A Multi-Wavelength Simultaneous Study of the Composition of the Halley Family Comet 8P/Tuttle

We report on simultaneous optical and infrared observations of the Halley Family comet 8P/Tuttle performed with the ESO Very Large Telescope. Such multi-wavelength and coordinated observations are a good example of what can be done to support space missions. From high resolution optical spectroscopy of the CN (0,0) 388 nm and NH₂ (0,9,0) 610 nm bands using UVES at UT2 we determined ¹²C/¹³C = 90 ± 10 and ¹⁴N/¹⁵N = 150 ± 20 in CN and we derived a nuclear spin temperature of NH₃ of 29 ± 1 K. These values are similar to those found in Oort-Cloud and Jupiter Family comets. From low resolution long slit spectroscopy with FORS1 at UT2 we determined the CN, C₃ and C₂ production rates and the parent and daughter scale lengths up to 5.2 10⁵ km tailward. From high resolution IR spectroscopy with CRIRES at UT1 we measured simultaneously the production rates and mixing ratios of H₂O, HCN, C₂H₂, CH₄, C₂H₆, and CH₃OH.     

Ground-Based Observations of the Martian Atmosphere in Support of Space Missions

Although Mars is a favored target for planetary exploration, there is still a need for complementary ground-based observing programs of the Martian atmosphere, and this need will remain in the future. Indeed, as the atmosphere is very tenuous (less than 0.01 bar at the surface), the lines are very narrow and a high spectral resolving power (above 10⁴) is required over large spectral intervals. In addition, ground-based observations of Mars allow the instantaneous mapping of the whole planet, and thus the study of diurnal effects, which cannot be achieved from an orbiter. Recent ground-based achievements about the Martian atmospheric science include the first detection of H₂O₂ in the submillimeter range, the measurement of winds from CO millimetric transitions, the first detection of CH₄ and the O₃, H₂O₂, H₂O, and CH₄ mapping in the infrared. With an ELT, it will be possible to study at high spatial resolution transient atmospheric phenomena and to search for traces of minor constituents with unprecedented sensitivity. With ALMA, it will be also possible to search for minor species and to map the mesospheric winds for better constraining the climate models.     

Coordinated Study on Solar Wind Turbulence During the Venus-Express, ACE and Ulysses Alignment of August 2007

At the end of August 2007, Venus, Earth and Ulysses were aligned within a few degrees. This unusual event gives the opportunity to attempt a coordinated study on the radial evolution of solar wind turbulence and coronal transients like CMEs between 0.7 and 1.4 AU. Interplanetary magnetic field data and moments of proton velocity distribution function such as density, speed and temperature are required for this programme and will be provided by ACE at Earth, Venus Express at Venus and Ulysses at 1.4 AU. This project has been recently proposed as a Coordinated Investigation Programme (CIP35) for the International Heliophysical Year.     

A new insight on the decreasing sea level trend over the Ionian basin in the last decades

Altimetry measurements over the Ionian region and tide gauge records along the southern Italian coasts have been combined to analyse the negative sea level trend over the Ionian basin in the last decades. The apparent decreasing trend should be better understood as an abrupt sea level drop in 1998 probably linked to changes in the surface circulation in the Ionian basin induced by the Eastern Mediterranean Transient, which changed from anticyclonic to cyclonic about March 1998. From then onwards, a rising rate of 7.9 ± 0.9 mm/year is observed over the basin.     

The DynaMICCS perspective

The DynaMICCS mission is designed to probe and understand the dynamics of crucial regions of the Sun that determine solar variability, including the previously unexplored inner core, the radiative/convective zone interface layers, the photosphere/chromosphere layers and the low corona. The mission delivers data and knowledge that no other known mission provides for understanding space weather and space climate and for advancing stellar physics (internal dynamics) and fundamental physics (neutrino properties, atomic physics, gravitational moments...). The science objectives are achieved using Doppler and magnetic measurements of the solar surface, helioseismic and coronographic measurements, solar irradiance at different wavelengths and in-situ measurements of plasma/energetic particles/magnetic fields. The DynaMICCS payload uses an original concept studied by Thalès Alenia Space in the framework of the CNES call for formation flying missions: an external occultation of the solar light is obtained by putting an occulter spacecraft 150 m (or more) in front of a second spacecraft. The occulter spacecraft, a LEO platform of the mini sat class, e.g. PROTEUS, type carries the helioseismic and irradiance instruments and the formation flying technologies. The latter spacecraft of the same type carries a visible and infrared coronagraph for a unique observation of the solar corona and instrumentation for the study of the solar wind and imagers. This mission must guarantee long (one 11-year solar cycle) and continuous observations (duty cycle > 94%) of signals that can be very weak (the gravity mode detection supposes the measurement of velocity smaller than 1 mm/s). This assumes no interruption in observation and very stable thermal conditions. The preferred orbit therefore is the L1 orbit, which fits these requirements very well and is also an attractive environment for the spacecraft due to its low radiation and low perturbation (solar pressure) environment. This mission is secured by instrumental R and D activities during the present and coming years. Some prototypes of different instruments are already built (GOLFNG, SDM) and the performances will be checked before launch on the ground or in space through planned missions of CNES and PROBA ESA missions (PICARD, LYRA, maybe ASPIICS).     

Duality properties of Gorringe–Leach equations

In the category of motions preserving the angular momentum direction, Gorringe and Leach exhibited two classes of differential equations having elliptical orbits. After enlarging slightly these classes, we show that they are related by a duality correspondence of the Arnold–Vassiliev type. The specific associated conserved quantities (Laplace–Runge–Lenz vector and Fradkin–Jauch–Hill tensor) are then dual reflections of each other.     

Structural control over equilibrium silicon and oxygen isotopic fractionation: A first-principles density-functional theory study

Isotopic fractionation factors for oxygen and silicon in selected silicates (quartz, enstatite, forsterite, lizardite, kaolinite) are calculated using first-principles methods based on density-functional theory. Good agreement between theory and experiment is found in the case of oxygen. In the case of silicon, agreement and differences with existing estimates of equilibrium fractionation factors are discussed. The relationship between silicon and oxygen fractionation factors, silicate polymerization degree and chemical composition is studied and compared with previous semi-empirical models.     

Oxygen isotopic signature of the skeletal microstructures in cultured corals: Identification of vital effects

In order to identify vital effect on oxygen isotopic ratio, we analyzed at micrometer size scale skeleton microstructures of a scleractinian coral Acropora, cultured under constant conditions. Measurements focused on the two crystalline units highlighted different isotopic signatures. Massive crystals (centers of calcification: COC) exhibit quasi-constant lowest values whereas fibers, the dominant units exhibit scattered distribution with amplitude of up to 5‰. Fiber oxygen isotopic ratios (δ¹⁸O) range from values similar to instantaneous deposition to equilibrium value. By comparing data obtained on the Acropora specimen and deep-sea corals grown under well constrained conditions, we infer that the scattered δ¹⁸O aragonite fibers indicate precipitation through kinetic precipitation. Thus, we argue for inherent biological feature typical to all coral genera. Modalities of COC formation remain ignored.The different isotopic signature of two mineral microstructures present in close proximity in coral skeleton can only be explained by compartment depositions related to different organic environments. Indeed, multiple secondary electron microscopy (SEM) observations favor interaction between mineral and organic matrix surface. Moreover, atomic forcing microscopy (AFM) investigations demonstrated thermodynamic changes induced by mineralization in presence of organic compounds. The combination of our results with previous published ones from biological studies, allows us proposing a consistent model of fiber skeleton formation. The prerequisite step of mineral growth unit precipitation would be initiated by organic matrix secretion, which defines spatial extension. Specific carriers supply ionic compounds of the crystals to ensure local supersaturation. However, possibly controlled by organic molecules, ionic amount would be limited, implying the supersaturation decline over the time. This could explain the progressive decrease of the coral growth rate. In this case, vital effect should not only bias isotopic fractionation through biological activity but the mechanism of skeleton deposition is imposed by specific chemical and/or physical conditions due to the presence of organic molecules. These conclusions derive from observations performed at high resolution.Therefore, isotopic ratio measured on millimeter scale for paleoclimatic purposes, result of the average of strongly heterogeneous values. It could explain vital effects shown by geochemical time series derived from tropical coral skeleton, including the high species and/or colony variability.