Martian minerals components at Gale crater detected by ... - IEEE Xplore

2013 2nd International Symposium on Instrumentation and Measurement, Sensor Network and Automation (IMSNA)

Martian minerals components at Gale crater detected by MRO CRISM hyperspectral images Yansong Xue

Shuanggen Jin

Shanghai Astronomical Observatory, Chinese Academy of Science Shanghai, China e-mail: [email protected]

Shanghai Astronomical Observatory, Chinese Academy of Science Shanghai, China e-mail: [email protected]

Abstract—Gale Crater on Mars has the layered structure of deposit covered by the Noachian/Hesperian boundary. Mineral identification and classification at this region can provide important constrains on environment and geological evolution for Mars. Although Curiosity rove has provided the in-situ mineralogical analysis in Gale, but it restricted in small areas. Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard the Mars Reconnaissance Orbiter (MRO) with enhanced spectral resolution can provide more information in spatial and time scale. In this paper, CRISM near-infrared spectral data are used to identify mineral classes and groups at Martian Gale region. By using diagnostic absorptions features analysis in conjunction with spectral angle mapper (SAM), detailed mineral species are identified at Gale region, e.g., kaolinite, chlorites, smectite, jarosite, and northupite. The clay minerals’ diversity in Gale Crater suggests the variation of aqueous alteration. The detection of northupite suggests that the Gale region has experienced the climate change from moist condition with mineral dissolution to dryer climate with water evaporation. The presence of ferric sulfate mineral jarosite formed through the oxidation of iron sulfides in acidic environments shows the experience of acidic sulfur-rich condition in Gale history. Keywords-Martain mineral;CRISM;MRO;Gale Crater

I.

INTRODUCTION

The aqueous alteration on Mars is directly related to the existence of life on Mars at past or present. Martian mineral detection and mapping can provide important constraints in Martian aqueous historyˈwhich can be used to assess the potential habitability of the planet. In-situ observations of the Martian rovers, such as Spirit, Opportunity and Curiosity have provided the mineralogical analysis of Martian surface, but restricting in limited areas. The Thermal Emission Spectrometer (TES) onboard Mars Global Surveyor (MGS) has provided the first detailed mineralogical survey [1]. Outcrops of crystalline gray hematite detected by TES indicated the existence of chemical precipitation of iron-enriched aqueous fluids, which was confirmed by Martian Rover Opportunity in the Merridiani Planum [2]. The detection of hydrated minerals provided the mineralogical evidence of the water on early Mars [3]. Hydrated minerals, particularly phyllosilicates, were mostly exposed in the ancient terrain units, such as Noachian, which indicates the age correlation for specific mineral [4].

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Most commons method for mineral identification is spectral analysis based on the spectral feature of given minerals, but the more precise classification needs to check the spectral angle [5]. The hyperspectral remote sensor can calculate the spectral angle. In this paper, combining spectral feature with spectral angle methods (SAM), CRISM near-infrared spectral data are used to identify mineral classes and distribution at Martian Gale region. After the introduction of the geologic setting of the studied Gale region in Section II, observation data processing and methods are presented in Section III. Section IV shows results and discussion on Martian mineral species identification. Finally, some conclusions are given in Section V.

GEOLOGIC SETTING IN STUDY AREA Gale crater locates in the northwest part of the Aeolis quadrangle region on Mars, which was chosen as the landing site of the Curiosity rover. Around its central peak, there is an enormous mound considered as sedimentary in origin [6]. Studies of impact crater densities in Gale crater have revealed that the formation age of the mound of deposit was ranged from 3.6 to 3.8 Ga, covering the Noachian/Hesperian boundary [7]. The layered structure of deposit in Gale indicated long and suitable transportation and precipitation by wind or liquid water [8]. Sedimentary sequence of mound in Gale Crater exhibited stratigraphic changes in lithology that were consistent with major mineralogic and climatic changes proposed by Bibring et al [4]. After landing of Curiosity, the more precise information has been acquired. The fine-grained Sedimentary rock at Yellowknife Bay has been discovered and its younger age indicated that the formation of clay mineral on Mars extended beyond Noachian time [9]. The composition analysis of sedimentary rock suggested that it was formed in aqueous environment characterized by neutral pH, low salinity, and variable redox states, which were inferred to represent a habitable fluvio-lacustrine environment [10]. However, detailed mineral species and rock components are not clear at whole Gale region as well as geological evolution.

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II.


III.

OBSERVATION AND DATA PROCESSING

A. CRISM observations The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard the Mars Reconnaissance Orbiter (MRO) is the first hyperspectral imager for Mars exploration. There are 544 channels covering the visible to near-infrared spcetra from 0.4 to 4.0 m. The CRISM instrument consists of two spectrometers (‘S” and “L”). The ‘‘S” spectrometer covers the wavelength range from 0.36 to 1.05 m and the ‘‘L” spectrometer covers the wavelength range from 1.0 to 3.9 m. Two operation modes for CRISM are avaliable with (1) a 72-channel mapping mode with spatial resolution of 200m/pixel and (2) a full 544-channel targeted mode with spatial resolution of 15-38 m/pixel [11]..CRISM can search evidence of aqueous or hydrothermal activity, and map and characterize the composition, geology, and stratigraphy of surface features, particularly the presence of indicative minerals of aqueous alteration, e.g., phyllosilicates, carbonate, sulfate, salt and oxides, which can be chemically altered or formed in the presence of water. All of these minerals have specific features in their visible-infrared spectral profile, which can be identified by CRISM. In addition, CRISM can characterize seasonal variations in dust and ice particulates in the Martian atmosphere. B. Data pre-processing CRISM ‘‘L” spectrometer data are converted from calibrated radiance to apparent re ectance and surface reflectance by a standard two-step procedure with photometric correction and atmospheric corrections. Prior to spectral analysis, the atmospheric and photometric correction of CRISM data cubes are needed, which are used to exclude the contribution of reflection of surface from the atmospheric emission. Photometric correction has been applied to CRISM data cubes through dividing by the cosine of the incidence angle, assuming that the Martian surface satisfies the Lambert’s emission law [12]. The CO2 absorption effect has been removed by using a ‘‘volcano scan” atmospheric correction [13]. In addition to atmospheric correction, algorithm of noise filtering was implemented to remove data spikes in the spectral and spatial domains [14]. IV.

chlorite group: chamosite, and the smectite group: nontronite and montmorillonite. The dominant two clay minerals are kaolinite and serpentine, both belonging to Kaoliniteserpentine group, which account for 90% of the clay minerals. 1) Kaolinite Kaolinite is a T-O clay mineral with the chemical composition Al2Si2O5 (OH)4. This group includes kaolinite and other rare hydrated forms, such as the dickite, nacrite, and halloysite. Figure 1 shows the kaolinite spectral profile retrieved from CRISM data. The absorption at 1.9 m shows the presence of crystallized water in hydrated mineral. The absorption near 1.4 m is caused by vibrations of inner hydroxyl groups between the tetrahedral and octahedral sheets in kaolin group minerals [15]. The absorption at 2.2 m is due to a combination of vibrations of 2Al-OH groups in the kaolinite mineral structure [16] 2) Chlorite The chlorites are a group of clay minerals, which can be divided into the following four endmembers based on their chemical composition including Clinochlore (Mg5Al)(AlSi3)O10(OH)8, Chamosite (Fe5Al)(AlSi3)O10(OH)8, Nimite (Ni5Al)(AlSi3)O10(OH)8, Pennantite (Mn,Al)6(Si,Al)4O10(OH)8. Although the range of chemical composition allows chlorite group minerals to exist over a wide range of temperature and pressure conditions, the cations of chlorite on Mars are dominated by Al, Fe, and Mg. Figure 2 shows the CRISM spectra of chlorite-bearing materials.

RESULTS AND DISCUSSION

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A. Clay minerals Clay minerals are hydrous phyllosilicates that can be classified as T-O or T-O-T layer structures according to their fundamental components of tetrahedral silicate sheets and octahedral hydroxide sheets. The T-O clay mineral includes kaolinite and serpentine group that are consist of one tetrahedral sheet and one octahedral sheet, while the T-O-T clay mineral is consists of an octahedral sheet sandwiched between two tetrahedral sheets, like chlorites and smectite group. There are 5 clay minerals detected in the Gale Crater. The Kaolinite-serpentine group: kaolinite and serpentine, the

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Figure 1. Kaolinite group mineral spectral profile.

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Chlorite spectral profile in frt000058a3

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Figure 3. Smectite group mineral spectral profile.

Chlorites are T-O-T layer structure phyllosilicates. Vertical lines are plotted at near 1.408, 1.480, 1.928, 2.014, 2.278, and 2.318 m. There are strong absorptions at 1.408 m and 1.480 m resulted from the overtone of OH stretching vibrations. The drop near 2.0 m is probably due to errors in atmospheric calibration [17]. Absorption band in the spectral profile from 2.2 to 2.5 m vary with substitution of cations, such as Al, Fe, and Mg. In chlorite spectral profile, the absorption at 2.33-2.35 m shifts towards the longer wavelengths as the ratio of magnesium increases [18]. The 2.25-2.35 m absorptions are resulted from combination of absorption of the Fe/Mg-OH rather than from Al-OH at 2.2 m [19][20]. In Figure 2, sharp absorption at 2.278 m indicates the high iron proportion in chlorite detected in Gale crater region. The absorption at 2.318 m demonstrates the presence of magnesium. Although spectral profile from 2.2 to 2.5 m suggested the chlorite in Gale is almost Fe-rich chamosite, the presence of an absorption at 1.48 m is uniquely diagnostic of prehnite that is a phyllosilicate of calcium and aluminium with the formula: Ca2Al(AlSi3O10)(OH)2. The absorption at 1.48 m with indicating existence of prehnite in Gale crater provides the evidence for hydrothermal or low-temperature metamorphic activity. 3) Smectite Smectite is family of T-O-T phyllosilicate clays with permanent layer charge because of the isomorphous substitution in each octahedral sheet. Smectite group includes Pyrophyllite, montmorillonite, Beidellite, nontronite, saponite, hectorite and sauconite. They are formed by the alteration of mafic minerals, weak linkage and substitution of cations. The most common smectite on Earth is Montmorillinite, the main constituent of bentonite derived by weathering of volcanic. In the Gale crater region, the dominated smetite is nontronite detected from the CRISM data. Figure 3 shows CRISM spectra of iron smectite bearing materials.

Figure 3 shows the absorption at near 2.3 and 2.39 m resulted from a combination of overtones of the Fe-OH, MgOH stretch, which indicates that the semetites in Gale crater is more likely the mixture of montmorillonite and nontronite. B. Salts:Sulfate and Carbonate Using SAM method (tolereance=0.100), the two important salts have been detected. The presence of salts (sulfate and carbonate) in Gale Crater indicates that some minerals could precipitate on the surface of Mars. The most import sulfate is Jarosite. It is hydrous sulfate of iron formed in ore deposits by the oxidation of iron sulfides and commonly associated with acid mine drainage and acid sulfate soil environments. There are 3 positive scenses for Jarosite using SAM (tolerance =0.100): frt00019dd9, hrs00004259 and frt0000b5a3. The northupite has been detected in Gale Crater using SAM (tolerance =0.100). Northupite is an uncommon evaporate mineral. This mineral is formed in water-rich environment. In addition, the water must evaporate for the mineral precipitation, indicating that the water input the environment remains below the net rate of evaporation. The presence of evaporating in Gale reveals the alteration of the environment from water-rich environment to mineral dissolution and dryer climate with water evaporation. V.

CONCLUSION

With the higher spatial resolution supplied by CRISM and identification method of diagnostic absorptions features, detailed mineral species are detected at Gale region, e.g., kaolinite, chlorites, smectite, jarosite, and northupite. The diversity of minerals at Gale Crater suggests the variation of aqueous alteration in space and time scale. The presence of northupite indicates the evaporation of salt at Gale Crater, which suggests that the Gale region has experienced the climate change from moist condition with mineral dissolution to dryer climate with water evaporation. The presence of ferric sulfate mineral jarosite formed through the oxidation of iron sulfides in acidic environments shows the experience of acidic sulfur-rich condition in Gale

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history. Furthermore, Mars has experienced geologic and climatic changes throughout its 4.5 Ga of existence. Phyllosilicates detected in ancient terrains showed that water was abundant in the Martian early history. Sulfate deposits began to form near the end of the Noachian period when acid-sulfate weathering has dominated. The Mars Reconnaissance Orbiter (MRO) CRISM data are used to identify mineral and produce the more precise classification, which can be used to constrain the geological and climate alteration processed on Mars. Furthermore, more comprehend the rock and mineral distribution of Martian surface in large scale is also useful for landing sites selection of the Mars Exploration Rover in the future [21]. This research is supported by the National Basic Research Program of China (973 Program) (Grant No. 2012CB720000), Main Direction Project of Chinese Academy of Sciences (Grant No. KJCX2-EW-T03), and Shanghai Science and Technology Commission Project (Grant No. 12DZ2273300).

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