V. Formisano

The Cluster Ion Spectrometry (CIS) Experiment

The Cluster Ion Spectrometry (CIS) experiment is a comprehensive ionic plasma spectrometry package on-board the four Cluster spacecraft capable of obtaining full three-dimensional ion distributions with good time resolution (one spacecraft spin) with mass per charge composition determination. The requirements to cover the scientific objectives cannot be met with a single instrument. The CIS package therefore consists of two different instruments, a Hot Ion Analyser (HIA) and a time-of-flight ion COmposition and DIstribution Function analyser (CODIF), plus a sophisticated dual-processor-based instrument-control and Data-Processing System (DPS), which permits extensive on-board data-processing. Both analysers use symmetric optics resulting in continuous, uniform, and well-characterised phase space coverage. CODIF measures the distributions of the major ions (H+, He+, He++, and O+) with energies from ~0 to 40 keV/e with medium (22.5°) angular resolution and two different sensitivities. HIA does not offer mass resolution but, also having two different sensitivities, increases the dynamic range, and has an angular resolution capability (5.6° × 5.6°) adequate for ion-beam and solar-wind measurements.

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.

South-polar features on Venus similar to those near the north pole

Venus has no seasons, slow rotation and a very massive atmosphere, which is mainly carbon dioxide with clouds primarily of sulphuric acid droplets. Infrared observations by previous missions to Venus revealed a bright ‘dipole’ feature surrounded by a cold ‘collar’ at its north pole. The polar dipole is a ‘double-eye’ feature at the centre of a vast vortex that rotates around the pole, and is possibly associated with rapid downwelling. The polar cold collar is a wide, shallow river of cold air that circulates around the polar vortex. One outstanding question has been whether the global circulation was symmetric, such that a dipole feature existed at the south pole. Here we report observations of Venus’ south-polar region, where we have seen clouds with morphology much like those around the north pole, but rotating somewhat faster than the northern dipole. The vortex may extend down to the lower cloud layers that lie at about 50 km height and perhaps deeper. The spectroscopic properties of the clouds around the south pole are compatible with a sulphuric acid composition.

A dynamic upper atmosphere of Venus as revealed by VIRTIS on Venus Express

The upper atmosphere of a planet is a transition region in which energy is transferred between the deeper atmosphere and outer space. Molecular emissions from the upper atmosphere (90–120 km altitude) of Venus can be used to investigate the energetics and to trace the circulation of this hitherto little-studied region. Previous spacecraft and ground-based observations of infrared emission from CO2, O2 and NO have established that photochemical and dynamic activity controls the structure of the upper atmosphere of Venus. These data, however, have left unresolved the precise altitude of the emission owing to a lack of data and of an adequate observing geometry. Here we report measurements of day-side CO2 non-local thermodynamic equilibrium emission at 4.3 µm, extending from 90 to 120 km altitude, and of night-side O2 emission extending from 95 to 100 km. The CO2 emission peak occurs at ∼115 km and varies with solar zenith angle over a range of ∼10 km. This confirms previous modelling, and permits the beginning of a systematic study of the variability of the emission. The O2 peak emission happens at 96 km ± 1 km, which is consistent with three-body recombination of oxygen atoms transported from the day side by a global thermospheric sub-solar to anti-solar circulation, as previously predicted.

Cassini Visual and Infrared Mapping Spectrometer Observations of Iapetus: Detection of CO2

The Visual and Infrared Mapping Spectrometer (VIMS) instrument aboard the Cassini spacecraft obtained its first spectral map of the satellite Iapetus in which new absorption bands are seen in the spectra of both the low-albedo hemisphere and the H2O ice-rich hemisphere. Carbon dioxide is identified in the low-albedo material, probably as a photochemically produced molecule that is trapped in H2O ice or in some mineral or complex organic solid. Other absorption bands are unidentified. The spectrum of the low-albedo hemisphere is satisfactorily modeled with a combination of organic tholin, poly-HCN, and small amounts of H2O ice and Fe2O3. The high-albedo hemisphere is modeled with H2O ice slightly darkened with tholin. The detection of CO2 in the low-albedo material on the leading hemisphere supports the contention that it is carbon-bearing material from an external source that has been swept up by the satellites orbital motion.

The Renazzo meteorite

SummaryAn imaging spectrometer developed for a space mission (Mars 94) is being used to study meteorites with solar illumination. It is shown that for a carbonaceous chondrite like the Renazzo meteorite it is possible to study also the internal composition of large chondrules, by making use of all the information of the image cube obtained. Inside chondrules, 3 typical materials are identified.

Venus Express: Scientific goals, instrumentation, and scenario of the mission

The first European mission to Venus (Venus Express) is described. It is based on a repeated use of the Mars Express design with minor modifications dictated in the main by more severe thermal environment at Venus. The main scientific task of the mission is global exploration of the Venusian atmosphere, circumplanetary plasma, and the planet surface from an orbiting spacecraft. The Venus Express payload includes seven instruments, five of which are inherited from the missions Mars Express and Rosetta. Two instruments were specially designed for Venus Express. The advantages of Venus Express in comparison with previous missions are in using advanced instrumentation and methods of remote sounding, as well as a spacecraft with a broad spectrum of capabilities of orbital observations.

Energetic magnetospheric oxygen in the magnetosheath and its response to IMF orientation: Cluster observations

[1] We present Cluster observations made during an outbound orbit on 10 December 2000. After exiting the magnetosphere at midlatitude, Cluster spent a long time skimming the magnetopause moving to lower latitude along an orbit approximately in the ZY GSM plane on the dusk flank of the magnetopause. During this time, magnetospheric oxygen with energy >10 keV was observed continuously both in the magnetosphere and in the magnetosheath by the Cluster Ion Spectrometry (CIS) plasma experiment. While the oxygen density is roughly constant in the magnetosheath throughout the event, its velocity shows a strong dependence on the magnetosheath magnetic field orientation: low speeds, corresponding to almost isotropic distribution functions, occur for northward magnetic field, and high speeds, corresponding to beam-like distribution function occur for southward magnetic field. Mainly, two different processes have been discussed to explain the energetic particles escaping from the magnetosphere: flow along reconnected magnetospheric and magnetosheath field lines or crossing of the magnetopause when the particle gyroradii are comparable with the magnetopause thickness. The presence of the oxygen population cannot be readily explained in the framework of the reconnection theory. Instead, the observations are successfully reproduced by a model based on magnetopause crossing by finite gyroradius, provided the magnetosheath convection is taken into account together with the magnetosheath magnetic field orientation. Moreover, the presence of quasi-periodic motion of the magnetopause surface with period of approximately 5 min are evidenced by the analysis.

PFS:A FOURIER SPECTROMETER FOR THE STUDY OF MARTIAN ATMOSPHERE

The Planetary Fourier Spectrometer PFS has been designed for the study of the atmosphere and soil of Mars. PFS has two infrared channels: a long wavelength (LW) channel with range 250 - 2000 cm-’ and a short wavelength (SW) channel with range 2000 - 8333 cm-‘. The spectral resolution is 2 cm-‘. Both channels work simultaneously. The field of view is 2” which covers 10 km on the Martian surface being observed from the pericenter at 300 km. The signal to noise ratio is better than 100 in a range of particular scientific interest (at 650 cm-’ , for example). The built-in pointing device allows to study the atmosphere over extreme regions like Hellas Planitia or Olympus Mons.

The Martian atmosphere in the region of the great volcanoes: Mariner 9 IRIS data revisited

Abstract The structure of the Martian atmosphere in the region of the Great Volcanoes has been investigated using the Mariner 9 IRIS data. Altogether, 337 spectra were studied; 334 of them were obtained in the afternoon between 13 and 18 h in the range Ls=314–348° with footprints less than 200 km . The remaining 3 spectra, which reveal pronounced water ice features, were obtained at Ls=98° near 16 h . All spectra were corrected for the recently discovered instrumental effect (Formisano et al. (Planet. Space Sci. 48 (2000) 569). It is shown that neglecting it would lead to an overestimate of the atmospheric temperature. Temperature profiles and aerosol opacities were retrieved in a self-consistent way. It is found that the aerosol opacity varies in the range 0.1 T surf >20 K ) after 17 h , when the solar zenith angle exceeds 80°. The surface temperature at the top of Arsia Mons changes by up to 30 K within one hour after 17 h , while the atmospheric temperature varies only by several degrees. We find that the atmospheric temperature above the top of Arsia has decreased by about 30 K between Ls=314° and 347°, whereas the aerosol opacity decreased from 0.3 to 0.1. In the latter case, water condensation occurs and, hence, aerosols are composed of dust and water ice. It is found that about 0.1 prμm of H2O ice needs to be included into the aerosol component to account for its spectral behavior in the continuum. The water ice clouds were observed near Martian aphelion (Ls=98°) at low Northern latitudes over Pavonis and Ascraeus Mons in the afternoon. Their visual opacity is about 0.46–0.48 (averaged over the FOV) and the mean particle size is found to be Rm=2– μm (assuming a normal particle size distribution). A comparison between the temperature profile obtained at Ls=98° and that derived for the same location and local time (15:40) at Ls=348°, shows that the atmospheric temperature near aphelion is about 20 K lower.