Television pictures of Phobos: first results

In February-March 1989, 37 television images of the Martian satellite Phobos were obtained by the Phobos 2 spacecraft from distances of 200-1100 km. These images provide an important supplement to the TV data from the American Mariner 9 and Viking spacecraft in coverage of t4e surface of Phobos and in resolution in certain regions, in spectral range, and in range of phase angles. They make it possible to refine the figure and topographic and geological maps of the surface of Phobos, its spectral and angular reflective characteristics, the surface composition and texture, and characteristics of the orbital and librational motion

High-Throughput Preparation of Uncontaminated Graphene-Oxide Aqueous Dispersions with Antioxidant Properties by Semi-Automated Diffusion Dialysis

A semi-automated diffusion-dialysis purification procedure is proposed for the preparation of uncontaminated graphene oxide (GO) aqueous dispersions. The purification process is integrated with analytical-signal processing to control the purification degree online by several channels: oxidation-reduction potential, conductivity, and absorbance. This approach reduces the amounts of reagents for chemical treatment during dialysis. The total transition metal (Mn and Ti) content was reduced to a sub-ppb level (assessed by slurry nebulization in inductively coupled plasma optical atomic emission spectroscopy). Purified aqueous GO samples possess good stability for about a year with a zeta-potential of ca. −40 mV and a lateral size of ca. sub-µm. Purified GO samples showed increased antioxidant properties (up to five times compared to initial samples according to chemiluminometry by superoxide-radical (O2−) generated in situ from xanthine and xanthine oxidase with the lucigenin probe) and significantly decreased peroxidase-like activity (assessed by the H2O2–L-012 system)

SiO2_2–TiO2_2 Binary Aerogels: A Small-Angle Scattering Study

Structural analysis in the range of characteristic sizes from 1 nm to ~1.5 μm was performed for SiO$_2$–TiO$_2$ aerogels prepared in supercritical CO$_2$, isopropanol, hexafluoroisopropanol, or methyl-tert-butylether using small-angle X-ray scattering and neutron scattering complementary methods. A two-level modelthat accounts for scattering by individual inhomogeneities and their aggregates, which have fractal properties,satisfactorily describes the aerogel structures over the entire range of scales. It is shown for the first time thatthe titania concentration is the key factor in the small-angle neutron and X-ray scattering by SiO$_2$–TiO$_2$ aero-gels. The phase composition of an aerogel does not sign ificantly affect the aerogel structure in the range ofscales from 1 nm to ~1.5 μm, as probed by small-angle X-ray and neutron scattering

Photoluminescent porous aerogel monoliths containing ZnEu-complex: the first example of aerogel modified with a heteronuclear metal complex

A procedure for the chemical immobilization of a new ZnII–EuIII heterobimetallic complex in the SiO2 aerogel matrix has been developed. In this Zn–Eu complex, a peripheral non-luminescent Zn ion acts as a binder to a silica matrix and prevents direct interaction of rare-earth ions with OH− and NH− groups in the silica matrix, which would have a detrimental effect on the luminescence of lanthanides. The procedure includes the synthesis of complexes, co-gelation of the obtained complex with SiO2 sol, the washing of lyogels, and their subsequent supercritical drying in CO2. The composition and properties of the obtained aerogels were investigated using a low-temperature nitrogen adsorption technique, helium pycnometry, FTIR, Raman, UV–visible, and luminescence spectroscopy, XPS, PXRD, SEM, TEM, TGA combined with mass spectrometry, and small-angle neutron scattering. The aerogels modified with the ZnII–EuIII complex demonstrated strong red luminescence upon excitation with UV light

Green and Sustainable Ultrasound-Assisted Anodic Electrochemical Preparation of Graphene Oxide Dispersions and Their Antioxidant Properties

A fast method for preparing aqueous graphene oxide (GO) dispersions by electrochemical oxidation of a graphite anode without preliminary intercalation with oxidizing agents is proposed. Ultrasonic probing was used in the modulation mode of ultrasonic waves (work/rest) for more efficient graphite oxidation–exfoliation. It is shown that the 4/2 s mode of ultrasonic modulation is the most effective due to the probe material’s low corrosion while maintaining the optimum synthesis temperature not exceeding 30–35 °C and achieving the best characteristics of the resulting product. Three cases of anodic oxidation of graphite to obtain graphene oxide were considered: (1) a combined cathode–anode compartment, (2) a split cathode–anode salt-bridged compartment, and (3) separated anode compartment with a 3.5 kDa dialysis membrane. It was determined that the approach to synthesis with a divided cathode–anode compartment makes it possible to obtain GO sheets with fewer defects compared to chemical methods or methods with a combined cathode–anode compartment and makes it possible to control the oxidation degree of the material (C:O ratio) by varying the current density. The prepared samples showed good stability for more than six months. The spectral and morphological characteristics were studied. Using chemiluminometry in the luminol/Co(II)/H2O2 system, the antioxidant properties concerning three key reactive oxygen species (H2O2, superoxide anion radical, and hydroxyl radical) were demonstrated. It was also shown that the prepared GO dispersions do not induce lipid and phospholipid peroxidation

OMEGA : Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité

International audienc

Perennial water ice identified around the Mars South pole

International audienceThe 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 2km, 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

OMEGA : Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité

International audienc

PHEBUS: A double ultraviolet spectrometer to observe Mercury's exosphere

International audienceProbing of Hermean exosphere by ultraviolet spectroscopy (PHEBUS) is a double spectrometer for the Extreme Ultraviolet range (55-155 nm) and the Far Ultraviolet range (145-315 nm) devoted to the characterization of Mercury's exosphere composition and dynamics, and surface-exosphere connections. This French-led instrument is implemented in a cooperative scheme involving Japan (detectors), Russia (scanner) and Italy (ground calibration). PHEBUS will address the following main scientific objectives relative to Mercury's exosphere: determination of the composition and the vertical structure of the exosphere; characterization of the exospheric dynamics: day to night circulation, transport between active and inactive regions; study of surface release processes; identification and characterization of the sources of exospheric constituents; detection and characterization of ionized species and their relation with the neutral atmosphere; space and time monitoring of exosphere/magnetosphere exchange and transport processes; study and quantification of escape, global scale source/sink balance and geochemical cycles synergistically with other experiments of BepiColombo (Mercury Sodium Atmospheric Spectral Imager (MSASI), Mercury Plasma Particle Experiment (MPPE) on Mercury Magnetospheric Orbiter (MMO); Mercury imaging X-ray spectrometer (MIXS), Search for exosphere refilling and emitted neutral abundance (SERENA) on Mercury Planetary Orbiter (MPO)). Two gratings and two detectors are used according to a specific, compact design. The spectrum detection is based on the photon counting method and is realized using micro-channel plate (MCP) detectors with Resistive Anode Encoder (RAE). Typical photocathodes are CsI or KBr for the extreme ultra-violet (EUV) range, CsTe for the far ultra-violet (FUV) range. Extra visible lines are monitored using a photo-multiplier (PM) that is also used in photon counting mode. In order to prevent sensitivity losses which are critical in UV ranges, a minimum of reflections is achieved inside the instrument using only an off-axis parabola and a set of holographic gratings. A one degree-of-freedom scanning system allows to probe, at the highest possible signal-to-noise ratio, selected regions and altitude ranges of interest. Different modes of observation will be used sequentially (vertical scans, along-orbit scans, grazing observations at twilight, etc.). During the mission, the instrument will be regularly calibrated on well chosen stars, in such a way to quantitatively estimate the overall degradation of the sensitivity of the instrument