High-calcium Pyroxene Research Articles

Spectral unmixing analysis for the lunar surface mineralogy using Chandrayaan-2 IIRS imagery

Hyperspectral imagery (HSI) in the visible to near-infrared wavelength region has a high potential for deciphering mineral compositions of terrestrial and planetary surfaces. Thus, ISRO's Imaging Infrared Spectrometer (IIRS) sensor onboard Chandrayaan-2 (Ch-2) orbiter provides an opportunity to utilise the hyperspectral observations to characterise the lunar surface minerals and composition significantly. Hence, a sensitivity study of hyperspectral observations of the IIRS sensor was carried out for the detection and mapping of various lunar minerals using spectral unmixing analysis. A common region within the hyperspectral image obtained from Chandrayaan-1's (Ch-1) Moon Mineralogy Mapper (M3) sensor and Ch-2 IIRS sensor has been identified in the South-East of the Taurus-Littrow valley nearby Gardner crater for comparison and validation purposes. Ch-2 IIRS is an advanced hyperspectral imaging spectrometer capable of collecting spectra over a wider spectral range (800 ​nm ​− ​5000 ​nm) with high spatial (~80 m) and spectral resolution (20 n m ​− ​25 ​n m ). To examine spectral unmixing analysis, an electromagnetic range (800 ​nm ​− ​2500 ​nm) in the near-infrared region was chosen for the Ch-2 IIRS sensor. An L 1 ​− ​ norm based denoising algorithm is used for mixed noise removal from both the IIRS and M3 reflectance datasets. Endmember extraction and fractional abundance estimation are carried out using the N-Findr algorithm and the fully-constrained least square method, respectively. Our results reveal different minerals such as high-calcium pyroxene (Clinopyroxene), low-calcium pyroxene (Orthopyroxene), and regolith surface (matured and younger). The results obtained from the IIRS and M3 observations are in strong agreement. Hence, the hyperspectral observations made by the IIRS sensor are extremely effective for describing the mineral and chemical compositions of the lunar surface. • Spectral unmixing analysis is executed to determine lunar surface mineralogy and their abundance using Hyperspectral data. • For comparative analysis, co-located datasets from Chandrayaan-2 (Ch-2) IIRS and Chandrayaan-1(Ch-1) M3 are investigated. • An L1-norm-based denoising algorithm is introduced to significantly improve the data quality by removing the complex noise. • The methodology can be automated to develop the lunar mineralogical and chemical map in a time-efficient and systematic way.

Orbital Observations of a Marker Horizon at Gale Crater

AbstractA dark‐toned, indurated, smooth horizon, and (or) bed (herein called “marker horizon”) is exposed across much of the northwestern, southwestern, and southeastern portions of Mount Sharp in Gale crater. Compact Reconnaissance Imaging Spectrometer for Mars spectra taken from the marker horizon exhibit evidence for the presence of high calcium pyroxene and other basaltic minerals in contrast to the hydrated sulfate signatures associated with strata above and below it. Mean dips for the marker horizon and sulfate‐bearing strata are 1–5° with almost all azimuths radially away from the center of Mount Sharp. The marker horizon thickness varies between <1 and 3 m and its elevation changes by 1.6 km across the mound. Surface slopes along the sulfate‐bearing strata above and below the marker horizon are typically 20°–40° compared to <5° surface slopes on the marker horizon. Features observed on the marker horizon include ridges, fractures, faults, layering, oval depressions, small craters, and possible yardangs/indurated bedforms. We interpret the marker horizon to be a single unit that formed contemporaneously across Mount Sharp during the same depositional sequence that created the sulfate‐bearing strata. Plausible formation mechanisms for the marker horizon include (1) emplacement of a more indurated sulfate unit, either from (a) primary deposition or (b) secondary diagenesis; (2) deposition of a more resistant sandstone unit during a brief drier period; (3) emplacement of a volcanic ash deposit laid down in the midst of the sulfate formation period; or (4) a lag deposit created during a drier period. Based on our observations, origins (1a) and (3) are the most plausible.

Occurrence of secondary minerals at Tharsis Montes of Mars: A critical assessment

Identification of phyllosilicates on Mars suggests the existence of an aqueous environment, indicating an active period in its evolutionary history. This study analysed the surface mineralogy of caldera and flank regions of Tharsis Montes using remote spectral analysis. Though a thick layer of dust obscures the surface of Tharsis volcanic province, relatively lesser dust regions provide a unique window for exploration. The reflectance data obtained from CRISM onboard Mars Reconnaissance Orbiter in the visible-infrared region is used for the mineralogical study. Spectral parameter indices were used to identify the distribution of minerals over the caldera and flank regions of Tharsis Montes. The spectral characterisation indicates the well-distributed presence of mafic minerals such as olivine with low-calcium pyroxene and plagioclase with the sparse presence of high-calcium pyroxene in the region. The dusty region, typically with a high TES DCI index and low thermal inertia values in the Tharsis Montes, shows a high concentration of olivine. Few regions identified as comparatively dust-free at the caldera and flank show the presence of secondary mafic minerals like FeMg bearing phyllosilicates. Our spectral analysis using nonlinear mixing models with the MICA spectral library indicates the occurrence of absorption features characteristic of hydrated minerals. The occurrence of the secondary mafic minerals, especially the phyllosilicates on Tharsis Montes suggest active weathering or hydrothermal alteration from episodic volcanic activity over time.

Compositional and morphological analysis of Gassendi crater

Gassendi impact crater is located on the western side of the visible lunar hemisphere just north of Mare Humorum. It has a diameter of 110 km, and it is a Floor Fractured Crater (FFC) belonging to Class-3 type that exhibits a wide annular depression or moat. Is Gassendi crater formed due to igneous intrusion or viscous relaxation? To investigate this, the analysis explores the compositional and morphological dimensions of the crater. The area studied has been found to contain various minerals such as LCP (Low Calcium Pyroxene), HCP (High Calcium Pyroxene), olivine, plagioclase, and mixtures of pyroxene and plagioclase. To differentiate between similar spectral profiles, Integrated Band Depth map (IBD) and Band Depth Parameter (BD) maps are generated using the M3 data. Features such as central peak complex, isolated mound, fractures, rimae, wall terraces, wall slumps, etc., have been identified and marked in the morphological map. We have also studied the morphometrical aspects of all the morphological features. Another impact crater just on the northern rim of Gassendi, Gassendi A crater shows the presence of LCP and olivine mineral along with extensive slumping, melt pool, and distorted northern rim. We have mapped the three mare regions towards the south of the crater floor and estimated their ages by using the CSFD technique. The present appearance of the Gassendi crater is mostly due to past volcanic activities rather than the result of the impact event.

Mineralogical survey of the anorthositic Feldspathic Highlands Terrane crust using Moon Mineralogy Mapper data

Spectroscopic data from the Moon Mineralogy Mapper (M3) instrument are used to study the mineralogy of the central peak or peak ring of 75 craters located in the lunar anorthositic Feldspathic Highlands Terrane (FHT-a), as defined by Jolliff et al. (2000). The thickness of South-Pole Aitken (SPA) ejecta at the location of the selected craters is estimated. Crustal thickness models are used with empirical cratering equations to estimate the depth of origin of the material excavated in the studied central peaks, and its distance to the crust-mantle interface. The goal of this survey is to study the composition of the FHT-a crust, and the extent of its potential lateral and vertical heterogeneities. High-Calcium Pyroxene (HCP) and featureless spectra are mostly detected throughout the entire FHT-a, whereas the number of pure plagioclase detections is small. No relationship between the central peak composition and the distance to SPA or the depth within the SPA ejecta is observed. The SPA ejecta material cannot be spectrally distinguished from crustal material. We interpret the paucity of plagioclase spectra in the FHT-a, which contrasts with more frequent plagioclase detections in the central peaks of craters sampling the crust in younger lunar terranes using identical spectroscopic techniques Martinot et al. (2018b), as a possible effect of terrane maturation, or of mixing with mafic components that mask their signature in the visible near-infrared. Overall, the FHT-a appears homogeneous laterally. However, data hint at a pyroxene compositional change with increasing depth, from high-calcium content in the upper crust towards less calcic compositions with increasing depth, which is consistent with prior studies of the architecture of the lunar crust.

Aqueous alteration of pyroxene in sulfate, chloride, and perchlorate brines: Implications for post-Noachian aqueous alteration on Mars

Abstract Both high and low calcium pyroxene minerals have been detected over large portions of the martian surface in addition to widespread salts in martian soils and dust. Calcium pyroxenes in martian meteorites are associated with secondary evaporite phases, including sulfates, chlorides, and perchlorates, suggesting the pyroxene may have been altered in saline solutions. Therefore, understanding pyroxene mineral weathering in high salinity brines may provide insight into past aqueous alteration on Mars. This study examines both solute-based dissolution rates and qualitative assessments of weathering textures developed during pyroxene-brine alteration experiments to link dissolution rates and textures and aid in interpreting weathering features observed in Mars meteorites and future pyroxene samples returned from Mars. Batch reactor dissolution experiments were conducted at 298 K to compare diopside (a high Ca-pyroxene) dissolution rates in water (18 MΩ cm−1 ultrapure water (UPW); activity of water (ɑH2O) = 1.0), 0.35 mol kg−1 NaCl (ɑH2O = 0.99), 0.35 mol kg−1 Na2SO4 (ɑH2O = 0.98), 2 mol kg−1 NaClO4 (ɑH2O = 0.90), 2.5 mol kg−1 Na2SO4 (ɑH2O = 0.95), 5.7 mol kg−1 NaCl (ɑH2O = 0.75), and 9 mol kg−1 CaCl2 (ɑH2O = 0.35) brines at pH 5–6.6 to determine how changing solution chemistry and activity of water influence pyroxene dissolution. Aqueous Si release rates and qualitative textural analyses indicate diopside dissolution rates are influenced by both solution chemistry and activity of water, with diopside weathering increasing along a trend from: 9 mol kg−1 CaCl2

Assessing martian bedrock mineralogy through “windows” in the dust using near-infrared and thermal infrared remote sensing

Much of Mars' surface is mantled by bright dust, which masks the spectral features used to interpret the mineralogy of the underlying bedrock. Despite the wealth of near-infrared (NIR) and thermal infrared (TIR) data returned from orbiting spacecraft in recent decades, the detailed bedrock composition of approximately half of the Martian surface remains relatively unknown due to dust cover. To address this issue, and to help gain a better understanding of the bedrock mineralogy in dusty regions, Dust Cover Index results from the Mars Global Surveyor Thermal Emission Spectrometer (TES) and analysis of images from the Mars Reconnaissance Orbiter Mars Color Imager (MARCI) were used to identify 63 small localized areas within the classical bright dusty regions of Arabia Terra, Elysium Planitia, and Tharsis Montes as potential “windows” through the dust; that is, areas where the dust cover is thin enough to permit infrared remote sensing of the underlying materials. The mineralogy of each candidate window was inferred using spectra from the Mars Express Observatoire pour la Mineralogie, l'Eau, les Glaces et l'Activité (OMEGA) NIR spectrometer and, where possible, TES. Twelve areas of interest returned spectra that are consistent with mineral species expected to be present at the regional scale, such as high- and low-calcium pyroxene, olivine, and iron-bearing glass. Distribution maps were created using previously defined index parameters for each species present within an area. High-quality TES spectra, if present within an area of interest, were deconvolved to estimate modal mineralogy and to support NIR interpretations. OMEGA data from Arabia Terra and Elysium Planitia are largely similar and indicate the presence of high-calcium pyroxene with significant contributions of glass and olivine, while TES data suggest an intermediate between the established compositions of the southern highlands and Syrtis Major. Limited data from Tharsis are consistent with low-calcium pyroxene mixed with lesser amounts of glass and high-calcium pyroxene. TES data from southern Tharsis correlate well with the previously inferred compositions of the Aonium and Mare Sirenum highlands immediately to the south. Of particular note is the detection of iron-bearing glass as a significant component of all three analyzed regions, especially in Tharsis. Overall, the underlying compositions of the classically dust-covered regions of Mars appear consistent with the compositions of adjacent and other low-albedo (not dust covered) regions of the planet identified in previous studies, with the noted contribution from iron-bearing glass.

Global classification of lunar reflectance spectra obtained by Kaguya (SELENE): Implication for hidden basaltic materials

A global classification map of lunar absorption spectra is developed under unified classification criteria by applying the K-means and ISODATA unsupervised classification methods. The spectra were obtained by the Spectral Profiler (SP) onboard the Kaguya (SELENE) lunar orbiter spacecraft. The spectra are mostly categorized into seven spectral groups by the K-means method: K1, K2, K3, K4, K5, K6, and K7. Then, each K-means group is divided into 66 total classes by the ISODATA method. The K1 and K3 groups are classified into 21 and 14 classes, respectively, for which the average spectra are high-calcium pyroxene (HCP)-abundant compared to the other groups. Both groups are mainly located on maria and pyroclastic deposits. However, while the K1 group can be found primarily near the center of large maria, the K3 group can be found mainly at small maria and the margins of large maria. The K2 group contains eight classes and shows average spectra, such as low-calcium pyroxene (LCP), in abundance, which are found mainly on the South Pole-Aitken (SPA) basin and on the coast of Mare Frigoris. The K5 (eight classes), K6 (two classes) and K7 (three classes) groups indicate average spectra with shallower absorption (between 0.9 µm and 1.2 µm wavelength) than those of the K1, K2, and K3 groups. These groups are located in highland regions, and the K5 group is located in high-albedo regions, such as fresh craters. The K6 group is found on nearside highland areas and the K7 group is found on farside highland areas. The K4 group with nine classes shows average spectra, such as mixtures of K1/K2/K3 and K5/K6/K7, and these classes are located around boundaries between mare/SPA and highland. In addition, one class is independently defined without using K-means and ISODATA because its spectra are unsuitable for automatic unsupervised classification. However, this class is still geologically meaningful.The average spectra of the ISODATA classes show not only the characteristics of the major host material belonging to a spectral group, but they also show the small influence of materials from other groups in nearby regions on that host material. This influence is considered to be caused by horizontal material mixing of materials in that location with the ejecta from nearby regions. However, occasionally the ISODATA classes of the K4, K5, and K6 groups influenced by the K1/K3 groups are clustered geographically in regions far from the K1/K3 regions. Some locations of the clusters correspond to locations of the well-known cryptomaria and small pyroclastic deposits. On the other hand, some locations of them also contain candidates of hidden subterranean basaltic materials, such as undiscovered cryptomare, dike, and sill estimated based on recent lunar gravitational anomalies. This agreement suggests to be appeared hidden basaltic materials by the material mixing occurring vertically. The total area of the clusters except for known cryptomaria is approximately two times larger than that of the known cryptomaria, and this area reaches approximately 20% of the total area of exposed maria. The total volume of hidden basaltic materials, except for the known cryptomaria, is estimated to be 104 to 106 km3, depending on assumptions of the relative abundance between cryptomare and dike/sill. This volume is comparable to that of the known cryptomaria and approximately 10% of that of the exposed mare.

Mineralogical Diversity and Geology of Humboldt Crater Derived Using Moon Mineralogy Mapper Data.

Moon Mineralogy Mapper (M3) spectroscopic data and high‐resolution imagery data sets were used to study the mineralogy and geology of the 207 km diameter Humboldt crater. Analyses of M3 data, using a custom‐made method for M3 spectra continuum removal and spectral parameters calculation, reveal multiple pure crystalline plagioclase detections within the Humboldt crater central peak complex, hinting at its crustal origin. However, olivine, spinel, and glass are observed in the crater walls and rims, suggesting these minerals derive from shallower levels than the plagioclase of the central peak complex. High‐calcium pyroxenes are detected in association with volcanic deposits emplaced on the crater's floor. Geologic mapping was performed, and the age of Humboldt crater's units was estimated from crater counts. Results suggest that volcanic activity within this floor‐fractured crater spanned over a billion years. The felsic mineralogy of the central peak complex region, which presumably excavated deeper material, and the shallow mafic minerals (olivine and spinel) detected in Humboldt crater walls and rim are not in accordance with the general view of the structure of the lunar crust. Our observations can be explained by the presence of a mafic pluton emplaced in the anorthositic crust prior to the Humboldt‐forming impact event. Alternatively, the excavation of Australe basin ejecta could explain the observed mineralogical detections. This highlights the importance of detailed combined mineralogical and geological remote sensing studies to assess the heterogeneity of the lunar crust.

The role of particle size in the laboratory reflectance spectra of pyroxenes: The case of the 670-nm minor feature

Reflectance spectroscopy is a very helpful tool for remote sensing investigations and has been widely used in terrestrial as well as planetary observations to study the surface composition. From this perspective, the visible (Vis) and near-infrared (NIR) regions of the spectrum, where several diagnostic absorption features of minerals are located, are well suited for the identification of such materials, in particular of rock-forming silicates. Among them, pyroxenes, which have been discovered on the surface of a number of different solar system bodies, play an important role.Up to now, both laboratory and remote sensing spectroscopic studies have been focused mainly on the two major bands at about 1 and 2µm (the so-called Band I and Band II, respectively), while little attention has been paid to the minor bands falling in the visible range. One of the most important of them, present in many pyroxenes as well as in olivines, is the weak feature (reflectance minimum) near 670nm, generally characterized by its variable wings (reflectance maxima) at about 570nm and 720nm. The intensity and the exact position of this feature depend on the type of pyroxene as well as on the grain size of the particles under consideration.In this work we present the Vis/NIR experimental reflectance spectra concerning enstatite and diopside, which are excellent representative of Low Calcium Pyroxenes (typically orthopyroxenes), and High Calcium Pyroxenes (typically clinopyroxenes) respectively. The results are very interesting and show a good correlation between the grain size of our samples and the relative intensities of the reflectance maxima occurring on both sides of the 670nm feature. A similar study performed on Acfer 353, a pyroxene-rich eucritic meteorite of the Howardite–Eucrite–Diogenite family, of putative Vestan origin, shows that also in this case the variability in the Vis region of the spectra is linked to the grain size of the meteoritic particles. The connection between grain size and the behavior of the 670nm feature can potentially be used to derive the average dimension of the regolith existing on the surface of planets and minor bodies.Both laboratory and observational study of the minor features, frequently ignored in the interpretation of the spectra acquired in remote sensing, can give complementary and useful information and thus can definitely contribute to a better knowledge of the mineralogy of planetary and asteroidal surfaces.

The central uplift of Ritchey crater, Mars

Ritchey crater is a ∼79km diameter complex crater near the boundary between Hesperian ridged plains and Noachian highland terrain on Mars (28.8°S, 309.0°E) that formed after the Noachian. High Resolution Imaging Science Experiment (HiRISE) images of the central peak reveal fractured massive bedrock and megabreccia with large clasts. Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectral analysis reveals low calcium pyroxene (LCP), olivine (OL), hydrated silicates (phyllosilicates) and a possible identification of plagioclase bedrock. We mapped the Ritchey crater central uplift into ten units, with 4 main groups from oldest and originally deepest to youngest: (1) megabreccia with large clasts rich in LCP and OL, and with alteration to phyllosilicates; (2) massive bedrock with bright and dark regions rich in LCP or OL, respectively; (3) LCP and OL-rich impactites draped over the central uplift; and (4) aeolian deposits. We interpret the primitive martian crust as igneous rocks rich in LCP, OL, and probably plagioclase, as previously observed in eastern Valles Marineris. We do not observe high-calcium pyroxene (HCP) rich bedrock as seen in Argyre or western Valles Marineris. The association of phyllosilicates with deep megabreccia could be from impact-induced alteration, either as a result of the Richey impact, or alteration of pre-existing impactites from Argyre basin and other large impacts that preceded the Ritchey impact, or both.

Modal mineralogy of the surface of Vesta: Evidence for ubiquitous olivine and identification of meteorite analogue

The observations of the surface of 4 Vesta by the Visible and Infrared Mapping Spectrometer (VIR) onboard the Dawn spacecraft reveals that its composition is dominated by pyroxenes with olivine in very localized spots. To derive new constraints on the surface composition of the asteroid, we apply a scattering model to VIR reflectance spectra. The model is first calibrated by performing a non-linear deconvolution of laboratory spectra of mineral mixtures and howardite, eucrite, diogenite (HED) meteorites. Abundance estimates of minerals are accurate to within 15–25% for the analyzed samples, while the estimated particle sizes are within the intervals of actual sizes. Grain size effects complicate spectral deconvolution and estimation of modal abundances of samples (both HED and mineral mixtures) that contain olivine. The magnesium-rich olivine detection threshold is 10–20% for large grain sizes (100sμm) and several 10s% for small grain sizes (<50μm). Major expected minerals (low-calcium pyroxenes, high-calcium pyroxenes, plagioclase and olivine) can provide satisfactory fits of VIR spectra with excellent residuals ⩽1%. Terrains with the strongest low-calcium pyroxene signatures are well representative of diogenites. The best fits of any unit are obtained by including Fo70 olivine at an abundance level of 10–20%, with an uncertainty of ∼10%. Olivine is therefore likely to be ubiquitous over the whole surface of Vesta. Olivine is coarser grained (a few hundred μm) than other minerals such as orthopyroxene and clinopyroxene (grain sizes typically smaller than 100μm). Both the grain size variance and the modal mineralogy are consistent with the lithologic size and mineral distributions of howardites containing olivine phenocryst-bearing melt. These howardites are the best petrologic analogues of Vesta. Such a surface assemblage could be the result of successive melting and mixing processes due to impacts. The compositional view confirms that Vesta underwent major homogenization processes, resulting in a relatively uniform modal mineralogy and explaining the lack of specific olivine enrichment in the Rheasilvia ejecta.

Near-infrared spectra of ferrous mineral mixtures and methods for their identification in planetary surface spectra

Iron-bearing minerals are a major component of planetary surfaces, and many can be identified by their characteristic absorption bands in the near-infrared (NIR). Here we present laboratory NIR spectra of a wide range of common Fe-bearing minerals (e.g., olivines, pyroxenes), glasses, and mineral/glass mixtures. We then use this suite of spectra to evaluate the effects of mixtures on mineral detection methods, including olivine and pyroxene spectral indices developed for the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) onboard Mars Reconnaissance Orbiter. We find that although these indices can be compromised by minerals with atypical compositions, mineral mixtures, and the presence of other ferrous minerals, these issues can generally be mitigated by visual inspection of the spectra. However, a special case occurs when the mineral or mixture in question is spectrally indistinguishable from a more common mineral. In particular, we show that spectra of high-calcium pyroxene mixed with Fe-bearing glass can be virtually indistinguishable from common Fe-bearing olivine compositions. This effect, combined with the fact that Fe-bearing glass is generally much more difficult to detect than other ferrous minerals, may be causing glass occurrences on planetary surfaces to be underreported. In support of this hypothesis, we use Mars Express OMEGA observations to show that previous olivine detections in the north polar sand sea on Mars are actually more consistent with local mixing of glass and pyroxene. To address these issues, we present an alternative ferrous mineral identification method based on the position and shape of the 1 and 2μm iron absorption bands, which are sensitive to mineralogy, composition, and mineral mixtures in planetary surface spectra, including glass and mixtures with glass. Using Chandrayaan-1 Moon Mineralogy Mapper (M3) observations of Aristarchus Crater on the Moon, we show that these band parameters can reveal subtle spectral variations and can produce mineralogical maps at an exceptional level of detail.

Surface composition of near-Earth Asteroid (4953) 1990 MU: Possible fragment of (6) Hebe

Near-Earth asteroids (NEAs) are interesting as both a threat to the Earth and as the immediate parent bodies of most meteorites. We observed NEA (4953) 1990 MU using the NASA Infrared Telescope Facility (IRTF) and University of Hawaii (U.H.) telescopes on Mauna Kea to constrain its surface composition and origin. The surface composition of 1990 MU is similar to ordinary chondrites (H chondrites). The calculated olivine and pyroxene chemistry of 1990 MU (Fa13.5±1.3 and Fs12.7±1.4) are consistent with the olivine and pyroxene chemistry ranges for H chondrites (Fa15–21 and Fs13–19) (Dunn, T.L., McCoy, T.J., Sunshine, J.M., McSween, H.Y. [2010]. Icarus 208, 789–797), although the estimated Fa value is at the lower end of the H chondrite range. The olivine abundance ratio of 1990 MU (0.57±0.03) is slightly higher but not inconsistent with H chondrites (0.47–0.55±0.03). The radar circular polarization ratio (same circular polarization state or SC/opposite circular polarization state or OC) (Benner, L.A.M., Ostro, S.J., Magri, C., Nolan, M.C., Howell, E.S., Giorgini, J.D., Jurgens, R.F., Margot, J.L., Taylor, P.A., Busch, M.W., Shepard, M.K. [2008]. Icarus, 198, 294–304) of 1990 MU is 0.36±0.03, which is higher than the mean SC/OC ratio for S-type NEAs (0.270±0.079). The 1990 MU SC/OC is also higher than those of (25143) Itokawa (0.27±0.04), (4179) Toutatis (0.29±0.01) and (433) Eros (0.28±0.06) suggesting a rougher surface at decimeter scale (Benner, L.A.M., Ostro, S.J., Magri, C., Nolan, M.C., Howell, E.S., Giorgini, J.D., Jurgens, R.F., Margot, J.L., Taylor, P.A., Busch, M.W., Shepard, M.K. [2008]. Icarus, 198, 294–304). We constrained the diameter of 1990 MU (4.4km) using the average albedo at 0.55μm of H chondrites (0.21) and absolute magnitude (H) of 14.1 (Flower, J.W., Chillemi J.R. [1992]. IRAS Asteroid Data Processing: The IRAS Minor Planet Survey, Philips Laboratory Technical Report PL-TR-92-2049. Jet Propulsion Laboratory, Pasadena, California, pp. 17–43). This diameter is higher than the 2.8km value from Harris et al. (Harris, A.W. et al. [2011]. Astron. J. 141, 10) using an albedo of 0.52 for 1990 MU. This albedo value is unusually high for H chondrites, which have an albedo range of 0.12–0.30. We compared olivine and pyroxene chemistries of 1990 MU with main belt Asteroid (6) Hebe, probable parent body of H chondrite meteorites and IIE irons (Gaffey, M.J., Gilbert, S.L. [1998]. Meteor. Planet. Sci. 33, 1281–1295), and found that 1990 MU has more high-calcium pyroxene than Hebe. Fayalite and ferrosilite values of the two asteroids are consistent with H chondrites but do not overlap each other. The differences could be due to compositional variations observed on Hebe by Gaffey and Gilbert (Gaffey, M.J., Gilbert, S.L. [1998]. Meteor. Planet. Sci. 33, 1281–1295), although the observed rotational variation in spectral parameters does not match well with those of 1990 MU.

Composition and structures of the subsurface in the vicinity of Valles Marineris as revealed by central uplifts of impact craters

Despite recent efforts from space exploration to sound the martian subsurface with RADAR, the structure of the martian subsurface is still unknown. Major geologic contacts or discontinuities inside the martian crust have not been revealed. Another way to analyze the subsurface is to study rocks that have been exhumed from depth by impact processes. The last martian mission, MRO (Mars Reconnaissance Orbiter), put forth a great deal of effort in targeting the central peaks of impact craters with both of its high resolution instruments: CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) and HiRISE (High Resolution Science Experiment). We analyzed the composition with CRISM and the physical characteristics on HiRISE of the rocks exhumed from depth from 31 impact craters in the vicinity of Valles Marineris. Our analyses revealed the presence at depth of two kinds of material: massive light-toned rocks and intact layers. Exhumed light-toned massive rocks are enriched in low calcium pyroxenes and olivine. Hydrated phases such as smectites and putative serpentine are present and may provide evidence of hydrothermal processes. Some of the rocks may represent portions of the volatile-rich, pre-Noachian martian primitive crust. In the second class of central peaks, exhumed layers are deformed, folded, and fractured. Visible-near infrared (VNIR) spectra suggest that they are composed of a mixture of olivine and high calcium pyroxene associated with hydrated phases. These layers may represent a Noachian volcanic accumulation of up to 18km due to Tharsis activity. The spatial distribution, as well as the in-depth distribution between the two groups of rocks exhumed, are not random and reveal a major geologic discontinuity below the Tharsis lava plateau. The contact may be vertical over several kilometers depth suggesting the pre-existence of a steep basin (early giant impact or subsidence basin) or sagduction processes.

The widespread occurrence of high-calcium pyroxene in bright-ray craters on the Moon and implications for lunar-crust composition

[1] We investigated the continuous spectral features of fresh craters on the Moon accompanied by distinctive bright rays, with cavity diameters between 8 and 24 km. We used the data from the Spectral Profiler onboard SELENE (Kaguya) to gain a better understanding of the composition of the lunar highland crust. We found that the observed spectra exhibited strong symmetric absorption around 1 μm and recognizable absorption around 1.3 μm. The spectra around a few craters showed a drastic change in the relative strengths of these two absorption bands s1.3/1.0 at different locations in and around the craters, indicating differences in the abundance of plagioclase and mafic minerals. In contrast, the spectra around most of the craters showed no significant variation in spectral shape, with an essentially constant s1.3/1.0. We analyzed the absorption features of the craters with an essentially constant s1.3/1.0 using the Modified Gaussian Model. We found that the strongest symmetric absorption bands were centered at 0.97–1.01 μm with s1.3/1.0 ≈ 0.2–0.6. Comparing these values with data from known samples, we concluded that high-calcium pyroxene (HCP) is the most plausible dominant mafic mineral identified from the observed spectra. The fact that we detected such HCP-dominant spectra among rayed craters widely spaced across the lunar highland implies that the major mafic component of some portions of the lunar crust is HCP rather than low-calcium pyroxene (LCP).

Compositional variability of the Marius Hills volcanic complex from the Moon Mineralogy Mapper (M3)

[1] Using the Moon Mineralogy Mapper(M3), we examine the Marius Hills volcanic complex for the first time from 0.46 to 2.97 μm. The integrated band depth at 1 μm separates the mare basalts on the plateau in two units: (1) a strong 1 μm band unit of localized lava flows within the plateau that has similar olivine-rich signatures to those of the nearby Oceanus Procellarum and (2) a weaker 1 μm band unit that characterizes most of the basalts of the plateau, which is interpreted as having a high-calcium pyroxene signature. Domes and cones within the complex belong to the high-calcium pyroxene plateau unit and are associated with the weakest 1 μm band observed on the plateau. This difference could be the result of higher silica content, more opaque minerals, and/or a weaker olivine content of the magma. Finally, the floor of Marius crater has one of the strongest olivine-rich signatures of the entire Marius Hills complex. These compositional differences are indicative of the long and complex volcanic history of the region. The first episode started before the emplacement of the surrounding basalts of the plateau and produced the high-calcium pyroxene flows present on the plateau and their associated domes and cones. The second episode occurred concurrently or slightly after the emplacement of the adjacent Procellarum basalts and produced the olivine-rich basalts seen within the plateau, outside the plateau, and in Marius crater. If the olivine content of the lava flows increases with time, the olivine-rich region on the floor of Marius crater may represent one of the latest episodes of volcanism exposed on the Marius Hills complex.

Reflectance spectra of analog anorthosites: Implications for lunar highland mapping

Lunar highland region and associated craters are mostly composed of anorthosite. In the present study, we studied the reflectance spectra of terrestrial anorthosites collected from Sittampundi Anorthosites Complex, which is considered as equivalent (simulant) of lunar highland anorthosites. The objective of the study is to interpret diagnostic spectral features of analog anorthosite for remotely exploring lunar highland region. Reflectance spectra of anorthosites were measured under two different environments, such as controlled field and laboratory conditions. In these two procedures, the laboratory spectra give clear, diagnostic spectral information in the present study. Reflectance spectra captured under 350–2500 nm covering UV, Visible, NIR, and SWIR part of the electromagnetic spectrum. The spectral characteristics of anorthosites measured under various parts of electromagnetic spectrum have diagnostic absorption features at 380–387, 700–740, 930–1100, 1160–1200, 1415, 1920, 2200 and 2330 nm correspondingly due to plagioclase UV absorption, Fe 3+ electron transition absorption, Fe 2+ pyroxene and olivine absorption, OH/Mn 3+ crystal transition absorption, pyroxene absorption, Al–OH absorption and Mg–OH absorption. Mineralogical and chemical analyses were carried out for four anorthosites and compared with the results of chemical component of lunar anorthosite. The percentage of plagioclase content, relative abundance of low and high calcium pyroxene and olivine in different anorthosite samples are correlated with the albedo range, absorption shape, absorption centers and band depth. The similarity in the diagnostic spectral features of the anolog anorthosite with lunar anorthosites could be effectively utilized for remotely mapping the lunar highland region.

Surface-compositional properties of the Malea Planum region of the Circum-Hellas Volcanic Province, Mars

We used Thermal Emission Spectrometer (TES), Thermal Emission Imaging System (THEMIS), High-Resolution Stereo Camera (HRSC), and Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité (OMEGA) data to assess the physical and compositional properties of the Malea Planum portion of the Circum-Hellas Volcanic Province (CHVP). Our analysis of surface materials shows that the thermal inertia decreases from north to south, and that there is greater dust cover on the flanks of the CHVP volcanoes than in their putative calderas. Local variations in thermal inertia in Malea Planum are likely due to variations in surface material caused by aeolian and periglacial/permafrost processes, whereas regional variations are likely due to seasonal deposition and sublimation of ice at higher latitudes. Spectral analysis of OMEGA data indicates the widespread presence of pyroxenes and/or olivine, particularly in the rims of craters that likely excavated volcanic materials. Dark materials occur throughout the CHVP, but are concentrated in topographic lows such as crater and caldera floors. Derivation of modal mineralogies from OMEGA data show a variation in composition of dark materials across Malea Planum: eastern dark deposits have higher olivine and low-calcium pyroxene contents, lower high-calcium pyroxene contents, and higher ratios of low-calcium to total pyroxene, relative to western dark deposits. Correlation with cratering-model age estimates suggests that the western deposits are associated with older features (3.8 Ga) than the eastern deposits (3.6 Ga), but these age differences are within uncertainties. Nevertheless, these results suggest a potential change in composition of volcanic materials in the Malea Planum portion of the CHVP with space, and possibly time.

Mineralogy of recent volcanic plains in the Tharsis region, Mars, and implications for platy-ridged flow composition

Volcanism on Mars occurred until recently, but the mineralogy of recent lava plains is poorly known because few regions display fresh outcrops devoid of dust. Using visible and near infrared data of the Mars Express probe, two new volcanic plains in Noctis Labyrinthus have been identified, and the existence of a volcanic plain on the floor of Echus Chasma has been confirmed. Crater retention ages estimated for these three plains range between 50 and 100 My, corresponding to the Late Amazonian. These plains represent an excellent opportunity to constrain the mineralogy of recent volcanic rocks. Results show that basaltic compositions with plagioclase and high calcium pyroxene are predominant. The low olivine proportion suggests that the apparent fluidity of these flat plains is not related to magmas being ultramafic. In addition, a platy-ridged texture is observed in two of the studied regions. Our study shows, for the first time, that this texture is associated with volcanic rocks, and that these rocks are of typical basaltic mineralogy. Finally, these volcanic plains are located more than 1000 km east of previously known Late Amazonian volcanic centers of the Tharsis region, an observation to be taken into account when considering models of recent volcanism on Mars.