E. Chatzitheodoridis

A conspicuous clay ovoid in nakhla: Evidence for subsurface hydrothermal alteration on mars with implications for astrobiology

Abstract A conspicuous biomorphic ovoid structure has been discovered in the Nakhla martian meteorite, made of nanocrystalline iron-rich saponitic clay and amorphous material. The ovoid is indigenous to Nakhla and occurs within a late-formed amorphous mesostasis region of rhyolitic composition that is interstitial to two clinopyroxene grains with Al-rich rims, and contains acicular apatite crystals, olivine, sulfides, Ti-rich magnetite, and a new mineral of the rhoenite group. To infer the origin of the ovoid, a large set of analytical tools was employed, including scanning electron microscopy and backscattered electron imaging, wavelength-dispersive X-ray analysis, X-ray mapping, Raman spectroscopy, time-of-flight secondary ion mass spectrometry analysis, high-resolution transmission electron microscope imaging, and atomic force microscope topographic mapping. The concentric wall of the ovoid surrounds an originally hollow volume and exhibits internal layering of contrasting nanotextures but uniform chemical composition, and likely inherited its overall shape from a preexisting vesicle in the mesostasis glass. A final fibrous layer of Fe-rich phases blankets the interior surfaces of the ovoid wall structure. There is evidence that the parent rock of Nakhla has undergone a shock event from a nearby bolide impact that melted the rims of pyroxene and the interstitial matter and initiated an igneous hydrothermal system of rapidly cooling fluids, which were progressively mixed with fluids from the melted permafrost. Sharp temperature gradients were responsible for the crystallization of Al-rich clinopyroxene rims, rhoenite, acicular apatites, and the quenching of the mesostasis glass and the vesicle. During the formation of the ovoid structure, episodic fluid infiltration events resulted in the precipitation of saponite rinds around the vesicle walls, altered pyrrhotite to marcasite, and then isolated the ovoid wall structure from the rest of the system by depositing a layer of iron oxides/hydroxides. Carbonates, halite, and sulfates were deposited last within interstitial spaces and along fractures. Among three plausible competing hypotheses here, this particular abiotic scenario is considered to be the most reasonable explanation for the formation of the ovoid structure in Nakhla, and although compelling evidence for a biotic origin is lacking, it is evident that the martian subsurface contains niche environments where life could develop.

Oxygen isotopic composition of carbonate in the nakhla meteorite: implications for the hydrosphere and atmosphere of mars

Abstract We have located small areas of siderite within the mesostasis of the Nakhla meteorite. High concentrations of Mn (up to ∼50% rhodochrosite) and elevated D/H ratios indicate that the siderite is not a terrestrial alteration product. The isotopic composition of oxygen in the siderite has been determined with the Manchester ISOLAB 54 ion microprobe. The siderite has δ 18 O = +34 ± 1‰, which is higher than any other martian carbonate yet reported. If the δ 18 O value is the result of equilibration with water at 2 /H 2 O produced during the degassing of Mars, and not modified subsequently isotopically. Formation from a water rich fluid at >60°C requires that the fluid was heavy isotope enriched relative to fluids produced during planetary degassing. An enrichment of 8–15‰ is consistent with theoretical outgassing models that are able to account for enhancements of Δ 17 O in martian alteration products. Estimated deposition temperatures would be raised to 80–170°C. The effect of a global scale fixation of martian CO 2 as carbonate operates in the opposite direction and could lead to a reduction in δ 18 O of the martian hydrosphere of a few permil.

The manchester isolab 54 ion microprobe

Abstract The Isolab 54 ion microprobe installed at the Department of Earth Sciences at the University of Manchester has been designed to measure isotopic abundances of elements with high precision from ions formed by secondary ionisation (SIMS), laser resonance ionisation (RIMS) or thermal ionisation (TIMS). This instrument has been extensively modified since its original installation to improve its precision and capabilities, and these improvements are detailed, as are applications for which the instrument has been used. The principal modifications were the installation and testing of a new type of ion detector (conversion dynode system, CDS), which has an ion-to-pulse conversion efficiency that has been constant to better than 2% over periods of many months, a method of integrating secondary ion currents to eliminate the effects of irreproducible instrumental isotopic fractionation, and a method of rapid electrostatic peak centring which can centre high mass resolution peaks on a detector to a precision of 2 ppm in mass in 1.2 s. Particular attention has been paid to in situ SIMS analysis of oxygen isotopes from insulating materials, where a spatial resolution of 10–20 μm with a precision of 1–2% has been achieved for both 17O/16O and 18O/16O. Analytical techniques for the measurement of carbon, nitrogen and osmium isotope ratios by SIMS are also described, together with the development of a technique for the measurement of strontium isotope ratios using laser resonance ionisation of sputtered neutral atoms.

Gripping tools for handling and assembly of microcomponents

In this paper a vacuum gripper for handling of microstructures in MST will be presented as well as the design, production and testing of two types of mechanical micro-grippers used for handling and assembly of microcomponents. One of them is with the possibility of optical force sensing.

New insights into the chemical and isotopic composition of human-body biominerals. I: Cholesterol gallstones from England and Greece.

We have analyzed gallstones from four patients of Europe and particularly from England (including samples from a mother and a daughter) and Greece. According to the XRD, FTIR, NMR and laser micro-Raman results the studied materials correspond to typical cholesterol monohydrate (ChM). The micro-morphology of cholesterol microcrystals was investigated by means of SEM-EDS. The XRF results revealed that Ca is the dominant non-organic metal in all gallstones (up to ∼1.95wt.%) together with Fe, Cu, Pb and Ni (up to ~19ppm for each metal). Gallstones from England contain additional Mn (up to ~87ppm) and Zn (up to ∼6ppm) while the sample of the mother contains negligible Zn and Mn, compared to that of her daughter, but significant As (~4.5ppm). All cholesterol gallstones examined are well enriched in potentially toxic metals (Pb, as well as Ni in one case) and metalloids (As also in one case) as compared to the global average. The position of Zn, which is a characteristic biometal, in the structure of cholesterol, was investigated by molecular simulation using the Accelrys Materials Studio(®) software. On the basis of IRMS results, all gallstones examined exhibit a very light δ(13)C signature (average δ(13)C ~-24‰ PDB). Gamma-ray spectrometry measurements indicate the presence of (214)Pb and (214)Bi natural radionuclides due to the (238)U series as well as an additional amount of (40)K.

The effect of spaceflight on growth of Ulocladium chartarum colonies on the international space station.

The objectives of this 14 days experiment were to investigate the effect of spaceflight on the growth of Ulocladium chartarum, to study the viability of the aerial and submerged mycelium and to put in evidence changes at the cellular level. U. chartarum was chosen for the spaceflight experiment because it is well known to be involved in biodeterioration of organic and inorganic substrates covered with organic deposits and expected to be a possible contaminant in Spaceships. Colonies grown on the International Space Station (ISS) and on Earth were analysed post-flight. This study clearly indicates that U. chartarum is able to grow under spaceflight conditions developing, as a response, a complex colony morphotype never mentioned previously. We observed that spaceflight reduced the rate of growth of aerial mycelium, but stimulated the growth of submerged mycelium and of new microcolonies. In Spaceships and Space Stations U. chartarum and other fungal species could find a favourable environment to grow invasively unnoticed in the depth of surfaces containing very small amount of substrate, posing a risk factor for biodegradation of structural components, as well as a direct threat for crew health. The colony growth cycle of U. chartarum provides a useful eukaryotic system for the study of fungal growth under spaceflight conditions.

Optical tweezers with enhanced efficiency based on laser-structured substrates

We present an optical nanotrapping setup that exhibits enhanced efficiency, based on localized plasmonic fields around sharp metallic features. The substrates consist of laser-structured silicon wafers with quasi-ordered microspikes on the surface, coated with a thin silver layer. The resulting optical traps show orders of magnitude enhancement of the trapping force and the effective quality factor.

Laser-machined layer-by-layer metallic photonic band-gap structures

Metallic photonic band-gap crystals operating in the microwave frequency range were fabricated by laser precision machining. They consist of stainless steel plates with a tetragonal lattice of holes and a lattice constant of 15 mm. Transmission measurements show that periodic crystals exhibit a cutoff frequency in the 8–18 GHz range, below which no propagation is allowed. The cutoff frequency can be easily tuned by varying the interlayer distance or the filling fraction of the metal. Combinations of plates with different hole diameters create defect modes with relatively sharp peaks, which are tunable. The experimental measurements are in good agreement with theoretical calculations.

Precision and reproducibility of in situ oxygen isotope ratio measurements on quartz obtained using an Isolab 54 ion microprobe

Abstract Ion probe techniques for measuring in situ 18O/16O ratios from insulating materials (particularly quartz) have been developed using an Isolab 54 ion microprobe. 18O/16O ratio measurements were obtained from a range of quartz standards for which 18O/16OSMOW ratios had been determined by conventional fluorination techniques. The correlation between the ratios obtained by ion probe and by conventional fluorination methods is high. Accurate absolute 18O/16OSMOW ratios can be obtained by normalisation to a well-characterised standard and the 1s deviation between the ion probe ratio and the conventionally determined ratio is 1.5‰ for a single measurement on the standard and a single measurement on the unknown sample. This measured scatter in normalised ratios is consistent with the typical measured uncertainty on a spot measurement being of the order of 1‰ and the uncertainty in the absolute ratio being derived from uncertainties added in quadrature. The data show no large systematic errors, demonstrating that the trueness of the mean of a number of ion probe determined ratios may be improved by repeated measurements. Detector stability and instrumental fractionation yield measured ratios (absolute in the sense that they are not normalised from day to day) which show a scatter of between 1 and 2‰ over periods of many weeks, an instrument stability which is an order of magnitude better than data published elsewhere. This level of stability opens the possibility of “standardless” ion probe oxygen isotope ratio measurements, certainly to an accuracy of 2‰ or better.

Biogenicity of an Early Quaternary iron formation, Milos Island, Greece

A ~2.0-million-year-old shallow-submarine sedimentary deposit on Milos Island, Greece, harbours an unmetamorphosed fossiliferous iron formation (IF) comparable to Precambrian banded iron formations (BIFs). This Milos IF holds the potential to provide clues to the origin of Precambrian BIFs, relative to biotic and abiotic processes. Here, we combine field stratigraphic observations, stable isotopes of C, S and Si, rock petrography and microfossil evidence from a ~5-m-thick outcrop to track potential biogeochemical processes that may have contributed to the formation of the BIF-type rocks and the abrupt transition to an overlying conglomerate-hosted IF (CIF). Bulk δ(13) C isotopic compositions lower than -25‰ provide evidence for biological contribution by the Calvin and reductive acetyl-CoA carbon fixation cycles to the origin of both the BIF-type and CIF strata. Low S levels of ~0.04 wt.% combined with δ(34) S estimates of up to ~18‰ point to a non-sulphidic depository. Positive δ(30) Si records of up to +0.53‰ in the finely laminated BIF-type rocks indicate chemical deposition on the seafloor during weak periods of arc magmatism. Negative δ(30) Si data are consistent with geological observations suggesting a sudden change to intense arc volcanism potentially terminated the deposition of the BIF-type layer. The typical Precambrian rhythmic rocks of alternating Fe- and Si-rich bands are associated with abundant and spatially distinct microbial fossil assemblages. Together with previously proposed anoxygenic photoferrotrophic iron cycling and low sedimentary N and C potentially connected to diagenetic denitrification, the Milos IF is a biogenic submarine volcano-sedimentary IF showing depositional conditions analogous to Archaean Algoma-type BIFs.