function of season, latitude and longitude, and their characteristics and variability on a geographic, seasonal, and interannual basis are discussed. We use water-ice and dust optical depth data provided by the Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES), covering nearly three northern spring and summer periods. We find that interannual variability exists in both the water ice and dust behavior, although there are trends that repeat year to year as well. The optical thickness of the north polar hood (NPH) exhibits interannually varying longitudinal structure, both during springtime recession and late-summer onset. We define the characteristics associated with the transition to and from the NPH and find that the disappearance occurs near L_s=75° and the reappearance near L_s=160-165°. We find that the late spring to early summer time frame is characterized by very low water-ice optical depths and enhanced dust activity, with a preference for lower water-ice and higher dust optical depths in the 0-90°W quadrant. We see possible evidence for stationary wavenumber 2 systems in a few of the maps examined.     

Constraining the source regions of lunar meteorites using orbital geochemical data

Lunar meteorites provide important new samples of the Moon remote from regions visited by the Apollo and Luna sample return missions. Petrologic and geochemical analysis of these meteorites, combined with orbital remote sensing measurements, have enabled additional discoveries about the composition and age of the lunar surface on a global scale. However, the interpretation of these samples is limited by the fact that we do not know the source region of any individual lunar meteorite. Here, we investigate the link between meteorite and source region on the Moon using the Lunar Prospector gamma ray spectrometer remote sensing data set for the elements Fe, Ti, and Th. The approach has been validated using Apollo and Luna bulk regolith samples, and we have applied it to 48 meteorites excluding paired stones. Our approach is able broadly to differentiate the best compositional matches as potential regions of origin for the various classes of lunar meteorites. Basaltic and intermediate Fe regolith breccia meteorites are found to have the best constrained potential launch sites, with some impact breccias and pristine mare basalts also having reasonably well‐defined potential source regions. Launch areas for highland feldspathic meteorites are much less well constrained and the addition of another element, such as Mg, will probably be required to identify potential source regions for these.     

Extension of atmospheric dust loading to high altitudes during the 2001 Mars dust storm: MGS TES limb observations

Mars Global Surveyor (MGS) visible (solarband bolometer) and thermal infrared (IR) spectral limb observations from the Thermal Emission Spectrometer (TES) support quantitative profile retrievals for dust opacity and particle sizes during the 2001 global dust event on Mars. The current analysis considers the behavior of dust lifted to altitudes above 30 km during the course of this storm; in terms of dust vertical mixing, particle sizes, and global distribution. TES global maps of visible (solarband) limb brightness at 60 km altitude indicate a global-scale, seasonally evolving (over 190-240° solar longitudes, L_S) longitudinal corridor of vertically extended dust loading (which may be associated with a retrograde propagating, wavenumber 1 Rossby wave). Spherical radiative transfer analysis of selected limb profiles for TES visible and thermal IR radiances provide quantitative vertical profiles of dust opacity, indicating regional conditions of altitude-increasing dust mixing ratios. Observed infrared spectral dependences and visible-to-infrared opacity ratios of dust scattering over 30-60 km altitudes indicate particle sizes characteristic of lower altitudes (cross-section weighted effective radius, ), during conditions of significant dust transport to these altitudes. Conditions of reduced dust loading at 30-60 km altitudes present smaller dust particle sizes . These observations suggest rapid meridional transport at 30-80 km altitudes, with substantial longitudinal variation, of dust lifted to these altitudes over southern hemisphere atmospheric regions characterized by extraordinary (m/s) vertical advection velocities. By L_S=230° dust loading above 50 km altitudes decreased markedly at southern latitudes, with a high altitude (60-80 km) haze of fine (likely) water ice particles appearing over 10°S-40°N latitudes.     

Magnitude of global contraction on Mars from analysis of surface faults: Implications for martian thermal history

Faults provide a record of a planet’s crustal stress state and interior dynamics, including volumetric changes related to long-term cooling. Previous work has suggested that Mars experienced a pulse of large-scale global contraction during Hesperian time. Here we evaluate the evidence for martian global contraction using a recent compilation of thrust faults. Fault-related strains were calculated for wrinkle ridges and lobate scarps to provide lower and upper bounds, respectively, on the magnitude of global contraction from contractional structures observed on the surface of Mars. During the hypothesized pulse of global contraction, contractional strain of −0.007% to −0.13% is indicated by the structures, corresponding to decreases in planetary radius of 112 m to 2.24 km, respectively. By contrast, consideration of all recognized thrust faults regardless of age produces a globally averaged contractional strain of −0.011% to −0.22%, corresponding to a radius decrease of 188 m to 3.77 km since the Early Noachian. The amount of global contraction predicted by thermal models is larger than what is recorded by the faults at the surface, paralleling similar studies for Mercury and the Moon, which suggests that observations of fault populations at the surface may provide tighter bounds on planetary thermal evolution than models alone.     

Spectral reflectance of Martian meteorites: Spectral signatures as a template for locating source region on Mars

Abstract— We report the spectral reflectance of Martian meteorites from 0.3‐2.6 microns for the purpose of cataloguing spectra and the association of their spectral properties with mineralogy and petrology. We fit the spectra to a series of overlapping, modified Gaussian absorptions using least squares fitting. The results are validated against established relationships between photon interactions with mineral chemistry and the band parameters. These resultant band parameters can be used to constrain interpretations of Martian reflectance spectra in the search for the source region of meteorites from Mars. The limitations of the fitting method are discussed.     

Observations of the north polar water ice annulus on Mars using THEMIS and TES

The Martian seasonal CO₂ ice caps advance and retreat each year. In the spring, as the CO₂ cap gradually retreats, it leaves behind an extensive defrosting zone from the solid CO₂ cap to the location where all CO₂ frost has sublimated. We have been studying this phenomenon in the north polar region using data from the THermal EMission Imaging System (THEMIS), a visible and infra-red (IR) camera on the Mars Odyssey spacecraft, and the Thermal Emission Spectrometer (TES) on Mars Global Surveyor. Recently, we discovered that some THEMIS images of the CO₂ defrosting zone contain evidence for a distinct defrosting phenomenon: some areas just south of the CO₂ cap edge are too bright in visible wavelengths to be defrosted terrain, but too warm in the IR to be CO₂ ice. We hypothesize that we are seeing evidence for a seasonal annulus of water ice (frost) that recedes with the seasonal CO₂ cap, as predicted by previous workers. In this paper, we describe our observations with THEMIS and compare them to simultaneous observations by TES and OMEGA. All three instruments find that this phenomenon is distinct from the CO₂ cap and most likely composed of water ice. We also find strong evidence that the annulus widens as it recedes. Finally, we show that this annulus can be detected in the raw THEMIS data as it is collected, enabling future long-term onboard monitoring.     

Methane evolution from UV-irradiated spacecraft materials under simulated martian conditions: Implications for the Mars Science Laboratory (MSL) mission

Fifteen organic and three inorganic compounds were tested for methane (CH₄) evolution under simulated martian conditions of 6.9 mbar; UVC (200-280 nm) flux of 4 W m⁻²; 20 °C; simulated optical depth of 0.1; and a Mars gas composition of CO₂ (95.3%), N₂ (2.7%), Ar (1.7%), O₂ (0.13%), and water vapor (0.03%). All three inorganic compounds (i.e., NaCl, CaCO₃, graphite) failed to evolve methane at the minimum detection level 0.5 ppm, or above. In contrast, all organic compounds evolved methane when exposed to UV irradiation under simulated martian conditions. The polycyclic aromatic hydrocarbon, pyrene, released the most methane per unit of time at 0.175 nmol CH₄ g⁻¹ h⁻¹, and a spectral reflectance target material used for the MER rovers and Phoenix lander released the least methane at 0.00065 nmol CH₄ cm⁻² h⁻¹. Methane was also released from UV-killed bacterial endospores of Bacillus subtilis. Although all organic compounds evolved methane when irradiated with UV photons under martian conditions, the concentrations of residual organics, biogenic signature molecules, and dead microbial cells should be relatively low on the exterior surfaces of the MSL rover, and, thus, not significant sources of methane contamination. In contrast, kapton tape was found to evolve methane at the rate of 0.00165 nmol CH₄ cm⁻² h⁻¹ (16.5 nmol m⁻² h⁻¹) under the UV and martian conditions tested. Although the evolution of methane from kapton tape was found to decline over time, the large amount of kapton tape used on the MSL rover (lower bound estimated at 3 m²) is likely to create a significant source of terrestrial methane contamination during the early part of the mission.     

Spatial inhomogeneity of the martian subsurface water distribution: implication from a global water cycle model

In an effort to test and to understand the global hydrogen distribution in the shallow subsurface of Mars retrieved by the Mars Odyssey gamma-ray spectrometer, the present state and movement of water are investigated by a coupled global subsurface-atmosphere water cycle model. It was found that the observed global subsurface hydrogen distribution is largely consistent with the modeled global water cycle, so a large fraction of hydrogen is likely to exist as water, at low and mid latitudes in the form of adsorbed water. Under the present climate the water content in the shallow subsurface becomes higher in the northern hemisphere than in the southern hemisphere as a result of global water cycle, regardless of the initial water distribution in the soil or adsorptive capacity. The higher annual maximum soil temperature in the south, stronger net northward transport of atmospheric water vapor, and the emission of vapor from the northern residual polar cap in northern summer contribute to this hemispheric asymmetry. The generally higher adsorptive capacity of clay minerals in the northern plains may further increase this bias. The longitudinal inhomogeneity is caused by several factors, such as thermal inertia, adsorptive capacity, and atmospheric surface pressure. The water abundance is locally high in low thermal inertia regions (e.g., Arabia Terra) and at deep places where the surface pressure is high (e.g., Hellas); it is low in soil with a low adsorptive capacity (e.g., Tharsis) and high thermal inertia regions (e.g., Solis Planum). Most of the soil humidity near the surface at low and mid latitudes may originate from the atmosphere. The model implies that the upper soil layer should be largely ice-free because otherwise an excessive sublimation and vapor emission into the atmosphere in warm seasons would violate the observational constraints. Moreover, the more uniform latitudinal variation of the observed hydrogen abundance near the surface compared to that of deeper layers is indicative of the presence of adsorbed water instead of ground ice because the adsorbed water content does not as steeply depend on latitude as the ground ice stability. Concerning the regolith mineralogy, montmorillonite can much better account for the observed water cycle than palagonite. While the presence of permanent ground ice appears likely in the polar region below a thin layer, large seasonal cycle of phase change between pore ice and adsorbed water may be possible. Regolith adsorption/desorption is neither negligible nor crucial for the seasonal atmospheric water cycle, but the surface-atmosphere coupling is a major prerequisite for the long-term evolution of subsurface water distribution.     

Linking the Chassigny meteorite and the Martian surface rock Backstay: Insights into igneous crustal differentiation processes on Mars

Abstract— In order to use igneous surface lithologies to constrain Martian mantle characteristics, secondary processes that lead to compositional modification of primary mantle melts must be considered. Crystal fractionation of a mantle‐derived magma at the base of the crust followed by separation and ascent of residual liquids to the surface is common in continental hotspot regions on Earth. The possibility that this process also takes place on Mars was investigated by experimentally determining whether a surface rock, specifically the hawaiite Backstay analyzed by the MER Spirit could produce a known cumulate lithology with a deep origin (namely the assemblages of the Chassigny meteorite) if trapped at the base of the Martian crust. Both the major cumulus and melt inclusion mineral assemblages of the Chassigny meteorite were produced experimentally by a liquid of Backstay composition within the pressure range 9.3 to 6.8 kbar with bulk water contents between 1.5 and 2.6 wt%. Experiments at 4.3 and 2.8 kbar did not produce the requisite assemblages. This agreement suggests that just as on Earth, Martian mantle‐derived melts may rise to the surface or remain trapped at the base of the crust, fractionate, and lose their residual liquids. Efficient removal of these residual liquids at depth would yield a deep low‐silica cumulate layer for higher magmatic water content; at lower magmatic water content this cumulate layer would be basaltic with shergottitic affinity.     

Alteration assemblages in the Miller Range and Elephant Moraine regions of Antarctica: Comparisons between terrestrial igneous rocks and Martian meteorites

The weathering products present in igneous terrestrial Antarctic samples were analyzed, and compared with those found in the four Miller Range nakhlite Martian meteorites. The aim of these comparisons was to determine which of the alteration phases in the Miller Range nakhlites are produced by terrestrial weathering, and what effect rock composition has on these phases. Antarctic terrestrial samples MIL 05031 and EET 96400, along with the Miller Range nakhlites MIL 03346 and 090032, were found to contain secondary alteration assemblages at their externally exposed surfaces. Despite the difference in primary mineralogy, the assemblages of these rocks consist mostly of sulfates (jarosite in MIL 05031, jarosite and gypsum in EET 96400) and iddingsite‐like Fe‐clay. As neither of the terrestrial samples contains sulfur‐bearing primary minerals, and these minerals are rare in the Miller Range nakhlites, it appears that SO₄^2?, possibly along with some of the Na⁺, K⁺, and Ca⁺ in these phases, was sourced from wind‐blown sea spray and biogenic emissions from the southern ocean. Cl enrichment in the terrestrially derived “iddingsite” of MIL 05031 and MIL 03346, and the presence of halite at the exterior edge of MIL 090032, can also be explained by this process. However, jarosite within and around the olivine‐bound melt inclusions of MIL 090136 is present in the interior of the meteorite and, therefore, is probably the product of preterrestrial weathering on Mars.     

Ages of rampart craters in equatorial regions on Mars: Implications for the past and present distribution of ground ice

Abstract— We are testing the idea of Squyres et al. (1992) that rampart craters on Mars may have formed over a significant time period and therefore the onset diameter (minimum diameter of a rampart crater) only reflects the ground ice depth at a given time. We measured crater size frequencies on the layered ejecta of rampart craters in three equatorial regions to derive absolute model ages and to constrain the regional volatile history. Nearly all rampart craters in the Xanthe Terra region are ?3.8 Gyr old. This corresponds to the Noachian fluvial activity that region. Rampart crater formation declines in the Hesperian, whereas onset diameters (minimum diameter) increase. No new rampart craters formed after the end of the Hesperian (?3 Gyr). This indicates a lowering of the ground ice table with time in the Xanthe Terra region. Most rampart craters in the Valles Marineris region are around 3.6 Gyr old. Only one large, probably Amazonian‐aged (?2.5 Gyr), rampart crater exists. These ages indicate a volatile‐rich period in the Early Hesperian and a lowering of the ground ice table with time in the Valles Marineris study region. Rampart craters in southern Chryse Planitia, which are partly eroded by fluvial activity, show ages around 3.9 Gyr. Rampart craters superposed on channels have ages between ?1.5 and ?0.6 Gyr. The onset diameter (3 km at ?1.5 Gyr) in this region may indicate a relatively shallow ground ice table. Loss of volatiles due to diffusion and sublimation might have lowered the ground ice table even in the southern Chryse Planitia region afterwards. In general, our study implies a formation of the smallest rampart craters within and/or shortly after periods of fluvial activity and a subsequent lowering of the ground ice table indicated by increasing onset diameter to the present. These results question the method to derive present equatorial ground ice depths from the onset diameter of rampart craters without information about their formation time.     

Testing the survival of microfossils in artificial martian sedimentary meteorites during entry into Earth’s atmosphere: The STONE 6 experiment

If life ever appeared on Mars, could we find traces of primitive life embedded in sedimentary meteorites? To answer this question, a 3.5-byr-old volcanic sediment containing microfossils was embedded in the heat shield of a space capsule in order to test survival of the rock and the microfossils during entry into the Earth’s atmosphere (the STONE 6 experiment). The silicified volcanic sediment from the Kitty’s Gap Chert (Pilbara, Australia) is considered to be an excellent analogue for Noachian-age volcanic sediments. The microfossils in the chert are also analogues for potential martian life. An additional goal was to investigate the survival of living microorganisms (Chroococcidiopsis) protected by a 2-cm thick layer of rock in order to test whether living endolithic organisms could survive atmospheric entry when protected by a rocky coating.Mineralogical alteration of the sediment due to shock heating was manifested by the formation of a fusion crust, cracks in the chert due to prograde and retrograde changes of α quartz to β quartz, increase in the size of the fluid inclusions, and dewatering of the hydromuscovite-replaced volcanic protoliths. The carbonaceous microfossils embedded in the chert matrix survived in the rock away from the fusion crust but there was an increase in the maturity index of the kerogen towards the crust. We conclude that this kind of sediment can survive atmospheric entry and, if it contains microfossils, they could also survive. The living microorganisms were, however, completely carbonised by flame leakage to the back of the sample and therefore non-viable. However, using an analytical model to estimate the temperature reached within the sample thickness, we conclude that, even without flame leakage, the living organisms probably need to be protected by at least 5 cm of rock in order to be shielded from the intense heat of entry.     

Melting in the martian mantle: Shergottite formation and implications for present‐day mantle convection on Mars

Abstract— Radiometric age dating of the shergottite meteorites and cratering studies of lava flows in Tharsis and Elysium both demonstrate that volcanic activity has occurred on Mars in the geologically recent past. This implies that adiabatic decompression melting and upwelling convective flow in the mantle remains important on Mars at present. I present a series of numerical simulations of mantle convection and magma generation on Mars. These models test the effects of the total radioactive heating budget and of the partitioning of radioactivity between crust and mantle on the production of magma. In these models, melting is restricted to the heads of hot mantle plumes that rise from the core‐mantle boundary, consistent with the spatially localized distribution of recent volcanism on Mars. For magma production to occur on present‐day Mars, the minimum average radioactive heating rate in the martian mantle is 1.6 times 10^?12 W/kg, which corresponds to 39% of the Wanke and Dreibus (1994) radioactivity abundance. If the mantle heating rate is lower than this, the mean mantle temperature is low, and the mantle plumes experience large amounts of cooling as they rise from the base of the mantle to the surface and are, thus, unable to melt. Models with mantle radioactive heating rates of 1.8 to 2.1 times 10 ^?12 W/kg can satisfy both the present‐day volcanic resurfacing rate on Mars and the typical melt fraction observed in the shergottites. This corresponds to 43–50% of the Wanke and Dreibus radioactivity remaining in the mantle, which is geochemically reasonable for a 50 km thick crust formed by about 10% partial melting. Plausible changes to either the assumed solidus temperature or to the assumed core‐mantle boundary temperature would require a larger amount of mantle radioactivity to permit present‐day magmatism. These heating rates are slightly higher than inferred for the nakhlite source region and significantly higher than inferred from depleted shergottites such as QUE 94201. The geophysical estimate of mantle radioactivity inferred here is a global average value, while values inferred from the martian meteorites are for particular points in the martian mantle. Evidently, the martian mantle has several isotopically distinct compositions, possibly including a radioactively enriched source that has not yet been sampled by the martian meteorites. The minimum mantle heating rate corresponds to a minimum thermal Rayleigh number of 2 times 10⁶, implying that mantle convection remains moderately vigorous on present‐day Mars. The basic convective pattern on Mars appears to have been stable for most of martian history, which has prevented the mantle flow from destroying the isotopic heterogeneity.     

Survival of endospores of Bacillus subtilis on spacecraft surfaces under simulated martian environments: implications for the forward contamination of Mars

Experiments were conducted in a Mars simulation chamber (MSC) to characterize the survival of endospores of Bacillus subtilis under high UV irradiation and simulated martian conditions. The MSC was used to create Mars surface environments in which pressure (8.5 mb), temperature (-80, -40, -10, or +23 degrees C), gas composition (Earth-normal N2/O2 mix, pure N2, pure CO2, or a Mars gas mix), and UV-VIS-NIR fluence rates (200-1200 nm) were maintained within tight limits. The Mars gas mix was composed of CO2 (95.3%), N2 (2.7%), Ar (1.7%), O2 (0.2%), and water vapor (0.03%). Experiments were conducted to measure the effects of pressure, gas composition, and temperature alone or in combination with Mars-normal UV-VIS-NIR light environments. Endospores of B. subtilis, were deposited on aluminum coupons as monolayers in which the average density applied to coupons was 2.47 x 10(6) bacteria per sample. Populations of B. subtilis placed on aluminum coupons and subjected to an Earth-normal temperature (23 degrees C), pressure (1013 mb), and gas mix (normal N2/O2 ratio) but illuminated with a Mars-normal UV-VIS-NIR spectrum were reduced by over 99.9% after 30 sec exposure to Mars-normal UV fluence rates. However, it required at least 15 min of Mars-normal UV exposure to reduce bacterial populations on aluminum coupons to non-recoverable levels. These results were duplicated when bacteria were exposed to Mars-normal environments of temperature (-10 degrees C), pressure (8.5 mb), gas composition (pure CO2), and UV fluence rates. In other experiments, results indicated that the gas composition of the atmosphere and the temperature of the bacterial monolayers at the time of Mars UV exposure had no effects on the survival of bacterial endospores. But Mars-normal pressures (8.5 mb) were found to reduce survival by approximately 20-35% compared to Earth-normal pressures (1013 mb). The primary implications of these results are (a) that greater than 99.9% of bacterial populations on sun-exposed surfaces of spacecraft are likely to be inactivated within a few tens of seconds to a few minutes on the surface of Mars, and (b) that within a single Mars day under clear-sky conditions bacterial populations on sun-exposed surfaces of spacecraft will be sterilized. Furthermore, these results suggest that the high UV fluence rates on the martian surface can be an important resource in minimizing the forward contamination of Mars.     

Mineral alteration induced by sand transport: A source for the reddish color of martian dust

The iron mineral thought to give the characteristic reddish color to martian dust could have formed through mechanical activation during sand transport. This has been demonstrated experimentally under conditions which are known to occur on Mars.     

Remote Sensing of Mars: Detection of Impact Craters on the Mars Global Surveyor DTM by Integrating Edge- and Region-Based Algorithms

This study integrates two different computer vision approaches, namely the circular Hough transform (CHT) and the determinant of Hessian (DoH), to detect automatically the largest number possible of craters of any size on the digital terrain model (DTM) generated by the Mars Global Surveyor mission. Specifically, application of the standard version of CHT to the DTM captured a great number of craters with diameter smaller than?~?50 km only, failing to capture larger craters. On the other hand, DoH was successful in detecting craters that were undetected by CHT, but its performance was deterred by the irregularity of the topographic surface encompassed: strongly undulated and inclined (trended) topographies hindered crater detection. When run on a de-trended DTM (and keeping the topology unaltered) DoH scored higher. Current results, although not optimal, encourage combined use of CHT and DoH for routine crater detection undertakings.     

Interpretation of Mars southern highlands high amplitude magnetic field with total gradient and fractal source modeling: New insights into the magnetic mystery of Mars

Using model studies, the total gradient (TG) of the Z-component magnetic field is shown to be a useful quantity for delineating sources of satellite-altitude magnetic anomalies; this field is used to constrain the location and lateral boundaries of sources of high amplitude magnetic anomalies of southern highlands of Mars. The TG field suggests two parallel linear and oppositely magnetized sources of 1000 and 1800 km length separated by 1000 km of region of intervening non-parallel sources. The simplest interpretation of the long, linear features is that they are zones of multitudinous crustal scale dikes formed in separate episodes of rifting, and not features associated with the mechanism of seafloor spreading. Forward modeling with uniformly magnetized sources suggests that magnetizations of the order of 10-50 A/m (40 km thickness) over ∼100 km width in the case of the southern source and of 12.5-27.5 A/m (40 km thickness) and ∼200 km width for the northern source are necessary to explain the Z-component amplitudes and features of the TG field. If the crustal magnetization on Mars were to be distributed fractally as on Earth, magnetizations matching the largest amplitude features on Mars may be spatially correlated from a 50-100 km distance range (β ∼ 3) to approaching nearly uniform magnetization (β ∼ 5) values. To keep magnetization intensity as small as possible, the higher end of β values are preferred, whereas, small amplitude anomaly features could be generated from sources with β ∼ 3. Many of the Mars anomaly features could be coalescence effects similar to the coalescence of anomaly features observed on http://icarus.cornell.edu/information/keywords.html.Earth.     

Slow degradation of ATP in simulated martian environments suggests long residence times for the biosignature molecule on spacecraft surfaces on Mars

Prelaunch planetary protection protocols on spacecraft are designed to reduce the numbers and diversity of viable bioloads on surfaces in order to mitigate the forward contamination of planetary surfaces. In addition, there is a growing appreciation that prelaunch spacecraft cleaning protocols will be required to reduce the levels of biogenic signature molecules on spacecraft to levels that will not compromise life-detection experiments on landers. The biogenic molecule, adenosine triphosphate (ATP) was tested for long-term stability under simulated Mars surface conditions of high UV flux, low temperature, low pressure, Mars atmosphere, and clear-sky dust loading conditions. Data on UV-induced ATP degradation rates were then extrapolated to a diversity of global conditions using a radiative transfer model for UV on Mars. The UV-induced degradation of ATP tested at 4.1 W m⁻² UVC (200-280 nm), −10 °C, 7.1 mb, 95% CO₂ gas composition, and an atmospheric opacity of τ=0.1 yielded a half-life for ATP of 1342 kJ m⁻²; or extrapolated to approximately 22 sols on equatorial Mars with an atmospheric opacity of τ=0.5. Temperature was found to moderately affect ATP degradation rates under martian conditions; tests at −80 or 20 °C yielded ATP half-lives of 2594 or 1183 kJ m⁻², respectively. The ATP degradation rates reported here are over 10 orders of magnitude slower than the UV-induced biocidal rates reported in the literature on the inactivation of strongly UV-resistant bacterial spores from Bacillus pumilus SAFR-032 [Schuerger, A.C., Richards, J.T., Newcombe, D.A., Venkateswaran, K.J., 2006. Icarus 181, 52-62]. Extrapolating results to global Mars conditions, residence times for a 99% reduction of ATP on spacecraft surfaces ranged from 158 sols on Sun-exposed surfaces to approximately 32,000 sols for the undersides of landers similar to Viking. However, spacecraft materials greatly affected the survival times of ATP under martian conditions. Stainless steel was found to enhance the UV degradation of ATP by over 2 orders of magnitude compared to ATP-doped iridited aluminum, graphite, and astroquartz coupons. Extrapolating these results to global conditions, ATP on stainless steel might be expected to persist between 2 and 320 sols for upper and lower surfaces of landers. Liquid chromatography-mass spectrometry data supported the conclusion that UV irradiation acted to remove the γ-phosphate group from ATP, and no evidence was observed for the UV-degradation of d-ribose or adenine moieties. Long residence times for ATP on spacecraft materials under martian conditions suggest that prelaunch cleaning protocols may need to be strengthened to mitigate against possible ATP contamination of life-detection experiments on Mars landers.