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1.
Abstract– We investigated three‐dimensional structures of comet Wild 2 coma particle impact tracks using synchrotron radiation (SR) X‐ray microtomography at SPring‐8 to elucidate the nature of comet Wild 2 coma dust particles captured in aerogel by understanding the capture process. All tracks have a similar entrance morphology, indicating a common track formation process near the entrance by impact shock propagation irrespective of impactor materials. Distributions of elements along the tracks were simultaneously measured using SR‐XRF. Iron is distributed throughout the tracks, but it tends to concentrate in the terminal grains and at the bottoms of bulbs. Based on these results, we propose an impact track formation process. We estimate the densities of cometary dust particles based on the hypothesis that the kinetic energy of impacting dust particles is proportional to the track volume. The density of 148 cometary dust particles we investigated ranges from 0.80 to 5.96 g cm?3 with an average of 1.01 (±0.25) g cm?3. Moreover, we suggest that less fragile crystalline particles account for approximately 5 vol% (20 wt%) of impacting particles. This value of crystalline particles corresponds to that of chondrules and CAIs, which were transported from the inner region of the solar system to the outer comet‐forming region. Our results also suggest the presence of volatile components, such as organic material and perhaps ice, in some bulbous tracks (type‐C).  相似文献   

2.
The Devasthal Fast Optical Telescope (DFOT) is a 1.3 meter aperture optical telescope, recently installed at Devasthal, Nainital. We present here the first results using an Hα filter with this telescope on a Wolf–Rayet dwarf galaxy Mrk 996. The instrumental response and the Hα sensitivity obtained with the telescope are (3.3 ± 0.3) × 10???15 erg s?1 cm?2/counts s?1 and 7.5 × 10???17 erg s?1 cm?2 arcsec?2 respectively. The Hα flux and the equivalent width for Mrk 996 are estimated as (132 ± 37) × 10?14 erg s?1 cm?2 and ～96 Å respectively. The star formation rate is estimated as 0.4 ± 0.1M ⊙ yr?1. Mrk 996 deviates from the radio-FIR correlation known for normal star forming galaxies with a deficiency in its radio continuum. The ionized gas as traced by Hα emission is found in a disk shape which is misaligned with respect to the old stellar disk. This misalignment is indicative of a recent tidal interaction in the galaxy. We believe that galaxy–galaxy tidal interaction is the main cause of the WR phase in Mrk 996.  相似文献   

3.
E.N. Wells  J. Veverka  P. Thomas 《Icarus》1984,58(3):331-338
An experimental study was undertaken to determine how the spectral and photometric properties of representative Martian areas are affected by fallout of atmospheric dust suspended during dust forms. A laboratory apparatus was used to simulate the uniform fallout and deposition of particles 1 to 5 μm in diameter. Spectral measurements from 0.4- to 1.2-μm wavelengths and photometric measurements at several wavelengths were made for a number of Mars-analog materials before and after deposition of 6 × 10?5 to 1.5 × 10?3 g/cm2 of simulated fallout. These results indicate that the spectral and photometric properties of Martian regions can be affected significantly even by minute amounts of fallout. For instance, the reflectance at 0.56 μm of an average dark area will increase by 35% after deposition of only 9 × 10?5 g/cm2, and by 70% after deposition of 1.5 × 10?4 g/cm2. Thus the fallout from even one dust storm season (～2 × 10?3 g/cm2) is sufficient to change significantly the spectral and photometric characteristics of the substrate material, if the fallout were ubiquitous over the surface and if no competing processes of dust removal from surface grains occured.  相似文献   

4.
Abstract– We have measured the isotopic composition and fluence of solar‐wind nitrogen in a diamond‐like‐carbon collector from the Genesis B/C array. The B and C collector arrays on the Genesis spacecraft passively collected bulk solar wind for the entire collection period, and there is no need to correct data for instrumental fractionation during collection, unlike data from the Genesis “Concentrator.” This work validates isotopic measurements from the concentrator by Marty et al. (2010, 2011) ; nitrogen in the solar wind is depleted in 15N relative to nitrogen in the Earth’s atmosphere. Specifically, our array data yield values for 15N/14N of (2.17 ± 0.37) × 10?3 and (2.12 ± 0.34) × 10?3, depending on data‐reduction technique. This result contradicts preliminary results reported for previous measurements on B/C array materials by Pepin et al. (2009) , so the discrepancy between Marty et al. (2010, 2011) and Pepin et al. (2009) was not due to fractionation of solar wind by the concentrator. Our measured value of 15N/14N in the solar wind shows that the Sun, and by extension the solar nebula, lie at the low‐15N/14N end of the range of nitrogen isotopic compositions observed in the solar system. A global process (or combination of processes) must have operated in interstellar space and/or during the earliest stages of solar system formation to increase the 15N/14N ratio of the solar system solids. We also report a preliminary Genesis solar‐wind nitrogen fluence of (2.57 ± 0.42) × 1012 cm?2. This value is higher than that derived by backside profiling of a Genesis silicon collector ( Heber et al. 2011a ).  相似文献   

5.
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6.
We present the observations of Cygnus X-3 carried out with the GT-48 gamma-ray telescope at the Crimean Astrophysical Observatory in 1994–1995. The mean gamma-ray flux at energy E>1012 eV is shown to be approximately equal to 1.3×10?11 cm?2 s?1. The flux in 1994 was much lower than that in 1995, being (6.2±2.6)×10?12 cm?2 s?1; i.e., it was statistically insignificant. The flux in 1995 was (2.7±0.7)×10?11 cm?2 s?1. Thus, the very high energy gamma-ray emission from Cyg X-3 is variable. These measurement results can be used to obtain upper limits on the flux from Cyg X-3 in 1994–1995.  相似文献   

7.
This work is the first detailed study of carbon phases in the ureilite Almahata Sitta (sample #7). We present microRaman data for diamond and graphite in Almahata Sitta, seven unbrecciated ureilites, and two brecciated ureilites. Diamond in Almahata Sitta was found to be distinct from that in unbrecciated and brecciated ureilites, although diamond in unbrecciated and brecciated ureilites is indistinguishable. Almahata Sitta diamond shows a peak center range of 1318.5–1330.2 cm?1 and a full width at half maximum (FWHM) range of 6.6–17.4 cm?1, representing a shock pressure of at least 60 kbar. The actual peak shock pressure may be higher than this due to postshock annealing, if shock synthesis is the source of ureilite diamonds. Diamond in unbrecciated and brecciated ureilites have peak center wave numbers closer to terrestrial kimberlite diamond, but show a wider range of FWHM than Almahata Sitta. The larger peak shift observed in Almahata Sitta may indicate the presence of lonsdaleite. Alternatively, the lower values in brecciated ureilites may be evidence of an annealing step either following the initial diamond‐generating shock or as a consequence of heating during reconsolidation of the breccia. Graphite in Almahata Sitta shows a G‐band peak center range of 1569.1–1577.1 cm?1 and a G‐band FWHM range of 24.3–41.6 cm?1 representing a formation temperature of 990 ± 120 °C. Amorphous carbon was also found. We examine the different theories for diamond formation in ureilites, such as chemical vapor deposition and shock origin from graphite, and explore explanations for the differences between Almahata Sitta and other ureilites.  相似文献   

8.
We have calculated the energy spectra of cosmic ray secondary antiprotons and positrons using the latest available data on inclusive reactions. Using the measured positron spectrum, we have found that the amount of matter traversed by the cosmic rays in the few GeV region to bem≈4.7±1.5 g cm?2 of interstellar hydrogen. The computed antiproton to proton ratio is about 4×10?4 for energies 5–10 GeV. This is sufficient to make observations of antiprotons feasible from balloon flights. We have also pointed out the type of information that can be obtained if accurate information of the spectra of these two components becomes available.  相似文献   

9.
Bells and Sharps have some mineralogical and chemical peculiarities that make their classification uncertain. For Bells, the40 Ar content at 890 × 10?8 cm3 STP/g is greater than the highest C1 chondrite value (Ivuna; 640), but close to the mean value for C2's (880). The21 Ne-exposure age of 0.38 ± 0.07 Ma is very short, and coincides with the distinctive cluster of five C2's (0.17 to 0.76 Ma). Very likely Bells belongs to the same cluster, in which case it comes from the C2 parent body. Hence the C2 parent body seems to contain transitional C1-C2 material, like Bells, within a few km of the region of C2 chondrites proper. Thus the radiogenic and especially the cosmogenic gases link Bells to the C2 group. For Sharps, the elemental concentrations of primordial Ar, Kr and Xe (127, 0.76 and 0.59, all 10?8 cc/g) are ～ 3 x higher than for any other H3 chondrite. While Sharps is classified as 3.4 based on five indicators of metamorphism, the very high concentration of remaining two parameters of the Sears et al. (1980) scheme — C and primordial36 Ar — (together with the high concentration of the volatile trace elements Bi, In and Tl) implies a classification of 3.0 for its volatile element content. The21 Ne-exposure age is 25.5 ± 2.5 Ma, placing Sharps in the second largest peak of the H-chondrite distribution. The nominal K-Ar and U, Th-He ages are 4.6 ± 0.2 and 4.2 ± 1.5 Ga, suggesting that Sharps has remained at low temperatures since its beginnings.  相似文献   

10.
The Mariner 9 infrared spectrometer obtained data over a large part of Mars for almost a year beginning late in 1971. Mars' infrared emission spectrum was measured from 200 to 2000 cm?1 with an apodized resolution of 2.4 cm?1. No significant deviation from terrestrial ratios of carbon (12C/13C) or oxygen (16O/18O; 16O/17O) isotopes was observed on Mars. The 12C/13C isotopic ratio was found to be terrestrial with an uncertainty of 15%. Upper limits have been calculated for several minor constituents. With an effective noise equivalent radiance of 1.2 × 10?9 W cm?2 sr?1/cm?1, new upper limits in centimeter-atmospheres of 2 × 10?5 for C2H2, 4 × 10?3 for C2H4, 3 × 10?3 for C2H6, 2 × 10?4 for CH4, 1 × 10?3 for N2O, 1 × 10?4 for NO2, 4 × 10?5 for NH3, 1 × 10?3 for PH3, 7 × 10?4 for SO2, and 1 × 10?4 for OCS have been derived.  相似文献   

11.
The pattern of radial growth of an extended spoke recorded in the Voyager 2 low-resolution ring movie has been examined. This feature is atypical in that it orbits Saturn at the corotational rate for 1½hr after the onset of its formation and then undergoes a 40-min acceleration to sustained Keplerian velocities. The spoke exhibits two modes of radial growth. The first is a diffusion of material radially inward (at a rate of 101 ± 4m sec?1) and outward (at a rate of 40 ± 5m sec?1) that occurs throughout the feature's life. The second mode is a short-lived, rapid outward propagation of material (at a rate of 730 ± 70m sec?1) that occurs for approximately the first 50 min of the spoke's Keplerian dynamical phase. This rapid propagation, presumably driven by Lorentz forces acting on the negatively charged spoke particulates, allows charge-to-mass ratios for these particulates to be calculated at the onset of the propagation (?60 ± 1C kg?1), the termination of the propagation (?22 ± 2C kg?1), and the final dissipation of the spoke (?1.5 ± 0.2C kg?1). The value at the termination of the rapid propagation can be taken as an upper limit on the particulate charge-to-mass ratios of spokes which exhibit Keplerian velocities throughout their lifetimes. A correlation between the dynamical phases and the radial growth modes of the atypical spoke is observed, one that seems consistent with the plasma cloud model of spoke formation and evolution proposed by C. K. Goertz and G. Morfill (1983, Icarus53, 219–229), taken in the limit of high charge density.  相似文献   

12.
Abstract— The recently discovered Jiddat al Harasis (JaH) 073 strewn field is the largest found so far in the Sultanate of Oman, covering an area of 19 × 6 km. The 3463 single stones collected range in weight from 52.2 kg down to <1 g (total weight 600.8 kg) and show a pronounced mass sorting. The strewn field shape can be approximated by a NW‐SE‐oriented ellipsoid, indicating an atmospheric entry from SE at a low angle relative to the surface. The meteorite belongs to the L6 ordinary chondrite group and shows S4 average shock grade. Smaller stones generally show a higher weathering grade resulting in a spread from W2 and W4. Enhanced weathering of the stones causing fragmentation after the fall is observed in sandy depressions. Five 14C measurements on stones of variable size and weathering grade yielded 14C from 3.8 to 49.9 dpm/kg. Three samples give a 14C/ 10Be age consistent with about 14.4 ka. For two samples the cosmogenic, trapped, and radiogenic noble gases were measured. The ratio of the 4He and 40Ar gas retention ages of 0.29 ± 0.10 and that of the 3He and 21Ne cosmic ray exposure ages of 0.36 ± 0.08 Ma indicate that JaH 073 experienced a complex exposure history and lost 4He and 40Ar due to a major collision. Fragmentation statistics indicate a single major atmospheric disruption and an originally relatively spherical shape of the object. Assuming the material collected represents the majority of fallen mass, and 90–99% of the original weight was lost by ablation, the pre‐atmospheric minimum radius of the meteoroid with density 3.4 g cm?3would have been at least 75 cm.  相似文献   

13.
We report and describe an L6 ordinary chondrite fall that occurred in Ardón, León province, Spain (longitude 5.5605°W, latitude 42.4364°N) on July 9th, 1931. The 5.5 g single stone was kept hidden for 83 yr by Rosa González Pérez, at the time an 11 yr old who had observed the fall and had recovered the meteorite. According to various newspaper reports, the event was widely observed in Northern Spain. Ardón is a very well‐preserved, fresh, strongly metamorphosed (petrologic type 6), and weakly shocked (S3) ordinary chondrite with well‐equilibrated and recrystallized minerals. The mineral compositions (olivine Fa23.7±0.3, low‐Ca pyroxene Fs20.4±0.2Wo1.5±0.2, plagioclase An10.3±0.5Ab84.3±1.2), magnetic susceptibility (log χ = 4.95 ± 0.05 × 10?9 m3 kg?1), bulk density (3.49 ± 0.05 g   cm?3), grain density (3.58 ± 0.05 g   cm?3), and porosity (2.5 vol%) are typical for L6 chondrites. Short‐lived radionuclides confirm that the meteorite constitutes a recent fall. The 21Ne and 38Ar cosmic ray exposure ages are both about 20–30 Ma, similar to values for many other L chondrites. The cosmogenic 22Ne/21Ne ratio indicates that preatmospheric Ardón was a relatively large body. The fact that the meteorite was hidden in private hands for 83 yr makes one wonder if other meteorite falls may have experienced the same fate, thus possibly explaining the anomalously low number of falls reported in continental Spain in the 20th century.  相似文献   

14.
Three types of meteoritic material are found on the Moon: micrometeorites, ancien planetesimal debris from the ‘early intense bombardment’, and debris of recent, crater-forming projectiles. Their amounts and compositions have been determined from trace element studies. The micrometeorite component is uniformly distributed over the entire lunar surface, but is seen most clearly in mare soils. It has a primitive, C1-chondrite-like composition, and comprises 1-1.5% of mature soils. Apparently it represents cometary debris. The mean annual influx rate is 2.4 × 10?9 g cm?2 yr?1. It shows no detectable time variation or dependence on selenographic position. The ancient component is seen in highland breccias and soils more than 3.9 AE old. It has a fractionated composition, with volatiles depleted relative to siderophiles. The abundance pattern does not match that of any known meteorite class. At least two varieties exist (LN and DN, with Ir/Au, Re/Au 0.25-0.5 and > 0.5 the C1 value). Both seem to represent the debris of planetesimals that produced the mare basins and highland craters during the first 700 Myr of the Moon's history. It appears that the LN and DN objects impacted at less then 10 km s?1, had diameters less than 100 km, contained more than 15% Fe, and were not internally differentiated. Both were depleted in volatiles; the LN objects also in refractories (Ir, Re). This makes it unlikely that the LN bodies served as important building blocks of the Moon. The crater-forming component has remained elusive. Only a possible hint of this component has been seen, in ejecta from Dune Crater and Apollo 12 KREEP glasses of Copernican (?) origin.  相似文献   

15.
Differences in texture and discovery location prompted us to analyze 16 irons from Morasko; one from Seeläsgen, known to have a similar composition; and a new mass found at Jankowo Dolne. These were analyzed in duplicate by instrumental neutron‐activation analysis (INAA). The results show that all 18 samples have very similar compositions, distinct from all other IAB irons except Burgavli; we conclude that they are all from a single shower. Eight of the samples were from regions with large amounts of cohenite (but were largely free of inclusions) and six were from samples with very little cohenite; we could find no resolvable difference in composition between these sets, a fact that suggests that the C contents of the metal phases were similar in the two areas. Although Morasko has been classified into the IAB main group (IAB‐MG), its Ir plots well outside the main group field on an Ir‐Au diagram. We considered the possibility that the low Ir reflected contamination by a melt from a IAB region that ponded and experienced fractional crystallization; however, because Morasko has Pt, W, and Ga values that are the same as the highest values in IAB‐MG, we rejected this model. We therefore conclude that Morasko formed from a different melt than the IAB‐MG irons; the Morasko melt was produced by impact heating, but one or more of the main Ir carriers did not melt, leaving much of the Ir in the unmelted residue. Copper is the only element that shows resolvable differences among Morasko samples. Most (13 of 18) samples have 149 ± 4 μg g?1 Cu, but three have 213 ± 10 μg g?1; we interpret this to mean that the low‐Cu samples have equilibrated with a Cu‐rich phase, whereas there was none of the latter phase within a few diffusion lengths of the samples with high Cu contents.  相似文献   

16.
We have measured the shape and absolute value of Venus' reflectivity spectrum in the 1.2-to 4.0-μm spectral region with a circular variable filter wheel spectrometer having a spectral resolution of 1.5%. The instrument package was mounted on the 91-cm telescope of NASA Ames Kuiper Airborne Observatory, and the measurements were obtained at an altitude of about 41,000 feet, when Venus had a phase angle of 86°. Comparing these spectra with synthetic spectra generated with a multiple-scattering computer code, we infer a number of properties of the Venus clouds. We obtain strong confirmatory evidence that the clouds are made of a water solution of sulfuric acid in their top unit optical depth and find that the clouds are made of this material down to an optical depth of at least 25. In addition, we determine that the acid concentration is 84 ± 2% H2SO4 by weight in the top unit optical depth, that the total optical depth of the clouds is 37.5 ± 12.5, and that the cross-sectional weighted mean particle radius lies between 0.5 and 1.4 μm in the top unit optical depth of the clouds. These results have been combined with a recent determination of the location of the clouds' bottom boundary [Marov et al., Cosmic Res.14, 637–642 (1976)] to infer additional properties about Venus' atmosphere. We find that the average volume mixing ratio of H2SO4 and H2O contained in the cloud material both equal approximately 2× 10?6. Employing vapor pressure arguments, we show that the acid concentration equals 84 ± 6% at the cloud bottom and that the water vapor mixing ratio beneath the clouds lies between 6 × 10?4 and 10?2.  相似文献   

17.
As part of a large‐scale survey of meteorite bulk and grain densities, porosities, and magnetic susceptibilities, we measured these properties for 174 stones from 106 achondritic meteorites. These include four lunar meteorites, 15 stones from 10 shergottites, nakhlites, and chassignites (SNCs), 96 stones from 56 howardites, eucrites, and diogenites (HEDs), 17 stones from nine aubrites, two angrites, and 16 stones from 10 ureilites, four stones of three acapulcoites, as well as four stones of three lodranites, and 15 stones from eight primitive achondrites. Those meteorites derived from basalts and crustal material of differentiated parent bodies have lower densities and magnetic susceptibilities, on an average, than the more primitive achondrites, which have a higher percentage metal. A notable exception is the one chassignite in the study (Chassigny), which has a high grain density of 3.73 ± 0.04 g cm?3. Ureilites have magnetic susceptibilities consistent with primitive achondrites, but lower grain densities. Porosities do not vary considerably between most of the groups, with most stones 5–14% porous, although on an average, ureilites and brachinites have lower porosities, with most stones less than 7% porous. For primitive achondrites, the higher metal content causes finds to exhibit weathering effects similar to what is observed in ordinary chondrites, with a reduction in grain density, magnetic susceptibility, and porosity as compared with unweathered falls. For lunites, SNCs, and HEDs, no such effect is observed. We also observe that grain density and magnetic susceptibility used in conjunction distinguish shergottites, nakhlites, and chassignites from each other. Shergottites and nakhlites have low grain densities (averaging 3.31 and 3.41 g cm?3, respectively) whereas Chassigny is 3.7 g cm?3. In magnetic susceptibility, shergottities and chassignites are similar (averaging 2.85 and 2.98 in log units of 10?9 m3 kg?1, respectively) with nakhlites averaging higher at 3.42.  相似文献   

18.
On November 20, 2008, the Buzzard Coulee H4 chondrite fell to Earth outside of Lloydminster, Alberta, Canada. Eighteen fresh samples obtained by the National Meteorite Collection of Canada, ranging from 8.80 to 109.14 g, were investigated in this study. Physical properties of the samples were first obtained using a suite of nondestructive techniques. The bulk density (Archimedean bead method: 3.48 ± 0.04 g cm?3; 3‐D laser imaging: 3.46 ± 0.03 g cm?3; micro‐computed tomography: 3.44 ± 0.03 g cm?3), porosity (6.2 ± 0.1%), bulk magnetic susceptibility (log χ: 5.364 ± 0.056 × 10?9 m3 kg?1 at 825 Hz; 5.329 ± 0.052 × 10?9 m3 kg?1 at 19,000 Hz), and other derived magnetic properties (frequency dependence: 8.7 ± 6.2%; degree of anisotropy A%: 22.0 ± 2.0%; ellipsoid shape B%: ?18.7 ± 8.7%) are typical of H chondrites. The coefficient of variation associated with the properties measured directly was low (0.10–1.15%), indicating that the samples are homogenous at the interfragment scale. The study then proceeded with detailed analyses at the intrafragment scale. Visual inspection of micro‐computed tomographic images allowed the identification of an anomalous large clast with low metal content in a fragment. Another fragment exhibited macroscopic shock veins that warranted further examination. These fragments were cut and polished thin sections prepared for petrological analysis by optical and scanning electron microscopy. Based on mineralogical and textural similarities with several chondrules, the large clast was interpreted to be a macrochondrule. In a larger context, this study proposes a protocol for the systematic investigation of extraterrestrial material that can be exported to other new meteorite falls and finds, and specimens from sample return mission.  相似文献   

19.
We present two-year-long observations of the flux of very-high-energy (～1012 eV) gamma rays from the active galactic nucleus Mk 501 performed with a Cherenkov detector at the Crimean Astrophysical Observatory. A gamma-ray flux from the object was shown to exist at confidence levels of 11 and 7 standard deviations for 1997 and 1998, respectively. The flux varied over a wide range. The mean flux at energies >1012 eV, as inferred from the 1997 and 1998 data, is (5.0±0.6)×10?11 and (3.7±0.6)×10?11 cm?2 s?1, respectively. The errors are the sum of statistical observational and modeling errors. The mean power released in the form of gamma rays is ～2×1043 erg s?1 sr?1.  相似文献   

20.
Abstract— We report in situ magnesium isotope measurements of 7 porphyritic magnesium‐rich (type I) chondrules, 1 aluminum‐rich chondrule, and 16 refractory inclusions (14 Ca‐Al‐rich inclusions [CAIs] and 2 amoeboid olivine aggregates [AOAs]) from the ungrouped carbonaceous chondrite Acfer 094 using a Cameca IMS 6f ion microprobe. Both AOAs and 9 CAIs show radiogenic 26Mg excesses corresponding to initial 26Al/27Al ratios between ～5 × 10?5 ～7 × 10?5 suggesting that formation of the Acfer 094 CAIs may have lasted for ～300,000 years. Four CAIs show no evidence for radiogenic 26Mg; three of these inclusions (a corundum‐rich, a grossite‐rich, and a pyroxene‐hibonite spherule CAI) are very refractory objects and show deficits in 26Mg, suggesting that they probably never contained 26Al. The fourth object without evidence for radiogenic 26Mg is an anorthite‐rich, igneous (type C) CAI that could have experienced late‐stage melting that reset its Al‐Mg systematics. Significant excesses in 26Mg were observed in two chondrules. The inferred 26Al/27Al ratios in these two chondrules are (10.3 ± 7.4) × 10?6 (6.0 ± 3.8) × 10?6 (errors are 2σ), suggesting formation 1.6+1.2‐0.6 and 2.2+0.4‐0.3 Myr after CAIs with the canonical 26Al/27Al ratio of 5 × 10?5. These age differences are consistent with the inferred age differences between CAIs and chondrules in primitive ordinary (LL3.0–LL3.1) and carbonaceous (CO3.0) chondrites.  相似文献   

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