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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.11.005 Byline: P. Wolkenberg, V. Formisano, G. Rinaldi, A. Geminale Keywords: Mars, Atmosphere, Climate; Mars; Atmospheres; Dynamics Abstract: We study the thermal fields over Olympus Mons separating seasons (northern spring and summer against southern spring and summer) and local time observations (day side versus night side). Temperature vertical profiles retrieved from Planetary Fourier Spectrometer on board Mars Express (PFS-MEX) data have been used. In many orbits (running north to south along a meridian) passing over the top of the volcano there is evidence of a hot air on top of the volcano, of two enhancement of the air temperature both north and south of it and in between a collar of air that is colder than nearby at low altitudes, and warmer than nearby at high altitudes. Mapping together many orbits passing over or near the volcano we find that the hot air has the tendency to form an hot ring around it. This hot structure occurs mostly between LT=10.00 and 15.00 and during the northern summer. Distance of the hot structure from the top of the volcano is about 600km (10[degrees] of latitude). The hot atmospheric region is 300-420km (5-7[degrees]) wide. Hot ring temperature contrasts of about 40K occur at 2km above the surface and decrease to 20K at 5km and to 10K at 10km. The atmospheric circulation over an area of 40[degrees]x40[degrees] (latitudes and longitudes) is affected by the topography and the presence of Olympus Mons (-133[degrees]W,18[degrees]N). We discuss also the thermal stability of the atmosphere over the selected area using the potential temperatures. The temperature field over the top of the volcano shows unstable atmosphere within 10km from the surface. Finally, we interpret the hot temperatures around volcano as an adiabatic compression of down-welling branch coming from over the top of volcano. Different air temperature profiles are observed in the same seasons during the night, or in different seasons. In northern spring-summer during the night the isothermal contours do not show the presence of the volcano until we reach close to the surface very much, where a thermal inversion is observed. The surface temperature shows higher values (by 10K) in correspondence of the scarp (an abrupt altimetry variation of roughly 5km) on south (6[degrees]N) and north (30[degrees]N) sides of volcano. During the southern spring-summer, on the contrary the isothermal curves run parallel to the surface even on top the volcano, just like the GCM have predicted. Author Affiliation: I.F.S.I., INAF, Via Fosso del Cavaliere, Rome, Italy Article History: Received 19 March 2009; Revised 21 October 2009; Accepted 4 November 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.05.019 Byline: M. Giuranna (a)(b), D. Grassi (a), V. Formisano (a), L. Montabone (c)(d), F. Forget (d), L. Zasova (a)(e) Keywords: Mars; polar caps; Mars; climate; Ices Abstract: The condensing CO.sub.2 south polar cap of Mars and the mechanisms of the CO.sub.2 ice accumulation have been studied through the analysis of spectra acquired by the Planetary Fourier Spectrometer (PFS) during the first two years of ESA's Mars Express (MEX) mission. This dataset spans more than half a martian year, from Ls[approximately equal to]330[degrees] to Ls[approximately equal to]194[degrees], and includes the southern fall season which is found to be extremely important for the study of the residual south polar cap asymmetry. The cap expands symmetrically and with constant speed during the fall season. The maximum extension occurs sometime in the 80[degrees]-90[degrees]Ls range, when the cap edges are as low as -40[degrees] latitude. Inside Hellas and Argyre basins, frost can be stable at lower latitudes due to the higher pressure values, causing the seasonal cap to be asymmetric. Within the seasonal range considered in this paper, the cap edge recession rate is approximately half the rate at which the cap edge expanded. The longitudinal asymmetries reduce during the cap retreat, and disappear around Ls[approximately equal to]145[degrees]. Two different mechanisms are responsible for CO.sub.2 ice accumulation during the fall season, especially in the 50[degrees]-70[degrees]Ls range. Here, CO.sub.2 condensation in the atmosphere, and thus precipitation, is allowed exclusively in the western hemisphere, and particularly in the longitudinal corridor of the perennial cap. In the eastern hemisphere, the cap consists mainly of CO.sub.2 frost deposits, as a consequence of direct vapor deposition. The differences in the nature of the surface ice deposits are the main cause for the residual south polar cap asymmetry. Results from selected PFS orbits have also been compared with the results provided by the martian general circulation model (GCM) of the Laboratoire de Meteorologie dynamique (LMD) in Paris, with the aim of putting the observations in the context of the global circulation. This first attempt of cross-validation between PFS measurements and the LMD GCM on the one hand confirms the interpretation of the observations, and on the other hand shows that the climate modeling during the southern polar night on Mars is extremely sensitive to the dynamical forcing. Author Affiliation: (a) Istituto di Fisica dello Spazio Interplanetario INAF-IFSI, Via del Fosso del Cavaliere 100, 00133 Roma, Italy (b) Centro Interdipartimentale di Studi e Attivita Spaziali CISAS - 'G. Colombo,' University of Padova, Via Venezia 15, 35131 Padova, Italy (c) Department of Physics & Astronomy, The Open University, Walton Hall, Milton Keynes MK7 6AA, United Kingdom (d) Laboratoire de Meteorologie Dynamique du CNRS, Universite Paris 6, BP99, 75252, Paris Cedex 05, France (e) Space Research Institute of Russian Academy of Sciences (IKI), Profsojuznaja 84/32, 117810 Moscow, Russia Article History: Received 20 November 2007; Revised 4 April 2008

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.01.018 Byline: M. Tschimmel (a), N.I. Ignatiev (b), D.V. Titov (a)(b), E. Lellouch (c), T. Fouchet (c)(d), M. Giuranna (e), V. Formisano (e) Keywords: Mars; Mars; atmosphere; Abundances; atmospheres; Atmospheres; structure; Infrared observations Abstract: New insight into the seasonal, diurnal and spatial distribution of water vapor on Mars has been obtained from analyzing the spectra of the short-wavelength channel (SW) of the Planetary Fourier Spectrometer (PFS) onboard Mars Express. The processed dataset, recorded between January 2004 and April 2005, covers the seasons from L.sub.S=331[degrees] of Mars Year 26 to L.sub.S=196[degrees] of the following year. In this period the mean column density around vernal equinox was 8.2 pr. [mu]m. The maximum values during northern summer were about 65 pr. [mu]m, located around 75[degrees] N latitude with a longitudinally inhomogeneous distribution. Regarding the atmospheric transport, the majority of polar water vapor remains in the north polar region while only about a quarter is transported southward. Geographically there are two water vapor maxima visible, over Arabia Terra and the Tharsis plateau, that are most likely caused both by atmosphere-ground interaction and by atmospheric circulation. A comparison with other instruments generally shows a good agreement, only the SPICAM results are systematically lower. Compared to the results from the PFS long-wavelength channel the results of this work are slightly higher. A strong discrepancy is visible northward of about 50[degrees] N during the northern summer that is possibly explained by a non-uniform vertical H.sub.2O mixing. In particular, a confinement of the water to the lower few kilometers yields a much better agreement between the retrieved column densities of the two PFS channels. Author Affiliation: (a) Max Planck Institute for Solar System Research, 37191 Katlenburg-Lindau, Germany (b) Space Research Institute (IKI RAN), Moscow 117997, Russia (c) Observatoire de Paris, LESIA, Meudon 92195, France (d) Universite Pierre et Marie Curie - Paris 6, UMR 8109, Paris 75005, France (e) Istituto di Fisica dello Spazio Interplanetario INAF-IFSI, 00133 Rome, Italy Article History: Received 3 July 2007; Revised 15 January 2008

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.08.028 Byline: F. Esposito (a), M. Giuranna (b), A. Maturilli (b), E. Palomba (b), L. Colangeli (a), V. Formisano (b) Keywords: Mars; surface; Photometry; Infrared observations Abstract: The Short Wavelength Channel of the Planetary Fourier Spectrometer (PFS) covers the 8333-1750 cm.sup.-1 (1.2-5.7 [mu]m) spectral range, that is well suited to study the reflectance properties of the martian soil. These properties vary with time due to the dust dynamics in the martian environment. Wind can blow off dust exposing soil and fresh rocks and can support grain mobility inducing local dust settling. We have analyzed PFS data from January 2004 to April 2005. A detailed photometric study of the radiance acquired from the planet has been performed in order to compare correctly measurements obtained at different viewing geometries and to produce a mosaic image of the planet. The results show good agreement with data from the Thermal Emission Spectrometer (on-board NASA Mars Global Surveyor orbiter), although some variations are observed. Some albedo changes could be due to small to medium scale dust storms. A very accurate estimation of the limb-darkening parameter has been computed from the analyzed data. The obtained values are compared with a surface roughness and a thermal inertia map in order to assess the relation between the limb-darkening parameter and the physical properties of surface. Author Affiliation: (a) INAF - Osservatorio Astronomico di Capodimonte (INAF-OAC), Via Moiariello 16, 80131 Napoli, Italy (b) INAF - Istituto di Fisica dello Spazio Interplanetario INAF-IFSI, Via del Fosso del Cavaliere 100, 00133 Roma, Italy Article History: Received 2 February 2006; Revised 25 August 2006

Saturn's icy satellites are among the main scientific objectives of the Cassini-VIMS (Visual and Infrared Mapping Spectrometer) experiment. This paper contains a first systematic and comparative analysis of the full-disk spectral properties of Dione, Enceladus, Epimetheus, Hyperion, Iapetus, Mimas, Phoebe, Rhea and Tethys as observed by VIMS from July 2004 to June 2005. The disk integrated properties (350-5100 nm reflectance spectra and phase curves at 550-2232 nm) and images of satellites are reported and discussed in detail together with the observed geometry. In general, the spectra in the visible spectral range are almost featureless and can be classified according to the spectral slopes: from the bluish Enceladus and Phoebe to the redder Iapetus, Hyperion and Epimetheus. In the 1000-1300 nm range the spectra of Enceladus, Tethys, Mimas and Rhea are characterized by a negative slope, consistent with a surface largely dominated by water ice, while the spectra of Iapetus, Hyperion and Phoebe show a considerable reddening pointing out the relevant role played by darkening materials present on the surface. In between these two classes are Dione and Epimetheus, which have a fiat spectrum in this range. The main absorption bands identified in the infrared are the 1520, 2020, 3000 nm [H.sub.2]O/OH bands (for all satellites), although Iapetus dark terrains show mostly a deep 3000 nm band while the 1520 and 2020 nm bands are very faint. In this spectral range, the Iapetus spectrum is characterized by a strong reddening. The C[O.sub.2] band at 4260 nm and the Fresnel ice peak around 3100 nm are evident only on Hyperion, Phoebe and Iapetus. The phase curves at 550 and at 2232 nm are reported for all the available observations in the 0[degrees]-144[degrees] range; Rhea shows an opposition surge at visible wavelengths in the 0.5[degrees]-1.17[degrees] interval. The improvement on the retrieval of the full-disk reflectance spectra can be appreciated by a direct comparison with ground-based telescopic data available from literature. Finally, data processing strategies and recent upgrades introduced in the VIMS-V calibration pipeline (flat-field and destriping-despiking algorithm) are discussed in appendices. Keywords: Saturn, satellites; Spectroscopy; Infrared observations; Image processing

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2005.12.022 Byline: V. Formisano (a), A. Maturilli (a), M. Giuranna (a), E. D'Aversa (a), M.A. Lopez-Valverde (b) Keywords: Mars; Mars; atmosphere; Atmospheres; composition Abstract: We report on PFS-MEX (Planetary Fourier Spectrometer on board Mars Express) limb observations of the non-Local Thermodynamic Equilibrium emission by CO and CO.sub.2 isotopic molecules. The CO emission is observed peaking at altitudes lower than the CO.sub.2 emission peak. Two orbits have been considered, which explore latitudes from 75 to 15[degrees] N, located in local time at 11:30 and 06:40, and with L.sub.s=138[degrees] and 168[degrees], respectively. In general in the season considered (northern summer) the emission intensity increases going to lower latitudes. The peak emission height is also decreasing with decreasing latitude. The CO.sub.2 isotopic molecules are emitting radiance out of proportion with respect to the normal isotopic abundance, which surely indicates a strong contribution from a large number of much weaker CO.sub.2 bands, a result that will demand careful theoretical modeling. By comparison with Hitran data base we can identify, among the emitting bands, the second hot band for the 626 and 636 molecule, while for the 628 and 627 emission from the third hot bands are very possible. Other minor bands or lines are also observed in emission for the first time in Mars. In one of the two orbits considered, the orbit 1234 of MEX, we also observe at altitudes 80-85 km scattered radiation, with indication of CO.sub.2 ice aerosols as scattering centers. At the same altitude the Pathfinder descending measurements show a temperature that allows CO.sub.2 condensation. Pathfinder measurements were at 03:00 local time, while our observations are for orbit 1234 showing CO.sub.2 ice signature at 11:30 local time. These non-LTE limb emissions, with their unprecedented spectral resolution in this portion of the near infrared and their sensitivity and geographical coverage, will represent in our opinion an excellent data set for testing current theoretical models of the martian upper atmosphere. Author Affiliation: (a) Istituto di Fisica dello Spazio Interplanetario IFSI-INAF, Via del Fosso del Cavaliere 100, 00113 Roma, Italy (b) Instituto de Astrofisica de Andalucia (CSIC), Apdo. 3004, 18080 Granada, Spain Article History: Received 23 May 2005; Revised 20 December 2005

The Visual and Infrared Mapping Spectrometer (VIMS) observed the Galilean satellites during the Cassini spacecraft's 2000/2001 flyby of Jupiter, providing compositional and thermal information about their surfaces. The Cassini spacecraft approached the jovian system no closer than about 126 Jupiter radii, about 9 million kilometers, at a phase angle of < 90[degrees], resulting in only sub-pixel observations by VIMS of the Galilean satellites. Nevertheless, most of the spectral features discovered by the Near Infrared Mapping Spectrometer (NIMS) aboard the Galileo spacecraft during more than four years of observations have been identified in the VIMS data analyzed so far, including a possible [sup.13]C absorption. In addition, VIMS made observations in the visible part of the spectrum and at several new phase angles for all the Galilean satellites and the calculated phase functions are presented. In the process of analyzing these data, the VIMS radiometric and spectral calibrations were better determined in preparation for entry into the Saturn system. Treatment of these data is presented as an example of the VIMS data reduction, calibration and analysis process and a detailed explanation is given of the calibration process applied to the Jupiter data. Keywords: Satellites; Galilean satellites; Jupiter system: Satellite surfaces: Surface composition; Space mission

During the Cassini-Jupiter flyby, VIMS observed Io at different phase angles, both in full sunlight and in eclipse. By using the sunlight measurements, we were able to produce phase curves in the visual through all the near infrared wavelengths covered by the VIMS instrument (0.85-5.1 [micro]m). The phase angle spanned from ~2[degrees] to ~120[degrees]. The measurements, done just after Io emerged from Jupiter's shadow, show an increase of about 15% in Io's reflectance with respect to what would be predicted by the phase curve. This behavior is observed at wavelengths > 1.2 [micro]m. Moreover, just after emergence from eclipse an increase of about 25% is observed in the depth of S[O.sub.2] frost bands at 4.07 and 4.35 [micro]m. At 0.879 < [lambda] < 1.04 [micro]m the brightening is 10-24%. Below [lambda] = 0.879 [micro]m the brightening, if present, should be less than the precision of our measurements (~5%). Apparently, these observations are not explained neither by a diverse spatial distribution of S[O.sub.2] on the Io' surface nor by atmospheric S[O.sub.2] condensation on the surface during the eclipse. Keywords: Io; Atmosphere; Infrared observations: Satellites of Jupiter

We report unusual and somewhat unexpected observations of the jovian satellite Io, showing strong methane absorption bands. These observations were made by the Cassini VIMS experiment during the Jupiter flyby of December/January 2000/2001. The explanation is straightforward: Entering or exiting from Jupiter's shadow during an eclipse, Io is illuminated by solar light which has transited the atmosphere of Jupiter. This light, therefore becomes imprinted with the spectral signature of Jupiter's upper atmosphere, which includes strong atmospheric methane absorption bands. Intercepting solar light refracted by the jovian atmosphere, Io essentially becomes a 'mirror' for solar occultation events of Jupiter. The thickness of the layer where refracted solar light is observed is so large (more than 3000 km at Io's orbit), that we can foresee a nearly continuous multi-year period of similar events at Saturn, utilizing the large and bright ring system. During Cassini's 4-year nominal mission, this probing technique should reveal information of Saturn's atmosphere over a large range of southern latitudes and times. Keywords: Occultations; Jupiter; Infrared observations

The Cassini Visual and Infrared Mapping Spectrometer (VIMS) is an imaging spectrometer coveting the wavelength range 0.3-5.2 [micro]m in 352 spectral channels, with a nominal instantaneous field of view of 0.5 mrad. The Cassini flyby of Jupiter represented a unique opportunity to accomplish two important goals: scientific observations of the jovian system and functional tests of the VIMS instrument under conditions similar to those expected to obtain during Cassini's 4-year tour of the saturnian system. Results acquired over a complete range of visual to near-infrared wavelengths from 0.3 to 5.2 [micro]m are presented. First detections include methane fluorescence on Jupiter, a surprisingly high opposition surge on Europa, the first visual-near-IR spectra of Himalia and Jupiter's optically-thin ring system, and the first near-infrared observations of the rings over an extensive range of phase angles (0-120[degrees]). Similarities in the center-to-limb profiles of [H.sup.+.sub.3] and C[H.sub.4] emissions indicate that the [H.sup.+.sub.3] ionospheric density is solar-controlled outside of the auroral regions. The existence of jovian N[H.sub.3] absorption at 0.93 [micro]m is confirmed. Himalia has a slightly reddish spectrum, an apparent absorption near 3 [micro]m, and a geometric albedo of 0.06 [+ or -] 0.01 at 2.2 [micro]m (assuming an 85-km radius). If the 3-[micro]m feature in Himalia's spectrum is eventually confirmed, it would be suggestive of the presence of water in some form, either free, bound, or incorporated in layer-lattice silicates. Finally, a mean ring-particle radius of 10 [micro]m is found to be consistent with Mie-scattering models fit to VIMS near-infrared observations acquired over 0-120[degrees] phase angle. Keywords: Jupiter; Jovian satellites; Jupiter's ring; Spectroscopy; Planetary atmospheres; Planetary surfaces; Cassini mission

Abstract: In the history of Mars exploration its atmosphere and planetary climatology aroused particular interest. In the study of the minor gases abundance in the Martian atmosphere, water vapour became especially important, both because it is the most variable trace gas, and because it is involved in several processes characterizing the planetary atmosphere. The water vapour photolysis regulates the Martian atmosphere photochemistry, and so it is strictly related to carbon monoxide. The CO study is very important for the so-called “atmosphere stability problem”, solved by the theoretical modelling involving photochemical reactions in which the H2O and the CO gases are main characters. The Planetary Fourier Spectrometer (PFS) on board the ESA Mars Express (MEX) mission can probe the Mars atmosphere in the infrared spectral range between 200 and 2000cm−1 (5–50μm) with the Long Wavelength Channel (LWC) and between 1700 and 8000cm−1 (1.2–5.8μm) with the Short Wavelength Channel (SWC). Although there are several H2O and CO absorption bands in the spectral range covered by PFS, we used the 3845cm−1 (2.6μm) and the 4235cm−1 (2.36μm) bands for the analysis of water vapour and carbon monoxide, respectively, because these ranges are less affected by instrumental problems than the other ones. The gaseous concentrations are retrieved by using an algorithm developed for this purpose. The PFS/SW dataset used in this work covers more than two and a half Martian years from Ls=62° of MY 27 (orbit 634) to Ls=203° of MY 29 (orbit 6537). We measured a mean column density of water vapour of about 9.6pr. μm and a mean mixing ratio of carbon monoxide of about 990ppm, but with strong seasonal variations at high latitudes. The seasonal water vapour map reproduces very well the known seasonal water cycle. In the northern summer, water vapour and CO show a good anticorrelation most of the time. This behaviour is due to the carbon dioxide and water sublimation from the north polar ice cap, which dilutes non-condensable species including carbon monoxide. An analogous process takes place during the winter polar cap, but in this case the condensation of carbon dioxide and water vapour causes an increase of the concentration of non-condensable species. Finally, the results show the seasonal variation of the carbon monoxide mixing ratio with the surface pressure. [Copyright &y& Elsevier]

Abstract: In this study we map the methane gas in the Martian atmosphere. The main goal of this work is to show the methane behaviour across the planet seasonally. To this aim, we analyze the strongest methane band in the short wavelength channel of the Planetary Fourier Spectrometer (PFS) on board ESA Mars Express (MeX) spacecraft. The optical line depth is used to derive the column density of methane. The maps thus obtained show the spatial variability of this non-condensable gas and how the gas is transported in the atmosphere due to the cycle of carbon dioxide. Moreover, the increase of methane over the north polar cap during local summer, which cannot be explained by global circulation, strongly suggests that there could be methane reservoir associated with the polar cap. [Copyright &y& Elsevier]

Abstract: A large number of spectra measured by the planetary Fourier spectrometer aboard the European Mars Express mission have been studied to identify the average properties of methane in the Martian atmosphere. Using the line at 3018cm−1, we have studied the seasonal, diurnal, and spatial variations of methane through the analysis of large averages of spectra (more than 1000 measurements). Methane mixing ratio has been obtained simultaneously with water vapour mixing ratio and water ice content, by best fitting (minimising the χ 2) the computed averages with synthetic spectra. These spectra were computed for different values of the three parameters (methane and water vapour mixing ratio, and water ice optical depth). The methane mixing ratio shows a slow decrease from northern spring to southern summer with an average value of 14±5ppbv (part per billion by volume) and it does not show a particular trend with latitude. The methane mixing ratio seems not to be uniform in longitude in the Martian atmosphere, as already reported by Formisano et al. [2004. Detection of methane in the atmosphere of Mars. Science 306, 1758–1761]. Two maxima are present at −40°E and +70°E longitude. In local time, the methane mixing ratio seems to follow the water vapour diurnal cycle. The most important point for future understanding is, however, that there are special orbits in which methane mixing ratio has a very high value. [Copyright &y& Elsevier]

Abstract: This work presents a review of the observations acquired by the planetary Fourier spectrometer (PFS) in the region of the Hellas basin. Taking advantage of the high spectral resolution of PFS, the vertical air temperature profile can be investigated with a previously unexperienced vertical resolution. Extensive comparisons with the expectations of EMCD 4.0 database highlight moderate discrepancies, strongly dependant on season. Namely, the morning observations acquired around L s=45° show a series of temperature deficiencies with recurrent spatial patterns in different observations, correlated with the topography profile. Trends of integrated dust loads as a function of the field of view (FOV) elevation are also described. Values are consistent with the retrieval hypothesis of a dust scale height equal to the gas one, even far from the season of main dust storms. [Copyright &y& Elsevier]

Abstract: The advance and retreat of the polar caps were one of the first observations that indicated Mars had seasons. Because a large portion of the atmosphere is cycled in and out of the seasonal caps during the year, the frost deposits play a significant role in regional and global atmospheric circulation. Understanding the nature of the seasonal polar caps is imperative if we are to understand the current Martian climate. In this study, we track the seasonal cap edges as a function of season and longitude for the fall and winter seasons (MY27), using data from the Planetary Fourier Spectrometer (PFS) onboard the Mars Express (MEX) ESA mission. Making use of the rapid rise (decrease) in surface temperature that occurs when CO2 ice is removed (deposited), in a first approach, we defined the advancing cap edge to be where the surface temperature drops below 150K, and the retreating cap edge where the surface temperature rises above 160K. In this case, starting from Ls∼50°, the edge progression speed start to be longitude dependent. In the hemisphere that extends form the eastern limit of the Hellas basin to the western limit of the Argyrae basin (and containing the two) the edges progression speed is about a half than that of the other hemisphere; the cap is thus asymmetric and, unexpectedly, no CO2 ice seems to be present inside the basins. This is because the above mentioned surface temperatures used in this approach to detect the cap edges are not adequate (too low) for the high-pressure regions inside the basins where, following the Clausius–Clapeyron''s law, the CO2 condensation temperature can be several degrees higher than that of the adjacent lower-pressure regions. In the second, final approach, special attention has been given to this aspect and the advancing and retreating cap edges are defined where, respectively, the surface temperatures drop below and rise above the CO2 condensation temperature for the actual surface pressure values. Now, the results show an opposite situation than the previous one, with the progression speed being higher and the cap more extended (up to −30° latitude) in the hemisphere containing the two major Martian basins. During the fall season, up to Ls∼50° the South Martian polar cap consists of CO2 frost deposits that advance towards lower latitudes at a constant speed of 10° of latitude per 15 degrees of Ls. The maximum extension (−40° latitude) of the South polar cap occurs somewhere in the 80°–90° Ls range. At the winter solstice, when the edges of the polar night start moving poleward, the cap recession has already started, in response to seasonal changes in insolation. The CO2 ice South polar cap will recede with a constant speed of ∼5° of latitude every 25° degrees of Ls during the whole winter. The longitudinal asymmetries reduce during the cap retreat and completely disappear around Ls=145°. [Copyright &y& Elsevier]

Abstract: The planetary fourier spectrometer (PFS) for the Venus Express mission is an infrared spectrometer optimized for atmospheric studies. This instrument has a short wavelength (SW) channel that covers the spectral range from 1700 to 11400cm−1 (0.9–5.5μm) and a long wavelength (LW) channel that covers 250–1700cm−1 (5.5–45μm). Both channels have a uniform spectral resolution of 1.3cm−1. The instrument field of view FOV is about 1.6 ° (FWHM) for the short wavelength channel and 2.8 ° for the LW channel which corresponds to a spatial resolution of 7 and 12km when Venus is observed from an altitude of 250km. PFS can provide unique data necessary to improve our knowledge not only of the atmospheric properties but also surface properties (temperature) and the surface-atmosphere interaction (volcanic activity). PFS works primarily around the pericentre of the orbit, only occasionally observing Venus from larger distances. Each measurements takes 4.5s, with a repetition time of 11.5s. By working roughly 1.5h around pericentre, a total of 460 measurements per orbit will be acquired plus 60 for calibrations. PFS is able to take measurements at all local times, enabling the retrieval of atmospheric vertical temperature profiles on both the day and the night side. The PFS measures a host of atmospheric and surface phenomena on Venus. These include the:(1) thermal surface flux at several wavelengths near 1μm, with concurrent constraints on surface temperature and emissivity (indicative of composition); (2) the abundances of several highly-diagnostic trace molecular species; (3) atmospheric temperatures from 55 to 100km altitude; (4) cloud opacities and cloud-tracked winds in the lower-level cloud layers near 50-km altitudes; (5) cloud top pressures of the uppermost haze/cloud region near 70–80km altitude; and (6) oxygen airglow near the 100km level. All of these will be observed repeatedly during the 500-day nominal mission of Venus Express to yield an increased understanding of meteorological, dynamical, photochemical, and thermo-chemical processes in the Venus atmosphere. Additionally, PFS will search for and characterize current volcanic activity through spatial and temporal anomalies in both the surface thermal flux and the abundances of volcanic trace species in the lower atmosphere. Measurement of the 15μm CO2 band is very important. Its profile gives, by means of a complex temperature profile retrieval technique, the vertical pressure-temperature relation, basis of the global atmospheric study. PFS is made of four modules called O, E, P and S being, respectively, the interferometer and proximity electronics, the digital control unit, the power supply and the pointing device. [Copyright &y& Elsevier]

Abstract: The first results of the Planetary Fourier Spectrometer (PFS) orbiting the planet Mars are reviewed and discussed here, with reference to a set of studies being published elsewhere. An average global spectrum ranging from 200 to 8200cm−1 is discussed by comparing it to the ISO SWS Martian spectrum and to the global synthetic spectrum computed using only CO2, CO, H2O gases. PFS is able to measure the vertical temperature–pressure profile in the Martian atmosphere and the temperature of the soil. The SW channel shows the major CO2 bands at 4.3 and 2.7μm. The bottom of the first band shows very clearly the non LTE emission of the high atmospheric CO2 gas, and the dust content in the atmosphere. In one of the first orbit passing over the Olympus Mons, the temperature field retrieved shows abnormal adiabatic cooling in the atmosphere above the mountain, while the soil temperature of the volcano is higher than the latitudinal profile expectation because of a better illumination from the sun. Many solar lines are observed, a few of them are studied and compared to ISO observations. [Copyright &y& Elsevier]

Abstract: Observations of water ice clouds and dust are among the main scientific goals of the Planetary Fourier Spectrometer (PFS), a payload instrument of the European Mars Express mission. We report some results, obtained in three orbits: 37, 41 and 68. The temperature profile, and dust and water ice cloud opacities are retrieved from the thermal infrared (long-wavelength channel of PFS) in a self-consistent way using the same spectrum. Orographic ice clouds are identified above Olympus (orbit 37) and Ascraeus Mons (orbit 68). Both volcanoes were observed near noon at Ls=337° and 342°, respectively. The effective radius of ice particles is preliminary estimated as 1–3μm, changing along the flanks. The corresponding visual opacity changes in the interval 0.2–0.4 above Olympus and 0.1–0.6 above Ascraeus Mons. In the case of Ascraeus Mons, the ice clouds were observed mainly above the Southern flank of the volcano with maximum opacity near the summit. In the case of Olympus, the clouds were found above both sides of the top. A different type of ice cloud is observed at latitudes above 50°N (orbit 68) in the polar hood: the effective particle radius is estimated to be 4μm. Below the 1mb level an inversion in the temperature profiles is found with maximum temperature at around 0.6mb. Along orbit 68 it appears above Alba Patera, then it increases to the north and decreases above the CO2 polar cap. Beginning from latitude 20°S above Tharsis (orbit 68), the ice clouds and dust contribute equally to the spectral shape. Further on, the ice clouds are found everywhere along orbit 68 up to the Northern polar cap, except the areas between the Northern flank of Ascraeus Mons (below 10km) and the edge of Alba Patera. Orbit 41 is shifted from the orbit 68 by roughly 180° longitude and passes through Hellas. Ice clouds are not visible in this orbit at latitudes below 80°S. The dust opacity is anticorrelated with the surface altitude. From 70°S to 25°N latitude the vertical dust distribution follows an exponential law with a scale height of 11.5±0.5km, which corresponds to the gaseous scale height near noon and indicates a well-mixed condition. The 9μm dust opacity, reduced to zero surface altitude, is found to be 0.25±0.05, which corresponds to a visual opacity of 0.5–0.7 (depending on the particle size). [Copyright &y& Elsevier]

Abstract: The evaluation of the planetary Fourier spectrometer performance at Mars is presented by comparing an average spectrum with the ISO spectrum published by Lellouch et al. [2000. Planet. Space Sci. 48, 1393.]. First, the average conditions of Mars atmosphere are compared, then the mixing ratios of the major gases are evaluated. Major and minor bands of CO2 are compared, from the point of view of features characteristics and bands depth. The spectral resolution is also compared using several solar lines. The result indicates that PFS radiance is valid to better than 1% in the wavenumber range 1800–4200cm−1 for the average spectrum considered (1680 measurements). The PFS monochromatic transfer function generates an overshooting on the left-hand side of strong narrow lines (solar or atmospheric). The spectral resolution of PFS is of the order of 1.3cm−1 or better. A large number of narrow features to be identified are discovered. [Copyright &y& Elsevier]

Abstract: The Planetary Fourier Spectrometer (PFS) experiment on board the Mars Express mission has two channels covering the 1.2–5μm (SWC) and the 5–50μm (LWC). The Long Wavelength Channel (LWC) measures the thermal emission spectrum of Mars between 200 and 2000cm−1 with a spectral resolution of 1.4cm−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. [Copyright &y& Elsevier]

Abstract: The Planetary Fourier Spectrometer (PFS) experiment on board the Mars Express mission has two channels covering the 1.2–5.5 m short wavelength channel (SWC) and the 5.5–45 m (LWC). The SWC measures part of the thermal emission spectrum and the solar reflected spectrum of Mars between 1700 and 8200cm−1 with a spectral resolution of 1.3cm−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 210–215K. 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. [Copyright &y& Elsevier]

Abstract: The Planetary Fourier Spectrometer (PFS) for the Mars Express mission is an infrared spectrometer optimised for atmospheric studies. This instrument has a short wave (SW) channel that covers the spectral range from 1700 to (1.2–) and a long-wave (LW) channel that covers 250– (5.5–). Both channels have a uniform spectral resolution of . The instrument field of view FOV is about (FWHM) for the Short Wavelength channel (SW) and (FWHM) for the Long Wavelength channel (LW) which corresponds to a spatial resolution of 7 and 12km when Mars is observed from an height of 250 km. PFS can provide unique data necessary to improve our knowledge not only of the atmosphere properties but also about mineralogical composition of the surface and the surface-atmosphere interaction. The SW channel uses a PbSe detector cooled to 200–220K while the LW channel is based on a pyroelectric () detector working at room temperature. The intensity of the interferogram is measured every 150nm of physical mirrors displacement, corresponding to 600nm optical path difference, by using a laser diode monochromatic light interferogram (a sine wave), whose zero crossings control the double pendulum motion. PFS works primarily around the pericentre of the orbit, only occasionally observing Mars from large distances. Each measurements take 4s, with a repetition time of 8.5s. By working roughly 0.6h around pericentre, a total of 330 measurements per orbit will be acquired 270 looking at Mars and 60 for calibrations. PFS is able to take measurements at all local times, facilitating the retrieval of surface temperatures and atmospheric vertical temperature profiles on both the day and the night side. [Copyright &y& Elsevier]

Abstract: This paper describes one of the sources of the data concerning the thermal structure of the Martian atmosphere, based on the thermal IR spectrometry method. It allows to investigate the Martian atmosphere below 55 km by retrieving the temperature profiles from the 15 μm CO2 band. This approach enables to reach the vertical resolution of several kilometers and the temperature accuracy of several Kelvins. An aerosol abundance, which influences the temperature profile, is obtained from the continuum of the same spectrum parallel with the temperature profile and is taken into account in the temperature retrieval procedure in a self consistent way. Although this method has the limited vertical resolution, it possesses a significant advantage: the thermal IR spectrometry allows to monitor the temperature profiles with a good coverage both in space and local time. The Planetary Fourier spectrometer on board of Mars Express has the spectral range from 250 to 8000 cm−1 and a high spectral resolution of about 2 cm−1. Vertical temperature profiles retrieval is one of the main scientific goals of the experiment. The important data are expected to be obtained on the vertical thermal structure of the atmosphere, and its dependence on latitude, longitude, season, local time, clouds and dust loadings. These results should give a significant input in the future MIRA, being included in the Chapter “Structure of the atmosphere from the surface to 100 km”. [Copyright &y& Elsevier]

We present here an evaluation of basic PFS sounding capabilities; results refer to the analysis of a single, calibrated spectrum. PFS is an infrared Fourier spectrometer on board of Mars Express mission. It covers the thermal infrared (250–1750 cm−1) with a resolution of 1.5 cm−1, as well as the near infrared (2000–8200 cm−1), with a resolution of 1.5 cm−1. It has been designed primarily to investigate the Martian atmosphere in its different cycles and interactions. This task can be achieved monitoring the fields of: (i) temperature (as a function of height) in the lower atmosphere, (ii) pressure, (iii) [H2O], and optical thickness at different wavenumbers related to (iv) water ice and (v) dust integrated contents. The above mentioned parameters can be retrieved from a single PFS measurement, taking advantage of the instrument’s wide spectral range and high resolution. Specific retrieval software is under development in IFSI – CNR. Its performance is evaluated using as a reference a wide dataset of simulated PFS observations. The synthetic spectra have been computed taking into account likely environmental conditions (extracted from the European Martian Climate Database) and the actual instrument noise. We present here the general structure of the code; realistic estimates of errors on retrieved quantities are also provided. Special attention is devoted to the evaluation of T(p) profile. These preliminary results demonstrate the capability of PFS to achieve its general scientific objectives. [Copyright &y& Elsevier]

During Cassini – Jupiter flyby occurred in December 2000, Visual–Infrared mapping spectrometer (VIMS) instrument took several image cubes of Jupiter at different phase angles and distances. We have analysed the spectral images acquired by the VIMS visual channel by means of a principal component analysis technique (PCA). The original data set consists of 96 spectral images in the 0.35–1.05 μm wavelength range. The product of the analysis are new PC bands, which contain all the spectral variance of the original data. These new components have been used to produce a map of Jupiter made of seven coherent spectral classes. The map confirms previously published work done on the Great Red Spot by using NIMS data. Some other new findings, presently under investigation, are presented. [Copyright &y& Elsevier]

ISHTAR or VENUS ORBITER is a mission to Venus similar to the mission Mars Express to Mars, with the use, possibly, of the same spacecraft and subsystems. This mission has been proposed to ESA for a feasibility study as a small mission (F2, F3). We shall describe here briefly the scientific objectives of the mission, and how could be implemented. The scientific objectives of the mission are evenly distributed in three broad areas: atmospheric science, planetary interior and surface, and interaction with the solar wind. Ishtar will study the surface and the atmosphere of the planet by making use of remote sensing instruments, and, if possible, by a descending meteorological balloon/lander. The model payload of the orbiter should include an Imaging Spectrometer, a Fourier Spectrometer, a Radar imaging/altimeter, a UV spectrometer and a Plasma Package studying also the Energetic Neutral Atoms population resulting from the plasma interaction with the planetary atmosphere. [Copyright &y& Elsevier]

Several procedures have been developed to support the strategy for the remote sensing of Mars with the experiment Planetary Fourier Spectrometer (PFS) on board of Mars Express. The instrument is a dual channel Infrared Fourier spectrometer, always pointing to nadir down to the planet, with the possibility of shifting from the nadir pointing by ±12.5°, ±25° perpendicularly to the ground track direction. Among these procedures, the Mars Express Simulator has been implemented in order to obtain useful information about the position of the spot traced by the PFS on Mars. This tool has provided the possibility to plan limb observations in some particular conditions, reflectance phase function measurements, global coverage, local time coverage and so on. [Copyright &y& Elsevier]

Several hundred spectra were obtained at latitudes > 65N in late northern winter (Ls = 322° −352°). Solar zenith angles ranged from 75° to 125°; however most of these spectra were observed in polar darkness. The data reveal complex spectral features, including a complex shape in the 15 μm CO2 band. Temperature profiles and aerosol opacities were retrieved in a self-consistent way. Temperature profiles show an inversion in the lowest 5 km above the local surface(below 0 km altitude). At higher levels the temperature decreases with altitude, reaching a minimum at 10 – 20 km, in such a way that the altitude of the minimum increases with latitude; above that level the temperature increases again up to 40–50 km. At latitudes ϕ <70 N the temperature in the atmosphere above the inversion is too high for CO2 condensation, but at 70–75 N in some cases the CO2 condensation occurs at the altitudes below 5 km. The maximal altitude of the possible CO2 condensation increases up to 20 km in the near polar region at 80–90 N. A near surface fog, consisting of the H2O ice particles, was found with typical values of the optical depth at 10 μm ranging from 0.1 to higher than 1. For an exponential model, its scale height was found to be 1–2 km, with a mean particle radius of about 1 μm (assuming a normal particle size distribution). Total water content in the fog is 1–10 prμm (10 – 100 ppm at −5 km surface altitude). Most of the spectral features in the range 200 – 1000 cm−1 are successfully reproduced by our model, except the spectra of anomalously cold areas, where more sophisticated model is needed, which should include the CO2 surface deposits and condensation clouds near the surface. Most of the spectra with these features are observed at latitudes > 80N and in some cold areas at 70–80N. [Copyright &y& Elsevier]

Abstract: Our purpose was a qualitative assessment of the impact of dust and water ice aerosols on the retrieved temperature profiles and the retrieval process itself in the Martian atmosphere. It aims to quantify the related uncertainties in the atmospheric temperature profiles derived from radiance measurements of the Planetary Fourier Spectrometer (PFS), currently operating on the Mars Express orbiter. In this study the effects of aerosol opacities on simulated data and retrieved temperature profiles were also investigated. From the analysis of the model atmosphere including dust and water ice with different size distributions it results that the dust component affects weighting functions and brightness temperatures less than water ice. A similar situation is also observed when different vertical distributions are considered. Unlike dust, water ice with different sizes of crystals evidently influences weighting functions and brightness temperatures. The impact of the considered water ice vertical distributions on brightness temperatures is noticeable only near 840cm−1. Considering different dust opacities, the largest differences—5K maximum—between retrieved temperature profiles were observed close to the surface, regardless assumptions on a size distribution or the refractive indices. Contrary to dust, the different sizes of water ice particles assumed during retrieval stronger affected the retrieved temperature profiles than water ice opacities. Moreover, the differences in the retrieved temperature profiles were amplified while wrong optical properties for dust as well as for water ice aerosol were assumed instead of the nominal case. This means that the wrong assumption can induce an additional source of the retrieval error and lead to unreasonable temperature profiles. In the cases of expected heavily loads water ice crystals, their size distribution in the Martian atmosphere should be known from other observations before the retrieval of the temperature profile is attempted. For the analyzed examples of real PFS measurements the impact of different dust vertical distributions on the retrieval of temperature profile is prominent only in layers close to the surface. However, these differences remain comparable with retrieval errors. All influences of dust on weighting functions, brightness temperatures and during retrieval can be neglected if the noise equivalent radiance (NER) of PFS is taken into account. [Copyright &y& Elsevier]

Abstract: The planetary fourier spectrometer (PFS) for the Mars express mission (MEX) is an infrared spectrometer operating in the wavelength range from 1.2 to 45μm by means of two spectral channels, called SWC (short wavelength channel) and LWC (long wavelength channel), covering, respectively, 1.2–5.5 and 5.5–45μm. The middle-spring Martian north polar cap (Ls∼40°) has been observed by PFS/MEX in illuminated conditions during orbit 452. The SWC spectra are here used to study the cap composition in terms of CO2 ice, H2O ice and dust content. Significant spectral variation is noted in the cap interior, and regions of varying CO2 ice grain sizes, water frost abundance, CO2 ice cover and dust contamination can be distinguished. In addition, we correlate the infrared spectra with an image acquired during the same orbit by the OMEGA imaging spectrometer and with the altimetry from MOLA data. Many of the spectra variations correlate with heterogeneities noted in the image, although significant spectral variations are not discernible in the visible. The data have been divided into five regions with different latitude ranges and strong similarities in the spectra, and then averaged. Bi-directional reflectance models have been run with the appropriate lighting geometry and used to fit the observed data, allowing for CO2 ice and H2O ice grain sizes, dust and H2O ice contaminations in the form of intimate granular mixtures and spatial mixtures. A wide annulus of dusty water ice surrounds the recessing CO2 seasonal cap. The inner cap exhibits a layered structure with a thin CO2 layer with varying concentrations of dark dust, on top of an H2O ice underneath ground. In the best-fits, the ices beneath the top layer have been considered as spatial mixtures. The results are still very good everywhere in the spectral range, except where the CO2 ice absorption coefficients are such that even a thin layer is enough to totally absorb the incoming radiation (i.e. the band is saturated). This only happens around 3800cm−1, inside the strong 2.7-μm CO2 ice absorption band. The effect of finite snow depth has been investigated through a layered albedo model. The thickness of the CO2 ice deposits increases with latitude, ranging from 0.5–1gcm−2 within region II to 60–80gcm−2 within the highest-latitude (up to 84°N) region V. Region I is at the cap edge and extends from 65°N to 72°N latitude. No CO2 ice is present in this region, which consists of relatively large grains of water ice (20μm), highly contaminated by dust (0.15wt%). The adjacent region II is a narrow region [76–79°N] right at the edge of the north residual polar cap. This region is very distinct in the OMEGA image, where it appears to surround the whole residual cap. The CO2 ice features are barely visible in these spectra, except for the strong saturated 2.7μm band. It basically consists of a thin layer of 5-mm CO2 ice on top of an H2O ice layer with the same composition as region I. A third interesting region III is found all along the shoulder of the residual cap [79–81°N]. It extends over 1.5km in altitude and over only 2° of latitude and consists of CO2 ice with a large dust content. It is an admixture of CO2 ice (3–4mm), with several tens of ppm by mass of water ice and more than 2ppt by mass of dust. The surface temperatures have been retrieved from the LWC spectra for each observation. We found an increase in the surface temperature in this region, indicating a spatial mixture of cold CO2 ice and warmer dust/H2O ice. Region IV is close to the top of the residual cap [81–84°N]; it is much brighter than region III, with a dust content 10 times lower than the latter. The CO2 grain size is 3mm and strong CO2 ice features are present in the data, indicating a thicker CO2 ice layer than in region II (1–2gcm−2). The final region V is right at the top of the residual cap (⩾84°N). It is “pure” CO2 ice (no dust) of 5mm grain sizes, with 30ppm by weight of water ice. The CO2 ice features are very pronounced and the 2.7μm band is saturated. The optical thickness is close to the semi-infinite limit (30–40gcm−2). Assuming a snowpack density of 0.5gcm−3, we get a minimum thickness of 1–2cm for the top-layer of regions II and III, 4–10cm for region IV, and ⩾60–80cm thickness for region V. These values are in close agreement with several recent results for the south seasonal polar cap. These results should provide new, useful constraints in models of the Martian climate system and volatile cycles. [Copyright &y& Elsevier]

Abstract: The Mars Express spacecraft has a highly inclined orbit around Mars and so has been able to observe the south pole of Mars in illuminated conditions at the end of the southern summer (). Spectra from the planetary Fourier spectrometer (PFS) short wavelength (SW) channel were recorded over the permanent ice cap to study its composition in terms of CO2 ice and H2O ice. Models are fitted to the observed data, which include a spatial mixture of soil (not covered by ice) and CO2 frost (with a specific grain size and a small amount of included dust and H2O ice). Two different kinds of spectra were observed: those over the permanent polar cap with almost pure CO2 ice, negligible water ice, no soil fraction required, and bright; and those over mixed terrain (at the edge of the cap or near troughs) containing a significant soil spatial fraction, more water ice and smaller CO2 grain size. The amount of water ice given by fits to scaled albedo models is less than 10ppm by weight. When using multi-stream reflectance models with the appropriate lighting geometry, the water amount must be 2–5 times greater than the albedo fit (less than 50ppm). At the periphery of the residual polar cap, we found a region almost completely covered by water frost, modeled as a mixture of micron-sized and sub-mm sized grains. Our result using a granular mixture of micron-sized grains of water ice and dust with the CO2 grains is different from the modeling of OMEGA polar cap observations using molecular mixtures. [Copyright &y& Elsevier]

Thermal infrared spectrometry in the range 6–40 μm with spectral resolution of 4.5–6.5 cm−1 was realized onboard of Venera 15 for the middle atmosphere of Venus investigations. The 3-D temperature and zonal wind fields (h, ϕ, LT) in the range 55–100 km and the 3-D aerosol field (h, ϕ, LT) in the range 55–70 km were retrieved and analyzed. The solar related waves at isobaric levels, generated by the absorbed solar energy, were investigated. In the thermal IR spectral range the, ν1, ν2 and ν3 SO2 and the H2O rotational (40 μm) and vibro-rotational (6.3 μm) absorption bands are observed and used for minor compounds retrieval. An advantage of the thermal infrared spectrometry method is that both the temperature and aerosol profiles, which need for retrieval of the vertical profiles of minor compounds, are evaluated from the same spectrum. The Fourier spectrometer on Venera-15 may be considered as a precursor of the Planetary Fourier Spectrometer (PI Prof. V. Formisano), which is included in the payload of the planned Venus Express mission. It has a spectral range 0.9–45 μm, separated into two channels: a short wavelength channel (SWC) in the range 0.9–5 μm and a long wavelength channel (LWC) from 6 to 45 μm, and spectral resolution of 1–2 cm−1. In the history of planetary Fourier spectrometry the PFS is a unique instrument, which possesses a short wavelength channel. A functioning of this instrument on the polar orbit with a good spatial and local time coverage will advance our knowledge in the fundamental problems of the Venus atmosphere. [Copyright &y& Elsevier]

Considering the possibility of outgassing from some localized sources on Mars, we have developed a one-dimensional photochemical model that includes methane (CH4), sulfur dioxide (SO2) and hydrogen sulfide (H2S). Halogens were considered but were found to have no significant impact on the martian atmospheric chemistry. We find that the introduction of methane into the martian atmosphere results in the formation of mainly formaldehyde (CH2O), methyl alcohol (CH3OH) and ethane (C2H6), whereas the introduction of the sulfur species produces mainly sulfur monoxide (SO) and sulfuric acid (H2SO4). Depending upon the flux of the outgassed molecules from possible hot spots, some of these species and the resulting new molecules may be detectable locally, either by remote sensing (e.g., with the Planetary Fourier Spectrometer on Mars Express) or in situ measurements. [Copyright &y& Elsevier]

In this paper, we present preliminary scientific results obtained from the analysis of VIMS (Visible and Infrared Mapping Spectrometer) lunar images and spectra. These data were obtained during the Cassini Earth flyby in August 1999. Spectral ratios have been produced in order to derive lunar mineralogical maps. Some spectra observed at the north-east lunar limb, show few unusual absorption features located at 0.357, 0.430 and 0.452 μm, the origin of which is presently unknown. [Copyright &y& Elsevier]

After the correction for the instrumental effect, Mariner-9 IRIS data were analysed to retrieve water vapour abundance in the southern hemisphere in late summer. Seasonal, latitudinal and diurnal variability of water vapour is studied. The major detected effect is the diurnal peak of H2O abundance, which decreases during the period from Ls = 293° to Ls = 345°. [Copyright &y& Elsevier]

The NOMAD spectrometer suite on the ExoMars Trace Gas Orbiter will map the composition and distribution of Mars׳ atmospheric trace species in unprecedented detail, fulfilling many of the scientific objectives of the joint ESA-Roscosmos ExoMars Trace Gas Orbiter mission. The instrument is a combination of three channels, covering a spectral range from the UV to the IR, and can perform solar occultation, nadir and limb observations. In this paper, we present the science objectives of the instrument and how these objectives have influenced the design of the channels. We also discuss the expected performance of the instrument in terms of coverage and detection sensitivity. [ABSTRACT FROM AUTHOR]

The Mars Express mission was launched in June 2003 and was inserted into orbit around Mars in December 2003. Its main objective is to study the Mars' subsurface, surface, atmosphere and interaction with the solar wind. A secondary objective is to study the martian moons, in particular the largest one Phobos, thanks to a near polar and elliptical orbit which allows the spacecraft to perform close flybys about every five months. The Mars Express data not only consist of high-resolution 3D color images, but also astrometric images, spectra from 0.18 to 20 μm, radar echoes, Doppler signals from gravity experiments, and ion data. A new view of the moons has emerged from this data set, favoring now the idea that they are not captured asteroids, but rather the result of a re-accretion following a major impact on Mars. This unique set of data is available in the ESA Planetary Science Archive (PSA) and mirror imaged in the NASA Planetary Data System (PDS). This paper presents an overview of the Mars Express Phobos flybys, the specificities of their operations and the scientific achievements. [ABSTRACT FROM AUTHOR]

Abstract: The origin of the Martian satellites presents a puzzle of long standing. Addressing the composition of Phobos will help constrain theories of its formation. Visible and near-infrared spectra of Phobos lack deep absorption features, making the compositional interpretation a tricky task. PFS/MEx and TES/MGS observations in the thermal infrared show several spectral features that can be used to investigate the composition of the surface. Our results show that the majority of the spectra are consistent with the presence of phyllosilicates, particularly in the area northeast of Stickney. This area corresponds to the “blue” region as defined by . Analysis of PFS and TES observations in the “red” region defined by are consistent with tectosilicates, especially feldspars/feldspathoids. We discuss several physical and chemical mechanisms that can act to eliminate or reduce the strength of bands in the VIS/NIR spectra, with possibly little or no effect in the mid-IR. Comparison of the TES and PFS data to the meteorites shows that no class of chondritic meteorites provide significant agreement with the spectral features observed. The lack of consistency of the PFS and TES spectra to analogs of ultraprimitive materials (organic residues) suggests that an origin via capture of a transneptunian object is not supported by these observations, although it cannot be completely ruled out. Derived surface temperatures from PFS and TES data are in very good agreement with brightness temperatures derived from Viking orbiter measurements, Earth-based observations, and values predicted by numerical models. Our results show that the surface temperature of Phobos varies with solar incidence angle and heliocentric distance, reconciling the different results. We collect and summarize the compositional clues for the origin of Phobos discussed in this paper, including our results. Currently, the most likely scenario is the in-situ formation of Phobos, although a capture of achrondrite-like meteorites is not ruled out. [Copyright &y& Elsevier]

Abstract: The MIPAS instrument on board Envisat, in Earth orbit, the PFS and OMEGA instruments on Mars Express, and VIRTIS on board Venus Express are currently providing a dataset of limb measurements of the CO2 atmospheric fluorescence emission at from the upper atmosphere of the three planets. These measurements represent an excellent dataset to perform comparative studies between the terrestrial planets’ upper atmospheres, and also to test our theoretical understanding of these emissions. In order to exploit these datasets, we apply a set of non-local thermodynamic equilibrium (non-LTE) models developed at the IAA/CSIC, in Granada, Spain, to a selection of data. In general, the models can explain the main spectral features of the measurements, and also the altitude and solar zenith angle variations. However, the simulations for Mars and Venus give an incorrect ratio of the emissions at two wavelengths, 4.4 and . In order to explain this deficiency, a revision of the most uncertain non-LTE energy transfer parameters has been performed. The quenching rate of quanta of high-energy CO2 states by CO2 itself could reduce the model-data discrepancy if increased by a factor 2–4, still within its current uncertainty range. This factor, however, is subject to the uncertainty in the thermal structure. A number of simulations with the non-LTE models were also used to study and compare the role of radiative transfer in this spectral region in the three terrestrial planets. Sensitivity studies of density and temperature are also presented, and they permit an analysis of how the differences between the planets and between the three instruments affect their sounding capabilities. [Copyright &y& Elsevier]

Abstract: We report here on CO limb observations in Mars, Venus and Earth and their model simulations. A comparative study of the CO emission, including the most recent spacecraft observations of the three planets’ atmospheres, has been performed. Strong daytime emissions near have been recently observed in the limb of the upper atmosphere of the three terrestrial planets by the Planetary Fourier Spectrometer on Mars Express (), the Visible and Infrared Thermal Imaging Spectrometer on Venus Express (), and the Michelson Interferometer for Passive Atmosphere Sounding on Envisat (). Those emissions are produced by solar pumping of molecular vibrations and non-local thermodynamic equilibrium (non-LTE) models are used to explain them in a consistent framework for the three atmospheres. The maximum of the emission occurs on Venus between 90 and 110km, on Mars above 60km, and on Earth around 68km. The observations show that the fundamental band dominates the CO non-LTE emission on Earth, while on Venus and Mars the larger contribution comes from the first hot band transition. The main goal of this study is to understand those differences and similarities with the help of theoretical simulations with optical thickness considerations, and compare the capability of space instrumentation for the remote sounding of the atmospheres in this spectral region. [Copyright &y& Elsevier]

Abstract: We have analyzed spectra of CO recorded with the instrument PFS onboard Mars Express in the (1–0) band. The dataset we used ranges in time from January until June 2004 ( until ; 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 () [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, , 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 and ). Such relative variations have been used on a statistical basis to derive main trends as a function of latitude for three ranges: –, 0– and 30–. For the first range, we seem to have an enhancement of the CO mixing ratio towards the northern latitudes, probably linked to the condensation in winter on the north polar cap. The situation for the two other 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 –, thus confirming the effect of seasonal condensation of on the north polar cap, but we have no agreement for other seasons. [Copyright &y& Elsevier]

Abstract: The Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board the ESA/Venus Express mission has technical specifications well suited for many science objectives of Venus exploration. VIRTIS will both comprehensively explore a plethora of atmospheric properties and processes and map optical properties of the surface through its three channels, VIRTIS-M-vis (imaging spectrometer in the 0.3–1μm range), VIRTIS-M-IR (imaging spectrometer in the 1–5μm range) and VIRTIS-H (aperture high-resolution spectrometer in the 2–5μm range). The atmospheric composition below the clouds will be repeatedly measured in the night side infrared windows over a wide range of latitudes and longitudes, thereby providing information on Venus''s chemical cycles. In particular, CO, H2O, OCS and SO2 can be studied. The cloud structure will be repeatedly mapped from the brightness contrasts in the near-infrared night side windows, providing new insights into Venusian meteorology. The global circulation and local dynamics of Venus will be extensively studied from infrared and visible spectral images. The thermal structure above the clouds will be retrieved in the night side using the 4.3μm fundamental band of CO2. The surface of Venus is detectable in the short-wave infrared windows on the night side at 1.01, 1.10 and 1.18μm, providing constraints on surface properties and the extent of active volcanism. Many more tentative studies are also possible, such as lightning detection, the composition of volcanic emissions, and mesospheric wave propagation. [Copyright &y& Elsevier]

Abstract: Venus Express is the first European mission to planet Venus. The mission aims at a comprehensive investigation of Venus atmosphere and plasma environment and will address some important aspects of the surface physics from orbit. In particular, Venus Express will focus on the structure, composition, and dynamics of the Venus atmosphere, escape processes and interaction of the atmosphere with the solar wind and so to provide answers to the many questions that still remain unanswered in these fields. Venus Express will enable a breakthrough in Venus science after a long period of silence since the period of intense exploration in the 1970s and the 1980s. The payload consists of seven instruments. Five of them were inherited from the Mars Express and Rosetta projects while two instruments were designed and built specifically for Venus Express. The suite of spectrometers and imaging instruments, together with the radio-science experiment, and the plasma package make up an optimised payload well capable of addressing the mission goals to sufficient depth. Several of the instruments will make specific use of the spectral windows at infrared wavelengths in order to study the atmosphere in three dimensions. The spacecraft is based on the Mars Express design with minor modifications mainly needed to cope with the thermal environment around Venus, and so a very cost-effective mission has been realised in an exceptionally short time. The spacecraft was launched on 9 November 2005 from Baikonur, Kazakhstan, by a Russian Soyuz-Fregat launcher and arrived at Venus on 11 April 2006. Venus Express will carry out observations of the planet from a highly elliptic polar orbit with a 24-h period. In 3 Earth years (4 Venus sidereal days) of operations, it will return about 2Tbit of scientific data. Telecommunications with the Earth is performed by the new ESA ground station in Cebreros, Spain, while a nearly identical ground station in New Norcia, Australia, supports the radio-science investigations. [Copyright &y& Elsevier]

Abstract: The Visual and Infrared Mapping Spectrometer (VIMS) instrument on the Cassini Saturn Orbiter returned spectral imaging data as the spacecraft undertook six close encounters with Titan beginning 7 July, 2004. Three of these flybys each produced overlapping coverage of two distinct regions of Titan''s surface. Twenty-four points were selected on approximately opposite hemispheres to serve as photometric controls. Six points were selected in each of four reflectance classes. On one hemisphere each control point was observed at three distinct phase angles. From the derived phase coefficients, preliminary normal reflectances were derived for each reflectance class. The normal reflectance of Titan''s surface units at 2.0178μm ranged from 0.079 to 0.185 for the most absorbing to the most reflective units assuming no contribution from absorbing haze. When a modest haze contribution of τ =0.1 is considered these numbers increase to 0.089–0.215. We find that the lowest three reflectance classes have comparable normal reflectance on either hemisphere. However, for the highest brightness class the normal reflectance is higher on the hemisphere encompassing longitude 14–65° compared to the same high brightness class for the hemisphere encompassing 122–156° longitude. We conclude that an albedo dichotomy observed in continental sized units on Titan is due not only to one unit having more areal coverage of reflective material than the other but the material on the brighter unit is intrinsically more reflective than the most reflective material on the other unit. This suggests that surface renewal processes are more widespread on Titan''s more reflective units than on its less reflective units. We note that one of our photometric control points has increased in reflectance by 12% relative to the surrounding terrain from July of 2004 to April and May of 2005. Possible causes of this effect include atmospheric processes such as ground fog or orographic clouds; the suggestion of active volcanism cannot be ruled out. Several interesting circular features which resembled impact craters were identified on Titan''s surface at the time of the initial Titan flyby in July of 2004. We traced photometric profiles through two of these candidate craters and attempted to fit these profiles to the photometric properties expected from model depressions. We find that the best-fit attempt to model these features as craters requires that they be unrealistically deep, approximately 70km deep. We conclude that despite their appearance, these circular features are not craters, however, the possibility that they are palimpsests cannot be ruled out. We used two methods to test for the presence of vast expanses of liquids on Titan''s surface that had been suggested to resemble oceans. Specular reflection of sunlight would be indicative of widespread liquids on the surface; we found no evidence of this. A large liquid body should also show uniformity in photometric profile; we found the profiles to be highly variable. The lack of specular reflection and the high photometric variability in the profiles across candidate oceans is inconsistent with the presence of vast expanses of flat-lying liquids on Titan''s surface. While liquid accumulation may be present as small, sub-pixel-sized bodies, or in areas of the surface which still remain to be observed by VIMS, the presence of large ocean-sized accumulations of liquids can be ruled out. The Cassini orbital tour offers the opportunity for VIMS to image the same parts of Titan''s surface repeatedly at many different illumination and observation geometries. This creates the possibility of understanding the properties of Titan''s atmosphere and haze by iteratively adapting models to create a best fit to the surface reflectance properties. [Copyright &y& Elsevier]

Abstract: Titan''s bulk density along with Solar System formation models indicates considerable water as well as silicates as its major constituents. This satellite''s dense atmosphere of nitrogen with methane is unique. Deposits or even oceans of organic compounds have been suggested to exist on Titan''s solid surface due to UV-induced photochemistry in the atmosphere. Thus, the composition of the surface is a major piece of evidence needed to determine Titan''s history. However, studies of the surface are hindered by the thick, absorbing, hazy and in some places cloudy atmosphere. Ground-based telescope investigations of the integral disk of Titan attempted to observe the surface albedo in spectral windows between methane absorptions by calculating and removing the haze effects. Their results were reported to be consistent with water ice on the surface that is contaminated with a small amount of dark material, perhaps organic material like tholin. We analyze here the recent Cassini Mission''s visual and infrared mapping spectrometer (VIMS) observations that resolve regions on Titan. VIMS is able to see surface features and shows that there are spectral and therefore likely compositional units. By several methods, spectral albedo estimates within methane absorption windows between 0.75 and 5μm were obtained for different surface units using VIMS image cubes from the Cassini-Huygens Titan Ta encounter. Of the spots studied, there appears to be two compositional classes present that are associated with the lower albedo and the higher albedo materials, with some variety among the brighter regions. These were compared with spectra of several different candidate materials. Our results show that the spectrum of water ice contaminated with a darker material matches the reflectance of the lower albedo Titan regions if the spectral slope from 2.71 to 2.79μm in the poorly understood 2.8-μm methane window is ignored. The spectra for brighter regions are not matched by the spectrum of water ice or unoxidized tholin, in pure form or in mixtures with sufficient ice or tholin present to allow the water ice or tholin spectral features to be discerned. We find that the 2.8-μm methane absorption window is complex and seems to consist of two weak subwindows at 2.7 and 2.8μm that have unknown opacities. A ratio image at these two wavelengths reveals an anomalous region on Titan that has a reflectance unlike any material so far identified, but it is unclear how much the reflectances in these two subwindows pertain to the surface. [Copyright &y& Elsevier]

Abstract: Venus Express is the first European mission to the planet Venus. Its payload consists of seven instruments and will investigate the atmosphere, the plasma environment, and the surface of Venus from orbit. Science planning is a complex process that takes into account requests from all experiments and the operational constraints. The planning of the science operations is based on synergetic approach to provide good coverage of science themes derived from the main mission goals. Typical observations in a single orbit—so-called “science cases” are used to build the mission science activity plan. The nominal science mission (from June 4, 2006 till October 2, 2007) is divided in nine phases depending on observational conditions, occurrences of the solar and Earth occultation, and particular science goals. The observation timelines for each phase were developed in a coordinated way to optimize the payload activity, maximize the overall mission science return, and to fit into the available mission budgets. [Copyright &y& Elsevier]

Abstract: The Visual Infrared Mapping Spectrometer (VIMS) onboard the CASSINI spacecraft obtained new spectral data of the icy satellites of Saturn after its arrival at Saturn in June 2004. VIMS operates in a spectral range from 0.35 to 5.2μm, generating image cubes in which each pixel represents a spectrum consisting of 352 contiguous wavebands. As an imaging spectrometer VIMS combines the characteristics of both a spectrometer and an imaging instrument. This makes it possible to analyze the spectrum of each pixel separately and to map the spectral characteristics spatially, which is important to study the relationships between spectral information and geological and geomorphologic surface features. The spatial analysis of the spectral data requires the determination of the exact geographic position of each pixel on the specific surface and that all 352 spectral elements of each pixel show the same region of the target. We developed a method to reproject each pixel geometrically and to convert the spectral data into map projected image cubes. This method can also be applied to mosaic different VIMS observations. Based on these mosaics, maps of the spectral properties for each Saturnian satellite can be derived and attributed to geographic positions as well as to geological and geomorphologic surface features. These map-projected mosaics are the basis for all further investigations. [Copyright &y& Elsevier]

Abstract: The Isidis Plantita region on Mars is a landing site favored by engineers for its inherent safety. The landing site of Beagle 2 was in this area, as was one of the prime backup landing sites for the Mars Exploration Rover Spirit. Therefore, it seems likely that for future lander missions to Mars this area will be on the shortlist. Within its first orbits Mars Express has passed over Isidis Planitia and the Beagle 2 landing site. From these passes we have derived first estimates of the surface temperature for a region covering the planned landing site of Beagle 2 using in the long wavelength channel (5–45μm) of the Planetary Fourier Spectrometer (PFS) on Mars Express. We have compared these temperatures with a map of surface temperatures for this area derived from a modeling with the Berlin Mars near Surface Thermal model (Helbert, J., Benkhoff, J. A new approach to assessing the burial depth of ground ice deposits and its application to proposed MER landing sites in Isidis Planitia. Journal of Geophysical Research 108(E12), ROV 28-1, 2003). [Copyright &y& Elsevier]