Spectra Of Mars Research Articles

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.

The RISOTTO radiative transfer and retrieval pipeline for the analysis of occultation spectra

We present a new radiative transfer and retrieval pipeline, referred to as RISOTTO, designed for observations made in occultation geometry. RISOTTO can retrieve accurate vertical profiles of the constituents of a planetary atmosphere using a Bayesian approach while simultaneously correcting for instrumental artefacts and uncertainties. The algorithm makes use of a rapid Abel integration scheme involving matrix multiplication, using pre-calculated gaseous cross-section data to calculate the integration along the line of sight, while also separating out any effects of transmission baseline variation. We assess its accuracy using synthetic solar occultation spectra of Mars and comparing it with the older more established NEMESIS radiative transfer and retrieval pipeline (Irwin et al. 2008, J. Quant. Spec. Radiat. Transf. 109, 1136–1150), and show that it can match its accuracy while also being able to more easily retrieve gases with substantial continuum absorption.

Molecular repertoire of Deinococcus radiodurans after 1 year of exposure outside the International Space Station within the Tanpopo mission

BackgroundThe extraordinarily resistant bacterium Deinococcus radiodurans withstands harsh environmental conditions present in outer space. Deinococcus radiodurans was exposed for 1 year outside the International Space Station within Tanpopo orbital mission to investigate microbial survival and space travel. In addition, a ground-based simulation experiment with conditions, mirroring those from low Earth orbit, was performed.MethodsWe monitored Deinococcus radiodurans cells during early stage of recovery after low Earth orbit exposure using electron microscopy tools. Furthermore, proteomic, transcriptomic and metabolomic analyses were performed to identify molecular mechanisms responsible for the survival of Deinococcus radiodurans in low Earth orbit.ResultsD. radiodurans cells exposed to low Earth orbit conditions do not exhibit any morphological damage. However, an accumulation of numerous outer-membrane-associated vesicles was observed. On levels of proteins and transcripts, a multi-faceted response was detected to alleviate cell stress. The UvrABC endonuclease excision repair mechanism was triggered to cope with DNA damage. Defense against reactive oxygen species is mirrored by the increased abundance of catalases and is accompanied by the increased abundance of putrescine, which works as reactive oxygen species scavenging molecule. In addition, several proteins and mRNAs, responsible for regulatory and transporting functions showed increased abundances. The decrease in primary metabolites indicates alternations in the energy status, which is needed to repair damaged molecules.ConclusionLow Earth orbit induced molecular rearrangements trigger multiple components of metabolic stress response and regulatory networks in exposed microbial cells. Presented results show that the non-sporulating bacterium Deinococcus radiodurans survived long-term low Earth orbit exposure if wavelength below 200 nm are not present, which mirrors the UV spectrum of Mars, where CO2 effectively provides a shield below 190 nm. These results should be considered in the context of planetary protection concerns and the development of new sterilization techniques for future space missions.E4zWdY8_EUi-Xs9W1QVdpEVideo

Ferrian saponite from the Santa Monica Mountains (California, U.S.A., Earth): Characterization as an analog for clay minerals on Mars with application to Yellowknife Bay in Gale Crater

Ferrian saponite from the eastern Santa Monica Mountain, near Griffith Park (Los Angeles, California), was investigated as a mineralogical analog to smectites discovered on Mars by the CheMin X-ray diffraction instrument onboard the Mars Science Laboratory (MSL) rover. The martian clay minerals occur in sediment of basaltic composition and have 02 l diffraction bands peaking at 4.59 A, consistent with tri-octahedral smectites. The Griffith saponite occurs in basalts as pseudomorphs after olivine and mesostasis glass and as fillings of vesicles and cracks and has 02 l diffraction bands at that same position. We obtained chemical compositions (by electron microprobe), X-ray diffraction patterns with a lab version of the CheMin instrument, Mossbauer spectra, and visible and near-IR reflectance (VNIR) spectra on several samples from that locality. The Griffith saponite is magnesian, Mg/(Mg+∑Fe) = 65–70%, lacks tetrahedral Fe 3+ and octahedral Al 3+ , and has Fe 3+ /∑Fe from 64 to 93%. Its chemical composition is consistent with a fully tri-octahedral smectite, but the abundance of Fe 3+ gives a nominal excess charge of +1 to +2 per formula unit. The excess charge is likely compensated by substitution of O 2− for OH − , causing distortion of octahedral sites as inferred from Mossbauer spectra. We hypothesize that the Griffith saponite was initially deposited with all its iron as Fe 2+ and was oxidized later. X-ray diffraction shows a sharp 001 peak at 15 A, 00 l peaks, and a 02 l diffraction band at the same position (4.59 A) and shape as those of the martian samples, indicating that the martian saponite is not fully oxidized. VNIR spectra of the Griffith saponite show distinct absorptions at 1.40, 1.90, 2.30–2.32, and 2.40 μm, arising from H 2 O and hydroxyl groups in various settings. The position of the ~2.31 μm spectral feature varies systematically with the redox state of the octahedrally coordinated Fe. This correlation may permit surface oxidation state to be inferred (in some cases) from VNIR spectra of Mars obtained from orbit, and, in any case, ferrian saponite is a viable assignment for spectral detections in the range 2.30–2.32 μm.

Mineralogy and morphology of geologic units at Libya Montes, Mars: Ancient aqueously derived outcrops, mafic flows, fluvial features, and impacts

AbstractThere is ample evidence of both ancient and long‐lasting fluvial activity and chemical alteration in the Libya Montes region south of Isidis Basin. The region hosts Noachian to Amazonian aged surface rocks with extensive outcrops of olivine‐ and pyroxene‐bearing material. Libya Montes also features surface outcrops and/or deposits hosting Fe/Mg‐smectite, Fe/Mg‐smectite mixed with carbonate and/or other Fe/Mg‐rich phyllosilicates, and Al‐smectite. These units likely formed through chemical alteration connected with hydrothermal activity resulting from the formation of the Isidis Basin and/or the pervasive fluvial activity throughout this region. The morphology and stratigraphy of the aqueous and mafic minerals are described using High Resolution Imaging Science Experiment and High Resolution Stereo Camera derived digital terrain models. Analyses of the Compact Reconnaissance Imaging Spectrometer for Mars spectra show variations in the chemistry of the Fe/Mg‐smectite from nontronite‐like exposures with spectral features near 2.29 and 2.4 µm more consistent with Fe3+2OH groups in the mineral structure, and saponite‐like outcrops with spectral features near 2.31 and 2.38 µm characteristic of Mg2+3OH groups. These Fe/Mg‐smectite bearing materials also have bands near 1.9 µm due to H2O and near 2.5 µm that could be due to the smectite, other phyllosilicates, and carbonates. All regions exhibiting carbonate features near 3.4–3.5 µm also have features consistent with the presence of olivine and Fe/Mg‐smectite, indicating that the carbonate signatures occur in rocks likely containing a mixture of these minerals. The Al‐smectite‐bearing rocks have bands near 1.41, 1.91, and 2.19 µm that are more consistent with beidellite than other Al‐phyllosilicates, indicating a higher‐temperature or diagenetically processed origin for this material. Our interpretation of the geologic history of this region is that ancient Noachian basaltic crustal materials experienced extensive aqueous alteration at the time of the Isidis impact, during which the montes were also formed, followed by emplacement of a rough olivine‐rich lava or melt, and finally the smooth pyroxene‐bearing caprock unit.

Investigation of Al-rich clays on Mars: Evidence for kaolinite–smectite mixed-layer versus mixture of end-member phases

Aluminous clay deposits on Mars are recognized from remotely sensed infrared spectral features similar to those of montmorillonite, beidellite, and/or kaolinite. The nature of aluminous clay deposits on Mars is of interest because they likely indicate a different formation mechanism than that of Fe–Mg clays, which are widespread on Mars and likely alteration products of the Fe–Mg-rich basaltic crust. The near-infrared reflectance spectra of aluminous martian clay deposits frequently display characteristics typical of both montmorillonite and kaolinite. The question arises whether such mixed character is due to the existence of end-member phases or to kaolinite–smectite mixed-layer (K–S). The issue is relevant because K–S implies the existence of a smectite precursor that alters into kaolinite, and thus constrains the timing and intensity of the alteration processes that generates it. A mixture of kaolinite and smectite end-members may indicate locally heterogeneous alteration processes, or alternatively, could result from the physical mixing of altered materials of different provenance. A group of natural K–S samples and synthetic kaolinite/smectite mixtures of known proportion, all of which had been thoroughly characterized in previous work using several analytical techniques, were investigated here using near-infrared (NIR) spectroscopy. The NIR spectral features correlate well with their kaolinite–smectite relative proportions. The shape of spectral features attributed to Al–OH in K–S is subtly different from those in physical mixtures of kaolinite and smectite. Based on qualitative comparison, some regions on Mars appear to have spectral signatures similar to K–S. We also applied a quantitative technique using the second derivative of spectra. In this technique, plots of the height of the features at (λ=) 2.21μm (band present in kaolinite and montmorillonite) and 2.17μm (kaolinite only) were able to discriminate between K–S and kaolinite–smectite physical mixtures, as they generated correlations with different slopes. The method of discrimination was applied to Mars spectra, which resulted in reasonable evidence for the existence of K–S in Nili Fossae and Mawrth Vallis, and mixtures of end-members in Mawrth Vallis and Leighton Crater. This is one of the first times that evidence for mixed-layer clay minerals, and particularly K–S, on Mars has been gathered. The ability to detect mixed-layer clays is an important step forward for further development of our understanding of the processes that generated clay on Mars.

A stringent upper limit to SO2in the Martian atmosphere

Surfur-bearing molecules have been found at the surface of Mars by the Viking lander, the Spirit and Opportunity rovers, and the OMEGA infrared spectrometer aboard Mars Express. However, no gaseous sulfur-bearing species have ever been detected in the Martian atmosphere. We search for SO2 signatures in the thermal spectrum of Mars at 7.4 μm using the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF). Data were obtained on Oct. 12, 2009 (Ls = 353 ◦ ), in the 1350–1360 cm −1 range, with a spatial resolution of 1 arcsec (after convolution over three pixels along the N-S axis and two steps along the E-W axis) and a resolving power of 80 000. To improve the signal-to-noise ratio (S/N), we co-added the Martian spectrum around the positions of nine selected SO2 transitions with a high S/N and no telluric contamination. From a mean spectrum, averaged over 35 pixels in the region of maximum continuum, we infer a 2σ upper limit of 0.3 ppb to the SO2 mixing ratio, assuming that our instrumental errors are combined according to Gaussian statistics. Our upper limit is three times lower than the upper limit derived by Krasnopolsky (2005, Icarus, 178, 487), who used the same technique on previous TEXES data. In addition, we derive an upper limit of 2 ppb at each spatial pixel of the region observed by TEXES, which covers the longitude ranges 50 E–170 E for latitudes above 30 N, 100 E–170 E for latitudes between 0 and 30 N, and 110 E–170 E for latitudes between 15 S and 0. The non-detection of localized SO2 sources in the observed area is consistent with a homogeneous distribution being expected around equinox for noncondensible species with a lifetime longer than the global mixing time. In view of the typically large SO2/CH4 ratio observed in terrestrial volcanoes, and assuming a comparable volcanic composition for Mars and the Earth, our result reaffirms that a volcanic origin is unlikely for any methane in the Martian atmosphere.

TheHerschel-SPIRE submillimetre spectrum of Mars

We have obtained the first continuous disk averaged spectrum of Mars from 450 to 1550 Ghz using the Herschel-SPIRE Fourier Transform Spectrometer. The spectrum was obtained at a constant resolution of 1.4 GHz across the whole band. The flux from the planet is such that the instrument was operated in "bright source" mode to prevent saturation of the detectors. This was the first successful use of this mode and in this work we describe the method used for observing Mars together with a detailed discussion of the data reduction techniques required to calibrate the spectrum. We discuss the calibration accuracy obtained and describe the first comparison with surface and atmospheric models. In addition to a direct photometric measurement of the planet the spectrum contains the characteristic transitions of 12CO from J 5-4 to J 13-12 as well as numerous H2O transitions. Together these allow the comparison to global atmospheric models allowing the mean mixing ratios of water and 12CO to be investigated. We find that it is possible to match the observed depth of the absorption features in the spectrum with a fixed water mixing ratio of 1 x 10-4 and a 12CO mixing ratio of 9 x 10-4

Diagenetic haematite and sulfate assemblages in Valles Marineris

Previous orbital mapping of crystalline gray haematite, ferric oxides, and sulfates has shown an association of this mineralogy with light-toned, layered deposits on the floor of Valles Marineris, in chaos terrains in the canyon’s outflow channels, and in Meridiani Planum. The exact nature of the relationship between ferric oxides and sulfates within Valles Marineris is uncertain. The Observatoire pour la Mineralogie, l’Eau, les Glaces et l’Activite (OMEGA) spectrometer initially identified sulfate and ferric oxides in the layered deposits of Valles Marineris. The Thermal Emission Spectrometer (TES) has also mapped coarse (gray) haematite in or at the base of these deposits. We use Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectra and Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) imagery from the Mars Reconnaissance Orbiter (MRO) to explore the mineralogy and morphology of the large layered deposit in central Capri Chasma, part of the Valles Marineris canyon system that has large, clear exposures of sulfate and haematite. We find kieserite (MgSO 4·H 2O) and ferric oxide (often crystalline red haematite) in the lower bedrock exposures and a polyhydrated sulfate without ferric oxides in the upper bedrock. This stratigraphy is duplicated in many other basinal chasmata, suggesting a common genesis. We propose the haematite and monohydrated sulfate formed by diagenetic alteration of a sulfate-rich sedimentary deposit, where the upper polyhydrated sulfate-rich, haematite-poor layers either were not buried sufficiently to convert to a monohydrated sulfate or were part of a later depositional phase. Based on the similarities between the Valles Marineris assemblages and the sulfate and haematite-rich deposits of Meridiani Planum, we hypothesize a common evaporite and diagenetic formation process for the Meridiani Planum sediments and the sulfate-bearing basinal Interior Layered Deposits.

The very early thermal state of Terra Cimmeria: Implications for magnetic carriers in the crust of Mars

Large areas of strongly magnetized crust are located in Terra Cimmeria and Terra Sirenum, in the southern highlands of Mars, the older terrains on the planet. The typical depth to the base of the magnetized layer, deduced from the magnetic spectrum of Mars and modeling of isolated magnetic anomalies, would ∼40–60 km. In this paper the thermal state of Terra Cimmeria is revisited by calculating heat flows and crustal geotherms consistent with a previous estimation of the effective elastic thickness of the lithosphere, and with crustal abundances of heat-producing elements based on surface measurements performed by the Mars Odyssey Gamma Ray Spectrometer. The results suggest that, at the time of formation of the magnetized terrains surface (which have a minimum age of 4.1 Ga), Curie depths for magnetite and hematite were shallower and similar, respectively, than the typical depth to the base of the magnetized layer. This implies that hematite is an important (if not dominant) contributor to the magnetization of the martian crust. However, an early warm climate would enhance the chance of magnetite to be a significant, even dominant, magnetization carrier in the lower portion of the magnetic layer.

Mineralogy of Juventae Chasma: Sulfates in the light‐toned mounds, mafic minerals in the bedrock, and hydrated silica and hydroxylated ferric sulfate on the plateau

Juventae Chasma contains four light‐toned sulfate‐bearing mounds (denoted here as A–D from west to east) inside the trough, mafic outcrops at the base of the mounds and in the wall rock, and light‐toned layered deposits of opal and ferric sulfates on the plateau. Hyperspectral visible/near‐infrared Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectra were used to identify monohydrated and polyhydrated sulfate (PHS) outcrops of layered material on the bright mounds. Most of the monohydrated sulfate signatures closely resemble those of szomolnokite (FeSO4·H2O), characterized by a water band near 2.08 μm, while some areas exhibit spectral features more similar to those of kieserite (MgSO4·H2O), with a band centered closer to 2.13 μm. The largest PHS outcrops occur on the top of mound B, and their spectral features are most consistent with ferricopiapite, melanterite, and starkeyite, but a specific mineral cannot be uniquely identified at this time. Coordinated analyses of CRISM maps, Mars Orbiter Laser Altimeter elevations, and High Resolution Imaging Science Experiment images suggest that mounds A and B may have formed together and then eroded into separate mounds, while mounds C and D likely formed separately. Mafic minerals (low‐Ca pyroxene, high‐Ca pyroxene, and olivine) are observed in large ∼2–10 km wide outcrops in the wall rock and in smaller outcrops ∼50–500 m across at the floor of the canyon. Most of the wall rock is covered by at least a thin layer of dust and does not exhibit strong features characteristic of these minerals. The plateau region northwest of Juventae Chasma is characterized by an abundance of light‐toned layered deposits. One region contains two spectrally unique phases exhibiting a highly stratified, terraced pattern. CRISM spectra of one unit eroded into swirling patterns with arc‐like ridges exhibit a narrow 2.23‐μm band assigned to hydroxylated ferric sulfate. A thin layer of a fractured material bearing an opaline silica phase is observed at the contact between the older plateau unit and the younger hydroxylated ferric sulfate‐bearing light‐toned layered deposits. Hydrothermal processes may have produced an acidic environment that fostered formation of the hydrated silica and hydroxylated ferric sulfate units.

Mars Global Surveyor Thermal Emission Spectrometer (TES) observations of variations in atmospheric dust optical depth over cold surfaces

The Mars Global Surveyor Thermal Emission Spectrometer (TES) instrument has returned over 200 million thermal infrared spectra of Mars taken between March 1999 and August 2004. This represents one of the most complete records of spatial and temporal changes of the martian atmosphere ever recorded by an orbiting spacecraft. Previous reports of the standard TES retrieval of aerosol optical depth have been limited to those observations taken over surfaces with temperatures above 210 K, limiting the spatiotemporal coverage of Polar Regions with TES. Here, we present an extension to the standard TES retrieval that better models the effects of cold surfaces below 200 K. This modification allows aerosol optical depth to be retrieved from TES spectra over a greater spatiotemporal range than was previously possible, specifically in Polar Regions. This new algorithm is applied to the Polar Regions to show the seasonal variability in dust and ice optical depth for the complete temporal range of the TES database (Mars Year 24, L s = 104 ° , 1 March 1999 to Mars Year 24, L s = 82 ° , 31 August 2004).

Global-scale near infrared variability on Mars: Analysis of 2003 Mars opposition observations from HST/NICMOS

We have used HST/NICMOS to observe approximately 57% of the martian surface in 7 narrow band filters (0.97, 1.08, 1.13, 1.66, 1.90, 2.12, and 2.15 μm) during the 2003 opposition ( L s ∼ 250 ° ) and at a resolution of ∼12 km/pixel. Principal components analysis (PCA) of the dataset has identified regional variability on scales of hundreds of kilometers associated with differences in the near-infrared spectrum of Mars. Visualization of the data in principal component space has allowed us to identify spectral endmembers associated with the south polar cap, the classic bright terrains, northern Syrtis Major, southern Syrtis Major, Tyrrhena Terra, and Acidalia Planitia. The two Syrtis Major endmembers and the Tyrrhena Terra endmember differ in their absolute reflectivities but have the same spectral shape at wavelengths longer than 1.6 μm. The Acidalia endmember is distinct from the other dark terrain endmembers because it exhibits a strong negative near-IR spectral slope. Comparisons with spectral library measurements cannot provide unique constraints on the surface mineralogy for these sparsely-sampled spectral data. However, the observed spectral variations between Tyrrhena Terra and Syrtis Major are consistent with variations in iron- and sulfur-bearing minerals, and the relatively strong negative spectral slope in the spectrum of Acidalia is consistent with the presence of hydrated alteration products. Additional comparison with previous NICMOS observations taken in 1997 at L s ∼ 150 ° indicate that the average near-IR spectral slope of the Acidalia region is more negative during the late northern fall than during the mid northern summer. This may indicate seasonal variations in the presence of either adsorbed water or re-hydrated minerals in the regolith of Acidalia.

Magnetic properties of Martian olivine basalts studied by terrestrial analogues

Here we present a comparison study of terrestrial olivine basalt and relatively un-weathered basalt studied by the Mars Exploration Rover Spirit on Mars. The Mossbauer spectra of terrestrial olivine basalt exhibit some characteristics that can also be seen in the Mars spectra. The results from Mossbauer spectroscopy on Mars indicate that the olivine in the rocks has undergone alteration at high temperatures (600–1,000°C), a process known to give rise to anomalously magnetic rocks on Earth. This suggests that if the rocks at Gusev crater had solidified in an external magnetic field of terrestrial magnitude, these would have become highly magnetic enough to explain the presence of magnetic anomalies on Mars.

Effects of chemical weathering on infrared spectra of Columbia River Basalt and spectral interpretations of martian alteration

We investigated the mineralogy of basalt weathering rinds and fresh basaltic rocks using visible/near-infrared (VNIR) ( λ = 0.4–2.5 μm) and thermal emission ( λ = 6–30 μm) spectroscopy to 1) constrain the effects of chemical weathering on rock spectra, and 2) further understand the context of infrared spectra of Mars, which may contain evidence for weathered rocks and particulates derived from them. VNIR spectra of weathered rock surfaces are generally redder and brighter than fresh surfaces. Thermal infrared spectra of weathered basalts show evidence for aluminous opal and clay minerals (or clay precursor mineraloids) in natural surfaces. Supporting VNIR observations generally do not show the same evidence for neoformed clays or silica because of their textural occurrence as thin coatings and microfracture-fill, and possibly due to poor crystallinity of the aluminosilicate weathering products in this context. Spectral trends observed at Mars, such as the detection of low to moderate (10–25%) abundances of silica and clay that are observed in the thermal infrared but not in the VNIR, are therefore consistent with trends observed for natural rock surfaces in the laboratory. The combined use of thermal infrared and VNIR suggest that vast areas of martian dark regions contain sandy–rocky basaltic materials with weathering rinds and thin coatings that could have formed in conditions of relatively low water/rock ratios.

Diffuse reflectance of altered olivine grains: Remote sensing detection and implications for Mars studies

The study of Mars linked to its climatic history, the presence of water and possible forms of life on the planet, are becoming more and more important in recent years. In this paper we present laboratory reflection measurements on olivine samples which are believed to be the product of alteration induced by their coexistence with water. The reflection spectra have been obtained in the wavelength range from 0.2 to 2.5 μ m and for different grain sizes; they exhibit, among various bands, some of which due to H 2 O and OH - , a characteristic absorption feature at about 0.64 μ m , whose emission wings at 0.56 and near 0.7 μ m have relative strengths which are size dependent and well correlated. The identification of such feature in the observed spectra of Mars would provide useful information about the grain size of the Martian regolith and, in association with other bands, also about the possible presence of olivine altered by water in the past.

A sensitive search for nitric oxide in the lower atmospheres of Venus and Mars: Detection on Venus and upper limit for Mars

High-resolution spectra of Venus and Mars at the NO fundamental band at 5.3 μm with resolving power ν / δ ν = 76 , 000 were acquired using the TEXES spectrograph at NASA IRTF on Mauna Kea, Hawaii. The observed spectrum of Venus covered three NO lines of the P-branch. One of the lines is strongly contaminated, and the other two lines reveal NO in the lower atmosphere at a detection level of 9 sigma. A simple photochemical model for NO and N at 50–112 km was coupled with a radiative transfer code to simulate the observed equivalent widths of the NO and some CO 2 lines. The derived NO mixing ratio is 5.5 ± 1.5 ppb below 60 km and its flux is ( 6 ± 2 ) × 10 7 cm −2 s −1 . Predissociation of NO at the (0–0) 191 nm and (1–0) 183 nm bands of the δ-system and the reaction with N are the only important loss processes for NO in the lower atmosphere of Venus. The photochemical impact of the measured NO abundance is significant and should be taken into account in photochemical modeling of the Venus atmosphere. Lightning is the only known source of NO in the lower atmosphere of Venus, and the detection of NO is a convincing and independent proof of lightning on Venus. The required flux of NO is corrected for the production of NO and N by the cosmic ray ionization and corresponds to the lightning energy deposition of 0.19 ± 0.06 erg cm −2 s −1 . For a flash energy on Venus similar to that on the Earth (∼ 10 9 J ), the global flashing rate is ∼90 s −1 and ∼6 km −2 y −1 which is in reasonable agreement with the existing optical observations. The observed spectrum of Mars covered three NO lines of the R-branch. Two of these lines are contaminated by CO 2 lines, and the line at 1900.076 cm −1 is clean and shows some excess over the continuum. Some photochemical reactions may result in a significant excitation of NO ( v = 1 ) in the lowest 20 km on Mars. However, quenching of NO ( v = 1 ) by CO 2 is very effective below 40 km. Excitation of NO ( v = 1 ) in the collisions with atomic oxygen is weak because of the low temperature in the martian atmosphere, and we do not see any explanation of a possible emission of NO at 5.3 μm. Therefore the data are treated as the lack of absorption with a 2 sigma upper limit of 1.7 ppb to the NO abundance in the lower atmosphere of Mars. This limit is above the predictions of photochemical models by a factor of 3.

Calibration of the Planetary Fourier Spectrometer long wavelength channel

The Planetary Fourier Spectrometer (PFS) experiment on board the Mars Express mission has two channels covering the 1.2–5 μm (SWC) and the 5–50 μm (LWC). The Long Wavelength Channel (LWC) measures the thermal emission spectrum of Mars between 200 and 2000 cm −1 with a spectral resolution of 1.4 cm −1, in absence of apodisation. We present here the calibration of this channel and its performance. The instrument calibration has been performed on ground, before launch, in space during Near Earth Verification (NEV) measurements, and at Mars. Special attention has been given to the problem of microvibrations on board the spacecraft. In order to obtain correct results, the source-instrument–detector interaction is studied very accurately. The instrument variations during a pericentre pass impose a complex procedure for the LW channel calibration, but fortunately the procedure adopted seems to work well. Samples of the calibrated data are given (as single spectrum and as an average over a few spectra) to show the performance of the experiment and its scientific potentialities.

Calibration of the Planetary Fourier Spectrometer short wavelength channel

The Planetary Fourier Spectrometer (PFS) experiment on board the Mars Express mission has two channels covering the 1.2–5.5 μ m short wavelength channel (SWC) and the 5.5–45 μ m (LWC). The SWC measures part of the thermal emission spectrum and the solar reflected spectrum of Mars between 1700 and 8200 cm −1 with a spectral resolution of 1.3 cm −1, in absence of apodisation. We present here the calibration of this channel and its performance. The instrument calibration has been performed on ground, before launch, in space during near earth verification (NEV) measurements, and at Mars. Special attention has been given to the problem of microvibrations on board the spacecraft. In order to obtain correct results, the source–instrument–detector interaction for the thermal part is studied very accurately. The instrument shows a nonlinear behaviour with source intensity. The SNR increases with amplification, hence high gain factors are usually used. The detector is, in space, cooled by a passive radiator, and works around 210–215 K. The calibration source (an internal lamp) shows variations during a pericentre pass and therefore impose a complex procedure for the SW channel calibration. Mechanical microvibrations strongly affect part of the spectrum. We discuss the validity of the present calibration, and indicate possible future developments. Samples of the calibrated data are given to show the performance of the experiment and its scientific potentialities.

Spectral identification of hydrated sulfates on Mars and comparison with acidic environments on Earth

We interpret recent spectral data of Mars collected by the Mars Exploration Rovers to contain substantial evidence of sulfate minerals and aqueous processes. We present visible/near-infrared (VNIR), mid-IR and Mössbauer spectra of several iron sulfate minerals and two acid mine drainage (AMD) samples collected from the Iron Mountain site and compare these combined data with the recent spectra of Mars. We suggest that the sulfates on Mars are produced via aqueous oxidation of sulfides known to be present on Mars from Martian meteorites. The sulfate-rich rock outcrops observed in Meridiani Planum may have formed in an acidic environment similar to AMD environments on Earth. Because microorganisms are typically involved in the oxidation of sulfides to sulfates in terrestrial AMD sites, sulfate-rich rock outcrops on Mars may be a good location to search for evidence of life on that planet. Whether or not life evolved on Mars, following the trail of sulfate minerals is likely to lead to aqueous processes and chemical weathering. Our results imply that sulfate minerals formed in Martian soils via chemical weathering, perhaps over very long time periods, and that sulfate minerals precipitated following aqueous oxidation of sulfides to form the outcrop rocks at Meridiani Planum.