This session welcomes all presentations on Mars' interior and surface processes. With three new missions arrived in early 2021 (Mars2020, Hope, Tianwen-1), Mars research is as active as ever, and new data come in on a daily basis. The aim of this session is to bring together disciplines as various as geology, geomorphology, geophysics, mineralogy, glaciology, and chemistry. We welcome presentations on either present or past Mars processes, either pure Mars science or comparative planetology, either observations or modeling or laboratory experiments (or any combination of those). New results on Mars science obtained from recent in situ and orbital measurements are particularly encouraged, as well as studies related to upcoming missions and campaigns (ExoMars, Mars Sample Return).
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Oral and Poster presentations and abstracts
With the deployment of a seismometer on the surface of Mars as part of NASA’s InSight mission,
the Seismic Experiment for Interior Structure (SEIS) has been collecting continuous data since early 2019.
The primary goal of InSight is to improve our understanding of the internal structure and dynamics of Mars, in
particular crust, mantle, and core. Here we describe constraints on the structure of the mantle of Mars based
on inversion of seismic body wave arrivals from a number of low-frequency marsquakes.
We consider 8 of the largest (moment magnitude is estimated to be between 3 and 4) low-frequency events with
dominant energy below 1 Hz for which P- and S-waves are identifiable, enabling epicentral distance estimation.
The 8 events occur in the distance range 25-75 degrees. Body wave arrivals that include the main P- and S-waves,
surface reflections (PP, PPP, SS, SSS), and core reflections (ScS) are picked using a set of complimentary methods
that allows to check for consistency. The resultant set of differential travel times (PP-P, PPP-P, SS-S,...) are
subsequently inverted for radial profiles of seismic P- and S-wave velocity, core size and mean density, and epicentral
location of the events. To determine interior structure, we rely on independent methods as a means of assessing the
robustness of the results.
We present a radial velocity model for the upper mantle of Mars, with implications for the thermo-chemical evolution
of the planet that match a cooling, differentiated body, and a thick lithosphere. Based on the location of the events,
we are able to constrain structure to the core-mantle-boundary, including the size of the core and its mean
density that point to large liquid and relatively light core, implying a significant complement of light alloying
elements. Our estimate of the average crustal thickness as seen by all events is compatible with the local crustal
thickness at the InSight landing determined from observations of converted phases.
How to cite: Khan, A. and the the InSight team: Crust, mantle and core structure of Mars from InSight seismic data, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-512, https://doi.org/10.5194/epsc2021-512, 2021.
The scattering of seismic waves is the signature of random heterogeneities, present in the lithospheric structure of a terrestrial planet. It is the result of refraction and reflection of the seismic waves generated by a quake, when they cross materials with different shear rigidity, bulk modulus, and density and therefore different seismic wave velocities, compared to the ambient space. On Earth, the seismic waves show relatively weak scattering, identified in later arriving coda waves that follow the main arrivals of body waves and decay with time. In contrast, seismic wave scattering is much more significant on the Moon, where the high heterogeneous structure of the lunar megaregolith, produced through millions of years of impact bombardment, is a structure that creates an extreme scattering environment.
The landing of the NASA InSight mission on Mars in 2018, which carried and deployed a seismometer for the first time on the Martian ground, offered a pristine dataset for the investigation and analysis of the characteristics of the scattering attenuation of the Martian crust and uppermost mantle which is important for understanding the structure of the Martian interior. Lognonné et al. (2020) used a methodology based on the radiative transfer model (Margerin et al., 1998) to offer the first constraints for the scattering and attenuation in the Martian crust. In this study, we performed a further examination based on more and newer events of the Martian Seismic Catalog (InSight Marsquake Service, 2021).
The Marsquake Catalog contains events that are categorized according to the frequency content of the seismic signal (Clinton et al., 2021). In this study, we used 19 events of 4 different families, namely the Low Frequency, Broadband, High Frequency, and Very High Frequency events, for our investigation. We focused our investigation on the characteristics of the S-coda waveforms and for this reason, we worked on the respective energy envelopes. We manually picked the envelopes, defining the time window of the S-coda waves, as well the frequency range for each event, directly from the spectrograms of the events' signals, using an appropriately developed visual tool.
We used a modeling approach (Dainty et al., 1974) that was developed for the computation of the energy envelopes of shallow events (Lunar impacts) and a diffusive, highly scattering layer, sitting over an elastic half-space. The energy envelope depends on the thickness of the diffusive layer, the range of the seismic ray, the diffusivity and the attenuation in the top layer, and the seismic wave velocity in the underneath elastic half-space. We analyzed all the tradeoffs between the terms of the modeling equation, namely the geometrical relationship of the velocity contrast between the diffusive layer and the elastic half-space with the seismic ray range and the diffusive layer thickness, the diffusivity with the diffusive layer thickness, and between the diffusivity and the velocity contrast of the two examined layers.
The presence of the aforementioned tradeoffs made the definition of a unique model a very hard task, as the information for the azimuthal characteristics of the signal is not available for the examined events. This is a limitation that exists in seismology only while working with one station, with the InSight seismometer being the only station on a planet, and the amplitude of the seismic signal is not big enough to perform a specific polarization analysis and derive the azimuthal origin of the recorded signal. For this reason, we reviewed the fit between the modeling and the data, depending on the frequency content of the events.
The Low Frequency and the Broadband events, which have a frequency content mainly below the tick noise detected at 1 Hz, could not satisfy the modeling approach of a simple diffusive layer. The spectral envelopes of the S-coda waves of these events are decaying very rapidly, which suggests an origin in a more elastic environment. This is in agreement with previous studies (Giardini et al., 2020) that suggest that these events are generated deeper in the Martian mantle. For this reason, we applied another approach to these signals, with an energy envelope equation designed for deep moonquakes (Dainty et al.,1974), but it was not either capable to fit the examined data envelopes, suggesting the absence of a very thick megaregolith structure on Mars.
Based on the results of the High Frequency (HF) and Very High Frequency (VF) events we observed a range of possible paths and diffusivities that can satisfy the data and we investigated the tradeoffs between the parameters of a modeling equation that control the shape of the energy envelope for the events. The analysis of these tradeoffs does not permit us to make any assumptions about the depth of the diffusive region in the Martian crust and the upper mantle as their azimuthal characteristics are unknown and therefore it is not feasible to tell if the difference in the result analysis reflects vertical or lateral variations of the uppermost diffusive layer in the Martian lithosphere.
The results of this study illustrate one of the challenges in working with single-station seismic data where event location information, including distance, azimuth, and depth are crucial for understanding the lateral variation in seismic properties of a planet. The existence of a seismic network on the planetary scale will improve the ability of phase peaking and location identification of the events and therefore it will give additional constraints for a similar analysis.
Clinton, J. F. et al. (2021). The Marsquake catalogue from InSight, sols 0–478.Phys Earth Planet In, 310:106595.
Dainty, A. M. et al. (1974). Seismic scattering and shallow structure of the Moon in Oceanus Procellarum.The Moon,9(1-2):11–29.
Giardini, D. et al. (2020). The seismicity of Mars.Nat Geosci, 13(3):205–212.InSight Marsquake Service (2021).
Mars Seismic Catalogue, InSight Mission; V5 2021-01-04.
Lognonné, P. et al. (2020). Constraints on the shallow elastic and anelastic structure of Mars from InSight seismic data.NatGeosci, 13(3):213–220.
Margerin, L. et al. (1998). Radiative transfer and diffusion of waves in a layered medium: new insight into coda Q.GeophysJ Int, 134(2):596–612.
How to cite: Karakostas, F., Schmerr, N., Maguire, R., Huang, Q., Kim, D., Lekić, V., Margerin, L., Nunn, C., Menina, S., Kawamura, T., Lognonné, P., Giardini, D., and Banerdt, B.: An analysis of the seismic scattering on Mars, using the InSight seismic data, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-258, https://doi.org/10.5194/epsc2021-258, 2021.
Radar data interpretation for subsurface analysis is based upon the comparison with simulations, to discriminate a subsurface echo from a surface reflector. Our goal is to detect subsurface ice at Mars’s midlatitudes — that have been shown to be present in the first tens of meters below the surface —, using data from the SHAllow RADar (SHARAD) onboard Mars Reconnaissance Orbiter (MRO).
We are specifically interested in looking into the southern midlatitudes of Mars, a highly craterized area with a variety of structures on the surface. This is why we have to be extra careful in the radar data analysis with the simulations, and we are faced with issues that are not necessarily present for the study of the poles.
We will present a method that allows us to complete the simulations and helps us to resolve further ambiguities.
Sounding the close subsurface of Mars’s midlatitudes
The MARSIS and SHARAD Nadir-looking radars have been sounding the surface of Mars since respectively 2005 and 2006, at different frequencies — between 1.8 and 5 MHz for MARSIS, and 20 MHz for SHARAD —. Their data have allowed us to better understand the composition and structure of the Martian subsurface.
On fathom radar profiles, echo coming from the subsurface from nadir could arrive with the same delay that surface echoes arriving from a slant direction. This ambiguity is classically resolved by simulation of the measurement from Digital Terrain Models (DTMs) as developed for MARSIS [3,4]: given a surface model and an orbitography, we can simulate the surface-related component of the signal. By comparing the radar data to the simulation, we can therefore — in theory — fully identify the subsurface reflectors.
The question is especially complex when the objective is to detect ice at Martian midlatitudes at depths lower than a few tens of meters. Furthermore, given that the radar signal mostly comes from the nadir and a limited area around, we will have a high sensibility for the variations in local slopes in the surface models used for the simulations.
In order to accurately simulate the surface component of the signal, the surface model resolution must be in the order of the wavelength or lower (15m for the case of SHARAD). This is why we will need higher resolution DTMs than the one mainly used for MARSIS simulations (MOLA). DTMs can be generated from different data types, but to have high resolution models, the privileged method is stereo photogrammetry . As an example, with the CTX camera onboard MRO, we can reach a typical resolution of 12 meters, compared to the 463 meters of MOLA.
The area that we are focusing on is located in Terra Cimmeria, around (172°E ; 39°S), and shows a number of canal-like structures, along with numerous craters. Those structures are located a few degrees off-nadir, therefore very close to the main surface echo, complicating the analysis with the simulations. In fact, a slight variation of the model from the actual topography can change the result of the simulation, and the process of stereo photogrammetry introducing noise, we will necessarily be faced with some differences between simulations and radar data. Another issue is that on this specific area, only MOLA and HRSC DTMs are available, with a maximum resolution of 200m per pixel, far from the 15m of the wavelength.
With the aforementioned issues, we are left with ambiguities that we cannot resolve as is, so we must find a way to get around it. We will therefore present a method that allows to complete the simulation by resolving the remaining ambiguities. This method applied to the area discussed above allowed us to study in details the echoes analyzed by  and to revisit the results.
 C. M. Stuurman et al., « SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars: SHARAD DETECTION OF ICE UTOPIA PLANITIA », Geophys. Res. Lett., vol. 43, no 18, p. 9484‑9491, sept. 2016
 R. Seu et al., « SHARAD sounding radar on the Mars Reconnaissance Orbiter », J. Geophys. Res., vol. 112, no E5, p. E05S05, may 2007
 J. -. Nouvel, A. Herique, W. Kofman and A. Safaeinili, "Radar signal simulation: Surface modeling with the Facet Method," in Radio Science, vol. 39, no. 1, pp. 1-17, Feb. 2004
 Y. Berquin, A. Herique, W. Kofman, et E. Heggy, « Computing low-frequency radar surface echoes for planetary radar using Huygens-Fresnel’s principle: COMPUTING RADAR SURFACE ECHOES », Radio Sci., vol. 50, no 10, p. 1097‑1109, oct. 2015
 R. A. Beyer, O. Alexandrov, et S. McMichael, « The Ames Stereo Pipeline: NASA’s Open Source Software for Deriving and Processing Terrain Data », Earth and Space Science, vol. 5, no 9, p. 537‑548, sept. 2018
 S. Adeli, E. Hauber, G. G. Michael, P. Fawdon, I. B. Smith, et R. Jaumann, « Geomorphological Evidence of Localized Stagnant Ice Deposits in Terra Cimmeria, Mars », J. Geophys. Res. Planets, p. 2018JE005772, june 2019
How to cite: Desage, L., Herique, A., and Kofman, W.: The first tens of meters of the Martian midlatitude subsurface: How to analyze SHARAD signal?, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-465, https://doi.org/10.5194/epsc2021-465, 2021.
Context On February 18th 2021, the Perseverance rover (NASA Mars 2020 mission) landed at Jezero crater, an ancient open-basin lake system measuring 50 Km in diameter. More precisely, the rover landed at the Octavia E. Butler Landing Site, which is located East of the delta in a dark crater floor unit, interpreted as the Undifferentiated Smooth Unit, between two distinct units: “Crater Floor Fractured 1” and “Crater Floor Fractured Rough” units. Since the landing, the rover has traveled around 40 m North and 60 m East from its initial location. From CRISM orbital data, this region is mainly pyroxene-bearing, with some olivine and hydrated minerals [1-3].
On-board the Perseverance rover, the SuperCam instrument [4-5] is being used as a remote-sensing facility to analyze rocks and soils targets. SuperCam is a suite of five coaligned techniques: just like ChemCam (onboard MSL/Curiosity rover on Mars since 2012), it uses the Laser Induced Breakdown Spectroscopy (LIBS) technique to determine the elementary composition of the targets, but it also uses Raman (for the first time in planetary science) and visible-infrared (VISIR - for the first time in situ) spectroscopic methods in order to access some mineralogical and structural information. A microphone gives access to some physical parameters of the sampled rocks (such as hardness ) as well as to some atmospheric parameters (wind direction ). These chemical and mineralogical analyses are contextualized thanks to a color remote micro-imager (RMI). In this study, we focus mainly on the LIBS results obtained so far.
Method We have used all the processed LIBS spectra acquired since the landing. Spectra have been processed with the following steps: denoise, background removal, wavelength calibration.
The SuperCam/LIBS technique can predict major elements such as SiO2, TiO2, Al2O3, FeO, MgO, CaO, Na2O, and K2O. The quantification of the LIBS data is achieved based on multivariate models, trained on more than 1000 spectra from 334 different known samples acquired in laboratory before launch [8-9]. Minor elements will be quantified in the future, and for now only peak areas are used. In this study we are using images from the SuperCam instrument  and from the MastCam-Z and Navcam cameras .
Results From the images, rocks in the workspace are presenting mainly two types of morphologies (Figure 1). Besides some float rocks, there are low-standing light-toned rocks called “pavers”, and high-standing dark-toned rocks. Pavers tend to have a more important dust cover, as they are in low-relief, compared to the high-standing rocks. The relation between the pavers and the high-standing rocks is not clear. Only a few images seem to show that the high standing rocks are directly related to the pavers, i-e that they correspond to the same material.
The LIBS elemental compositions are indeed essentially similar between these two types of morphologies (Figure 2). Some elements show extreme values, such as CaO, MgO and FeO, but these elevated values are observed in both morphologies and seem to be related to particular phases that have been sampled in both types of rocks.
One important observation concerns the point-to-point dispersion among each rock, whatever the rock type. This shows that the granulometry of these rocks is quite important, with grains of at least 300 microns (which is the LIBS spot size). Several grains have indeed been observed in the RMI and Watson images, consistent with this hypothesis.
Figure 1: A. NavCam image of the workspace, sol 66 (N_LRGB_0066_RAS_0032208_CYP_S_STERONVJ01); B. MastCam image showing pavers and high standing dark-toned rocks (ZCAM03130). NASA/Caltech-JPL-MSSS/ASU.
Figure 2: A. Na2O+K2O vs SiO2 content of the 19 rocks analyzed by SuperCam/LIBS. B. CaO vs MgO; C. Na2O vs Al2O3. Low standing rocks are shown as squares, High standing rocks as triangles, and float rocks as circles.
How to cite: Cousin, A., Anderson, R., Forni, O., Benzerara, K., Mangold, N., Beck, P., Dehouck, E., Ollila, A., Meslin, P.-Y., Gibbons, E., Gasnault, O., Beyssac, O., Lassue, J., Frydenvang, J., Vogt, D., Pilleri, P., Schröder, S., Clegg, S., Maurice, S., and Wiens, R.: Observations of Rocks in Jezero Landing Site: SuperCam/LIBS technique overview of results from the first six months of operations., Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-644, https://doi.org/10.5194/epsc2021-644, 2021.
Introduction: Meridiani Planum is a relatively plain area located at the Martian equator, south of Arabia Terra, approximately ranging from longitude 350°E to 10°E. Heavily cratered Noachian-aged terrains constitute the oldest geological unit in the region, where several channels and valley networks have left their imprint on the surface . A series of younger terrains were then emplaced in some areas, likely during Late Noachian/Early Hesperian epochs .
Meridiani Planum shows signs of a diversified and complex history of aqueous activity in many locations. In addition to the evidence provided by the numerous valley networks, data from OMEGA and CRISM orbital spectrometers have revealed the presence of Fe/Mg phyllosilicates and sulfates throughout the area . These hydrated minerals usually form by alteration in aqueous environments. Older, Noachian-aged, areas are generally characterized by the presence of Fe/Mg phyllosilicates, while younger capping units may display both phyllosilicates and sulfates. Regional differences in mineralogy, hydration, and morphology imply that the aqueous conditions probably varied over time.
Advancing our knowledge on the aqueous processes that left their imprint on this area could provide new insight on the past climate and habitability of Mars. Noachian terrains are of particular interest, as they date back to a period which is largely recognized as the most suitable for hosting habitable conditions on the planet.
Materials and method: We selected a small crater in the northern part of Meridiani Planum (figure 1), centred at 359.96°E, 2.45°N and approximately 20 km wide. The crater is part of the exposed Noachian-aged terrains of the region and is surrounded to the south and east by younger terrains, which overlie part of its ejecta.
Both mineralogical and geomorphological characteristics were investigated using MRO-based instruments CRISM, HiRISE and CTX. Infrared data (1.0-2.6 μm) from CRISM spectrometer was used to assess the mineralogical composition of the terrains inside the crater. This information was then integrated with HiRISE high-resolution camera data to identify and correlate with compositional information the different morphologies within the crater's area. Additionally, images from CTX camera were used to provide surrounding context.
Figure 1: CTX image of the region of interest. The green lines trace CRISM footprint, showing the coverage of the spectral data analysed.
Results: Phyllosilicates, specifically Fe/Mg-rich smectite clays, are found in a wide area of the crater’s interior. The spectra obtained from CRISM are displayed in figure 2, they show absorption features near 1.4, 1.9, and 2.3 μm, with additional combination tones near 2.4 μm, and sometimes 2.5 μm. The exact position of some bands depends on the relative proportions of Fe and Mg: for example, the 2.3 μm band shifts to shorter wavelengths as Fe is exchanged for Mg .
We identify two distinct spectral classes for the smectites (Figure 2): the first is compatible with laboratory spectra of Fe-rich smectites, e.g. nontronite, while the second with the spectra of more Mg-rich smectites, such as saponite. The position and shape of the 2.3, 2.4 and 2.5 μm features are slightly different for the two classes. Figure 3 shows the absorption details for both CRISM and laboratory spectra.
Fe-rich smectites tend to be concentrated in limited areas of the crater, mostly close to its southern border. Further investigation is needed on this point to clarify the reasons for this specific distribution.
Figure 2: averaged spectra obtained for the areas which show the presence of Fe/Mg smectites: red is from predominantly Fe-rich smectite areas, green is from Mg-rich areas.
Figure 3: (left) Laboratory spectra of Nontronite (Fe-rich smectite) and Saponite (Mg-rich smectite). (right) Absorption details of the spectra from figure 2.
The spectral signature of the remaining terrains implies the presence of pyroxenes. Usually, these areas tend to be darker and dunes of a fine-grained material are frequently observed.
Terrains which retain signs of hydration show an interesting variety of morphologies, however, a common feature is that they all show polygonal fracture patterns to some extent (figure 4).
Figure 4: Cracking patterns on the crater’s hydrated terrains as observed with HiRISE. Approximate location is marked by a plus sign in figure 1.
Interpretation and discussion of the results: A possible explanation for the observed cracking patterns is related to desiccation. Desiccation is caused by water evaporation or migration: as a result of the water loss, the terrain shrinks and cracks.
Cracking patterns, correlating with the presence of sedimentary materials (e.g. clays or sulfates), are found in various Martian terrains and could be markers of ancient lacustrine environments . The Noachian geologic setting, in association with terrains that show evidence of past aqueous activity, reinforces this hypothesis.
Noachian paleo-lakes are a top-priority setting for astrobiological research as they might have been suitable environments to support and preserve traces of microbial life . Nevertheless, a different origin for these features is not ruled out and further investigation is required.
Conclusions: Meridiani Planum is undoubtedly an area which was subject to significant water alteration. Fe/Mg smectites detected in the northern Noachian-aged terrains of Meridiani Planum, in association with polygonal fracture patterns, could be related with the existence of ancient paleo-lake environments, making this area an interesting spot for astrobiological research. The information available on these areas is still limited: in order to provide context to MER Opportunity’s observations, previous studies mainly focused on the younger capping terrains lying south of the crater we examined. The results obtained here can be a worthwhile starting point for better understanding the evolutionary history of Meridiani Planum’s oldest terrains.
Acknowledgments: Featured camera images were obtained from NASA’s Planetary Data System (PDS).
References:  Williams et al. (2017) GRL, 44, 1669-1678.  Hynek et al. (2002) JGR, 107, 5088.  Flahaut et al. (2015) Icarus, 248, 269-288.  Viviano-Beck et al. (2014) JGR, 119, 1403-1431.  El-Maarry et al. (2014) Icarus, 241, 248-268.  Vago et al. (2017) Astrobiology, 17,471-510.
How to cite: Baschetti, B., Altieri, F., Carli, C., Frigeri, A., and Sgavetti, M.: Mineralogical and Geomorphological Characterisation of a 20-km-wide Crater in Older Meridiani Planum, Mars, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-143, https://doi.org/10.5194/epsc2021-143, 2021.
The recently landed Perseverance rover from the Mars2020 mission is the first rover to select samples with the future objective of taking them back to the Earth in the Mars Sample Return future mission. Until then, Martian meteorites are still the only samples that we have on Earth to study the composition and formation of Mars. Due to the scarce abundance and the importance of these samples, the development of non-destructive characterization methodologies is of great importance. In this case, the Martian Shergottite NWA1950, considered one of the less studied Martian meteorites, has been selected with the double objective of performing the characterization of its original and altered minerals and of contributing to ascertain the degradation reactions.
Instead of using the classical methods of analysis, a non-destructive analytical methodology that make use of spectroscopic techniques has been used. This approach could also be employed to study other meteorites or even in the future returned samples from Mars. The analytical methodology proposed is mainly based on the effectiveness of Raman microscopy for the molecular characterization, assisted by Energy Dispersive X-Ray Fluorescence (ED-XRF) and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS) to clarify the distribution of elements in the sample. In addition, Raman microscopy and µ-ED-XRF imaging analyses also allows performing the characterization of the whole surface of the meteorite obtaining the molecular and elemental distributions maps respectively.
Results and Discussion
The applied methodology on the NWA1950 sample showed a main matrix composed of pyroxenes and olivines. The identification of pyroxenes showed the presence of both, ortopyroxenes (low in Ca) and clinopyroxenes (high in Ca). Different olivines with different proportions of fayalite (Fe2SiO4):forsterite (Mg2SiO4) were detected by Raman, specifically olivines varying from 63 to 77% of Mg content. The study of the olivines also showed different degradations on them. The most common degradation suffered by the olivines was the oxidation of part of the iron(II) resulting in the identification of hematite (Fe2O3) grains over olivines enriched in Mg content due to the partial Fe loss after its oxidation. In other cases, the oxidation of the iron present in the olivine lead to the formation of magnetite (Fe3O4). Both reactions should lead also to the formation of silica (SiO2) and this study has identified vitreous silica by Raman spectroscopy in the olivines with less than 69% Forsterire. This observation may indicate the initial oxidation of the olivine occurred on Mars and therefore the quartz was transformed into vitreous silica due to the high temperatures and pressures suffered by the meteorite after the shock.
Among the minor compounds, it is important to highlight the presence of ilmenite (FeTiO3). In this case, the Raman bands obtained for ilmenite are shifted to higher wavenumbers than the theoretical ones. This may be indicative of a shocked Ilmenite, subjected to the high pressures of the ejection, and therefore indicating its possible Martian origin. In addition, Ilmenite can be oxidized into TiO2 that can appear as different polymorphs, rutile and anatase mainly. In this case, the identified polymorph was anatase that is formed at low temperatures, indicating that anatase is not an alteration compound from Mars but rather a terrestrial alteration mineral formed after the oxidation of ilmenite once the meteorite was on Earth.
Merrillite (Ca9NaMg(PO4)7) was also detected as an important mineral phase in this meteorite. The elemental calcium and phosphorous ED-XRF distributions can be appreciated in Figure 1, showing the overlap between these two elements, matching perfectly with the molecular Raman distribution of merrillite in one of the faces of the meteorite.
Figure 1. ED-XRF elemental distribution maps of Ca and P, showing in orange the overlaping of both elements (top) and the Raman image showing the molecular distribution of merrillite (down).
Iron chromites (FeCr2O4) were also detected, by means of Raman and SEM-EDS microscopic techniques, as abundant particles distributed all along the surface of the meteorite by means of Raman and SEM-EDS.
Two different calcites were identified by Raman microscopy. One of them is due to the presence of terrestrial calcite with its main characteristic band at 1086 cm-1. However, most were shocked calcites due to the shift of the main Raman band to higher wavenumbers (to 1088 and even to 1089 cm-1), suggesting again the effect of the pressure that suffered the meteorite and thus showing the Martian origin of these shocked calcites. The non-shocked calcites should be considered as terrestrial weathering compounds.
Finally, some sulfides were identified as chalcocite (Cu2S) and acanthite (β-Ag2S) by means of Raman and SEM-EDS microscopy. The origin of acanthite cannot be confirmed as Martian because if argentite (α-Ag2S), the high temperature stable phase of silver sulfide, was formed during the harsh conditions that suffered the meteorite during its ejection from Mars, the formation of argentite is reversible when the pressure ceases, and after the entrance in Earth atmosphere, the acanthite will be formed again.
As can be seen, the employed analytical methodology allowed us to characterize the original Martian mineral composition of the meteorite as well as the presence of alterations minerals originated in Mars but also after terrestrial weathering processes. In none of the analyses the sample was manipulated or treated chemically nor physically, all the measurements were performed over the surface of a thin section of the meteorite. Therefore, the same non-destructive analytical methodology could be followed for the characterization of other meteorites from other origins and also for the Mars samples when they are back on the Earth as first non-destructive characterization step that can lead to much information.
How to cite: Madariaga, J. M., Coloma, L., García-Florentino, C., Huidobro, J., Torre-Fdez, I., Aramendia, J., Castro, K., and Arana, G.: Characterization of original and altered mineral phases of the Martian shergottite NWA1950 by means of non-destructive analytical techniques. Implications for the analyses of future returned samples from Mars, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-645, https://doi.org/10.5194/epsc2021-645, 2021.
There is a very significant body of evidence for a dense Martian atmosphere during the Noachian period, about 3.8 Ga ago. At that point in the evolution of the red planet water was present in the surface of Mars, and ancient surface features indicate that it flew through significant regions of its surface. We have studied Allan Hills 84001. an orthopiroxenite formed about 4.1 Ga ago. It is a meteorite widely known because  found microscopic structures that were suggested to be magnetotactic microbe fossils. In particular, in our CSIC laboratory I have studied with some of my PhD students the carbonate globules contained in this meteorite . We discovered in a ALH84001,82 thin section (Fig. 1) that they were formed near the rock fractures, as consequence of the precipitation of Mg- and Fe-rich carbonates from an aqueous solution.
Figure 1. Thin section of ALH 84001. The square grid is mm-sized. This optical microscope transmitted light reveals the main minerals forming the rock and many fractures as consequence, at least, of two impacts while the rock formed part of Mars’ surface. Water penetrated into the fractures and produced the carbonate globules (see also Fig. 2)
Interestingly, we found distinctive layers in the walls of the carbonate globules. They indicate that the globules growth occurred under several flooding stages. As they exhibit differentiated elemental chemistry, it could reflect distinctive chemical solutes, being probably evidence of chemically-distinguishable fluids produced by environmental differences [3-4]. To explain liquid water presence at that time is challenging because the young Sun was less luminous than today: about was ~25% lower than nowadays. Consequently, being Mars about 1.5 times more distant from the Sun than the Earth, the solar energy available on Mars was ~1/3 of what gets the Earth today. Then we need to invoke an atmospheric greenhouse effect. Early Mars atmospheric composition is not well constrained, but it was probably mostly composed of CO2 with a surface pressure between a few hundreds of mbars to a few bars . Large amounts of CO2 and H2O were probably released by the substantial Tharsis volcanism during the mid-Noachian. These species probably contributed, but other greenhouse gases have been proposed to solve the enigma (Fig. 3). Some of them are photochemically unstable and rapidly exhausted, unless continuously outgassed by volcanoes. The discovery of sulphate salts in Mars’ surface  have promoted the relevance of SO2 as greenhouse, and strength the possibility of an astrobiological catalytic environment in presence of water and N-bearing species [3-4]. The study at microscale of Martian meteorites (exemplified with the previous ALH84001 study) can be useful to understand the geological context and get new insight about the presence of biosignatures.
Figure 2. ALH 84001 carbonate globules. Left) Optical microscope transmitted light where the rounded globules appear in brown. Right) One of the globules emphasized with a EDX mapping to show the different Fe-content of the layering.
Concerning the presence of water in Mars’ surface and subsurface at different epochs, the evidence arrived from Martian meteorites indicates a progressive water depletion probably due to the evolving surface environment, finally reaching the current harsh conditions. For example, clear evidence for Amazonian acidic liquid water on Mars surface was found, producing aqueous alteration minerals . A dense atmosphere associated with volcanic outgassing during the Noachian period could have promoted significant deceleration, and disruption of fragile chondritic asteroids. In such circumstances the arrival of meteorite powders was a way to promote catalytic reactions at the Martian surface. Given that the early Mars was subjected to a continuous rain of chondritic materials when it experienced significant hydrothermal activity, I identify a potential astrobiology environment
All this growing evidence about the role of the aqueous alteration and the formation of secondary minerals also supports the evidence for a wet Mars environment. The role of collisional gardening in the early stages of Mars' evolution is also out of doubt from the study of the oldest Martian meteorites . In fact, new evidence for a massive water sequestration has been recently presented . To search for the pathways of water towards the interior of Mars we should study impact fractures in the crust of Mars, and their role to host potential biota. Probably the transient nature of aquifers in Mars was restricting the regions to develop life, but future mission searches in depth could get new clues.
This research has been funded by PGC2018-097374-B-I00 (MCI-AEI-FEDER, UE). US Antarctic meteorites are recovered by the Antarctic Search for Meteorites (ANSMET) program funded by NSF and NASA, and characterized and curated by the Department of Mineral Sciences of the Smithsonian Institution and Astromaterials Acquisition and Curation Office at NASA Johnson Space Center.
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How to cite: Trigo-Rodríguez, J. M. and Trišić, J.: What can be learned from Allan Hills 84001 carbonate globules about aqueous alteration processes in the Martian crust?, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-803, https://doi.org/10.5194/epsc2021-803, 2021.
Olivine, (Mg, Fe)2SiO4, is a mineral composed of the two endmembers of its solid solution series: forsterite (Fo, Mg2SiO4) and fayalite (Fa, Fe2SiO4). It is a silicate mineral present in Mars usually alongside with plagioclase and pyroxene, as they are all present in basalts and igneous rocks. The forsterite and fayalite proportions in the olivine is a key factor in order to study this type of rocks.
Active and upcoming Mars missions will study areas of ancient Mars using, among others, Raman spectroscopy in the instrumental payload, being a relevant technique for space exploration. There are several papers proposing Raman spectroscopy to quantify the ratio Fo/Fa based on the wavenumbers of the two most intense bands. However, the proposed calibration models have an uncertainty of around 10 %, too high to obtain reliable conclusions form the studied samples. In this work a new model that greatly improves the accuracy and uncertainty is presented.
2. Data set
A collection of Raman spectra from olivines with a known composition was collected to develop a calibration model for the determination of the metallic content (Mg, Fe) of the mineral. The collection included 64 data points from 14 different research papers where different Raman instruments and acquisition parameters were used, which eliminates any possible bias that the instrumentation could introduce in the model. In addition to the set of olivines used for the calibration, a commercial pure olivine of known metallic concentration, Fo89.5±1.8Fa10.5±0.5, was used as the standard to validate the proposed models. This olivine was analyzed by WD-XRF and its mineral purity was checked by XRD. The Raman measurements were carried out with an Invia High Resolution micro-Raman spectrometer (Renishaw, UK) instrument, using a 532 nm excitation laser with a spectral resolution of 1 cm-1.
3. Results and Discussion
Two different regression curves were developed to characterize the olivine concentration ratio by Raman spectroscopy using their two main Raman features (OB1, 812-825 cm-1, and OB2, 837-857 cm-1). These regression curves with their residuals can be observed in Figure 1 and Figure 2 and their equations are shown in Equation 1 and 2, respectively. The two red lines depicted in the calibration curve plots represent the calculated confidence interval for all the data at a 95 % confidence level.
OB1 (cm-1) = 3.63·10-4·Fox2 + 0.0667·Fox + 814.2 (Equation 1)
OB2 (cm-1) = 3.00·10-4·Fox2 + 0.142·Fox + 839.6 (Equation 2)