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A fracture mechanics model is developed for the initiation and propagation of a crack through a porous ice layer of finite thickness under gravitational overburden. It is found that surface cracks generated in response to a tidally induced stress field may penetrate through the entire outer brittle layer if a subsurface ocean is present on Europa. Such penetration is found to be very unlikely in the absence of an ocean. A cycloidal crack would then form as a sequence of near instantaneous discrete failures, each extending roughly the brittle layer thickness in range, linked with a much lower apparent propagation speed set by the moving tidal stress field. The implications of this porous ice fracture model for ice-penetrating radar scattering loss and seismic activity are quantified. 相似文献
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The dynamic strength of an ordinary chondrite 总被引：1，自引：0，他引：1
Abstract– Dynamic and quasistatic unconfined compression experiments were performed on samples of the L5 ordinary chondrite MacAlpine Hills (MAC) 88118. The dynamic compressive strength measurements are the first of its kind for a stony meteorite, and indicate that the material tested here exhibits significant increase in compressive strength with increasing strain rate. This increase in compressive strength is larger than the increases typically observed in terrestrial rock specimens compressed over a similar range of strain rates. The details of the failure process are investigated by recording images of the experiments in real time. Specifically, the crack growth speeds in the dynamic compression experiments are measured from ultrahigh‐speed images. These speeds are significantly lower than the speeds observed in terrestrial analogs that are typically used in numerical investigations of large‐scale impacts. The implications of these measurements of strength and failure process are explored in the contexts of atmospheric disruption of meteors and impact cratering/disruption of asteroids. 相似文献
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Abstract— The ice flow conditions of a 100 times 100 km area of Victoria Land, Antarctica were analyzed with the synthetic aperture radar (SAR) technique. The area includes a number of meteorite concentration sites, in particular the Allan Hills ice fields. Regional ice flow velocities around the Midwestern and Near‐western ice fields and the Allan Hills main ice field are shown to be ≤2.5 m yr?1. These sites are located on a horseshoe‐shaped area that bounds an area characterized by higher ice flow velocities of up to 5 m yr?1. Meteorite find locations on the Elephant Moraine are located in this “high ice flow” area. The SAR derived digital elevation model (DEM) shows atypical low surface slopes for Antarctic conditions, which are the cause for the slow ice movements. Numerous ice rises in the area are interpreted to cap sub‐ice obstacles, which were formed by tectonic processes in the past. The ice rises are considered to represent temporary features, which develop only during warm stages when the regional ice stand is lowered. Ice depressions, which develop in warm stages on the lee side of ice rises, may act as the sites of temporary build‐up of meteorite concentrations, which turn inoperative during cold stages when the regional ice level rises and the ice rises disappear. Based on a simplified ice flow model, we argue that the regional ice flow in cold stages is reduced by a factor of at least 3. 相似文献
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Thermal stresses are potentially important drivers of Io's tectonics and mountain building. It has been hypothesized that sustained local or regional shut down of heat-pipe volcanism on Io could lead to deep crustal heating and large compressive stresses [McKinnon, W.B., Schenk, P.M., Dombard, A.J., 2001. Geology 29, 103-106]. Such large stresses would then be relieved by thrust faulting and uplifting of crustal blocks, producing mountains like those observed on Io. Here we analyze the tectonic consequences of the heat-pipe model in detail, considering both the initial thermal stress state of a basalt or peridotite crust created by heat-pipe volcanism, and relative roles of subsidence stresses (due to burial of preexisting layers) and thermal stresses arising from variable volcanism and changes in crustal (∼lithosphere) thickness. We limit the magnitude of the potential subsidence stresses in our study, because the magnitude of subsidence stresses can be quite large, if not dominant. Results indicate that for a fixed crustal thickness, the region of failure and faulting moves closer to the surface as eruption rate decreases and time increases. When the crust melts at its base as volcanism decreases (as might occur under steady state tidal heating), resulting in crustal thinning, the region of failure is brought even closer to the surface. Naturally, when compressive, subsidence stresses are included, the vertical extent of crust in brittle failure thickens to include most of the lithosphere. In contrast, increases in eruption rate cause the extent of the region in compressional failure to decrease and be driven very deep in the crust (in the absence of sufficient subsidence stress). Therefore, regions of declining volcanism are more likely to produce mountains, whereas regions of extensive or increasing volcanism are less likely to do so. This is consistent with the observation of a global anticorrelation between mountains and volcanic centers on Io. Finally, we find that the choice of crustal composition/rheology (dry basalt vs. dry peridotite) has little effect on our results implying that basalt, peridotite and komatiite are all similarly “stiff” in the Io environment. 相似文献
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Two opposing models to explain the geological features observed on Europa’s surface have been proposed. The thin-shell model states that the ice shell is only a few kilometers thick, transfers heat by conduction only, and can become locally thinner until it exposes an underlying ocean on the satellite’s surface. According to the thick-shell model, the ice shell may be several tens of kilometers thick and have a lower convective layer, above which there is a cold stagnant lid that dissipates heat by conduction. Whichever the case, from magnetic data there is strong support for the presence of a layer of salty liquid water under the ice. The present study was performed to examine whether the possibility of convection is theoretically consistent with surface heat flows of ∼100-200 mW m−2, deduced from a thin brittle lithosphere, and with the typical spacing of 15-23 km proposed for the features usually known as lenticulae. It was obtained that under Europa’s ice shell conditions convection could occur and also account for high heat flows due to tidal heating of the convective (nearly isothermal) interior, but only if the dominant water ice rheology is superplastic flow (with activation energy of 49 kJ mol−1; this is the rheology thought dominant in the warm interior of the ice shell). In this case the ice shell would be ∼15-50 km thick. Furthermore, in this scenario explaining the origin of the lenticulae related to convective processes requires ice grain size close to 1 mm and ice thickness around 15-20 km. 相似文献
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Rónadh COX Lissa C. F. ONG Masahiko ARAKAWA Kate C. SCHEIDER 《Meteoritics & planetary science》2008,43(12):2027-2048
Abstract— Ice thickness estimates and impactor dynamics indicate that some impacts must breach Europa's ice crust; and outcomes of impact experiments using ice‐over‐water targets range from simple craters to chaos‐like destroyed zones, depending on impact energy and ice competence. First‐order impacts‐into thick ice or at low impact energy‐produce craters. Second‐order impacts punch through the ice, making holes that resemble raft‐free chaos areas. Third‐order impacts‐into thinnest ice or at highest energy‐produce large irregular raft‐filled zones similar to platy chaos. Other evidence for an impact origin for chaos areas comes from the size‐frequency distribution of chaos+craters on Europa, which matches the impact production functions of Ganymede and Callisto; and from small craters around the large chaos area Thera Macula, which decrease in average size and density per unit area as a function of distance from Thera's center. There are no tiny chaos areas and no craters >50 km diameter. This suggests that small impactors never penetrate, whereas large ones (ÜberPenetrators: >2.5 km diameter at average impact velocity) always do. Existence of both craters and chaos areas in the size range 2–40 km diameter points to spatial/temporal variation in crust thickness. But in this size range, craters are progressively outnumbered by chaos areas at larger diameters, suggesting that probability of penetration increases with increasing scale of impact. If chaos areas do represent impact sites, then Europa's surface is older than previously thought. The recalculated resurfacing age is 480 (‐302/+960) Ma: greater than prior estimates, but still very young by solar system standards. 相似文献
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Hypervelocity impacts into ice‐topped layered targets: Investigating the effects of ice crust thickness and subsurface density on crater morphology 
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下载免费PDF全文 Many bodies in the outer solar system are theorized to have an ice shell with a different subsurface material below, be it chondritic, regolith, or a subsurface ocean. This layering can have a significant influence on the morphology of impact craters. Accordingly, we have undertaken laboratory hypervelocity impact experiments on a range of multilayered targets, with interiors of water, sand, and basalt. Impact experiments were undertaken using impact speeds in the range of 0.8–5.3 km s?1, a 1.5 mm Al ball bearing projectile, and an impact incidence of 45°. The surface ice crust had a thickness between 5 and 50 mm, i.e., some 3–30 times the projectile diameter. The thickness of the ice crust as well as the nature of the subsurface layer (liquid, well consolidated, etc.) have a marked effect on the morphology of the resulting impact crater, with thicker ice producing a larger crater diameter (at a given impact velocity), and the crater diameter scaling with impact speed to the power 0.72 for semi‐infinite ice, but with 0.37 for thin ice. The density of the subsurface material changes the structure of the crater, with flat crater floors if there is a dense, well‐consolidated subsurface layer (basalt) or steep, narrow craters if there is a less cohesive subsurface (sand). The associated faulting in the ice surface is also dependent on ice thickness and the substrate material. We find that the ice layer (in impacts at 5 km s?1) is effectively semi‐infinite if its thickness is more than 15.5 times the projectile diameter. Below this, the crater diameter is reduced by 4% for each reduction in ice layer thickness equal to the impactor diameter. Crater depth is also affected. In the ice thickness region, 7–15.5 times the projectile diameter, the crater shape in the ice is modified even when the subsurface layer is not penetrated. For ice thicknesses, <7 times the projectile diameter, the ice layer is breached, but the nature of the resulting crater depends heavily on the subsurface material. If the subsurface is noncohesive (loose) material, a crater forms in it. If it is dense, well‐consolidated basalt, no crater forms in the exposed subsurface layer. 相似文献
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《Icarus》1986,68(2):252-265
Estimates of the brittle lithosphere thickness derived from the width and spacing of extensional tectonic features, coupled with lithospheric strength envelopes (brittle and ductile yield stress versus depth) appropriate for ice, allow the quantitative determination of early thermal profiles and lithospheric strength and stability on Ganymede. Furrows and grooves indicate brittle lithospheric thicknesses of 5–10 and 2–5 km, respectively, assuming that their spacing is controlled by an extensional instability or that their width is controlled by the intersection depth of their bounding faults. Plots of the brittle and ductile yield stress versus depth for the icy lithosphere of Ganymede show a linear increase in brittle strength with depth to a maximum at the brittle-ductile transition, followed by an exponential decrease in ductile yield stress with depth. Because the depth to the brittle-ductile transition depends primarily on the thermal gradient, the thickness of the brittle lithosphere can be used to calculate early thermal profiles of 1.5–6 and 4.5–20°/km during the formation of the furrows and grooves, respectively. Lithospheric strength, the integral of the yield stress versus depth curve, varied from 30–125 GPa m when the furrows formed to 5–30 GPa m when the grooves formed, which correspond to maximum yield stresses of 6–11 and 2.5–6 MPa, respectively. These results indicate that the thermal gradient and lithospheric strength varied laterally by as much as a factor of 5 and that Ganymede cooled in a highly inhomogeneous manner with significant lateral thermal anomalies. Finally, this analysis provides a straightforward explanation for the stability of large remnants of cratered terrain such as Galileo Regio that had a low thermal gradient and strong lithosphere in contrast to small remnants of cratered terrain that were fractured and broken up by grooved terrain as a result of higher thermal gradients and weaker lithospheres. 相似文献
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Henning Haack John Schutt Anders Meibom Ralph Harvey 《Meteoritics & planetary science》2007,42(10):1727-1733
Abstract— Following discoveries of blue ice areas in Greenland resembling meteorite‐bearing blue ice fields in Antarctica, a surface search of several of the most promising sites was carried out in August 2003. The ice fields are located in Kong Christian X Land, in northeastern Greenland around 74°N at elevations between 2100 and 2400 m. No meteorites were found in any of the localities that were searched. Evidence of occasional significant melting (filled crevasses and melt sheets) suggest that summer temperatures are sometimes high enough that dark rocks, like meteorites, can melt through the upper layers of ice. Small terrestrial rocks and cryogenite were found down to 50 cm below the ice surface. Meter‐sized terrestrial rocks were found on top of the ice downstream from nunataks. These rocks shade the ice below, and since they were apparently too massive to warm up during warm days, they remained at the surface as the surrounding ice ablated away. Our findings strongly suggest that Greenland is currently unlikely to harbor significant meteorite concentrations on blue ice fields. 相似文献
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Daniel Ozdín Jozef Plavčan Michaela Horňáčková Pavel Uher Vladimír Porubčan Pavel Veis Jozef Rakovský Juraj Tóth Patrik Konečný Ján Svoreň 《Meteoritics & planetary science》2015,50(5):864-879
The Ko?ice meteorite was observed to fall on 28 February 2010 at 23:25 UT near the city of Ko?ice in eastern Slovakia and its mineralogy, petrology, and geochemistry are described. The characteristic features of the meteorite fragments are fan‐like, mosaic, lamellar, and granular chondrules, which were up to 1.2 mm in diameter. The fusion crust has a black‐gray color with a thickness up to 0.6 mm. The matrix of the meteorite is formed mainly by forsterite (Fo80.6); diopside; enstatite (Fs16.7); albite; troilite; Fe‐Ni metals such as iron and taenite; and some augite, chlorapatite, merrillite, chromite, and tetrataenite. Plagioclase‐like glass was also identified. Relative uniform chemical composition of basic silicates, partially brecciated textures, as well as skeletal taenite crystals into troilite veinlets suggest monomict breccia formed at conditions of rapid cooling. The Ko?ice meteorite is classified as ordinary chondrite of the H5 type which has been slightly weathered, and only short veinlets of Fe hydroxides are present. The textural relationships indicate an S3 degree of shock metamorphism and W0 weathering grade. Some fragments of the meteorite Ko?ice are formed by monomict breccia of the petrological type H5. On the basis of REE content, we suggest the Ko?ice chondrite is probably from the same parent body as H5 chondrite Morávka from Czech Republic. Electron‐microprobe analysis (EMPA) with focused and defocused electron beam, whole‐rock analysis (WRA), inductively coupled plasma mass and optical emission spectroscopy (ICP MS, ICP OES), and calibration‐free laser induced breakdown spectroscopy (CF‐LIBS) were used to characterize the Ko?ice fragments. The results provide further evidence that whole‐rock analysis gives the most accurate analyses, but this method is completely destructive. Two other proposed methods are partially destructive (EMPA) or nondestructive (CF‐LIBS), but only major and minor elements can be evaluated due to the significantly lower sample consumption. 相似文献
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As the Dawn mission approaches a successful conclusion at Ceres, it seems time to assess how its findings have sharpened the picture of Ceres’s evolution. Before Dawn, we inferred from Ceres's bulk density of about 2100 kg m?3 that Ceres contained about 25% water by mass. Thermodynamic modeling of the interior evolution suggested that the original accreted ice had to melt even if only long‐lived radionuclides were present, leading to the aqueous alteration of the original chondritic silicates and differentiation of the altered silicates from any remaining water, consistent with telescopic detection of aqueously altered silicates (serpentine and clay minerals) on Ceres’s surface. Earth‐based observations of Ceres’s shape were not accurate enough to constrain the extent of differentiation of its interior. Dawn's results confirm these early findings and extend them dramatically to reveal an evolved and active small planet, probably even today, due to water/ice‐driven processes. A nearly uniform global distribution of surface mineralogy, which includes Mg‐serpentines, ammoniated clays, and salts including carbonates, suggests extensive, endogenous, planet‐wide aqueous alteration. Local exceptions show salt‐rich deposits of varied composition, which suggests subsurface heterogeneities. Concentration of Fe below carbonaceous chondrite levels suggests chemical fractionation, leading to Ceres being chemically differentiated. The high spatial uniformity of element abundance measurements of equatorial regolith also indicates that some ice‐rock fractionation occurred on a global scale. Even some local exposures of ice are seen, especially in higher latitudes and in low‐illumination regions that must be very young, as surface water ice is unstable on time scales of 1–1000 years under Ceres’s surface temperatures. Subsurface ice is also likely in abundance at higher latitudes in at least the upper few meters of the surface, as suggested by near‐surface H‐rich polar deposits. Observations of bright ice deposits in permanently shadowed regions suggest cold‐trapping of migrating H2O across the surface. Gravity field measurements indicate a concentration of mass toward the center and near isostatic equilibrium, consistent with at least some mass differentiation driven by water‐related processes. Abundant small and midsize craters but relaxed or missing large craters suggest a stiff upper crust with water abundance lower than 30 vol%. A sharp decrease in viscosity at ~40 km depth suggests the occurrence of a small fraction of liquid, consistent with earlier thermophysical models. Surface cryogenic features, such as flows, extrusions, and domes, some geologically very recent, are evidence of active water/ice‐driven subsurface processes. Ceres experienced extensive water‐related processes and at least some mass and chemical fractionation and is probably active today, consistent with previous moderate heating thermodynamic models. Clearly, Ceres is a “wet,” evolved planet at the edge of the inner solar system, as described in this special issue. We conclude with a list of questions suggested by the Dawn findings; they especially regard the state and fate of water and its role in driving past and possibly current chemical and physical activity in this dwarf planet. 相似文献
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To investigate the evolution of any processes on planetary surfaces in the outer Solar System, the rheological properties of non-water ices were studied by means of a sound velocity measurement system and a uniaxial deformation apparatus. A pulse transmission method was used to obtain longitudinal (Vp) and transverse (Vs) wave velocities through solid nitrogen and methane at temperatures ranging from 5 to 64 K and from 5 to 90 K, respectively. The measured velocities confirmed that the solid methane and solid nitrogen samples were non-porous polycrystalline samples without any cracks and bubbles inside. Compression tests at constant strain-rate were performed for solid nitrogen and methane at temperatures of 5-56 K and 5-77 K, respectively, at strain-rates of 10−4-10−2 s−1. Both brittle and ductile behavior was observed for solid nitrogen and methane under these conditions. The maximum strength of solid nitrogen was observed to be 9 MPa in the brittle failure mode, and that of solid methane was 10 MPa. These low strengths cannot support cantaloupe structures with the topographic undulation larger than several kilometers found on Triton’s surface, suggesting that other materials such as H2O ice could underlay solid methane and nitrogen and support these structures. 相似文献
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Nadine G. Barlow 《Meteoritics & planetary science》2006,41(10):1425-1436
Abstract— Mars Global Surveyor (MGS) and Mars Odyssey data are being used to revise the Catalog of Large Martian Impact Craters. Analysis of data in the revised catalog provides new details on the distribution and morphologic details of 6795 impact craters in the northern hemisphere of Mars. This report focuses on the ejecta morphologies and central pit characteristics of these craters. The results indicate that single‐layer ejecta (SLE) morphology is most consistent with impact into an ice‐rich target. Double‐layer ejecta (DLE) and multiple‐layer ejecta (MLE) craters also likely form in volatile‐rich materials, but the interaction of the ejecta curtain and target‐produced vapor with the thin Martian atmosphere may be responsible for the large runout distances of these ejecta. Pancake craters appear to be a modified form of double‐layer craters where the thin outer layer has been destroyed or is unobservable at present resolutions. Pedestal craters are proposed to form in an icerich mantle deposited during high obliquity periods from which the ice has subsequently sublimated. Central pits likely form by the release of vapor produced by impact into ice‐soil mixed targets. Therefore, results from the present study are consistent with target volatiles playing a dominant role in the formation of crater morphologies found in the Martian northern hemisphere. 相似文献
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James B. Garvin James W. Head David R. Marchant Mikhail A. Kreslavsky 《Meteoritics & planetary science》2006,41(10):1659-1674
Abstract— An impact crater 26.8 km in diameter, located in the northern lowlands (70.32°N, 266.45°E) at the base of the flanking slopes of the shield volcano Alba Patera, is characterized by highly unusual deposits on its southeastern floor and interior walls and on its southeastern rim. These include multiple generations of distinctive arcuate ridges about 115–240 m in width and lobate deposits extending down the crater wall and across the crater floor, forming a broad, claw‐like, ridged deposit around the central peak. Unusual deposits on the eastern and southeastern crater rim include frost, dunes, and a single distal arcuate ridge. Based on their morphology and geometric relationships, and terrestrial analogs from the Mars‐like Antarctic Dry Valleys, the floor ridges are interpreted to represent drop moraines, remnants of the previous accumulation of snow and ice, and formation of cold‐based glaciers on the crater rim. The configuration and superposition of the ridges indicate that the accumulated snow and ice formed glaciers that flowed down into the crater and across the crater floor, stabilized, covering an area of about 150 km2 produced multiple individual drop moraines due to fluctuation in the position of the stable glacier front. Superposition of a thin mantle and textures attributed to a recent ice‐age period (?0.5–2 Myr ago) suggest that the glacial deposits date to at least 4–10 Myr before the present. At least five phases of advance and retreat are indicated by the stratigraphic relationships, and these may be related to obliquity excursions. These deposits are in contrast to other ice‐related modification and degradation processes typical of craters in the northern lowlands, and may be related to the distinctive position of this crater in the past atmospheric circulation pattern, leading to sufficient preferential local accumulation of snow and ice to cause glacial flow. 相似文献
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Abstract– We present a case modeling study of impact crater formation in H2O‐bearing targets. The main goal of this work was to investigate the postimpact thermal state of the rock layers modified in the formation of hypervelocity impact craters. We present model results for a target consisting of a mixture of H2O‐ice and rock, assuming an ice/water content variable with depth. Our model results, combined with results from previous work using dry targets, indicate that for craters larger than about 30 km in diameter, the onset of postimpact hydrothermal circulation is characterized by two stages: first, the formation of a mostly dry, hot central uplift followed by water beginning to flow in and circulate through the initially dry and hot uplifted crustal rocks. The postimpact thermal field in the periphery of the crater is dependent on crater size: in midsize craters, 30–50 km in diameter, crater walls are not strongly heated in the impact event, and even though ice present in the rock may initially be heated enough to melt, overall temperatures in the rock remain below melting, undermining the development of a crater‐wide hydrothermal circulation. In large craters (with diameters more than 100 km or so), the region underneath the crater floor and walls is heated well above the melting point of ice, thus facilitating the onset of an extended hydrothermal circulation. These results provide preliminary constraints in characterizing the many water‐related features, both morphologic and spectroscopic, that high‐resolution images of Mars are now detecting within many Martian craters. 相似文献
17.
《Planetary and Space Science》2007,55(10):1225-1245
The process of tide-driven walking, proposed as a major mechanism for strike–slip displacement on Europa, is modeled using a finite-element numerical simulation of the behavior of viscoelastic material. For material parameters that are plausible for the water ice composing Europa's crust, the simulation confirms earlier analytic results for strike–slip displacement along a crack that penetrates down to the liquid water substrate. The finite element code permits testing other cases as well. Of considerable interest is whether tidal walking can operate if a crack penetrates not to liquid but only as far as warm, relatively viscous ice. In such a case, significant displacement can be driven, but only if the threshold value of the compressive force needed to lock the fault is near the value of the overburden stress at the bottom of the crack. Such special conditions are not needed for displacement if the crack penetrates to the underlying ocean. 相似文献
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Abstract— The results of a systematic field mapping campaign at the Haughton impact structure have revealed new information about the tectonic evolution of mid‐size complex impact structures. These studies reveal that several structures are generated during the initial compressive outward‐directed growth of the transient cavity during the excavation stage of crater formation: (1) sub‐vertical radial faults and fractures; (2) sub‐horizontal bedding parallel detachment faults; and (3) minor concentric faults and fractures. Uplift of the transient cavity floor toward the end of the excavation stage produces a central uplift. Compressional inward‐directed deformation results in the duplication of strata along thrust faults and folds. It is notable that Haughton lacks a central topographic peak or peak ring. The gravitational collapse of transient cavity walls involves the complex interaction of a series of interconnected radial and concentric faults. While the outermost concentric faults dip in toward the crater center, the majority of the innermost faults at Haughton dip away from the center. Complex interactions between an outward‐directed collapsing central uplift and inward collapsing crater walls during the final stages of crater modification resulted in a structural ring of uplifted, intensely faulted (sub‐) vertical and/or overturned strata at a radial distance from the crater center of ?5.0–6.5 km. Converging flow during the collapse of transient cavity walls was accommodated by the formation of several structures: (1) sub‐vertical radial faults and folds; (2) positive flower structures and chaotically brecciated ridges; (3) rollover anticlines in the hanging‐walls of major listric faults; and (4) antithetic faults and crestal collapse grabens. Oblique strike‐slip (i.e., centripetal) movement along concentric faults also accommodated strain during the final stages of readjustment during the crater modification stage. It is clear that deformation during collapse of the transient cavity walls at Haughton was brittle and localized along discrete fault planes separating kilometer‐size blocks. 相似文献
19.
Oliver BOTTA Zita MARTINS Christian EMMENEGGER Jason P. DWORKIN Daniel P. GLAVIN Ralph P. HARVEY Renato ZENOBI Jeffrey L. BADA Pascale EHRENFREUND 《Meteoritics & planetary science》2008,43(9):1465-1480
Abstract— –We have analyzed ice samples and meteorites from the LaPaz region of Antarctica to investigate the composition of polycyclic aromatic hydrocarbons (PAHs) and amino acids with the goal to understand whether or not there is a compositional relationship between the two reservoirs. Four LL5 ordinary chondrites (OCs) and one CK carbonaceous chondrite were collected as part of the 2003/2004 ANSMET season. Ice samples collected from directly underneath the meteorites were extracted. In addition, exhaust particles from the snowmobiles used during the expedition were collected to investigate possible contributions from this source. The meteorite samples, the particulate matter and solid‐state extracts of the ice samples and the exhaust filters were subjected to two‐step laser mass spectrometry (L2MS) to investigate the PAH composition. For amino acids analysis, the meteorites were extracted with water and acid hydrolyzed, and the extracts were analyzed with offline OPA/NAC derivatization combined with liquid chromatography with UV fluorescence detection and time of flight mass spectrometry (LC‐FD/ToF‐MS). PAHs in the particulate matter of the ice were found to be qualitatively similar to the meteorite samples, indicating that micron‐sized grains of the meteorite may be embedded in the ice samples. The concentration levels of dissolved PAHs in all the ice samples were found to be below the detection limit of the L2MS. The PAH composition of the snowmobile exhaust is significantly different to the one in particulate matter, making it an unlikely source of contamination for Antarctic meteorites. The amino acids glycine, β‐alanine and γ‐amino‐n‐butyric acid that were detected at concentrations of 3 to 19 parts per billion (ppb) are probably indigenous to the Antarctic meteorites. Some of the LaPaz ice samples were also found to contain amino acids at concentration levels of 1 to 33 parts per trillion (ppt), in particular α‐aminoisobutyric acid (AIB), an abundant non‐protein amino acid of extraterrestrial origin found in some carbonaceous chondrites. We hypothesize that this amino acid could have been extracted from Antarctic micrometeorites and the particulate matter of the meteorites during the concentration procedure of the ice samples. 相似文献
20.
Max P. BERNSTEIN Jason P. DWORKIN Scott A. SANDFORD Louis J. ALLAMANDOLA 《Meteoritics & planetary science》2001,36(3):351-358
Abstract— The polycyclic aromatic hydrocarbon (PAH) naphthalene was exposed to ultraviolet radiation in H2O ice under astrophysical conditions, and the products were analyzed using infrared spectroscopy and high‐performance liquid chromatography. As we found in our earlier studies on the photoprocessing of coronene in H2O ice, aromatic alcohols and ketones (quinones) were formed. The regiochemistry of the reactions is described and leads to specific predictions of the relative abundances of various oxidized naphthalenes that should exist in meteorites if interstellar ice photochemistry influenced their aromatic inventory. Since oxidized PAHs are present in carbon‐rich meteorites and interplanetary dust particles (IDPs), and ubiquitous in and fundamental to biochemistry, the delivery of such extraterrestrial molecules to the early Earth may have played a role in the origin and evolution of life. 相似文献