Water sorption on martian regolith analogs: Thermodynamics and near-infrared reflectance spectroscopy

The near-infrared reflectance spectra of the martian surface present strong absorption features attributed to hydration water present in the regolith. In order to characterize the relationships between this water and atmospheric vapor and decipher the physical state of water molecules in martian regolith analogs, we designed and built an experimental setup to measure near-IR reflectance spectra under martian atmospheric conditions. Six samples were studied that cover part of the diversity of Mars surface mineralogy: a hydrated ferric oxide (ferrihydrite), two igneous samples (volcanic tuff, and dunite sand), and three potential water rich soil materials (Mg-sulfate, smectite powder and a palagonitic soil, the JSC Mars-1 regolith stimulant). Sorption and desorption isotherms were measured at 243 K for water vapor pressure varying from 10⁻⁵ to ∼0.3 mbar (relative humidity: 10⁻⁴ to 75%). These measurements reveal a large diversity of behavior among the sample suite in terms of absolute amount of water adsorbed, shape of the isotherm and hysteresis between the adsorption and desorption branches. Simultaneous in situ spectroscopic observations permit a detailed analysis of the spectral signature of adsorbed water and also point to clear differences between the samples. Ferric (oxy)hydroxides like ferrihydrite or other phases present in palagonitic soils are very strong water adsorbent and may play an important role in the current martian water cycle by allowing large exchange of water between dust-covered regions and atmosphere at diurnal and seasonal scales.     

Thermal alteration of nontronite and montmorillonite: Implications for the martian surface

To test the effects of meteorite impacts on martian phyllosilicate deposits, we heated two smectites (nontronite and montmorillonite) to temperatures ranging from 350 °C to 1150 °C for durations of 4-24 h in two different atmospheres, under air and a steady flow of CO₂. Samples were analyzed using X-ray diffraction (XRD) and near-infrared (NIR) and mid-infrared (MIR) reflectance spectroscopy. Interlayer water was lost after heating to temperatures of ∼400 °C. Between 400 °C and 700 °C, nontronite converted to an intermediary phase which conserved the XRD pattern of untreated nontronite with the exception of the 0 0 1 peak. Nanocrystalline high-temperature phases formed for both smectites at temperatures between 700 °C and 1000 °C. Finally, after being heated to temperatures above ∼1100 °C, the samples melted and recrystallized into secondary phases. Secondary high-temperature phases included sillimanite and cristobalite for both smectites plus hematite for nontronite. NIR and MIR reflectance spectra significantly evolved with increasing temperature. NIR spectra of smectites showed that 1.4 and 1.9 μm bands decrease in intensity and disappear above 700 °C. Similarly, the 2.2-2.3 μm metal-OH band showed a decrease in intensity as well as an overall shift towards lower wavelengths (for nontronite) due to the thermal resistance of the Al-OH bond compared to the Fe-OH bond. NIR spectra of montmorillonite showed a gradual increase in band depth up to temperatures between 500 °C and 600 °C, then decreased with increasing temperature. In the MIR spectra of samples heated to temperatures above ∼1100 °C, newly formed bands confirmed the secondary phases identified by XRD. Similarities between the NIR spectra of our heated samples and the phyllosilicates in some martian craters imply that these phyllosilicates were altered by the impact-generated heat and thus were not formed post-impact. In addition, NIR reflectance spectra provide a proxy for shock temperatures of smectites up to 700 °C while MIR is optimum for identification of high-temperature phases of smectites above 700 °C.     

A search for basaltic-to-intermediate glasses on Mars: Assessing martian crustal mineralogy

Multiple datasets have demonstrated that the crust of Mars is fundamentally basaltic. However, spectral libraries used to interrogate thermal infrared spectra of Martian dark regions through spectral deconvolution have heretofore lacked mafic glasses despite the importance of amorphous phases (or phases with amorphous-like spectral signatures) in Martian mineralogy. To establish the presence and importance of basaltic-to-intermediate glasses in Martian lithologies, we created five such glasses, obtained their thermal infrared spectra and included the spectra in a library used to deconvolve nine regional Thermal Emission Spectrometer spectra from Mars. We employed the nonnegative least squares (NNLS) deconvolution method, which yields deconvolved phase abundances and the uncertainties associated with those abundances. The basaltic-to-intermediate glasses do not appear in the deconvolution solutions, indicating they are not globally or regionally important phases. Because Martian igneous or impact processes are capable of basaltic-to-intermediate glass formation, the lack of such glasses in the deconvolved mineralogies suggests either the glasses did not form in detectable quantities or they (or their signatures) have been removed. The masking or replacement of basaltic-to-intermediate glasses through alteration is supported by the appearance in the deconvolution solutions of amorphous phases (e.g., silica-rich glasses, opal) or phases with amorphous-like spectral signatures (e.g., clays, zeolites) that commonly form through aqueous alteration of mafic glasses. The glasses may still be important to local-scale thermal infrared studies given the basaltic nature of Mars and the variety of local-scale lithologies detected by various missions. The regional mineralogies derived from the NNLS deconvolution analysis divide into five statistically separable groups, which provide insight into regional trends in mineralogy.     

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.     

Midinfrared spectra and optical constants of bulk hematite: Comparison with particulate hematite spectra

Hematite is an iron oxide that is very important for the study of climatic evolution of Mars. It can occur in three forms: nanophase (dark purple), fine-grained (red) and coarse-grained (gray).In a previous work, we studied the influence of particle size and shape on the infrared spectra (in the wavelength range 6.25-50 μm) of submicron red hematite particles and found that bulk optical constants did not fit the spectra of very fine particles with several classes of models.In the present paper, we derive bulk optical constants of a sample of the same parent material of hematite already used in a previous work in order to determine the particulate optical constants. As a first result we find that, also in this case, bulk and particulate optical constants are different from each other. Furthermore, we show that these bulk optical constants, although derived starting from the same parent material of hematite and used with a model adopting the laboratory measured grain size distribution of the sample, cannot be used to reproduce the spectra of submicron particles. Our results can help the scientific community to appropriately model the contribution of hematite submicron grains to the martian dust for a better understanding of the geologic evolution of the planet.     

Mineralogical constraints on the high-silica martian surface component observed by TES

The Thermal Emission Spectrometer (TES) has observed a high-silica material in the dark regions of Mars that is spectrally similar to obsidian glass and may have a volcanic origin. An alternate interpretation is that the spectrally amorphous material consists of clay minerals or some other secondary material, formed by chemical alteration of surface rocks. The regions where this material is observed (e.g., Acidalia Planitia) have relatively high spectral contrast, suggesting that the high-silica material exists as coarse particulates, indurated soils or cements, within rocks, or as indurated coatings on rock surfaces. The geologic interpretation of this spectral result has major implications for understanding magmatic evolution and weathering processes on Mars. One of the complications in interpreting spectral observations of glasses and clay minerals is that both are structurally and compositionally complex. In this study, we perform a detailed spectroscopic analysis of indurated smectite clay minerals and relate their thermal emission spectral features to structural and crystal chemical properties. We examine the spectral similarities and differences between smectite clay minerals and obsidian glass from a structural-chemical perspective, and make further mineralogical interpretations from previous TES results. The results suggest that neither smectite clays nor any clay mineral with similar structural and chemical properties can adequately explain TES observations of high-silica materials in some martian dark regions. If the spectrally amorphous materials observed by TES do represent an alteration product, then these materials are likely to be poorly crystalline aluminosilicates. While all clay minerals have Si/O ratios ?0.4, the position of the emissivity minimum at Mars suggests a Si/O ratio of 0.4-0.5. The spectral observation could be explained by the existence of a silica-rich alteration product, such as Al- or Fe-bearing opal, an intimate physical mixture of relatively pure silica and other aluminosilicates (such as clay minerals or clay precursors), or certain zeolites. The chemical alteration of basaltic rocks on Mars to phyllosilicate-poor, silica-rich alteration products provides a geologically reasonable and consistent explanation for the global TES surface mineralogical results.     

Fresnel modeling of hematite crystal surfaces and application to martian hematite spherules

The gray crystalline hematite at Meridiani Planum first discovered by the Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES) instrument occurs as spherules that have been interpreted as concretions. Analysis of the TES and mini-TES spectra shows that no 390 cm⁻¹ feature is present in the characteristic martian hematite spectrum. Here, we incorporate the mid-IR optical constants of hematite into a simple Fresnel reflectance model to understand the effect of emission angle and crystal morphology on the presence or absence of the 390 cm⁻¹ feature in an IR hematite spectrum. Based on the results we offer two models for the internal structure of the martian hematite spherules.     

Comparison of the Raman spectra of ion irradiated soot and collected extraterrestrial carbon

We use a low pressure flame to produce soot by-products as possible analogues of the carbonaceous dust present in diverse astrophysical environments, such as circumstellar shells, diffuse interstellar medium, planetary disks, as well as in our own Solar System. Several soot samples, displaying an initial chemical diversity from aromatic to aliphatic dominated material, are irradiated with 200-400 keV H⁺, He⁺, and Ar⁺⁺ ions, with fluences comprised between 10¹⁴ and 10¹⁶ ions/cm², to simulate expected radiation induced modification on extraterrestrial carbon. The evolution of the samples is monitored using Raman spectroscopy, before, during, and after irradiation. A detailed analysis of the first- and second-order Raman spectra is performed, using a fitting combination of Lorentzian and/or Gaussian-shaped bands. Upon irradiation, the samples evolve toward an amorphous carbon phase. The results suggest that the observed variations are more related to vacancy formation than ionization processes. A comparison with Raman spectra of extraterrestrial organic matter and other irradiation experiments of astrophysically relevant carbonaceous materials is presented. The results are consistent with previous experiments showing mostly amorphization of various carbonaceous materials. Irradiated soots have Raman spectra similar to those of some meteorites, IDPs, and Comet Wild 2 grains collected by the Stardust mission. Since the early-Sun expected irradiation fluxes sufficient for amorphization are compatible with accretion timescales, our results support the idea that insoluble organic matter (IOM) observed in primitive meteorites has experienced irradiation-induced amorphization prior to the accretion of the parent bodies, emphasizing the important role played by early solar nebula processing.     

IRTF spectra for 17 asteroids from the C and X complexes: A discussion of continuum slopes and their relationships to C chondrites and phyllosilicates

In order to gain further insight into their surface compositions and relationships with meteorites, we have obtained spectra for 17 C and X complex asteroids using NASA’s Infrared Telescope Facility and SpeX infrared spectrometer. We augment these spectra with data in the visible region taken from the on-line databases. Only one of the 17 asteroids showed the three features usually associated with water, the UV slope, a 0.7 μm feature and a 3 μm feature, while five show no evidence for water and 11 had one or two of these features. According to DeMeo et al. (2009), whose asteroid classification scheme we use here, 88% of the variance in asteroid spectra is explained by continuum slope so that asteroids can also be characterized by the slopes of their continua. We thus plot the slope of the continuum between 1.8 and 2.5 μm against slope between 1.0 and 1.75 μm, the break at ∼1.8 μm chosen since phyllosilicates show numerous water-related features beyond this wavelength. On such plots, the C complex fields match those of phyllosilicates kaolinite and montmorillonite that have been heated to about 700 °C, while the X complex fields match the fields for phyllosilicates montmorillonite and serpentine that have been similarly heated. We thus suggest that the surface of the C complex asteroids consist of decomposition products of kaolinite or montmorillonite while for the X complex we suggest that surfaces consist of decomposition products of montmorillonite or serpentine. On the basis of overlapping in fields on the continuum plots we suggest that the CI chondrites are linked with the Cgh asteroids, individual CV and CR chondrites are linked with Xc asteroids, a CK chondrite is linked with the Ch or Cgh asteroids, a number of unusual CI/CM meteorites are linked with C asteroids, and the CM chondrites are linked with the Xk asteroids. The associations are in reasonable agreement with chondrite mineralogy and albedo data.     

Assessing spectral evidence of aqueous activity in two putative martian paleolakes

We evaluate the evidence for the presence of mineral spectral signatures indicative of the past presence of water at two putative paleolakes on Mars using observations by the Mars Reconnaissance Orbiter (MRO) Compact Reconnaissance Image Spectrometer for Mars (CRISM). CRISM spectra of both sites are consistent with laboratory spectra of Mg-rich phyllosilicates. Our analysis represents the first detailed evaluation of these locations. The spatial occurrence and association with topographic features within the craters is distinctly different for the two sites. The occurrence of these minerals supports the conclusion that water was once active in the areas sampled by these craters. The distribution of the phyllosilicates in Luqa does not provide distinctive evidence for the presence of a previous standing body of water and is consistent with either impact emplacement or post-impact alteration. For Cankuzo, the phyllosilicate distribution provides evidence of a layer in the crater wall indicative of aqueous activity, but does not require a paleolake.     

Quantitative compositional analysis of martian mafic regions using the MEx/OMEGA reflectance data 1. Methodology, uncertainties and examples of application

The Mars Express Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité (OMEGA) collected an unprecedented visible and near-infrared hyperspectral dataset covering the low albedo regions of Mars. We investigate the ability to infer modal abundance of surfaces of these regions from a radiative transfer model developed by Shkuratov et al. [Shkuratov, Y., Starukhina, L., Hoffmann, H., Arnold, G., 1999. Icarus 137, 235-246] and adapted to basaltic surfaces by Poulet and Erard [Poulet F., Erard, S., 2004. J. Geophys. Res. 109 (E2), doi:10.1029/2003JE002179]. From OMEGA measurements of mafic surfaces, we develop several sensitivity tests to assess the extent to which the model can be applied to predict pyroxene composition (high-calcium phase and low-calcium phase), abundance of almost neutral components (plagioclase) in the near-infrared wavelength as well as grain sizes, by using a library of selected end-members. Results of the sensitivity tests indicate that the scattering model can estimate both abundances and grain sizes of major basaltic materials of low albedo regions within uncertainties (±5 to 15 vol%). The model is then applied to data from dissected cratered terrains located in Terra Meridiani. The derived grain size including uncertainties is in the 50-500 μm range. This is consistent with the thermal inertia and albedo of this region, which indicates a fine sand-sized surface with little dust. The abundances of plagioclase (43-57%) and pyroxenes (35-45±10%, including 11±5% of low-calcium phase) are in good agreement with previous basalt-like compositions of low albedo regions from thermal infrared spectral measurements. The method presented in this paper will provide a valuable tool for evaluating the modal mineralogy of other mafic regions of Mars observed in the near-infrared wavelength range.     

Space weathering and the interpretation of asteroid reflectance spectra

Lunar-style space weathering is well understood, but cannot be extended to asteroids in general. The two best studied Asteroids (433 Eros and 243 Ida) exhibit quite different space weathering styles, and neither exhibits lunar-style space weathering. It must be concluded that at this time the diversity and mechanisms of asteroid space weathering are poorly understood. This introduces a significant unconstrained variable into the problem of analyzing asteroid spectral data. The sensitivity of asteroid surface material characterizations to space weathering effects - whatever their nature - is strongly dependent upon the choice of remote sensing methodology. The effects of space weathering on some methodologies such as curve matching are potentially devastating and at the present time essentially unmitigated. On other methodologies such as parametric analysis (e.g., analyses based on band centers and band area ratios) the effects are minimal. By choosing the appropriate methodology(ies) applied to high quality spectral data, robust characterizations of asteroid surface mineralogy can be obtained almost irrespective of space weathering. This permits sophisticated assessments of the geologic history of the asteroid parent bodies and of their relationships to the meteorites. Investigations of the diversity of space weathering processes on asteroid surfaces should be a fruitful area for future efforts.     

Spectral unmixing for mineral identification in pancam images of soils in Gusev crater, Mars

The objective of this work is to propose an automated unmixing technique for the analysis of 11-channel Mars Exploration Rover Panoramic Camera (MER/Pancam) spectra. Our approach is to provide a screening tool for identifying unique/distinct reflectance spectra. We demonstrate the utility of this unmixing technique in a study of the mineralogy of the bright salty soils exposed by the rover wheels in images of Gusev crater regions known as Paso Robles (Sols 400,426), Arad (Sol 721), and Tyrone (Sol 790). The unmixing algorithm is based on a novel derivation of the Nonnegative Matrix Factorization technique and includes added features that preclude the adverse effects of low abundance materials that would otherwise skew the unmixing. In order to create a full 11-channel spectrum out of the left and right eye stereo pairs, we also developed a new registration procedure that includes rectification and disparity calculation of the images. We identified two classes of endmember spectra for the bright soils imaged on Sols 426 and 790. One of these endmember classes is also observed for soils imaged on Sols 400 and 721 and has a unique spectral shape that is distinct from most iron oxide, sulfate and silicate spectra and differs from typical martian surface spectra. Instead, its unique spectral character resembles the spectral shape of the ferric sulfate minerals fibroferrite (Fe³⁺(SO₄)(OH) · 5H₂O) and ferricopiapite and the phosphate mineral ferristrunzite . The other endmember class is less consistent with specific minerals and is likely a mixture of altered volcanic material and some bright salts. Further analyses of data from Sols 400 and 790 using an anomaly detection algorithm as a tool for detecting low abundance materials additionally suggests the identification of the sulfate mineral paracoquimbite (Fe₂(SO₄)₃ · 9H₂O). This spectral study of Pancam images of the bright S- and P-enriched soils of Gusev crater identifies specific ferric sulfate and ferric phosphate minerals that are consistent with the unique spectral properties observed here in the 0.4-1 μm range.     

Stability of hydrous minerals on the martian surface

The presence of water-bearing minerals on Mars has long been discussed, but little or no data exist showing that minerals such as smectites and zeolites may be present on the surface in a hydrated state (i.e., that they could contain H₂O molecules in their interlayer or extra-framework sites, respectively). We have analyzed experimental thermodynamic and X-ray powder diffraction data for smectite and the most common terrestrial zeolite, clinoptilolite, to evaluate the state of hydration of these minerals under martian surface conditions. Thermodynamic data for clinoptilolite show that water molecules in its extra-framework sites are held very strongly, with enthalpies of dehydration for Ca-clinoptilolite up to three times greater than that for liquid water. Using these data, we calculated the Gibbs free energy of hydration of clinoptilolite and smectite as a function of temperature and pressure. The calculations demonstrate that these minerals would indeed be hydrated under the very low-P (H₂O) conditions existing on Mars, a reflection of their high affinities for H₂O. These calculations assuming the partial pressure of H₂O and the temperature range expected on Mars suggest that, if present on the surface, zeolites and Ca-smectites could also play a role in affecting the diurnal variations in martian atmospheric H₂O because their calculated water contents vary considerably over daily martian temperature ranges. The open crystal structure of clinoptilolite and existing hydration and kinetic data suggest that hydration/dehydration are not kinetically limited. Based on these calculations, it is possible that hydrated zeolites and clay minerals may explain some of the recent observations of significant amounts of hydrogen not attributable to water ice at martian mid-latitudes.     

Effects of surface roughness and graybody emissivity on martian thermal infrared spectra

Slopes are present in martian apparent surface emissivity observations collected by the Thermal Emission Spectrometer (TES) and the Thermal Emission Imaging System (THEMIS). These slopes are attributed to misrepresenting the surface temperature, either through incorrect assumptions about the maximum emissivity of surface materials or the presumption of a uniform surface temperature within the field of view. These incorrect assumptions leave distinct characteristics in the resulting apparent emissivity data that can be used to gain a better understanding of the surface properties. Surfaces with steep slopes typically have a variable surface temperatures within the field of view that cause distinct and highly variable slopes in apparent emissivity spectra based on the observing conditions. These properties are documented on the southwestern flank of Apollinaris Patera and can be reasonably approximated by modeled data. This spectral behavior is associated with extremely rough martian surfaces and includes surfaces south of Arsia Mons and near Warrego Valles that also appear to have high slopes in high resolution images. Surfaces with low maximum values of emissivity have apparent emissivity spectra with more consistent spectral slopes that do not vary greatly based on observing conditions. This spectral surface type is documented in Terra Serenum and is consistent with associated high resolution images that do not indicate the presence of a surface significantly rougher that the surrounding terrain.     

Preferential low-pH dissolution of pyroxene in plagioclase-pyroxene mixtures: Implications for martian surface materials

Acid weathering of plagioclase-pyroxene mixtures has been investigated with an open system kinetic dissolution model. The modeling reveals that elevated plagioclase/pyroxene ratios observed in some low-albedo martian regions and atmospheric dust could be partially caused by preferential dissolution of pyroxenes at pHs below ∼3-4. Surface materials with smaller grain sizes, affected by lower pH fluids, and/or exposed to longer durations of acid weathering would be enriched in plagioclase. If preferential dissolution is responsible for the observed mineral ratios, the dissolution process likely occurred on a large scale, such as weathering by acid atmospheric precipitates. If dissolution was continuous, modeled timeframes required to produce a high plagioclase/pyroxene ratio are short on geologic timescales; however, it is likely that acid weathering on Mars was episodic, possibly occurring over a longer period of time.     

Discovery of jarosite within the Mawrth Vallis region of Mars: Implications for the geologic history of the region

Analysis of visible to near infrared reflectance data from the MRO CRISM hyperspectral imager has revealed the presence of an ovoid-shaped landform, approximately 3 by 5 km in size, within the layered terrains surrounding the Mawrth Vallis outflow channel. This feature has spectral absorption features consistent with the presence of the ferric sulfate mineral jarosite, specifically a K-bearing jarosite (KFe₃(SO₄)₂(OH)₆). Terrestrial jarosite is formed through the oxidation of iron sulfides in acidic environments or from basaltic precursor minerals with the addition of sulfur. Previously identified phyllosilicates in the Mawrth Vallis layered terrains include a basal sequence of layers containing Fe-Mg smectites and an upper set of layers of hydrated silica and aluminous phyllosilicates. In terms of its fine scale morphology revealed by MRO HiRISE imagery, the jarosite-bearing unit has fracture patterns very similar to that observed in Fe-Mg smectite-bearing layers, but unlike that observed in the Al-bearing phyllosilicate unit. The ovoid-shaped landform is situated in an east-west bowl-shaped depression superposed on a north sloping surface. Spectra of the ovoid-shaped jarosite-bearing landform also display an anomalously high 600 nm shoulder, which may be consistent with the presence of goethite and a 1.92 μm absorption which could indicate the presence of ferrihydrite. Goethite, jarosite, and ferrihydrite can be co-precipitated and/or form through transformation of schwertmannite, both processes generally occurring under low pH conditions (pH 2-4). To date, this location appears to be unique in the Mawrth Vallis region and could represent precipitation of jarosite in acidic, sulfur-rich ponded water during the waning stages of drying.     

Plausible parent bodies for enstatite chondrites and mesosiderites: Implications for Lutetia's fly-by

We present new irradiation experiments performed on the enstatite chondrite Eagle (EL6) and the mesosiderite Vaca Muerta. These experiments were performed with the aims of (a) quantifying the spectral effect of the solar wind on their parent asteroid surfaces and (b) identifying their parent bodies within the asteroid belt. For Vaca Muerta we observe a reddening and darkening of the reflectance spectrum with progressive irradiation, consistent with what is observed in the cases of silicates and silicate-rich meteorites such as OCs and HEDs. For Eagle we observe little spectral variation, and therefore we do not expect to observe a significant spectral difference between EC meteorites and their parent bodies. We evaluated possible parent bodies for both meteorites by comparing their VNIR spectra (before and after irradiation) with those of ∼400 main-belt asteroids. We found that 21 Lutetia (Rosetta's forthcoming fly-by target) and 97 Klotho (both Xc types in the new Bus-DeMeo taxonomy) have physical properties compatible with those of enstatite chondrite meteorites while 201 Penelope, 250 Bettina and 337 Devosa (all three are Xk types in the Bus-DeMeo taxonomy) are compatible with the properties of mesosiderites.     

Experimental evidence for the potential impact ejection of viable microorganisms from Mars and Mars-like planets

Bacterial spores (Bacillus subtilis), cyanobacteria (Chroococcidiopsis sp.), and lichen (Xanthoria elegans) embedded in martian analogue rock (gabbro) were exposed to shock pressures between 5 and 50 GPa which is the range of pressures observed in martian meteorites. The survival of Bacillus subtilis and Xanthoria elegans up to 45 GPa and of Chroococcidiopsis sp. up to 10 GPa supports the possibility of transfer of life inside meteoroids between Mars and Earth and it implies the potential for the transfer of life from any Mars-like planet to other habitable planets in the same stellar system.     

Modeling diffusion advection in the mass transfer of water vapor through martian regolith

Diffusion advection is an effect in diffusive multicomponent mass transfer that occurs when the flux vectors of the individual components do not add up to zero. This can be a significant effect for the mass transfer of water vapor from subsurface ice or liquid reservoirs through porous regolith at martian temperatures and pressures. Ignoring diffusion advection and using Fick's law alone to calculate the flux under these conditions will result in an erroneously small value while using a measured flux to calculate a diffusivity will result in an erroneously high value. The inaccuracy in both cases increases with temperature. The literature contains several examples of erroneous treatment of this effect. The correct approach is well-known from other applications of mass transfer and takes diffusion advection into account in the appropriate amount regardless of the temperature and pressure and reduces to the simple Fick's law when conditions warrant. In this way, there is no need to decide under what conditions diffusion advection is or is not important. It can be used in the transition region to pure Knudsen diffusion in a fashion similar to that used with the more limited Fickian approach.