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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

Author(s): F. Poulet (corresponding author) [1]; J.-P. Bibring [1]; J. F. Mustard [2]; A. Gendrin [2]; N. Mangold [3]; Y. Langevin [1]; R. E. Arvidson [4]; B. Gondet [1]; C. [...]

Spectra from Cassini's Visual and Infrared Mapping Spectrometer reveal that the horizontal structure, height, and optical depth of Titan's clouds are highly dynamic. Vigorous cloud centers are seen to rise from the middle to the upper troposphere within 30 minutes and dissipate within the next hour. Their development indicates that Titan's clouds evolve convectively; dissipate through rain; and, over the next several hours, waft downwind to achieve their great longitude extents. These and other characteristics suggest that temperate clouds originate from circulation-induced convergence, in addition to a forcing at the surface associated with Saturn's tides, geology, and/or surface composition., The atmosphere of Saturn's largest moon, Titan, contains methane, which, like water on Earth, can exist as a gas, ice, and liquid. This moon is hypothesized to resemble Earth, with [...]

Author(s): C. Sotin (corresponding author) [1]; R. Jaumann [2]; B. J. Buratti [3]; R. H. Brown [4]; R. N. Clark [5]; L. A. Soderblom [6]; K. H. Baines [3]; G. [...]

Author(s): Roger N. Clark (corresponding author) [1]; Robert H. Brown [2]; Ralf Jaumann [3]; Dale P. Cruikshank [4]; Robert M. Nelson [5]; Bonnie J. Buratti [5]; Thomas B. McCord [6]; [...]

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