2009 .

(18 publications)

V. Eymet, R. Fournier, J.-L. Dufresne, S. Lebonnois, F. Hourdin, and M. A. Bullock. Net exchange parameterization of thermal infrared radiative transfer in Venus' atmosphere. Journal of Geophysical Research (Planets), 114:E11008, 2009. [ bib | DOI | ADS link ]

Thermal radiation within Venus atmosphere is analyzed in close details. Prominent features are identified, which are then used to design a parameterization (a highly simplified and yet accurate enough model) to be used in General Circulation Models. The analysis is based on a net exchange formulation, using a set of gaseous and cloud optical data chosen among available referenced data. The accuracy of the proposed parameterization methodology is controlled against Monte Carlo simulations, assuming that the optical data are exact. Then, the accuracy level corresponding to our present optical data choice is discussed by comparison with available observations, concentrating on the most unknown aspects of Venus thermal radiation, namely the deep atmosphere opacity and the cloud composition and structure.

F. Billebaud, J. Brillet, E. Lellouch, T. Fouchet, T. Encrenaz, V. Cottini, N. Ignatiev, V. Formisano, M. Giuranna, A. Maturilli, and F. Forget. Observations of CO in the atmosphere of Mars with PFS onboard Mars Express. Planetary and Space Science, 57:1446-1457, 2009. [ bib | DOI | ADS link ]

We have analyzed spectra of CO recorded with the instrument PFS onboard Mars Express in the (1-0) 4.7μm band. The dataset we used ranges in time from January until June 2004 ( LS=331o.17 until LS=51o.61; end of Mars Year 26, beginning of Mars Year 27). The aim of this work was to determine the amplitude of the CO mixing ratio departures from the mean globally averaged value currently admitted ( 83×10-4) [Kaplan, L.D., Connes, J., Connes, P., 1969. Carbon monoxide in the martian atmosphere. Astron. J. 157, L187-L192] as a function of season, local time and location on the planet. We therefore processed the data from 90 calibrated orbits. The globally averaged CO mixing ratio value we derive from our dataset, 11.1×10-4, is compatible with the range found by Kaplan et al. [1969. Carbon monoxide in the martian atmosphere. Astron. J. 157, L187-L192], although somewhat higher than the “standard” value. However, the CO mixing ratio we retrieve exhibits large variations (roughly between 3×10-4 and 18×10-4). Such relative variations have been used on a statistical basis to derive main trends as a function of latitude for three LS ranges: 331- 360o, 0- 30o and 30- 52o. For the first LS range, we seem to have an enhancement of the CO mixing ratio towards the northern latitudes, probably linked to the CO2 condensation in winter on the north polar cap. The situation for the two other LS ranges is not so clear, mainly as we lack data on the southern hemisphere. We roughly agree with the work of Krasnopolsky [2007. Long-term spectroscopic observations of Mars using IRTF/CSHELL: mapping of O2 dayglow, CO and search for CH4. Icarus 190, 93-102] for LS=331- 360o, thus confirming the effect of seasonal condensation of CO2 on the north polar cap, but we have no agreement for other seasons.

J.-B. Madeleine, F. Forget, J. W. Head, B. Levrard, F. Montmessin, and E. Millour. Amazonian northern mid-latitude glaciation on Mars: A proposed climate scenario. Icarus, 203:390-405, 2009. [ bib | DOI | ADS link ]

Recent geological observations in the northern mid-latitudes of Mars show evidence for past glacial activity during the late Amazonian, similar to the integrated glacial landsystems in the Dry Valleys of Antarctica. The large accumulation of ice (many hundreds of meters) required to create the observed glacial deposits points to significant atmospheric precipitation, snow and ice accumulation, and glacial flow. In order to understand the climate scenario required for these conditions, we used the LMD (Laboratoire de Météorologie Dynamique) Mars GCM (General Circulation Model), which is able to reproduce the present-day water cycle, and to predict past deposition of ice consistent with geological observations in many cases. Prior to this analysis, however, significant mid-latitude glaciation had not been simulated by the model, run under a range of parameters. In this analysis, we studied the response of the GCM to a wider range of orbital configurations and water ice reservoirs, and show that during periods of moderate obliquity ( ε = 25-35deg) and high dust opacity ( τdust = 1.5-2.5), broad-scale glaciation in the northern mid-latitudes occurs if water ice deposited on the flanks of the Tharsis volcanoes at higher obliquity is available for sublimation. We find that high dust contents of the atmosphere increase its water vapor holding capacity, thereby moving the saturation region to the northern mid-latitudes. Precipitation events are then controlled by topographic forcing of stationary planetary waves and transient weather systems, producing surface ice distribution and amounts that are consistent with the geological record. Ice accumulation rates of 10 mm yr -1 lead to the formation of a 500-1000 m thick regional ice sheet that will produce glacial flow patterns consistent with the geological observations.

S. Guerlet, T. Fouchet, B. Bézard, A. A. Simon-Miller, and F. Michael Flasar. Vertical and meridional distribution of ethane, acetylene and propane in Saturns stratosphere from CIRS/Cassini limb observations. Icarus, 203:214-232, 2009. [ bib | DOI | ADS link ]

Measuring the spatial distribution of chemical compounds in Saturn's stratosphere is critical to better understand the planet's photochemistry and dynamics. Here we present an analysis of infrared spectra in the range 600-1400 cm -1 acquired in limb geometry by the Cassini spacecraft between March 2005 and January 2008. We first determine the vertical temperature profiles from 3 to 0.01 hPa, at latitudes ranging from 70degN to 80degS. We infer a similar meridional temperature gradient at 1-2 hPa as in recent previous studies [Fletcher, L.N., Irwin, P.G.J., Teanby, N.A., Orton, G.S., Parrish, P.D., de Kok, R., Howett, C., Calcutt, S.B., Bowles, N., Taylor, F.W., 2007. Icarus 189, 457-478; Howett, C.J.A., Irwin, P.G.J., Teanby, N.A., Simon-Miller, A., Calcutt, S.B., Fletcher, L.N., de Kok, R., 2007. Icarus 190, 556-572]. We then retrieve the vertical profiles of C2H6 and C2H2 from 3 to 0.01 hPa and of C3H8 around 1 hPa. At 1 hPa, the meridional variation of C2H2 is found to follow the yearly averaged solar insolation, except for a strong equatorial mole fraction of 8×10-7, nearly two times higher than expected. This enhancement in abundance can be explained by the descent of hydrocarbon-rich air, with a vertical wind speed at the equator of 0.250.1 mm/s at 1 hPa and 0.40.15 mm/s at 0.1 hPa. The ethane distribution is relatively uniform at 1 hPa, with only a moderate 25% increase from 35degS to 80degS. Propane is found to increase from north to south by a factor of 1.9, suggesting that its lifetime may be shorter than Saturn's year at 1 hPa. At high altitudes (1 Pa), C2H2 and C2H6 abundances depart significantly from the photochemical model predictions of Moses and Greathouse [Moses, J.I., Greathouse, T.K., 2005. J. Geophys. Res. 110, 9007], except at high southern latitudes (62, 70 and 80degS) and near the equator. The observed abundances are found strongly depleted in the 20-40degS region and enhanced in the 20-30degN region, the latter coinciding with the ring's shadow. We favor a dynamical explanation for these anomalies.

F. Lefèvre and F. Forget. Observed variations of methane on Mars unexplained by known atmospheric chemistry and physics. Nature, 460:720-723, 2009. [ bib | DOI | ADS link ]

The detection of methane on Mars has revived the possibility of past or extant life on this planet, despite the fact that an abiogenic origin is thought to be equally plausible. An intriguing aspect of the recent observations of methane on Mars is that methane concentrations appear to be locally enhanced and change with the seasons. However, methane has a photochemical lifetime of several centuries, and is therefore expected to have a spatially uniform distribution on the planet. Here we use a global climate model of Mars with coupled chemistry to examine the implications of the recently observed variations of Martian methane for our understanding of the chemistry of methane. We find that photochemistry as currently understood does not produce measurable variations in methane concentrations, even in the case of a current, local and episodic methane release. In contrast, we find that the condensation-sublimation cycle of Mars carbon dioxide atmosphere can generate large-scale methane variations differing from those observed. In order to reproduce local methane enhancements similar to those recently reported, we show that an atmospheric lifetime of less than 200days is necessary, even if a local source of methane is only active around the time of the observation itself. This implies an unidentified methane loss process that is 600 times faster than predicted by standard photochemistry. The existence of such a fast loss in the Martian atmosphere is difficult to reconcile with the observed distribution of other trace gas species. In the case of a destruction mechanism only active at the surface of Mars, destruction of methane must occur with an even shorter timescale of the order of ˜1hour to explain the observations. If recent observations of spatial and temporal variations of methane are confirmed, this would suggest an extraordinarily harsh environment for the survival of organics on the planet.

F. González-Galindo, F. Forget, M. A. López-Valverde, and M. Angelats i Coll. A ground-to-exosphere Martian general circulation model: 2. Atmosphere during solstice conditionsThermospheric polar warming. Journal of Geophysical Research (Planets), 114:E08004, 2009. [ bib | DOI | ADS link ]

A ground-to-exosphere Martian general circulation model is applied to study the thermal and dynamical structure of the upper Martian atmosphere during solstitial conditions. Special attention is paid to the reproduction of the thermospheric polar warming observed by Mars Odyssey during southern hemisphere (SH) summer solstice. The intensity and latitudinal distribution of this polar warming are successfully reproduced by the model. The heating balance and the dynamical structure of the upper atmosphere are studied. It is shown that a strong interhemispheric transport produces a convergence and descent of air over the winter pole, producing an adiabatic heating and a polar warming. This structure confirms previous results made by other models. The most novel aspect of this study is a sensitivity study showing the importance of the tides excited in situ in the upper atmosphere. These tides are critical to the simulated thermal and dynamical structure and remain key components of the interhemispheric transport mechanism responsible for the thermospheric polar warming. The day-night temperature differences created by these in situ tides produce a day-night transport that reinforces the summer-to-winter circulation and the descent of air over the pole, becoming an essential factor for this thermospheric polar warming. The effect of upward propagating nonmigrating tides is also studied.

R. Moreno, E. Lellouch, F. Forget, T. Encrenaz, S. Guilloteau, and E. Millour. Wind measurements in Mars' middle atmosphere: IRAM Plateau de Bure interferometric CO observations. Icarus, 201:549-563, 2009. [ bib | DOI | ADS link ]

The IRAM Plateau de Bure Interferometer has been used to map the CO(1-0) rotational line in Mars' middle atmosphere. Absolute winds and thermal profiles were retrieved during the 1999, 2001, 2003 and 2005 planet's oppositions. The observations sampled various seasons ( L=143, 196, 262, 317 and 322), and different dust situations (clear, global storm, regional storm). The absolute winds were derived by measuring directly the Doppler lineshifts. The main zonal circulation near 50 km is dominated by strong retrograde winds, with typical velocities of 70-170 m/s, strongly varying seasonally, latitudinally, and longitudinally (in particular between morning and evening). Comparison of the retrieved temperature with a general circulation model indicates that the model often underestimates the temperatures in the middle (20-50 km) atmosphere, and overestimates them above 50 km.

A. Määttänen, T. Fouchet, O. Forni, F. Forget, H. Savijärvi, B. Gondet, R. Melchiorri, Y. Langevin, V. Formisano, M. Giuranna, and J.-P. Bibring. A study of the properties of a local dust storm with Mars Express OMEGA and PFS data. Icarus, 201:504-516, 2009. [ bib | DOI | ADS link ]

We present observations of a local dust storm performed by the OMEGA and PFS instruments aboard Mars Express. OMEGA observations are used to retrieve the dust single-scattering albedo in the spectral range 0.4-4.0 μm. The single-scattering albedo shows fairly constant values between 0.6 and 2.6 μm, and a sharp decrease at wavelengths shorter than 0.6 μm, in agreement with previous studies. It presents a small absorption feature due to ferric oxide at 0.9 μm, and a strong absorption feature due to hydrated minerals between 2.7 and 3.6 μm. We use a statistical method, the Independent Component Analysis, to determine that the dust spectral signature is decoupled from the surface albedo, proving that the retrieval of the single-scattering albedo is reliable, and we map the dust optical thickness with a conventional radiative transfer model. The effect of the dust storm on the atmospheric thermal structure is measured using PFS observations. We also simulate the thermal impact of the dust storm using a one-dimensional atmospheric model. A comparison of the retrieved and modeled temperature structures suggests that the dust in the storm should be confined to the 1-2 lowest scale heights of the atmosphere. However, the observed OMEGA reflectance in the CO 2 absorption bands does not support this suggestion.

R. Melchiorri, T. Encrenaz, P. Drossart, T. Fouchet, F. Forget, D. Titov, L. Maltagliati, F. Altieri, M. Vincendon, Y. Langevin, and J. P. Bibring. OMEGA/Mars Express: South Pole Region, water vapor daily variability. Icarus, 201:102-112, 2009. [ bib | DOI | ADS link ]

Polar regions on Mars are the most suitable places to observe water vapor daily variability because in any observation crossing the Pole we can observe very different local time and because the poles are considered to be the main permanent and seasonal water reservoir of the planet. We report on a daily variability of water vapor in the South Pole Region (SPR), observed by OMEGA/Mars Express during the south spring-summer period ( Ls250deg-270deg) outside the CO 2 ice cap, that has never been observed before by other instruments. We have been able to estimate an increase of few precipitable microns during the day. A possible scenario includes the presence of regolith, or another component that could gather water from the atmosphere, adsorbing the water into the surface during the night time and desorbing it as soon as the Sun reaches sufficient height to heat the ground. This hypothesis is even more plausible considering the presence of observed local enhancements in the morning sections associated with the illumination of the Sun and the total absence in the data for water ice.

F. González-Galindo, F. Forget, M. A. López-Valverde, M. Angelats i Coll, and E. Millour. A ground-to-exosphere Martian general circulation model: 1. Seasonal, diurnal, and solar cycle variation of thermospheric temperatures. Journal of Geophysical Research (Planets), 114:E04001, 2009. [ bib | DOI | ADS link ]

We present the extension to the thermosphere of a Martian general circulation model, the first able to self-consistently study the whole Martian atmosphere from the surface to the exosphere. We describe the parameterizations developed to include physical processes important for thermospheric altitudes. The results of a simulation covering 1 full Martian year are presented, focusing on the seasonal, diurnal, and day-to-day variability of the temperatures in the exobase region. The seasonal variation of the zonal mean temperatures in the upper atmosphere is of about 100 K, mostly due to the variation of the solar forcing. The temperature of the mesopause ranges between 115 and 130 K, with little seasonal and day-night variations. Its pressure level undergoes significant seasonal and day-night variations. Comparisons with SPICAM observations show that the modeled mesopause is too low and too warm. A similar study for the homopause shows that it is located higher in the atmosphere during solstices, owing to reinforced mixing by a stronger circulation. Important day-night temperature differences are found in the thermosphere, ranging from about 60 K at aphelion to 110 K at perihelion. This diurnal cycle is slightly perturbed by the day-to-day variations of temperature, dominated by waves with periods of 2 to 6 sols and amplitude of 30 K. The model reproduces the observed solar cycle variation in temperatures when using a UV heating efficiency of 16%, slightly lower than the theoretical value. The seasonal variation of temperatures is overestimated by the model, in comparison with the available measurements.

A. Coustenis, S. K. Atreya, T. Balint, R. H. Brown, M. K. Dougherty, F. Ferri, M. Fulchignoni, D. Gautier, R. A. Gowen, C. A. Griffith, L. I. Gurvits, R. Jaumann, Y. Langevin, M. R. Leese, J. I. Lunine, C. P. McKay, X. Moussas, I. Müller-Wodarg, F. Neubauer, T. C. Owen, F. Raulin, E. C. Sittler, F. Sohl, C. Sotin, G. Tobie, T. Tokano, E. P. Turtle, J.-E. Wahlund, J. H. Waite, K. H. Baines, J. Blamont, A. J. Coates, I. Dandouras, T. Krimigis, E. Lellouch, R. D. Lorenz, A. Morse, C. C. Porco, M. Hirtzig, J. Saur, T. Spilker, J. C. Zarnecki, E. Choi, N. Achilleos, R. Amils, P. Annan, D. H. Atkinson, Y. Bénilan, C. Bertucci, B. Bézard, G. L. Bjoraker, M. Blanc, L. Boireau, J. Bouman, M. Cabane, M. T. Capria, E. Chassefière, P. Coll, M. Combes, J. F. Cooper, A. Coradini, F. Crary, T. Cravens, I. A. Daglis, E. de Angelis, C. de Bergh, I. de Pater, C. Dunford, G. Durry, O. Dutuit, D. Fairbrother, F. M. Flasar, A. D. Fortes, R. Frampton, M. Fujimoto, M. Galand, O. Grasset, M. Grott, T. Haltigin, A. Herique, F. Hersant, H. Hussmann, W. Ip, R. Johnson, E. Kallio, S. Kempf, M. Knapmeyer, W. Kofman, R. Koop, T. Kostiuk, N. Krupp, M. Küppers, H. Lammer, L.-M. Lara, P. Lavvas, S. Le Mouélic, S. Lebonnois, S. Ledvina, J. Li, T. A. Livengood, R. M. Lopes, J.-J. Lopez-Moreno, D. Luz, P. R. Mahaffy, U. Mall, J. Martinez-Frias, B. Marty, T. McCord, C. Menor Salvan, A. Milillo, D. G. Mitchell, R. Modolo, O. Mousis, M. Nakamura, C. D. Neish, C. A. Nixon, D. Nna Mvondo, G. Orton, M. Paetzold, J. Pitman, S. Pogrebenko, W. Pollard, O. Prieto-Ballesteros, P. Rannou, K. Reh, L. Richter, F. T. Robb, R. Rodrigo, S. Rodriguez, P. Romani, M. Ruiz Bermejo, E. T. Sarris, P. Schenk, B. Schmitt, N. Schmitz, D. Schulze-Makuch, K. Schwingenschuh, A. Selig, B. Sicardy, L. Soderblom, L. J. Spilker, D. Stam, A. Steele, K. Stephan, D. F. Strobel, K. Szego, C. Szopa, R. Thissen, M. G. Tomasko, D. Toublanc, H. Vali, I. Vardavas, V. Vuitton, R. A. West, R. Yelle, and E. F. Young. TandEM: Titan and Enceladus mission. Experimental Astronomy, 23:893-946, 2009. [ bib | DOI | ADS link ]

TandEM was proposed as an L-class (large) mission in response to ESAs Cosmic Vision 2015-2025 Call, and accepted for further studies, with the goal of exploring Titan and Enceladus. The mission concept is to perform in situ investigations of two worlds tied together by location and properties, whose remarkable natures have been partly revealed by the ongoing Cassini-Huygens mission. These bodies still hold mysteries requiring a complete exploration using a variety of vehicles and instruments. TandEM is an ambitious mission because its targets are two of the most exciting and challenging bodies in the Solar System. It is designed to build on but exceed the scientific and technological accomplishments of the Cassini-Huygens mission, exploring Titan and Enceladus in ways that are not currently possible (full close-up and in situ coverage over long periods of time). In the current mission architecture, TandEM proposes to deliver two medium-sized spacecraft to the Saturnian system. One spacecraft would be an orbiter with a large host of instruments which would perform several Enceladus flybys and deliver penetrators to its surface before going into a dedicated orbit around Titan alone, while the other spacecraft would carry the Titan in situ investigation components, i.e. a hot-air balloon (Montgolfière) and possibly several landing probes to be delivered through the atmosphere.

B. Langlais, F. Leblanc, T. Fouchet, S. Barabash, D. Breuer, E. Chassefière, A. Coates, V. Dehant, F. Forget, H. Lammer, S. Lewis, M. Lopez-Valverde, M. Mandea, M. Menvielle, A. Pais, M. Paetzold, P. Read, C. Sotin, P. Tarits, S. Vennerstrom, G. Branduardi-Raymont, G. Cremonese, J. G. M. Merayo, T. Ott, H. Rème, J. G. Trotignon, and J. E. Walhund. Mars environment and magnetic orbiter model payload. Experimental Astronomy, 23:761-783, 2009. [ bib | DOI | ADS link ]

Mars Environment and Magnetic Orbiter was proposed as an answer to the Cosmic Vision Call of Opportunity as a M-class mission. The MEMO mission is designed to study the strong interconnections between the planetary interior, atmosphere and solar conditions essential to understand planetary evolution, the appearance of life and its sustainability. MEMO provides a high-resolution, complete, mapping of the magnetic field (below an altitude of about 250 km), with an yet unachieved full global coverage. This is combined with an in situ characterization of the high atmosphere and remote sensing of the middle and lower atmospheres, with an unmatched accuracy. These measurements are completed by an improved detection of the gravity field signatures associated with carbon dioxide cycle and to the tidal deformation. In addition the solar wind, solar EUV/UV and energetic particle fluxes are simultaneously and continuously monitored. The challenging scientific objectives of the MEMO mission proposal are fulfilled with the appropriate scientific instruments and orbit strategy. MEMO is composed of a main platform, placed on a elliptical (130 × 1,000 km), non polar (77deg inclination) orbit, and of an independent, higher apoapsis (10,000 km) and low periapsis (300 km) micro-satellite. These orbital parameters are designed so that the scientific return of MEMO is maximized, in terms of measurement altitude, local time, season and geographical coverage. MEMO carry several suites of instruments, made of an exospheric-upper atmosphere package, a magnetic field package, and a low-middle atmosphere package. Nominal mission duration is one Martian year.

S. Lebonnois, P. Rannou, and F. Hourdin. The coupling of winds, aerosols and chemistry in Titan's atmosphere. Philosophical Transactions of the Royal Society of London Series A, 367:665-682, 2009. [ bib | DOI | ADS link ]

G. Tobie, M. Choukroun, O. Grasset, S. Le Mouélic, J. I. Lunine, C. Sotin, O. Bourgeois, D. Gautier, M. Hirtzig, S. Lebonnois, and L. Le Corre. Evolution of Titan and implications for its hydrocarbon cycle. Philosophical Transactions of the Royal Society of London Series A, 367:617-631, 2009. [ bib | DOI | ADS link ]

A. Spiga and F. Forget. A new model to simulate the Martian mesoscale and microscale atmospheric circulation: Validation and first results. Journal of Geophysical Research (Planets), 114:E02009, 2009. [ bib | DOI | ADS link ]

The Laboratoire de Météorologie Dynamique (LMD) Mesoscale Model is a new versatile simulator of the Martian atmosphere and environment at horizontal scales ranging from hundreds of kilometers to tens of meters. The model combines the National Centers for Environmental Prediction(NCEP)-National Center for Atmospheric Research (NCAR) fully compressible nonhydrostatic Advanced Research Weather Research and Forecasting (ARW-WRF) dynamical core, adapted to Mars, with the LMD-general circulation model (GCM) comprehensive set of physical parameterizations for the Martian dust, CO2, water, and photochemistry cycles. Since LMD-GCM large-scale simulations are also used to drive the mesoscale model at the boundaries of the chosen domain of interest, a high level of downscaling consistency is reached. To define the initial state and the atmosphere at the domain boundaries, a specific “hybrid” vertical interpolation from the coarse-resolution GCM fields to the high-resolution mesoscale domain is used to ensure the stability and the physical relevancy of the simulations. Used in synoptic-scale mode with a cyclic domain wrapped around the planet, the mesoscale model correctly replicates the main large-scale thermal structure and the zonally propagating waves. The model diagnostics of the near-surface pressure, wind, and temperature daily cycles in Chryse Planitia are in accordance with the Viking and Pathfinder measurements. Afternoon gustiness at the respective landing sites is adequately accounted for on the condition that convective adjustment is turned off in the mesoscale simulations. On the rims of Valles Marineris, intense daytime anabatic (˜30 m s-1) and nighttime katabatic (˜40 m s-1) winds are predicted. Within the canyon corridors, topographical channeling can amplify the wind a few kilometers above the ground, especially during the night. Through large-eddy simulations in Gusev Crater, the model describes the mixing layer growth during the afternoon, and the associated dynamics: convective motions, overlying gravity waves, and dust devil-like vortices. Modeled temperature profiles are in satisfactory agreement with the Miniature Thermal Emission Spectrometer (Mini-TES) measurements. The ability of the model to transport tracers at regional scales is exemplified by the model's prediction for the altitude of the Tharsis topographical water ice clouds in the afternoon. Finally, a nighttime “warm ring” at the base of Olympus Mons is identified in the simulations, resulting from adiabatic warming by the intense downslope winds along the flanks of the volcano. The surface temperature enhancement reaches +20 K throughout the night. Such a phenomenon may have adversely affected the thermal inertia derivations in the region.

L. H. Roach, J. F. Mustard, S. L. Murchie, J.-P. Bibring, F. Forget, K. W. Lewis, O. Aharonson, M. Vincendon, and J. L. Bishop. Testing evidence of recent hydration state change in sulfates on Mars. Journal of Geophysical Research (Planets), 114:E00D02, 2009. [ bib | DOI | ADS link ]

The East Candor Interior Layered Deposit (ILD) has signatures of mono- and polyhydrated sulfate in alternating layers that give insight into the processes which formed these layered deposits and on the environmental conditions acting on them since then. We use orbital data to explore multiple hypotheses for how these deposits formed: (1) sulfate-bearing ILDs experience hydration changes on seasonal to a few years timescales under current Mars environmental conditions; (2) the deposits experience hydration under recent Mars conditions but require the wetter climate of high obliquity; and (3) the kieserite could be an original or diagenetic part of a complex evaporite mineral assemblage. Modeled climatology shows recent Mars environmental conditions might pass between multiple sulfate fields. However, comparison of Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité (OMEGA) and Compact Reconnaissance Imaging Spectrometer (CRISM) observations of the same ILD do not show changes in hydration over 2 Mars years. Low temperatures might slow the kinetics of that transition; it is likely that more clement conditions during periods of high obliquity are needed to overcome mineral metastability and hydrate kieserite-bearing deposits. We find the alternate model, that the deposit is a cyclic evaporite sequence of mono- and polyhydrated sulfates, also plausible but with an unexplained dearth of Fe sulfates.

F. Leblanc, B. Langlais, T. Fouchet, S. Barabash, D. Breuer, E. Chassefière, A. Coates, V. Dehant, F. Forget, H. Lammer, S. Lewis, M. Lopez-Valverde, M. Mandea, M. Menvielle, A. Pais, M. Paetzold, P. Read, C. Sotin, P. Tarits, and S. Vennerstrom. Mars Environment and Magnetic Orbiter Scientific and Measurement Objectives. Astrobiology, 9:71-89, 2009. [ bib | DOI | ADS link ]

In this paper, we summarize our present understanding of Mars' atmosphere, magnetic field, and surface and address past evolution of these features. Key scientific questions concerning Mars' surface, atmosphere, and magnetic field, along with the planet's interaction with solar wind, are discussed. We also define what key parameters and measurements should be performed and the main characteristics of a martian mission that would help to provide answers to these questions.

Such a mission - Mars Environment and Magnetic Orbiter (MEMO) - was proposed as an answer to the Cosmic Vision Call of Opportunity as an M-class mission (corresponding to a total European Space Agency cost of less than 300 M). MEMO was designed to study the strong interconnection between the planetary interior, atmosphere, and solar conditions, which is essential to our understanding of planetary evolution, the appearance of life, and its sustainability.

The MEMO main platform combined remote sensing and in situ measurements of the atmosphere and the magnetic field during regular incursions into the martian upper atmosphere. The micro-satellite was designed to perform simultaneous in situ solar wind measurements. MEMO was defined to conduct:

Four-dimensional mapping of the martian atmosphere from the surface up to 120 km by measuring wind, temperature, water, and composition, all of which would provide a complete view of the martian climate and photochemical system;

Mapping of the low-altitude magnetic field with unprecedented geographical, altitude, local time, and seasonal resolutions;

A characterization of the simultaneous responses of the atmosphere, magnetic field, and near-Mars space to solar variability by means of in situ atmospheric and solar wind measurements.

F. Forget, F. Montmessin, J.-L. Bertaux, F. González-Galindo, S. Lebonnois, E. Quémerais, A. Reberac, E. Dimarellis, and M. A. López-Valverde. Density and temperatures of the upper Martian atmosphere measured by stellar occultations with Mars Express SPICAM. Journal of Geophysical Research (Planets), 114:E01004, 2009. [ bib | DOI | ADS link ]

We present one Martian year of observations of the density and temperature in the upper atmosphere of Mars (between 60 and 130 km) obtained by the Mars Express ultraviolet spectrometer Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars (SPICAM). Six hundred sixteen profiles were retrieved using stellar occultations technique at various latitude and longitude. The atmospheric densities exhibit large seasonal fluctuations due to variations in the dust content of the lower atmosphere which controls the temperature and, thus, the atmospheric scale height, below 50 km. In particular, the year observed by SPICAM was affected by an unexpected dust loading around Ls = 130deg which induced a sudden increase of density above 60 km. The diurnal cycle could not be analyzed in detail because most data were obtained at nighttime, except for a few occultations observed around noon during northern winter. There, the averaged midday profile is found to slightly differ from the corresponding midnight profile, with the observed differences being consistent with propagating thermal tides and variations in local solar heating. About 6% of the observed mesopause temperatures exhibits temperature below the CO2 frost point, especially during northern summer in the tropics. Comparison with atmospheric general circulation model predictions shows that the existing models overestimate the temperature around the mesopause (above 80 to 100 km) by up to 30 K, probably because of an underestimation of the atomic oxygen concentration which controls the CO2 infrared cooling.