Patrick Pinet

Global Mineralogical and Aqueous Mars History Derived from OMEGA/Mars Express Data

Global mineralogical mapping of Mars by the Observatoire pour la Mineralogie, lEau, les Glaces et lActivité (OMEGA) instrument on the European Space Agencys Mars Express spacecraft provides new information on Mars geological and climatic history. Phyllosilicates formed by aqueous alteration very early in the planets history (the “phyllocian” era) are found in the oldest terrains; sulfates were formed in a second era (the “theiikian” era) in an acidic environment. Beginning about 3.5 billion years ago, the last era (the “siderikian”) is dominated by the formation of anhydrous ferric oxides in a slow superficial weathering, without liquid water playing a major role across the planet.

Orientation and distribution of recent gullies in the southern hemisphere of Mars: Observations from High Resolution Stereo Camera/Mars Express (HRSC/MEX) and Mars Orbiter Camera/Mars Global Surveyor (MOC/MGS) data

Geologically recent small gullies on Mars display morphologies consistent with erosion by water or by debris flows. Suggested formation models are divided into two main categories: (1) groundwater or (2) melting of near-surface ice/snow sourced from the atmosphere. We have measured location and orientation and recorded the local contexts of gullies to constrain the likely models of gully formation. More than 22,000 Mars Orbiter Camera Narrow Angle (MOC NA) and >120 Mars Express High Resolution Stereo Camera (HRSC) images in the southern hemisphere were searched for gullies. Discrete gullied slope sections with consistent orientation were recorded rather than individual gullies. Slope setting (impact crater, valley wall, etc.), location, and orientation were recorded for each slope section. More than 750 MOC images with gullies (>900 distinct gullied slope sections) and more than 40 HRSC images (>380 distinct gullied slope sections) were identified. From both MOC and HRSC, gullies were found to be most common between 30 and 50 degrees latitude and to have an overall pole facing preference. The preferred gully orientation for HRSC is southeast rather than south in MOC, owing to illumination effects that make gullies difficult to detect on south- to southwest-facing slopes in HRSC. In both MOC and HRSC surveys, higher-latitude gullies show less preference for pole facing than those at mid latitudes. Both data sets produced similar results, demonstrating that our data are reliable. We suggest that the observed latitudinal and orientation distributions of gullies show that insolation and atmospheric conditions play a key role in gully formation.

Discrimination between maturity and composition of lunar soils from integrated Clementine UV‐visible/near‐infrared data: Application to the Aristarchus Plateau

The reflectance spectrum of a lunar soil is mainly dominated by the composition and the degree of exposure to space weathering processes such as micrometeorite bombardment and solar wind implantation. The spectral alteration effects of space weathering should be removed for accurately investigating the composition of the lunar surface using remote sensing data. In this paper we show that the integration of the Clementine UV-visible (UVVIS) and near-infrared (NIR) channels provides an improved evaluation of the spectral alteration. The depth of the mafic absorption feature at 0.95 μm is also better defined by combining the UVVIS and NIR data. Laboratory spectra of lunar soil samples indicate that the continuum slope derived from the 1500/750 nm ratio is closely related to the concentration of fine-grained submicroscopic iron (Is). The continuum slope therefore provides an evaluation of the spectral alteration of the surface, which can be subtracted from the 1 or 2 μm absorption band depths to retrieve compositional information. This method has been applied to the Aristarchus plateau, which exhibits a broad range of mineralogical composition and maturity. A nine-channel multispectral mosaic of 680 Clementine images of the Aristarchus plateau has been processed. Eight telescopic spectra have been used to check the validity of the reduction process for the near infrared bands. The 1 μm absorption band, once corrected for spectral alteration, provides an evaluation of the initial FeO content in mafic silicates (mafic iron). Lunar soil samples show that it is possible to quantitatively map mafic iron with this technique. Our results are in good agreement with those obtained using the algorithm of Lucey et al. [1995,1998a], which is based on UVVIS bands alone. The mafic iron content and total iron content which can be derived from the combined UVVIS and NIR data sets are less sensitive to local slopes than that derived from Lucey et al.s method. This new method could therefore be useful for investigating areas at middle to high latitudes. Removing spectral alteration from the 2000/1500 nm ratio also makes possible a better discrimination between olivine and pyroxene within identified mare basalts on the Aristarchus plateau.

Local and regional lunar regolith characteristics at Reiner Gamma Formation: Optical and spectroscopic properties from Clementine and Earth‐based data

A detailed remote sensing survey of the Reiner Gamma Formation (RGF) region by means of Earth-based telescopic and Clementine multispectral imaging has been made in the UV-visible-near-infrared domain. The spectral mixture analysis reveals the existence of three basic end-members relevant for modeling the observed spectral variations in the RGF vicinity. These are MB (mare background), SWS (southwest swirl), and RGS (Reiner Gamma soil). The first two components exhibit spectral characteristics consistent with a prevailing contribution of mature mare soils for the surroundings (MB) and of immature mare crater-like soils (RGS) at RGF. The third intermediate-albedo component (SWS) has general characteristics of a mature mare soil, but with a redder continuum slope. The reported observation can be modeled by a mechanism which would remove the finest fraction in the soil (particle diameter < 45 μm) at RGF and redistribute it in the vicinity with a laterally variable proportion and local accumulations such as at SWS site. According to the available set of in situ data documenting variations in the chemical composition, in the distribution of particle sizes, and in the degree of maturity with depth in the mare regolith, the characteristics depicted at RGF are those of a subsurface soil layer from a depth of the order of 0.3 - 0.8 m. In our view, the simplest way to account for the whole body of information available from the present work lies in the proposition that in the area of RGF the uppermost layer of the regolith has been optically and mechanically modified by a process involving the fall of fragments of a low-density cometary nucleus previously disrupted by tidal interaction in the Earth-Moon system. We recognize, however, that in the present state of knowledge, one cannot rule out the hypothesized existence of a zone of seismically modified terrain peripheral to the Imbrium or Orientale basins just beneath the mare surface that would be the actual source of the RGF magnetic anomaly.

Gruithuisen domes region: A candidate for an extended nonmare volcanism unit on the Moon

Small lunar areas known as red spots are thought to represent good candidates for nonmare volcanic units predating or contemporaneous with the period of mare volcanism. In this study, we present imaging telescopic and orbital Clementine multispectral surveys of the Gruithuisen region, located in the northwestern border of Mare Imbrium, which contains Imbrian age domical features of likely viscous volcanic origin with spectral characteristics of red spot areas. A rather spectrally homogeneous unit having typical characteristics of red spots is found to coincide with the material within the morphological boundaries of the Gruithuisen Delta, Gamma and Northwest domes. An extended “dome-like” unit is identified spectrally and surrounds and extends to the west and the north of the domes. This unit shows spectral characteristics close to those of the domes, suggesting the presence of a significant amount of dome material extending many kilometers away from the domes themselves. Both the spectral characteristics of the dome and the dome-like unit are clearly different from those of highlands and the surrounding mare basalts. The spectral identification of a widespread dome-like unit suggests that the specific style of eruption that is inferred for the formation of the domes (i.e., viscous flows of possible more silicic composition) might have occurred on a regional scale in this part of the Moon, prior to the Iridum event about 3.8 Gyr ago. This volcanic style appears to be more widespread in the early part of lunar history than previously thought.

Composition of the lunar surface as will be seen from SMART-1: A simulation using Clementine data

[1]xa0We present a new technique for remote sensing determination of lunar surface composition in the context of the SMART-1 mission. The technique is based on spectral and composition data obtained by Lunar Soil Characterization Consortium for a few particle-size separates of lunar soils. We map the abundance of TiO2 and FeO, pyroxene content, maturity degree (Is/FeO), and a characteristic size of particles. Comparison of the TiO2 and FeO abundance maps with proper distributions obtained by Lucey et al. [2000a] shows high correlation. We found also an inverse correlation between the Is/FeO distribution and Lucey et al.s [2000b] parameter OM. Application of this approach shows that fresh mare crater regolith is characterized with a higher abundance of pyroxenes, coarse particles, and low maturity degree. The pyroxene abundance map can be used to identify pyroclastic regions. An excess of small particles is predicted for highland areas. We note appreciable variations of the characteristic size of particles in mare regions. Our preliminary results for the Reiner-γ formation show that there is no composition anomaly for the TiO2 and FeO abundance, in agreement with previous analyses. Our maps also indicate that the formation contains a surface material characterized with low maturity and high degree of crystallinity, consistent with the occurrence of immature regolith possibly contaminated with dust.

Mapping of an ophiolite complex by high‐resolution visible‐infrared spectrometry

The Sumail massif of the Oman peridotite has been surveyed by the high spectral resolution imager HyMap. The field measurements have been taken simultaneously to the HyMap campaign with a GER 3700 spectrometer. To compare the two data sets, further calibration and atmospheric correction are made through empirical line corrections. A continuum removal by a modified Gaussian model on reflectance is then performed for each pixel to minimize atmospheric scattering and shadowing effects. Classification from spectral distance is established using field observations and comparisons at full spectral resolution to identify peridotite subunits (harzburgites and dunites) and to distinguish plagioclase-wehrlites from gabbros. Detections of hydrothermal transformations of olivine in serpentines and their alteration in carbonates along fracture networks, characterized by narrow spectral signatures, validate the classification. This demonstrates the utility of the high spectral resolution and the development of appropriate processing methods for geological identifications.

Coordinated analyses of orbital and Spirit Rover data to characterize surface materials on the cratered plains of Gusev Crater, Mars

[1]xa0Comparison of the Mars Exploration Rover Spirits Pancam (0.4 to 1.0 μm) and Mars Express Observatoire pour la Mineralogie lEau, les Glaces et lActivite (OMEGA) (0.4 to 2.5 μm) spectral reflectance data over Spirits traverses shows that Gusev cratered plains are dominated by nanophase ferric-oxide-rich dust covering weakly altered basaltic sands. This interpretation is also consistent with both observations from OMEGA data covering plains beyond the traverse region and interpretations of data from the other payload instruments on the Spirit Rover. OMEGA observations of relatively low albedo regions where dust has presumably been stripped by dust devils show negative spectral reflectance slopes from 1.5 to 2.5 μm and moderately masked spectral features which are indicative of olivine or pyroxene. High-albedo regions north and south of the Spirit landing site have flat spectral reflectance slopes and few spectral features, although all spectra have a nanophase ferric-oxide absorption edge between 0.4 and 0.75 μm. Comparison of THEMIS-derived thermal inertia values with OMEGA-derived spectral parameters shows that although the dust cover can be optically thick (0.4 to 2.5 μm wavelength region) in some areas, it is not thick enough (∼1 cm) to mask the thermal inertia of the underlying substrate for areas included in this study.

The Mars NetLander panoramic camera

The panoramic camera (PanCam) imaging experiment is designed to obtain high-resolution multispectral stereoscopic panoramic images from each of the four Mars NetLander 2005 sites. The main scientific objectives to be addressed by the PanCam experiment are (1) to locate the landing sites and support the NetLander network sciences, (2) to geologically investigate and map the landing sites, and (3) to study the properties of the atmosphere and of variable phenomena. To place in situ measurements at a landing site into a proper regional context, it is necessary to determine the lander orientation on ground and to exactly locate the position of the landing site with respect to the available cartographic database. This is not possible by tracking alone due to the lack of on-ground orientation and the so-called map-tie problem. Images as provided by the PanCam allow to determine accurate tilt and north directions for each lander and to identify the lander locations based on landmarks, which can also be recognized in appropriate orbiter imagery. With this information, it will be further possible to improve the Mars-wide geodetic control point network and the resulting geometric precision of global map products. The major geoscientific objectives of the PanCam lander images are the recognition of surface features like ripples, ridges and troughs, and the identification and characterization of different rock and surface units based on their morphology, distribution, spectral characteristics, and physical properties. The analysis of the PanCam imagery will finally result in the generation of precise map products for each of the landing sites. So far comparative geologic studies of the Martian surface are restricted to the timely separated Mars Pathfinder and the two Viking Lander Missions. Further lander missions are in preparation (Beagle-2, Mars Surveyor 03). NetLander provides the unique opportunity to nearly double the number of accessible landing site data by providing simultaneous and long-term observations at four different surface locations which becomes especially important for studies of variable surface features as well as properties and phenomena of the atmosphere. Major changes on the surface that can be detected by PanCam are caused by eolian activities and condensation processes, which directly reflect variations in the prevailing near-surface wind regime and the diurnal and seasonal volatile and dust cycles. Atmospheric studies will concentrate on the detection of clouds, measurements of the aerosol contents and the water vapor absorption at 936 nm. In order to meet these objectives, the proposed PanCam instrument is a highly miniaturized, dedicated stereo and multispectral imaging device. The camera consists of two identical camera cubes, which are arranged in a common housing at a fixed stereo base length of 11 cm. Each camera cube is equipped with a CCD frame transfer detector with 1024×1024 active pixels and optics with a focal length of 13 mm yielding a field-of-view of 53°×53° and an instantaneous filed of view of 1.1 mrad. A filter swivel with six positions provides different color band passes in the wavelength range of 400–950 nm. The camera head is mounted on top of a deployable scissors boom and can be rotated by 360° to obtain a full panorama, which is already covered by eight images. The boom raises the camera head to a final altitude of 90 cm above the surface. Most camera activities will take place within the first week and the first month of the mission. During the remainder of the mission, the camera will operate with a reduced data rate to monitor time-dependent variations on a daily basis. PanCam is a joint German/French project with contributions from DLR, Institute of Space Sensor Technology and Planetary Exploration, Berlin, Institut dAstrophysique Spatiale, CNRS, Orsay, and Service dAeronomie, CNRS, Verrieres-le-Buisson.

Modern slope processes on the moon

Slope movements of material in lunar craters are investigated based on remote spectral studies carried out on board the Clementine spacecraft, and data obtained during the large-scale survey on board the LRO (Lunar Reconnaissance Orbit) spacecraft. The morphological analysis of crater forms based on large-scale images and spectral and spectropolarized assessments of the exposition age (or maturity) of the slope material has led to the conclusion that the formation process of observed outcrops probably is a modern feature. The lower age limit of these structures is estimated at 40–80 years. Thus, slope movements of surface materials can continue at the present time, regardless of the age of the crater studied. Slope movements of crushed granular material lead to fresh outcrops of subsurface layers of marine or continental landscapes and, therefore, extend our capabilities to research the deep material of the Moon. To analyze this phenomenon, craters of 16 and 30 km have been selected. The length of fresh outcrops, while depending strongly on the dimensions of the craters, can be up to several kilometers. In connection with this, the prospect appears of remote analysis of rocks that came to the surface from depths of at least several hundred meters. In this case, there are openings for the contact analysis of subsurface material without the use of labor-intensive operations associated with the delivery of equipment for deep drilling to the lunar surface.