Alteration of five organic compounds by glow discharge plasma and UV light under simulated Mars conditions

The Viking missions to Mars failed to detect any organic material in regolith samples. Since then, several removal mechanisms of organic material have been proposed. Two of these proposed methods are removal due to exposure to plasmas created in dust devils and exposure to UV irradiation. The experiments presented here were performed to identify similarities between the two potential removal mechanisms and to identify any compounds produced from these mechanisms that would have been difficult for the Viking instruments to detect. Five organic compounds, phenanthrene, octadecane, octadecanoic acid, decanophenone and benzoic acid, were exposed to a glow discharge plasma created in simulated martian atmospheres as might be present in dust devils, and to UV irradiation similar to that found at the surface of Mars. Glow discharge exposure was carried out in a chamber with 6.9 mbar pressure of a Mars like gas composed mostly of carbon dioxide. The plasma was characterized using emission spectroscopy and found to contain cations and excited neutral species including carbon dioxide, carbon monoxide, and nitrogen. UV irradiation experiments were performed in a Mars chamber which simulates the temperature, pressure, atmospheric composition, and UV fluence rates of equatorial Mars. The non-volatile residues left after each exposure were characterized by mass loss, infrared spectroscopy and high resolution mass spectrometry. Oxidized, higher molecular weight versions of the parent compounds containing carbonyl, hydroxyl and alkenyl functional groups were identified. The presence of these oxidized compounds suggests that searches for organic material in soils on Mars use instrumentation suitable for detection of compounds which contain the above functional groups. Discussions of possible reaction mechanisms are given.     

Evaluation of the intermediate-term periodicities in solar and cosmic ray activities during cycle 23

In this paper we investigate the presence and temporal evolution of galactic cosmic rays (GCRs) time-series and three solar parameters, namely the daily sunspot number, the coronal green line and the 10.7 cm solar radio flux over the period 1996–2003 by the wavelet technique. A number of short- and intermediate-term quasi-periodicities were also detected in both GCR and solar parameters. For the short-term range, we have identified quasi-periods of 16–30 days, 40–55 days, 60–70 days, 80–90 days and 80–100 days. In the case of intermediate range, the significant periods were 120–140 days, 150–170 days, 190–210 days, 240–260 days, ≈1.09 yr. and ≈1.23 yr. The wavelet power spectra show that all the above-mentioned periods are intermittent in nature and occurred in different time-series in different intervals. The result exhibits that the well-known “Rieger period” of (150–160 days) was prominent in both GCR and solar data sets during the ascending phase of cycle 23. Possible reasons behind the observed periods were discussed with the help of previous results and existing numerical models.     

Evaluating techniques for sampling stream crayfish (Paranephrops planifrons)

We evaluated several capture and analysis techniques for estimating abundance and size structure of freshwater crayfish (Paranephrops planifrons) (koura) from a forested North Island, New Zealand stream to provide a methodological basis for future population studies. Direct observation at night and collecting with baited traps were not considered useful. A quadrat sampler was highly biased toward collecting small individuals. Handnetting at night and estimating abundances using the depletion method were not as efficient as handnetting on different dates and analysing by a mark‐recapture technique. Electrofishing was effective in collecting koura from different habitats and resulted in the highest abundance estimates, and mark‐recapture estimates appeared to be more precise than depletion estimates, especially if multiple recaptures were made. Handnetting captured more large crayfish relative to electrofishing or the quadrat sampler.     

Gemini-N mid-IR observations of the dust properties of the ejecta excavated from Comet 9P/Tempel 1 during Deep Impact

We present mid-infrared spectra and images from the Gemini-N (+MICHELLE) observational campaign of Comet 9P/Tempel 1 before, during, and after its encounter with Deep Impact. We use our thermal grain model to probe the 10 μm properties of the dust grains in the coma of the comet. Before impact (3 July 2005 UT), and more than 24 h after impact (5, 16, and 28 July 2005 UT), the comet dust grains were composed mostly of amorphous olivine, and were relatively large (peak of the grain size distribution ). For the night of impact, we extract spectra by centering on the nucleus, and offset 1″ from the nucleus in the direction of the impact ejecta plume. We find small dust grains (∼0.2 μm) of a diverse mineralogy (amorphous olivine, amorphous pyroxene, amorphous carbon, and crystalline olivine) populating the ejecta. The submicron sized dust grains move faster than the other, larger grains (?0.7 μm), with amorphous olivine and amorphous carbon traveling together, and amorphous pyroxene and crystalline olivine dispersing at a similar rate. Deriving a velocity law from a time-of-flight analysis, we find that the material traveled with a velocity law scaled by and with a power of p=0.5. This velocity power-law requires a sustained release of grains for the duration of 45-60 min after impact. Since the mineral species are traveling at different speeds, and there was a sustained release of grains due to a possible “gas-plume,” we conclude that the different minerals did not originate from grain aggregates destroyed by the impact, but instead arise from an inhomogeneous nucleus.     

In search of a hidden long-term isolated sub-chondritic Nd/Nd reservoir in the deep mantle: Implications for the Nd isotope systematics of the Earth

Here we search for evidence of the existence of a sub-chondritic ¹⁴²Nd/¹⁴⁴Nd reservoir that balances the Nd isotope chemistry of the Earth relative to chondrites. If present, it may reside in the source region of deeply sourced mantle plume material. We suggest that lavas from Hawai’i with coupled elevations in ¹⁸⁶Os/¹⁸⁸Os and ¹⁸⁷Os/¹⁸⁸Os, from Iceland that represent mixing of upper mantle and lower mantle components, and from Gough with sub-chondritic ¹⁴³Nd/¹⁴⁴Nd and high ²⁰⁷Pb/²⁰⁶Pb, are favorable samples that could reflect mantle sources that have interacted with an Early-Enriched Reservoir (EER) with sub-chondritic ¹⁴²Nd/¹⁴⁴Nd.High-precision Nd isotope analyses of basalts from Hawai’i, Iceland and Gough demonstrate no discernable ¹⁴²Nd/¹⁴⁴Nd deviation from terrestrial standards. These data are consistent with previous high-precision Nd isotope analysis of recent mantle-derived samples and demonstrate that no mantle-derived material to date provides evidence for the existence of an EER in the mantle.We then evaluate mass balance in the Earth with respect to both ¹⁴²Nd/¹⁴⁴Nd and ¹⁴³Nd/¹⁴⁴Nd. The Nd isotope systematics of EERs are modeled for different sizes and timing of formation relative to ε¹⁴³Nd estimates of the reservoirs in the μ¹⁴²Nd = 0 Earth, where μ¹⁴²Nd is ((measured ¹⁴²Nd/¹⁴⁴Nd/terrestrial standard ¹⁴²Nd/¹⁴⁴Nd)−1 * 10⁻⁶) and the μ¹⁴²Nd = 0 Earth is the proportion of the silicate Earth with ¹⁴²Nd/¹⁴⁴Nd indistinguishable from the terrestrial standard. The models indicate that it is not possible to balance the Earth with respect to both ¹⁴²Nd/¹⁴⁴Nd and ¹⁴³Nd/¹⁴⁴Nd unless the μ¹⁴²Nd = 0 Earth has a ε¹⁴³Nd within error of the present-day Depleted Mid-ocean ridge basalt Mantle source (DMM). The 4567 Myr age ¹⁴²Nd-¹⁴³Nd isochron for the Earth intersects μ¹⁴²Nd = 0 at ε¹⁴³Nd of +8 ± 2 providing a minimum ε¹⁴³Nd for the μ¹⁴²Nd = 0 Earth. The high ε¹⁴³Nd of the μ¹⁴²Nd = 0 Earth is confirmed by the Nd isotope systematics of Archean mantle-derived rocks that consistently have positive ε¹⁴³Nd.If the EER formed early after solar system formation (0-70 Ma) continental crust and DMM can be complementary reservoirs with respect to Nd isotopes, with no requirement for significant additional reservoirs. If the EER formed after 70 Ma then the μ¹⁴²Nd = 0 Earth must have a bulk ε¹⁴³Nd more radiogenic than DMM and additional high ε¹⁴³Nd material is required to balance the Nd isotope systematics of the Earth.     

Molecular H2O in armenite, BaCa2Al6Si9O30·2H2O, and epididymite, Na2Be2Si6O15·H2O: Heat capacity, entropy and local-bonding behavior of confined H2O in microporous silicates

Armenite, ideal formula BaCa₂Al₆Si₉O₃₀·2H₂O, and its dehydrated analog BaCa₂Al₆Si₉O₃₀ and epididymite, ideal formula Na₂Be₂Si₆O₁₅·H₂O, and its dehydrated analog Na₂Be₂Si₆O₁₅ were studied by low-temperature relaxation calorimetry between 5 and 300 K to determine the heat capacity, C_p, behavior of their confined H₂O. Differential thermal analysis and thermogravimetry measurements, FTIR spectroscopy, electron microprobe analysis and powder Rietveld refinements were undertaken to characterize the phases and the local environment around the H₂O molecule.The determined structural formula for armenite is Ba_0.88(0.01)Ca_1.99(0.02)Na_0.04(0.01)Al_5.89(0.03)Si_9.12(0.02)O₃₀·2H₂O and for epididymite Na_1.88(0.03)K_0.05(0.004)Na_0.01(0.004)Be_2.02(0.008)Si_6.00(0.01)O₁₅·H₂O. The infrared (IR) spectra give information on the nature of the H₂O molecules in the natural phases via their H₂O stretching and bending vibrations, which in the case of epididymite only could be assigned. The powder X-ray diffraction data show that armenite and its dehydrated analog have similar structures, whereas in the case of epididymite there are structural differences between the natural and dehydrated phases. This is also reflected in the lattice IR mode behavior, as observed for the natural phases and the H₂O-free phases. The standard entropy at 298 K for armenite is S° = 795.7 ± 6.2 J/mol K and its dehydrated analog is S° = 737.0 ± 6.2 J/mol K. For epididymite S° = 425.7 ± 4.1 J/mol K was obtained and its dehydrated analog has S° = 372.5 ± 5.0 J/mol K. The heat capacity and entropy of dehydration at 298 K are Δ = 3.4 J/mol K and ΔS^rxn = 319.1 J/mol K and Δ = −14.3 J/mol K and ΔS^rxn = 135.7 J/mol K for armenite and epididymite, respectively. The H₂O molecules in both phases appear to be ordered. They are held in place via an ion-dipole interaction between the H₂O molecule and a Ca cation in the case of armenite and a Na cation in epididymite and through hydrogen-bonding between the H₂O molecule and oxygen atoms of the respective silicate frameworks. Of the three different H₂O phases ice, liquid water and steam, the C_p behavior of confined H₂O in both armenite and epididymite is most similar to that of ice, but there are differences between the two silicates and from the C_p behavior of ice. Hydrogen-bonding behavior and its relation to the entropy of confined H₂O at 298 K is analyzed for various microporous silicates.The entropy of confined H₂O at 298 K in various silicates increases approximately linearly with increasing average wavenumber of the OH-stretching vibrations. The interpretation is that decreased hydrogen-bonding strength between a H₂O molecule and the silicate framework, as well as weak ion-dipole interactions, results in increased entropy of H₂O. This results in increased amplitudes of external H₂O vibrations, especially translations of the molecule, and they contribute strongly to the entropy of confined H₂O at T < 298 K.     

Complete preservation of ophiolite suite from south Andaman,India: A mineral-chemical perspective

Field studies supplemented by petrographic analyses clearly reveal complete preservation of ophiolite suite from Port Blair (11°39′N: 92°45′E) to Chiriyatapu (11°30′24″N: 92°42′30″E) stretch of South Andaman. The ophiolite suite reveals serpentinite at the base which is overlain unconformably by cumulate ultramafic-mafic members with discernible cumulus texture and igneous layering. Basaltic dykes are found to cut across the cumulate ultramafic-mafic members. The succession is capped by well exposed pillow basalts interlayered with arkosic sediments. Olivine from the basal serpentinite unit are highly magnesian (Fo_80.1–86.2). All clinopyroxene analyses from cumulate pyroxenite, cumulate gabbro and basaltic dyke are discriminated to be ‘Quad’ and are uniformly restricted to the diopside field. Composition of plagioclase in different lithomembers is systematically varying from calcic to sodic endmembers progressively from cumulate pyroxenite to pillow basalt through cumulate gabbro and basaltic dyke. Plagioclase phenocrysts from basaltic dyke are found to be distinctly zoned (An_60.7-An_35.3) whereas groundmass plagioclase are relatively sodic (An₃₃-An_23.5). Deduced thermobarometric data from different lithomembers clearly correspond to the observed preservation of complete ophiolite suite.     

Periglacial climate at the 2.5 Ma onset of Northern Hemisphere glaciation inferred from the Whippoorwill Formation, northern Missouri, USA

The Whippoorwill Formation is a gleyed diamicton that is present locally within bedrock depressions beneath the oldest glacial till in northern Missouri, USA. Stratigraphy, paleomagnetism, and cosmogenic-nuclide burial ages show that it was deposited between the Matuyama-Gauss magnetostratigraphic boundary at 2.58 Ma and the first advance of the Laurentide ice sheet into Missouri at 2.47 ± 0.19 Ma. High cosmogenic-nuclide concentrations also show that the constituents of the Whippoorwill Formation experienced long exposure at a stable landscape surface with erosion rates of 1-2 m/Ma. However, cosmogenic-nuclide concentrations are invariant with depth below the Whippoorwill Formation surface, indicating active mixing of the soil profile shortly before burial by till. The Whippoorwill Formation retains numerous features indicative of cryoturbation. Therefore, we interpret it as a buried Gelisol, a soil formed under periglacial conditions in the presence of permafrost. At the onset of Northern Hemisphere glaciation, climate cooling established permafrost conditions and accelerated erosion by inducing landscape instability. Thus, weathered regolith materials were mobilized and redeposited by gelifluction shortly before the ice sheet overrode the landscape.     

In situ U–Pb SIMS (IN-SIMS) micro-baddeleyite dating of mafic rocks: Method with examples

An in situ U–Pb SIMS (IN-SIMS) method to date micro-baddeleyite crystals as small as 3 μm is presented with results from three samples that span a variety of ages and geologic settings. The method complements ID-TIMS geochronology by extending the range of dateable crystals to sizes smaller than can be recovered by physical separation. X-ray mapping and BSE imaging are used to locate target grains in thin section, followed by SIMS analysis on a CAMECA ims 1270, using the field aperture in the transfer column to screen out ions from host phases. Internal age precisions for the method are anticipated to range from 0.1% for Precambrian rocks to 3–7% for Phanerozoic rocks. Results establish a 2689 ± 5 Ma age for mafic dikes in the Wyoming craton, USA, a 1540 ± 30 Ma age for a subaerial lava flow from the Thelon Basin of northern Canada, and a 457 ± 34 Ma age for mafic dikes in the platform sequence of southeastern Siberia. The method is ideal for relatively non-destructive dating of small samples such as extraterrestrial rocks and precious terrestrial samples.