Laboratory measurements of reflectance spectra of rocks and minerals at multiple viewing geometries are important for interpreting spacecraft data of planetary surfaces. However, efficiently acquiring such measurements is challenging, as it requires a custom goniometer that can accommodate multiple, bulky samples beneath a movable light source and detector. Most spectrogoniometric laboratory work to date has focused on mineral mixtures and particulates, yet it is also critical to characterize natural rock surfaces to understand the influence of texture and alteration. We designed the Three-Axis N-sample Automated Goniometer for Evaluating Reflectance (TANAGER) specifically to rapidly acquire spectra of natural rock surfaces across the full scattering hemisphere. TANAGER has its light source and the spectrometer’s fiber optic mounted on motorized rotating and tilting arcs, with a rotating azimuth stage and six-position sample tray, all of which are fully motorized and integrated with a Malvern PanAnalytical ASD FieldSpec4 Hi-Res reflectance spectrometer. Using well-characterized color calibration targets, we have validated the accuracy and repeatability of TANAGER spectra. We also confirm that the system introduces no discernable noise or artifacts. All design schematics and control software for TANAGER are open-source and available for use and modification by the larger scientific community.

AbstractIron oxide and hydroxide minerals, likely responsible for Mars' distinctive red color, offer critical insights into the planet's ancient and current climate, as well as its potential habitability. Several previous studies attributed Mars' reddish hue to anhydrous hematite (Fe2O3) and suggested that its formation is a geologically young process. Recent analyses by the Mars Science Laboratory (MSL) rover revealed the presence of volatiles and amorphous materials in the surface fines and dust, but mineralogy remained unresolved. Here, we present evidence that poorly crystalline ferrihydrite (Fe5O8H · nH2O) is responsible for the red color of the Martian dust, as identified through a combination of orbital (CRISM & OMEGA), in-situ (MSL ChemCam, MER Pancam and Pathfinder IMP), and laboratory visible near-infrared spectra. We employ quantitative spectral analyses, which demonstrate that among various iron oxyhydroxides, ferrihydrite is most consistent with the observed Martian dust spectra. In addition, our dehydration experiments show that ferrihydrite does not transform into other more crystalline iron oxide phases when exposed to present-day Martian conditions. The preservation of ferrihydrite until present time is inconsistent with a sustained warm climate after it was formed, since warm conditions would favor transformation into more crystalline hematite and/or goethite. We propose that the formation of abundant ferrihydrite indicates a cool, wet environment in the last stages of early Mars, favorable to oxidative conditions, followed by a transition to a hyper-arid erosional environment that has persisted to the present day.IntroductionIdentifying the dominant iron oxide phases in Martian dust can provide quantitative constraints on the planet’s ancient chemical environments and climate conditions. On Earth iron oxides form under specific environmental conditions including pH, temperature, redox state, and water availability (Cornell & Schwertmann, 2003). The reddish coloration of the Martian surface has been investigated since the early telescopic observations that hinted at the presence of impure iron ore known as limonite, which contains the crystalline iron (oxy)hydroxide mineral goethite (α-FeOOH) (Adams & McCord, 1969; Dollfus, 1957; Sagan et al., 1965; Sharonov, 1961). Subsequent ground-based telescopic and laboratory observations attributed the reddish hue to the presence of pigmentary anhydrous hematite (α-Fe2O3; termed “nanophase NpOx”) dispersed in the surface regolith and/or coating of rocks (Bell et al., 1990; Morris et al., 1989). Based on the lack of water absorption features at near infrared (NIR) wavelengths (1 – 2.5 μm)as determined by ESA’s Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité (OMEGA) spectrometer, it was argued that the anhydrous and dusty regions contain ferric oxides, possibly hematite or maghemite (γ-Fe2O3)(Bibring et al., 2006). Furthermore, a widely used mineralogical model (Bibring et al., 2006) proposed that these anhydrous ferric oxides in Martian dust formed by continuous oxidation and weathering under water-poor surface conditions during the Amazonian period, which spans from approximately 3 billion years ago to the present.Early spacecraft observations revealed a distinctive 3 μm hydration feature in the Martian dust spectrum (Murchie et al., 1993; Pimentel et al., 1974) well before the weaker NIR spectral features associated with alteration minerals were identified (Bibring et al., 2006). Later evaluation of the OMEGA data noted that the large 3 μm absorption band is deeper in the observations of bright, dusty regions when compared to dark, less dusty terrains (Jouglet et al., 2007; Milliken et al., 2007). The increased strength of this absorption band in dusty regions was attributed to either higher abundances of water adsorbed on grain surfaces due to the large surface to volume ratio of the dust particles (e.g. Zent & Quinn, 1997) or H2O bound in hydrated minerals in the dust. Audouard et al. (2014), using ten years’ worth of OMEGA data, showed that the 3-µm band can be attributed to tightly bound H2O and/or hydroxyl groups in the mineral structure of the dust. NASA’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) also indicated a deep absorption centered at 3 µm (Murchie et al., 2019) in bright, dusty regions. Finally, laboratory reflectance investigations of Martian meteorite ALH 84001 revealed a 3-μm hydration band, which was attributed to H2O, although no bands were observed at 1.4 or 1.9 µm (Bishop et al., 1998). Basaltic volcanic glasses also typically include a broad 3-µm band due to H2O without the weaker 1.4 or 1.9 µm (e.g. Bishop, 2019).Data collected by the MIMOSII Mössbauer instrument (MB) on the Mars Exploration Rovers (MER) showed the existence of coarse-grained hematite and goethite in specific rock outcrops as well as the ubiquitous presence of undetermined iron oxide phase (“nanophase NpOx”) in the fine dust (Morris et al., 2006). While MER MB data can be used to determine the Fe oxidation state (Fe3+/FeT) it is more difficult to distinguish the mineralogy of ferric iron present in the Martian dust (Morris & Klingelhöfer, 2008). This difficulty arises because in the microcrystal range, the distinct characteristics of different iron oxides gradually disappear as particle size and crystallinity decrease, resulting in broad and diffuse spectral lines (Coey, 1974; Murad & Schwertmann, 1980). Further, characterization of nanophase components is difficult in mixtures. However, data from MERs showed that the iron concentration in the fine dust is positively correlated with sulfur and chlorine abundances, while dark olivine-rich soils contained lower abundances of these elements, suggesting that iron in the dust is a product of chemical alteration (Ming et al., 2008; Morris et al., 2006; Yen et al., 2005). The MERs were also equipped with a series of magnet arrays designed to analyze airfall dust. The analysis of the magnetic targets using MB spectral and imaging systems identified two distinct ferric iron endmembers in the dust: one comprising strongly magnetic and dark-colored magnetite, and the other an unidentified bright-colored (oxy)hydroxide exhibiting weak magnetic properties (Goetz et al., 2005; Madsen et al., 2009). Earlier results from the Mars Pathfinder mission (Madsen et al., 1999), which utilized five magnets of varying strengths, indicated that the magnetic properties of Martian soil are likely due to small amounts of maghemite present in intimate association with silicate particles, suggesting that the dust particles are composites containing both magnetic and non-magnetic components.NASA’s Mars Science Laboratory (MSL) rover provided several key chemistry and mineralogy measurements of Martian dust and soils. The Chemistry and Camera (ChemCam) instrument utilized its laser-induced breakdown spectroscopy (LIBS) capability to analyze the composition of airfall dust. In each of the initial laser shots from a series of 50 shots on dusty rock surfaces and calibration targets that collected dust over the years, ChemCam consistently detected a hydrogen signal that exhibited no diurnal variation, suggesting that hydrogen is chemically bound within the dust particles (Lasue et al., 2018; Meslin et al., 2013). Samples from the dust covered sand dune known as “Rocknest” were measured with the Chemistry and Mineralogy (CheMin) X-ray diffraction instrument. These measurements revealed that up to scooped soil is X-ray amorphous and that ~20 wt. % of the amorphous component consists of iron oxides (Bish et al., 2013; Blake et al., 2013). In addition, the Alpha Particle X-ray Spectrometer (APXS) instrument analyzed air fall dust on the science observation tray. These measurements (Berger et al., 2016) indicated that the dust is compositionally similar to the bulk basaltic Mars crust (Gellert & Yen, 2019; McLennan & Taylor, 2008), but is enriched in SO3, Cl and Fe, which is in agreement with MER observations (Goetz et al., 2005). Both APXS and ChemCam measurements suggested that the amorphous iron oxide component observed at “Rocknest” soils may be linked to dust (Berger et al., 2016; Lasue et al., 2018). The Sample Analysis at Mars (SAM) instrument, which includes a gas chromatograph and a quadrupole mass spectrometer, detected volatile species (H2O, SO2, CO2 & O2) when the ’Rocknest’ sample was heated to ~835 °C (Leshin et al., 2013). This finding  suggested that H2O is bound to the amorphous component of the sample, as the CheMin instrument did not detect any crystalline phyllosilicate minerals in this sample (Leshin et al., 2013).Here we report the spectral detection of ferrihydrite (Fe5O8H · nH2O) – a poorly crystalline X-ray amorphous and hydrated iron oxide mineral – using a combination of orbital, in-situ and laboratory visible near-infrared (VNIR) spectra. In addition, we show that ferrihydrite is stable under simulated present-day Martian conditions (UV irradiation, 6 mbar pressure, CO2 atmosphere). We then discuss its importance and implications for the past climate and habitability on Mars.

We have studied the properties of the Nili Fossae olivine lithology from orbital data and in situ by the Mars 2020 rover at the Séítah unit in Jezero crater. We used the geochemistry collected by the rover’s instruments to calculate the viscosity and relative flow distance of the Séítah unit. Based on the low viscosity and distribution of the unit we postulate a ponded lava flow origin for the olivine rich unit at Séítah. We calculate an approximate depth for the cumulate layer of the lava pond based on the viscosity of the unit and model of Worster et al. (1993). We show that the resolution of orbital data is inadequate to map the phyllosilicate 2.38 μm band and demonstrate that it can be supplemented by in situ data from Mars 2020 SuperCam Laser Induced Breakdown Spectroscopy (LIBS) and reflectance observations to show that the low Al phyllosilicate in the olivine cumulate in the Séítah formation is either talc, serpentine, hectorite, Fe/Mg smectite, saponite or stevensite. We discuss two intertwining aspects of the history of the lithology: 1) the potential emplacement and properties of the cumulate layer within a ponded lava flow, using previously published models of ponded lava flows and lava lakes, and 2) the limited extent of post emplacement alteration, including phyllosilicate and carbonate alteration.

During the NASA Perseverance rover’s exploration of the Jezero crater floor, purple-hued coatings were commonly observed on rocks. These features likely record past water-rock-atmosphere interactions on the crater floor, and understanding their origin is important for constraining timing of water activity and habitability at Jezero. Here we characterize the morphologic, chemical, and spectral properties of the crater floor rock coatings using color images, visible/near-infrared reflectance spectra, and chemical data from the Mastcam-Z and SuperCam instruments. We show that coatings are common and compositionally similar across the crater floor, and consistent with a mixture of dust, fine regolith, sulfates, and ferric oxides indurated as a result of one or more episodes of widespread surface alteration. All coatings exhibit a similar smooth homogenous surface with variable thickness, color, and spatial extent on rocks, likely reflecting variable oxidation and erosional expressions related to formation and/or exposure age. Coatings unconformably overlie eroded natural rock surfaces, suggesting relatively late deposition that may represent one of the last aqueous episodes on the Jezero crater floor. While more common at Jezero, these coatings may be consistent with rock coatings previously observed in-situ at other landing sites and may be related to duricrust formation, suggesting a global alteration process on Mars that is not unique to Jezero. The Perseverance rover likely sampled these rock coatings on the crater floor and results from this study could provide important context for future investigations by the Mars Sample Return mission aimed at constraining the geologic and aqueous history of Jezero crater.

We have studied the observed properties of the Nili Fossae olivine-phyllosilicate-carbonate lithology from orbital data and in situ by the Mars 2020 rover at the Séítah unit in Jezero crater, including: 1) composition 2) grain size 3) inferred viscosity (calculated based on geochemistry collected by SuperCam (Wiens et al., 2022)). Based on the low viscosity and distribution of the unit we postulate a flood lava origin for the olivine-phyllosilicate-carbonate at Séítah. We include a new CRISM map of the phyllosilicate 2.38 μm band and use in situ data from Mars 2020 SuperCam Laser Induced Breakdown Spectroscopy (LIBS) and VISIR and MastCam-Z observations to show that the phyllosilicate in the olivine cumulate in the Séítah formation is either talc, serpentine, hectorite, Fe/Mg smectite, saponite or stevensite. We discuss two intertwining aspects of the history of the lithology: 1) the emplacement and properties of the cumulate layer within a lava lake, based on terrestrial analogs in the Pilbara, Western Australia, and using previously published models of flood lavas and lava lakes, and 2) the limited extent of post emplacement alteration, including phyllosilicate and carbonate alteration.

The first samples collected by the Perseverance rover on the Mars 2020 mission were from the Maaz formation, a lava plain that covers most of the floor of Jezero crater. Laboratory analysis of these samples back on Earth will provide important constraints on the petrologic history, aqueous processes, and timing of key events in Jezero. However, interpreting these samples will require a detailed understanding of the emplacement and modification history of the Maaz formation. Here we synthesize rover and orbital remote sensing data to link outcrop-scale interpretations to the broader history of the crater, including Mastcam-Z mosaics and multispectral images, SuperCam chemistry and reflectance point spectra, RIMFAX ground penetrating radar, and orbital hyperspectral reflectance and high-resolution images. We show that the Maaz formation is composed of a series of distinct members corresponding to basaltic to basaltic andesite lava flows. The members exhibit variable spectral signatures dominated by high-Ca pyroxene, Fe-bearing feldspar, and hematite, which can be tied directly to igneous grains and altered matrix in abrasion patches. Spectral variations correlate with morphological variations, from recessive layers that produce a regolith lag in lower Maaz, to weathered polygonally fractured paleosurfaces and crater-retaining massive blocky hummocks in upper Maaz. The Maaz members were likely separated by one or more extended periods of time, and were subjected to variable erosion, burial, exhumation, weathering, and tectonic modification. The two unique samples from the Maaz formation are representative of this diversity, and together will provide an important geochronological framework for the history of Jezero crater.

The SuperCam instrument onboard Perseverance rover has remote imaging (RMI), VISIR, LIBS, Raman and Time-Resolved Luminescence (TRL) capabilities. RMI images of the rocks at the Octavia Butler landing site have revealed important granular texture diversities. VISIR raster point observations have revealed important differences in the 2.10-2.50 µm infrared range (metal-hydroxides); many include water features at 1.40±0.04 and 1.92±0.02 µm [1]. LIBS observations on the same points analyzed by VISIR revealed important differences in the concentrations of major elements, suggesting mineral grain sizes larger than the laser beam (300-500 µm). LIBS and VISIR show coherent results in some rock surfaces that are consistent with an oxy-hydroxide (e.g., ferrihydrite) [1]. LIBS elemental compositions are consistent with pyroxenes, feldspars, and more often feldspar-like glass, often enriched in silica. Olivine compositions [1, 2] have been observed so far in LIBS data (up to Sol 140) exclusively in rounded regolith pebbles. They have not yet been observed in the rocks themselves, which are MgO-poor compared to regolith and are consistent with FeO bearing pyroxenes (e.g., hedenbergite, ferrosilite). A 3x3 LIBS and VISIR raster (9x9 mm) acquired on a low-standing rock on sol 90 exemplifies these finding. A dark L-shaped filled void sampled by points 1 and 2 with possible ferrihydrite (H seen in LIBS and VISIR spectra). Point 5 contains abundant silica and alkali elements but is Al-depleted relative to feldspars, consistent with dacitic glass composition. Point 7 has TiO2 content consistent with ilmenite. Comparisons to (igneous) Martian meteorites are potentially useful, e.g. [3], to explain the presence of several minerals, although most Martian meteorites are olivine-rich, e.g., more mafic than the rocks at the landing site. In summary, the bedrock at Octavia Butler landing site can be interpreted as showing evidence for relatively coarse-grained weathered pyroxenes, iron and titanium oxides and feldspars, while the local soil contains pebbles from a different source (richer in MgO) incorporating olivine grains. References: [1] Mandon et al. 2021 Fall AGU, New Orleans, LA, 13-17 Dec. ; [2] Beyssac et al. 2021 Fall AGU, New Orleans, LA, 13-17 Dec. ; [3] Garcia-Florentino et al.(2021), Talanta, 224, 121863.

Images from the Mars Science Laboratory (MSL) mission of lacustrine sedimentary rocks of Vera Rubin ridge on “Mt. Sharp” in Gale crater, Mars, have shown stark color variations from red to purple to gray. These color differences cross-cut stratigraphy and are likely due to diagenetic alteration of the sediments after deposition. However, the chemistry and timing of these fluid interactions is unclear. Determining how diagenetic processes may have modified chemical and mineralogical signatures of ancient martian environments is critical for understanding the past habitability of Mars and achieving the goals of the MSL mission. Here we use visible/near-infrared spectra from Mastcam and ChemCam to determine the mineralogical origins of color variations in the ridge. Color variations are consistent with changes in spectral properties related to the crystallinity, grain size, and texture of hematite. Coarse-grained gray hematite spectrally dominates in the gray patches and is present in the purple areas, while nanophase and fine-grained red crystalline hematite are present and spectrally dominate in the red and purple areas. We hypothesize that these differences were caused by grain size coarsening of hematite by diagenetic fluids, as observed in terrestrial analogs. In this model, early primary reddening by oxidizing fluids near the surface was followed during or after burial by bleaching to form the gray patches, possibly with limited secondary reddening after exhumation. Diagenetic alteration may have diminished the preservation of biosignatures and changed the composition of the sediments, making it more difficult to interpret how conditions evolved in the paleolake over time.

The Mastcam-Z radiometric calibration targets mounted on the NASA’s Perseverance rover proved to be effective in the calibration of Mastcam-Z images to reflectance (I/F) over the first 350 sols on Mars. Mastcam-Z imaged the calibration targets regularly to perform reflectance calibration on multispectral image sets of targets on the Martian surface. For each calibration target image, mean radiance values were extracted for 41 distinct regions of the targets, including patches of color and grayscale materials. Eight strong permanent magnets, placed under the primary target, attracted magnetic dust and repelled it from central surfaces, allowing the extraction of radiance values from eight regions relatively clean from dust. These radiances were combined with reflectances obtained from laboratory measurements, a one-term linear fit model was applied, and the slopes of the fits were retrieved as estimates of the solar irradiance and used to convert Mastcam-Z images from radiance to reflectance. Derived irradiance time series are smoothly varying in line with expectations based on the changing Mars-Sun distance, being only perturbed by a few significant dust events. The deposition of dust on the calibration targets was largely concentrated on the magnets, ensuring a minimal influence of dust on the calibration process. The fraction of sunlight directly hitting the calibration targets was negatively correlated with the atmospheric optical depth, as expected. Further investigation will aim at explaining the origin of a small offset observed in the fit model employed for calibration, and the causes of a yellowing effect affecting one of the calibration targets materials.

The Perseverance rover, Mars 2020 mission, landed on the surface of the Jezero Crater, on February, 18th 2021. This Martian crater is suspected to have hosted a paleolake as evidenced by the numerous detections of aqueously-altered phases and thus is a promising candidate for the search for past Martian life. The SuperCam instrument, elaborated by a consortium of American and European laboratories, plays a leading role in this investigation thanks to its highly versatile payload providing rapid, synergistic, fine-scale mineralogy, chemistry, and color imaging. After its landing, the first measurements of Martian targets with the infrared spectrometer of SuperCam (IRS) showed new instrumental behaviors that had to be characterized and calibrated to derive unbiased science data. The IRS radiometric response has thus been calibrated using periodic observations of the Aluwhite SuperCam Calibration Target (SCCT). Parasitic effects were understood and mitigated, and the instrumental dark and noise are characterized and modeled. The reflectance calibrated data products, provided periodically on the NASA Planetary Data System, are corrected from the main instrumental features.

The exploration of the surface geology of Venus has been hampered by its inhospitable conditions and thick and opaque atmosphere. Fundamental properties, such as crustal composition and heterogeneity remain poorly constrained. Multiple analytical techniques are required to better understand its geology. A spectroscopy-based study laboratory study of the emissivity properties of Venus-relevant igneous rocks, measured at 440 °C by Dyar et al. (2020b; https://doi.org/10.1029/2020GL090497) shows that the use of multiple atmospheric windows in the 1-μm region can provide strong constraints on the FeO content of Venus-relevant igneous rocks, and by extension, the type of igneous rock. These results will improve our ability to map the surface geology of Venus remotely.

The exploration of the surface geology of Venus has been hampered by its inhospitable conditions and thick and opaque atmosphere. Fundamental properties, such as crustal composition and heterogeneity remain poorly constrained. Multiple analytical techniques are required to better understand its geology. A spectroscopy-based study laboratory study of the emissivity properties of Venus-relevant igneous rocks, measured at 440 °C by Dyar et al. (2020b; https://doi.org/10.1029/2020GL090497) shows that the use of multiple atmospheric windows in the 1-µm region can provide strong constraints on the FeO content of Venus-relevant igneous rocks, and by extension, the type of igneous rock. These results will improve our ability to map the surface geology of Venus remotely.