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Author(s): M. C. De Sanctis (corresponding author) [1]; F. Capaccioni [1]; M. Ciarniello [1]; G. Filacchione [1]; M. Formisano [1]; S. Mottola [2]; A. Raponi [1]; F. Tosi [1]; D. [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2010.03.012 Byline: L. Le Deit (a)(b), O. Bourgeois (b), D. Mege (b), E. Hauber (a), S. Le Mouelic (b), M. Masse (b), R. Jaumann (a), J.-P. Bibring (c) Keywords: Geological processes; Mars, Surface; Mineralogy Abstract: An extensive layered formation covers the high plateaus around Valles Marineris. Mapping based on HiRISE, CTX and HRSC images reveals these layered deposits (LDs) crop out north of Tithonium Chasma, south of Ius Chasma, around West Candor Chasma, and southwest of Juventae Chasma and Ganges Chasma. The estimated area covered by LDs is [approximately equal to]42,300km.sup.2. They consist of a series of alternating light and dark beds, a 100m in total thickness that is covered by a dark unconsolidated mantle possibly resulting from their erosion. Their stratigraphic relationships with the plateaus and the Valles Marineris chasmata indicate that the LDs were deposited during the Early- to Late Hesperian, and possibly later depending on the region, before the end of the backwasting of the walls near Juventae Chasma, and probably before Louros Valles sapping near Ius Chasma. Their large spatial coverage and their location mainly on highly elevated plateaus lead us to conclude that LDs correspond to airfall dust and/or volcanic ash. The surface of LDs is characterized by various morphological features, including lobate ejecta and pedestal craters, polygonal fractures, valleys and sinuous ridges, and a pitted surface, which are all consistent with liquid water and/or water ice filling the pores of LDs. LDs were episodically eroded by fluvial processes and were possibly modified by sublimation processes. Considering that LDs correspond to dust and/or ash possibly mixed with ice particles in the past, LDs may be compared to Dissected Mantle Terrains currently observed in mid- to high latitudes on Mars, which correspond to a mantle of mixed dust and ice that is partially or totally dissected by sublimation. The analysis of CRISM and OMEGA hyperspectral data indicates that the basal layer of LDs near Ganges Chasma exhibits spectra with absorption bands at [approximately equal to]1.4[mu]m, and [approximately equal to]1.9[mu]m and a large deep band between [approximately equal to]2.21 and [approximately equal to]2.26[mu]m that are consistent with previous spectral analysis in other regions of LDs. We interpret these spectral characteristics as an enrichment of LDs in opaline silica or by Al-phyllosilicate-rich layers being overlain by hydroxylated ferric sulfate-rich layers. These alteration minerals are consistent with the aqueous alteration of LDs at low temperatures. Author Affiliation: (a) Institute of Planetary Research, German Aerospace Center (DLR), Berlin, Germany (b) Laboratoire de Planetologie et de Geodynamique de Nantes, CNRS UMR-6112, Universite de Nantes, France (c) Institut d'Astrophysique Spatiale, Universite Paris 11, Orsay Campus, France Article History: Received 14 October 2009; Revised 3 March 2010; Accepted 10 March 2010

The composition of the ancient martian crust is a key ingredient in deciphering the environment and evolution of early Mars. We present an analysis of the composition of large craters in the martian northern plains based on data from spaceborne imaging spectrometers. Nine of the craters have excavated assemblages of phyllosilicates from ancient, Noachian crust buried beneath the plains' cover. The phyllosilicates are indistinguishable from those exposed in widespread rotations in the southern highlands, demonstrating that liquid water once altered both hemispheres of Mars. 10.1126/science.1189013

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.10.007 Byline: F. Poulet (a), R.E. Arvidson (b), J.-P. Bibring (a), B. Gondet (a), D. Jouglet (a), Y. Langevin (a), R.V. Morris (c) Keywords: Mars, Surface; Mineralogy; Spectroscopy Abstract: We present an analysis comparing observations acquired by the Mars Express Observatoire pour la Mineralogie l'Eau, les Glaces et l'Activite (OMEGA) and Phoenix lander measurements. Analysis of OMEGA data provides evidence for hydrous and ferric phases at the Phoenix landing site and the surrounding regions. The 3[mu]m hydration band deepens with increasing latitude, along with the appearance and deepening of a 1.9[mu]m H.sub.2O band as latitude increases [approximately equal to]60[degrees] polewards. A water content of 10-11% is derived from the OMEGA data for the optical surface at the Phoenix landing site compared to 1-2% derived for subsurface soil by Phoenix lander measurements. The hydration of these regions is best explained by surface adsorbed water onto soil grains. No evidence for carbonate or perchlorate-bearing phases is evident from OMEGA data, consistent with the relatively small abundances of these phases detected by Phoenix. The identification of spectral features consistent with hydrated phases (possibly zeolites) from OMEGA data covering regions outside the landing site and the ubiquitous ferric absorption edge suggest that chemical weathering may play a role in the arctic soils. Author Affiliation: (a) Institut d'Astrophysique Spatiale, CNRS/Universite Paris-Sud, Orsay, France (b) Department of Earth and Planetary Sciences, Washington University, St. Louis, MO, USA (c) NASA Johnson Space Center, Houston, TX 77058, USA Article History: Received 20 July 2009; Revised 20 September 2009; Accepted 2 October 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.04.018 Byline: D. Loizeau (a)(b), N. Mangold (c), F. Poulet (a), V. Ansan (c), E. Hauber (d), J.-P. Bibring (a), B. Gondet (a), Y. Langevin (a), P. Masson (b), G. Neukum (e) Keywords: Mars, Surface; Mineralogy; Spectroscopy; Infrared observations Abstract: The Mawrth Vallis region contains an extensive (at least 300kmx400km) and thick ([greater than or equal to]300m), finely layered (at meter scale), clay-rich unit detected by OMEGA. We use OMEGA, HRSC DTMs derived from stereoscopic imagery, HRSC color imagery and high resolution imagery such as MOC, CTX and HiRISE to characterize the geometry and the composition of the clay-rich unit at the regional scale. Our results show that the clay-bearing unit can be divided into sub-units on the basis of differences in color and composition. In false-color visible imagery, alternating white/bluish and orange/red colored units correspond to a compositional succession of, respectively, Al- and Fe- or Mg-phyllosilicate rich material. Geological cross-sections are presented along the principal outcrops of the region in order to define the stratigraphy of these sub-units. This method shows that the dips of the sub-units are frequently close to the slopes of the present topography, except for scarps visible at the dichotomy boundary, inside impact craters walls, and outcrops inside Mawrth Vallis. In addition to the Al- and Fe- or Mg-phyllosilicate rich sub-units, an altered surface is identified as the lower basement unit. We propose two possible end-member scenarios to explain the derived stratigraphy: (1) alteration of volcaniclastic, aeolian or aqueous layered deposits of various compositions by groundwater, resulting in distinct altered rocks; or (2) Alteration coeval with the deposition of sediments under varying chemical conditions, in wet pedodiagenetic environment. Author Affiliation: (a) IAS-UMR8617, Universite Paris-Sud XI, Bat. 121, 91405 Orsay cedex, France (b) IDES-UMR8148, Universite Paris-Sud XI, Bat. 509, 91405 Orsay cedex, France (c) LPGN-UMR6112, Universite de Nantes, 2 rue de la Houssiniere, BP 92208, 44322 Nantes cedex 3, France (d) Institute for Planetary Exploration, DLR, Rutherfordstr. 2, 12489 Berlin, Germany (e) Freie Universitaet Berlin, FR Planetologie und Fernerkundung, Malteserstr. 74-100, 12249 Berlin, Germany Article History: Received 19 August 2008; Revised 10 April 2009; Accepted 14 April 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.07.022 Byline: F. Altieri (a), L. Zasova (b), E. D'Aversa (a), G. Bellucci (a), F.G. Carrozzo (a), B. Gondet (c), J.-P. Bibring (c) Keywords: Mars; Atmosphere; Atmosphere; Composition; Spectroscopy Abstract: We present a method to derive the 2D maps of the O.sub.2 (a.sup.1 [DELTA].sub.g) airglow emission at 1.27[mu]m from the OMEGA/MEx nadir observations. The OMEGA imaging capabilities allow monitoring the 2D distribution, daily and seasonal variation of the O.sub.2 emission intensities with a detection limit of 4 MR. The highest values, of the order of [approximately equal to]31 MR, are found on the south pole for 11h Atmospheric waves crossing the terminator on the southern polar regions are observed for the first time during the MY28 early spring. The spatial scale of the waves ranges from 100 to 130km, and the intensity fluctuations are of the order of 4MR. This study confirms the high potentiality of O.sub.2 (a.sup.1 [DELTA].sub.g) day glow as a passive tracer of the martian atmosphere dynamics at high latitudes. Author Affiliation: (a) IFSI - INAF, Via del Fosso del Cavaliere 100, 00133 Rome, Italy (b) Space Research Institute, 84/32 Profsoyuznaya Str., 117997 Moscow, Russia (c) Institut d'Astrophysique Spatiale, BAcentst. 121, Universite Paris-Sud, 91405 Orsay Cedex, France Article History: Received 22 July 2008; Revised 18 June 2009; Accepted 6 July 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.05.020 Byline: F.G. Carrozzo (a), G. Bellucci (a), F. Altieri (a), E. D'Aversa (a), J.-P. Bibring (b) Keywords: Mars; Mineralogy; Ices; Frost; Spectroscopy Abstract: This paper reports on mapping of water frost and ice on Mars, in the range of latitudes between 30[degrees]S and 30[degrees]N. The study has been carried out by analysing 2485 orbits acquired during almost one martian year by the Mars Express/OMEGA imaging spectrometer. Water frost/ice is identified by the presence of [approximately equal to]1.5[mu]m, [approximately equal to]2[mu]m and [approximately equal to]3.0[mu]m absorptions. Although the orbits analysed in this study cover all seasons, water frost/ice is observed only near the aphelion seasons, at Ls=19[degrees] and at Ls=98-150[degrees]. Water frost/ice is detected mainly on the southern hemisphere between 15[degrees]S and 30[degrees]S latitude while it has not been identified within 15[degrees]S-15[degrees]N. In the northern hemisphere, the water frost/ice detection is complicated by the presence of clouds. Usually, water frost/ice is found in shadowed areas, while in few cases it is exposed to the sunlight. This indicates a clear relationship with the local illumination conditions on the slopes which favour the water frost/ice deposition on the surface when the temperatures are very low. OMEGA observations span from 10 to 17LT and the frost/ice is detected mainly between 15 and 16LT, with practically no detection before 13LT. We think this is due to the fact that the 10-12LT observations occur at large distances and it is not a local time effect. A thermal model is used to determine the deposition conditions on the sloped surfaces where water frost/ice has been found. There, daily atmospheric saturation does not occur on pole facing 10-25[degrees] slopes with current water vapour abundances but only by assuming values greater than 40pr[mu]m. Moreover, the water frost/ice is not detected during the northern winter, even if the thermal model foresees daily saturation on 25[degrees] slopes. Author Affiliation: (a) Istituto Nazionale di Astrofisica - Istituto Fisica Spazio Interplanetario (IFSI), Via del Fosso del Cavaliere 100, 00133 Rome, Italy (b) Institut d'Astrophysique Spatiale (IAS), BAcentstiment 121, Universite Paris Sud, 91405 Orsay Cedex, France Article History: Received 12 January 2009; Revised 4 May 2009; Accepted 23 May 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.12.012 Byline: Mathieu Vincendon (a), Y. Langevin (a), F. Poulet (a), A. Pommerol (b), M. Wolff (c), J.-P. Bibring (a), B. Gondet (a), D. Jouglet (a) Keywords: Mars; atmosphere; Mars; surface; Mars; climate; Radiative transfer; Infrared observations Abstract: The time variations of spectral properties of dark martian surface features are investigated using the OMEGA near-IR dataset. The analyzed period covers two Mars years, spanning from early 2004 to early 2008 (includes the 2007 global dust event). Radiative transfer modeling indicates that the apparent albedo variations of low to mid-latitude dark regions are consistent with those produced by the varying optical depth of atmospheric dust as measured simultaneously from the ground by the Mars Exploration Rovers. We observe only a few significant albedo changes that can be attributed to surface phenomena. They are small-scaled and located at the boundaries between bright and dark regions. We then investigate the variations of the mean particle size of aerosols using the evolution of the observed dark region spectra between 1 and 2.5 [mu]m. Overall, we find that the observed changes in the spectral slope are consistent with a mean particle size of aerosols varying with time between 1 and 2 [mu]m. Observations with different solar zenith angles make it possible to characterize the aerosol layer at different altitudes, revealing a decrease of the particle size of aerosols as altitude increases. Author Affiliation: (a) Institut d'Astrophysique Spatiale, CNRS/Universite Paris Sud, BAcentstiment 121, 91405 Orsay, France (b) Laboratoire de Planetologie de Grenoble, UJF/CNRS, BAcentst. D de Physique, B.P. 53, 38041 Grenoble Cedex 9, France (c) Space Science Institute, 18970 Cavendish Road, Brookfield, WI 53045, USA Article History: Received 18 June 2008; Revised 5 December 2008; Accepted 11 December 2008

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2007.11.034 Byline: M. Vincendon, Y. Langevin, F. Poulet, J.-P. Bibring, B. Gondet, D. Jouglet Keywords: Mars; polar caps; Mars; atmosphere; Radiative transfer; Ices; IR spectroscopy; Mars; climate Abstract: The time evolution of atmospheric dust at high southern latitudes on Mars has been determined using observations of the south seasonal cap acquired in the near infrared (1-2.65 [mu]m) by OMEGA/Mars Express in 2005. Observations at different solar zenith angles and one EPF sequence demonstrate that the reflectance in the 2.64 [mu]m saturated absorption band of the surface CO.sub.2 ice is mainly due to the light scattered by aerosols above most places of the seasonal cap. We have mapped the total optical depth of dust aerosols in the near-IR above the south seasonal cap of Mars from mid-spring to early summer with a time resolution ranging from one day to one week and a spatial resolution of a few kilometers. The optical depth above the south perennial cap is determined on a longer time range covering southern spring and summer. A constant set of optical properties of dust aerosols is consistent with OMEGA observations during the analyzed period. Strong variations of the optical depth are observed over small horizontal and temporal scales, corresponding in part to moving dust clouds. The late summer peak in dust opacity observed by Opportunity in 2005 propagated to the south pole contrarily to that observed in mid spring. This may be linked to evidence for dust scavenging by water ice-rich clouds circulating at high southern latitudes at this season. Author Affiliation: Institut d'Astrophysique Spatiale, CNRS/Universite Paris Sud, BAcentstiment 121, 91405 Orsay, France Article History: Received 13 April 2007; Revised 1 November 2007

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2007.11.031 Byline: F. Poulet (a), R.E. Arvidson (b), C. Gomez (a), R.V. Morris (c), J.-P. Bibring (a), Y. Langevin (a), B. Gondet (a), J. Griffes (b)(d) Keywords: Mars; surface; Mineralogy; Spectroscopy Abstract: Analyses of Mars Express OMEGA hyperspectral data (0.4-2.7 [mu]m) for Terra Meridiani and western Arabia Terra show that the northern mantled cratered terrains are covered by dust that is spectrally dominated by nanophase ferric oxides. Dark aeolian dunes inside craters and dark streaks extending from the dunes into the intercrater areas in mantled cratered terrains in western Arabia Terra have similar pyroxene-rich signatures demonstrating that the dunes supply dark basaltic material to create dark streaks. The dissected cratered terrains to the south of the mantled terrains are dominated spectrally by both low-calcium and high-calcium pyroxenes with abundances of 20-30% each retrieved from nonlinear radiative transfer modeling. Spectra over the hematite-bearing plains in Meridiani Planum are characterized by very weak but unique spectral features attributed to a mixture of a dark and featureless component (possibly gray hematite) and minor olivine in some locations. Hydrated minerals (likely hydrous ferric sulfates and/or hydrous hydroxides) associated with poorly ferric crystalline phases are found in the etched terrains to the north and east of the hematite-bearing plains where erosion has exposed [approximately equal to]1km of section of layered outcrops with high thermal inertias. These materials are also found in numerous craters in the northern Terra Meridiani and may represent outliers of the etched terrain materials. A few localized spots within the etched terrain also exhibit the spectral signature of Fe-rich phyllosilicates. The ensemble of observations show that the evidence for aqueous processes detected by the Opportunity Rover in Meridiani Planum is widespread and confirms the extended presence of surface or near-surface water over this large region of Mars. The scenarios of formation of Terra Meridiani ('dirty' acidic evaporite, impact surge or weathering of volcanic ash) cannot satisfactorily explain the mineralogy derived from the OMEGA observations. The formation of the etched terrains is consistent with leaching of iron sulfides and formation of sulfates and hydrated iron oxides, either in-place or via transport and evaporation of aqueous fluids and under aqueous conditions less acidic than inferred from rocks examined by Opportunity. Author Affiliation: (a) Institut d'Astrophysique Spatiale, Universite Paris-Sud, 91405 Orsay Cedex, France (b) Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130, USA (c) NASA Johnson Space Center, Houston, TX 77058, USA (d) Center for Earth and Planetary Studies, National Air & Space Museum, Smithsonian Institution, Washington, DC 20013, USA Article History: Received 25 January 2007; Revised 22 October 2007