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.     

Space Weathering of Small Solar System Bodies

Micrometeorite bombardment and irradiation by solar wind and cosmic ions cause variations in the optical properties of the small Solar System bodies surface materials. These space weathering processes are reasonably well understood for the Moon and S-type asteroids. The research is based on laboratory experiments performed by several groups on meteorites and minor bodies surface analogues, whose results have been applied to the spectral modeling and interpretation of observations from large surveys and space missions. Recent results from young asteroidal families, and the relation between spectral slopes and dynamical properties, have stressed the role of the solar wind exposure timescale. Space weathering processes remain poorly investigated in the case of other types of asteroids, and they are still unclear in the case of outer Solar System bodies, due to a strong dependence of the weathering process on the original composition.     

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.     

Defining organominerals: Comment on ‘Defining biominerals and organominerals: Direct and indirect indicators of life’ by Perry et al. (2007, Sedimentary Geology, 201, 157–179)

The paper by Perry et al. (2007, Defining biominerals and organominerals: Direct and indirect indicators of life, Sedimentary Geology, 201, 157–179) proposes to introduce “the new term ‘organomineral’” to describe mineral products whose formation is induced by by-products of biological activity, dead and decaying organisms, or nonbiological organic compounds, to be distinguished from the biomineral components of living organisms. The substantive ‘organomineral’, however, is not new: it was first introduced in 1993, with basically the same definition and distinction from biominerals, at the 7th International Symposium on Biomineralization (Défarge and Trichet, 1995, From biominerals to ‘organominerals’: The example of the modern lacustrine calcareous stromatolites from Polynesian atolls, Bulletin de l'Institut Océanographique de Monaco, n° spéc. 14, vol. 2, pp. 265–271). Thereafter, more than twenty-five papers by various authors have been devoted to organominerals and organomineral formation (‘organomineralization’) processes. Only two of these papers are cited by Perry et al., and without any reference to the definitions, or even the terms ‘organomineral’ or ‘organomineralization’, which they included. Moreover, Perry et al. tend to enlarge the original concept of organomineral to encompass all minerals containing organic matter, whether these organic compounds are active or passive in the mineralization, which introduces ambiguities detrimental to a fine understanding of present and past geobiological processes. Finally, Perry et al. propose to consider organominerals as indirect biosignatures that could be used in the search for evidence of life in the geological record and extraterrestrial bodies. This latter proposition also is problematical, in that organominerals may be formed in association with prebiotic or abiotic organic matter.     

Structural features of humic acids from a sedimentary sequence in the Guadiana estuary (Portugal–Spain border)

The structural characteristics of humic acids (HAs) from two different depths of a sedimentary sequence representing the last 13 kyr in the valley of Guadiana river estuary (SW Portugal/Spain border) have been approached using a combination of spectroscopic techniques, wet chemical degradation methods (sequential oxidation with sodium persulfate followed by KMnO₄, and oxidation with RuO₄) and analytical pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) in the presence and absence of tetramethylammonium hydroxyde (TMAH). The aim was to obtain complementary information on the sources and alteration of the organic matter (OM) provided by a previous study on the vertical distribution of terrestrial and phytoplankton biogeochemical markers in the sequence. Both the FT-IR (Fourier transformed infrared) and ¹³C NMR (nuclear magnetic resonance) spectra showed a close similarity with the structural characteristics of the HA samples. NMR signals in the alkyl region (0–45 ppm) as well as FT-IR band patterns typical for methoxyl-substituted aromatic rings pointed to the presence of an important aliphatic domain, as well as to lignin-derived compounds. This finding was confirmed using analytical pyrolysis. In addition, the main TMAH thermochemolysis products were typical lignin-derived methoxyphenols with both guaicyl and syringyl nuclei. The detection of methoxyphenol units with three to six carbon atom (C₃–C₆) side chains suggests that lignin and possibly suberin were only partially degraded. Compounds arising from proteins and polysaccharides were also detected, although in lesser and varying amount. The major products from persulfate oxidation were series of n-alkanes (C₁₆–C₃₃ with clear odd/even predominance) and n-fatty acids, both saturated (C₁₀–C₂₆ with strong even/odd predominance) and unsaturated, which may arise from the above aliphatic biomacromolecules. The major products from permanganate oxidation of the persulfate residue were α,ω-diacids (C₆–C₁₁) originating from oxidation of the ether bonds linking the building blocks constituting the core of the HA structure. Aromatic compounds (phenols, methoxy-dimethoxybenzene carboxylic acid and benzene di-, tri-, tetra- and pentacarboxylic acids), most probably derived from the aromatic backbone of the HAs, that may also include lignin moieties as well as other polyphenols (flavonoids and tannins) were also detected. The RuO₄ oxidation also released series of n-alkanes (C₁₆–C₃₃), linear saturated fatty acids (C₁₀–C₂₈) and α,ω-diacids (C₇–C₂₅), as well as traces of benzene polycarboxylic acids. Regarding the usefulness of the various techniques used, they provide complementary information. Indeed, spectroscopic techniques and analytical pyrolysis provide information on the backbone of the HAs, and on their origin, whereas the oxidative degradations provide different information on the structural features of the HA, particularly the nature of the linking between the building blocks. In general, the data support the idea that the HAs still contain information about the signature of aliphatic and aromatic biomacromolecules contributing to the OM deposited. The presence of lignin-derived residues suggests a large input from terrestrial carbon throughout the core.