F. Altieri

Perennial water ice identified in the south polar cap of Mars.

The inventory of water and carbon dioxide reservoirs on Mars are important clues for understanding the geological, climatic and potentially exobiological evolution of the planet. From the early mapping observation of the permanent ice caps on the martian poles, the northern cap was believed to be mainly composed of water ice, whereas the southern cap was thought to be constituted of carbon dioxide ice. However, recent missions (NASA missions Mars Global Surveyor and Odyssey) have revealed surface structures, altimetry profiles, underlying buried hydrogen, and temperatures of the south polar regions that are thermodynamically consistent with a mixture of surface water ice and carbon dioxide. Here we present the first direct identification and mapping of both carbon dioxide and water ice in the martian high southern latitudes, at a resolution of 2 km, during the local summer, when the extent of the polar ice is at its minimum. We observe that this south polar cap contains perennial water ice in extended areas: as a small admixture to carbon dioxide in the bright regions; associated with dust, without carbon dioxide, at the edges of this bright cap; and, unexpectedly, in large areas tens of kilometres away from the bright cap.

The mawrth vallis region of mars: A potential landing site for the mars science laboratory (MSL) mission

The primary objective of NASAs Mars Science Laboratory (MSL) mission, which will launch in 2011, is to characterize the habitability of a site on Mars through detailed analyses of the composition and geological context of surface materials. Within the framework of established mission goals, we have evaluated the value of a possible landing site in the Mawrth Vallis region of Mars that is targeted directly on some of the most geologically and astrobiologically enticing materials in the Solar System. The area around Mawrth Vallis contains a vast (>1 × 10⁶ km²) deposit of phyllosilicate-rich, ancient, layered rocks. A thick (>150 m) stratigraphic section that exhibits spectral evidence for nontronite, montmorillonite, amorphous silica, kaolinite, saponite, other smectite clay minerals, ferrous mica, and sulfate minerals indicates a rich geological history that may have included multiple aqueous environments. Because phyllosilicates are strong indicators of ancient aqueous activity, and the preservation potential of biosignatures within sedimentary clay deposits is high, martian phyllosilicate deposits are desirable astrobiological targets. The proposed MSL landing site at Mawrth Vallis is located directly on the largest and most phyllosilicate-rich deposit on Mars and is therefore an excellent place to explore for evidence of life or habitability.

Infrared observations of Jovian aurora from Juno's first orbits: Main oval and satellite footprints

The Jovian Infrared Auroral Mapper (JIRAM) is an imager/spectrometer on board NASA/Juno mission for the study of the Jovian aurorae. The first results of JIRAMs imager channel observations of the H3+ infrared emission, collected around the first Juno perijove, provide excellent spatial and temporal distribution of the Jovian aurorae, and show the morphology of the main ovals, the polar regions, and the footprints of Io, Europa and Ganymede. The extended Io “tail” persists for ~3 hours after the passage of the satellite flux tube. Multi-arc structures of varied spatial extent appear in both main auroral ovals. Inside the main ovals, intense, localized emissions are observed. In the southern aurora, an evident circular region of strong depletion of H3+ emissions is partially surrounded by an intense emission arc. The southern aurora is brighter than the north one in these observations. Similar, probably conjugate emission patterns are distinguishable in both polar regions.

Preliminary results on the composition of Jupiter's troposphere in hot spot regions from the JIRAM/Juno instrument

The Jupiter InfraRed Auroral Mapper (JIRAM) instrument on board the Juno spacecraft performed observations of two bright Jupiter hot spots around the time of the first Juno pericenter passage on 27 August 2016. The spectra acquired in the 4–5 µm spectral range were analyzed to infer the residual opacities of the uppermost cloud deck as well as the mean mixing ratios of water, ammonia, and phosphine at the approximate level of few bars. Our results support the current view of hot spots as regions of prevailing descending vertical motions in the atmosphere but extend this view suggesting that upwelling may occur at the southern boundaries of these structures. Comparison with the global ammonia abundance measured by Juno Microwave Radiometer suggests also that hot spots may represent sites of local enrichment of this gas. JIRAM also identifies similar spatial patterns in water and phosphine contents in the two hot spots.

Mars Express measurements of surface albedo changes over 2004–2010

Abstract The pervasive Mars dust is continually transported between the surface and the atmosphere. When on the surface, dust increases the albedo of darker underlying rocks and regolith, which modifies climate energy balance and must be quantified. Remote observation of surface albedo absolute value and albedo change is however complicated by dust itself when lifted in the atmosphere. Here we present a method to calculate and map the bolometric solar hemispherical albedo of the martian surface using the 2004–2010 OMEGA imaging spectrometer dataset. This method takes into account aerosols radiative transfer, surface photometry, and instrumental issues such as registration differences between visible and near-IR detectors. Resulting albedos are on average 17% higher than previous estimates for bright surfaces while similar for dark surfaces. We observed that surface albedo changes occur mostly during the storm season due to isolated events. The main variations are observed during the 2007 global dust storm and during the following year. A wide variety of change timings are detected such as dust deposited and then cleaned over a martian year, areas modified only during successive global dust storms, and perennial changes over decades. Both similarities and differences with previous global dust storms are observed. While an optically thin layer of bright dust is involved in most changes, this coating turns out to be sufficient to mask underlying mineralogical near-IR spectral signatures. Overall, changes result from apparently erratic events; however, a cyclic evolution emerges for some (but not all) areas over long timescales.

The comparative exploration of the ice giant planets with twin spacecraft: Unveiling the history of our Solar System

Abstract In the course of the selection of the scientific themes for the second and third L-class missions of the Cosmic Vision 2015–2025 program of the European Space Agency, the exploration of the ice giant planets Uranus and Neptune was defined “a timely milestone, fully appropriate for an L class mission”. Among the proposed scientific themes, we presented the scientific case of exploring both planets and their satellites in the framework of a single L-class mission and proposed a mission scenario that could allow to achieve this result. In this work we present an updated and more complete discussion of the scientific rationale and of the mission concept for a comparative exploration of the ice giant planets Uranus and Neptune and of their satellite systems with twin spacecraft. The first goal of comparatively studying these two similar yet extremely different systems is to shed new light on the ancient past of the Solar System and on the processes that shaped its formation and evolution. This, in turn, would reveal whether the Solar System and the very diverse extrasolar systems discovered so far all share a common origin or if different environments and mechanisms were responsible for their formation. A space mission to the ice giants would also open up the possibility to use Uranus and Neptune as templates in the study of one of the most abundant type of extrasolar planets in the galaxy. Finally, such a mission would allow a detailed study of the interplanetary and gravitational environments at a range of distances from the Sun poorly covered by direct exploration, improving the constraints on the fundamental theories of gravitation and on the behavior of the solar wind and the interplanetary magnetic field.

Mapping of hydrocarbons and H3+ emissions at Jupiter's north pole using Galileo/NIMS data

In this paper we report the mapping of H3+, C2H2, and CH4 as derived by an unexploited Galileo/Near-Infrared Mapping Spectrometer (NIMS) data set. As previously observed, hydrocarbons emissions appear to be located in the internal part of the auroral main oval, where CH4 3 µm vibrational band intensity ratios suggest that nonthermal excitation mechanisms, such as auroral particle precipitation and/or Joule heating, are responsible for the observed emissions. Temperature estimation are in good agreement for the CH4-emitting region on the hot spot, while the values obtained for H3+ are lower in comparison with Cassini/visual and infrared mapping spectrometer and ground-based data. C2H2 emission overlaps the CH4 one only at higher latitudes >75°N, indicating that different energetic particles are at work inside the main oval polar ward. CH4 is also found on the northern section of the main oval (135°< longitude <190°, 60°< latitude <90°N). The present investigation results have implications on the Juno/Jovian InfraRed Auroral Mapper observation planning as well as on the codes that will be used to retrieve temperatures and densities of all the emitting species involved in the Jupiter auroral processes.

Results of measurements with the Planetary Fourier Spectrometer onboard Mars Express: Clouds and dust at the end of southern summer. A comparison with OMEGA images

We discuss the results of measurements made with the Planetary Fourier Spectrometer (PFS) onboard the Mars Express spacecraft. The data were obtained in the beginning of the mission and correspond to the end of summer in the southern hemisphere of Mars (Ls ∼ 340°). Three orbits are considered, two of which passed through volcanoes Olympus and Ascraeus Mons (the height above the surface is about +20 km), while the third orbit intersects lowland Hellas (−7 km). The influence of the relief on the properties of the aerosol observed is demonstrated: clouds of water ice with a visual optical thickness of 0.1–0.5 were observed above volcanoes, while only dust was found during the observations (close in time) along the orbit passing through Hellas in low and middle latitudes. This dust is homogeneously mixed with gas and has a reduced optical thickness of 0.25±0.05 (at v = 1100 cm−1). In addition to orographic clouds, ice clouds were observed in this season in the northern polar region. The clouds seen in the images obtained simultaneously by the mapping spectrometer OMEGA confirm the PFS results. Temperature inversion is discovered in the north polar hood below the level 1 mbar with a temperature maximum at about 0.6 mbar. This inversion is associated with descending movements in the Hadley cell.

Clusters of cyclones encircling Jupiter’s poles

The familiar axisymmetric zones and belts that characterize Jupiter’s weather system at lower latitudes give way to pervasive cyclonic activity at higher latitudes. Two-dimensional turbulence in combination with the Coriolis β-effect (that is, the large meridionally varying Coriolis force on the giant planets of the Solar System) produces alternating zonal flows. The zonal flows weaken with rising latitude so that a transition between equatorial jets and polar turbulence on Jupiter can occur. Simulations with shallow-water models of giant planets support this transition by producing both alternating flows near the equator and circumpolar cyclones near the poles. Jovian polar regions are not visible from Earth owing to Jupiter’s low axial tilt, and were poorly characterized by previous missions because the trajectories of these missions did not venture far from Jupiter’s equatorial plane. Here we report that visible and infrared images obtained from above each pole by the Juno spacecraft during its first five orbits reveal persistent polygonal patterns of large cyclones. In the north, eight circumpolar cyclones are observed about a single polar cyclone; in the south, one polar cyclone is encircled by five circumpolar cyclones. Cyclonic circulation is established via time-lapse imagery obtained over intervals ranging from 20 minutes to 4 hours. Although migration of cyclones towards the pole might be expected as a consequence of the Coriolis β-effect, by which cyclonic vortices naturally drift towards the rotational pole, the configuration of the cyclones is without precedent on other planets (including Saturn’s polar hexagonal features). The manner in which the cyclones persist without merging and the process by which they evolve to their current configuration are unknown.

CO2 non‐LTE limb emissions in Mars' atmosphere as observed by OMEGA/Mars Express

We report on daytime limb observations of Mars upper atmosphere acquired by the OMEGA instrument on board the European spacecraft Mars Express. The strong emission observed at 4.3 μm is interpreted as due to CO 2 fluorescence of solar radiation and is detected at a tangent altitude in between 60 and 110 km. The main value of OMEGA observations is that they provide simultaneously spectral information and good spatial sampling of the CO 2 emission. In this study we analyzed 98 dayside limb observations spanning over more than three Martian years, with a very good latitudinal and longitudinal coverage. Thanks to the precise altitude sounding capabilities of OMEGA, we inferred the vertical profiles of the non-LTE emission at each wavelength and we studied their dependence on several geophysical parameters, such as the solar illumination and the tangent altitude. The dependence of the non-LTE emission on solar zenith angle and altitude follows a similar behavior to that predicted by the non-LTE model. According to our non-local thermodynamic equilibrium model (Non-LTE), the pressure level where the peak of the emission is found remains constant at ∼0.03±0.01 Pa, and we have shown with SPICAM stellar occultation retrievals that the seasonal variations of constant pressure level altitudes correlate well with the variations of the OMEGA peak emission altitudes, although the exact pressure level can not be defined with the SPICAM nighttime data. The tangent altitude of this atmospheric layer depends on the structure of the whole atmosphere below, and represents a strong validation tool for atmospheric models. We thus compared the altitude of OMEGA peak emission with the tangent altitude of the 0.03 Pa level predicted by the LMD-Mars Global Circulation Model. However, the peak emission altitudes from OMEGA present a much larger variability than the tangent altitude of the 0.03 Pa level predicted by the GCM; this variability could be possibly due to unresolved atmospheric waves. Further studies using this strong CO 2 limb emission data are proposed.