From Classical Theory to Quantum Gravity

While it has been generally accepted for decades that general relativity and quantum theory are inconsistent, and that therefore general relativity must yield to a new theory of gravity compatible with quantum principles, the way to the new theory is still very unclear. A major obstacle is the lack of any experimental indicators as to where general relativity might break down. I speculate on the different ways in which a quantum theory including gravity might emerge from present-day theory and use these speculations to examine a number of promising lines for new experiments.     

Stable iron isotopes and microbial mediation in red pigmentation of the Rosso Ammonitico (mid-late Jurassic, Verona area, Italy)

The iron (Fe) isotopic composition of 17 Jurassic limestones from the Rosso Ammonitico of Verona (Italy) have been analyzed by Multiple-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS). Such analysis allowed for the recognition of a clear iron isotopic fractionation (mean -0.8 per thousand, ranging between -1.52 to -0.06 per thousand) on a millimeter-centimeter scale between the red and grey facies of the studied formation. After gentle acid leaching, measurements of the Fe isotopic compositions gave delta(56)Fe values that were systematically lower in the red facies residues (median: -0.84 per thousand, range: -1.46 to +0.26 per thousand) compared to the grey facies residues (median: -0.08 per thousand, range: -0.34 to +0.23 per thousand). In addition, the red facies residues were characterized by a lighter delta(56)Fe signal relative to their corresponding leachates. These Fe isotopic fractionations could be a sensitive fingerprint of a biotic process; systematic isotopic differences between the red and grey facies residues, which consist of hematite and X-ray amorphous iron hydroxides, respectively, are hypothesized to have resulted from the oxidizing activity of iron bacteria and fungi in the red facies. The grey Fe isotopic data match the Fe isotopic signature of the terrestrial baseline established for igneous rocks and low-C(org) clastic sedimentary rocks. The Fe isotopic compositions of the grey laminations are consistent with the influx of detrital iron minerals and lack of microbial redox processes at the water-interface during deposition. Total Fe concentration measurements were performed by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) (confirmed by concentration estimations obtained by MC-ICP-MS analyses of microdrilled samples) on five samples, and resultant values range between 0.30% (mean) in the grey facies and 1.31% (mean) in the red facies. No correlation was observed between bulk Fe content and pigmentation or between bulk Fe content and Fe isotopic compositions. The rapid transformation of the original iron oxyhydroxides to hematite could have preserved the original isotopic composition if it had occurred at about the same temperature. This paper supports the use of Fe isotopes as sensitive tracers of biological activities recorded in old sedimentary sequences that contain microfossils of iron bacteria and fungi. However, a careful interpretation of the iron isotopic fractionation in terms of biotic versus abiotic processes requires supporting data or direct observations to characterize the biological, (geo)chemical, or physical context in relation to the geologic setting. This will become even more pertinent when Fe isotopic studies are expanded to the interplanetary realm.     

Effects of heavy particle irradiation and diet on object recognition memory in rats

On long-duration missions to other planets astronauts will be exposed to types and doses of radiation that are not experienced in low earth orbit. Previous research using a ground-based model for exposure to cosmic rays has shown that exposure to heavy particles, such as ⁵⁶Fe, disrupts spatial learning and memory measured using the Morris water maze. Maintaining rats on diets containing antioxidant phytochemicals for 2 weeks prior to irradiation ameliorated this deficit. The present experiments were designed to determine: (1) the generality of the particle-induced disruption of memory by examining the effects of exposure to ⁵⁶Fe particles on object recognition memory; and (2) whether maintaining rats on these antioxidant diets for 2 weeks prior to irradiation would also ameliorate any potential deficit. The results showed that exposure to low doses of ⁵⁶Fe particles does disrupt recognition memory and that maintaining rats on antioxidant diets containing blueberry and strawberry extract for only 2 weeks was effective in ameliorating the disruptive effects of irradiation. The results are discussed in terms of the mechanisms by which exposure to these particles may produce effects on neurocognitive performance.     

Reports to COSPAR from the International Lunar Exploration Working Group (ILEWG)

In accordance with its charter, the International Lunar Exploration Working Group (ILEWG) reports to COSPAR, and a summary was given at the Beijing COSPAR 2006 Assembly on ILEWG activities conducted since the previous COSPAR 2004 assembly held in Paris. This included reports from the 6th and 7th ILEWG International Conference on Exploration and Utilization of the Moon, held respectively in Udaipur, India on 22–26 November 2004 (ICEUM6) and in Toronto, Canada on 18–23 September 2005 (ICEUM7). We give in this issue of Advances in Space Research the “lunar declarations” from these ICEUM conferences, as well as for the ICEUM8 conference held in Beijing immediately after the 2006 COSPAR Assembly. One year after the COSPAR Beijing assembly, the 9th ILEWG International Conference on Exploration and Utilization of the Moon (ICEUM9), was held in Sorrento, Italy on 18–23 September 2007. We report also in this issue the “Sorrento Lunar Declaration” in advance of the ILEWG formal report to be given at the COSPAR Assembly to be held in Montreal, Canada in July 2008.     

Monte Carlo calibration of the response of the University of Chicago’s Cosmic Ray Nuclei Experiment (CRNE) on IMP-8 to electrons above 0.5 MeV

Modern instrument-simulation techniques offer the possibility of increasing the scientific yield from archival space datasets. In this paper, we report on a simulation of the electron response of the University of Chicago’s Cosmic Ray Nuclei Experiment (CRNE) instrument on the IMP-8 satellite. IMP-8/CRNE returned data from 1973 to 2006. The CRNE particle telescope was designed to measure the isotopic composition of Galactic cosmic-ray (GCR) nuclei and has also been used in many studies of protons and ions above 10 MeV/nucleon from solar energetic particle (SEP) events. But CRNE also functions as a highly-capable detector for solar electrons above 0.5 MeV, an energy range that has not been extensively studied. Utilization of the CRNE electron data has heretofore been limited by the fact that CRNE was never calibrated for electrons. We have therefore used the GEANT4 Monte Carlo simulation package to model the CRNE response to electrons and (separately) protons for multiple energies and incident angles. The results were used to compute the energy- and angle-dependence of the effective area and the energy-dependence of the geometric factor. The response to protons, which was already well understood, was used to verify the mass model, the simulation settings, and the post-processing software. Our simulation of the IMP-8/CRNE electron response now allows analysis of hundreds of relativistic solar electron events observed by CRNE over the years, including studies of evolution of electron energy spectra with high time resolution. We show examples of these results and briefly discuss potential applications to future scientific investigations.     

Pilotage non linéaire en temps minimum d'un engin spatial propulsé

Spacecraft missions may call upon great amplitude changes of attitude within a minimum of time. With a view to define an absolute performance criterion for the spacecraft and, if need be, to guide the research towards the definition of piloting algorithms, it is necessary to determine the open loop optimal control. A numerical method, based on the Pontryagin Maximum Principle, has been defined to carry out this study. It has been applied to the non linear problem of the three-dimensional piloting of a rigid powered spacecraft in atmosphere-free vacuum.     

Global measurement of the Earth gravity field using a gradiometric satellite

Two techniques are able to permit a significant progress in the global measurement of the Earth gravity field: satellite to satellite tracking and gradiometry. The preliminary results concerning the study of a gradiometric satellite to be launched by Ariane are presented.After stating the scientific objectives and the mission specifications, one focuses on the definition of the gradiometer and the gradiometric satellite. After analysis of the problems associated with gradiometry based upon differential accelerometry, one presents the Cactus accelerometer design evolution and the implications on the satellite configuration and interfaces with the gradiometer. Finally a short mission analysis is presented.