火星磁层中O^＋离子分布的理论研究     

史建魁 《天文学报》1999,40(1):76-82

对火星磁层中背阳面区来自电离层的Ｏ＋离子沿磁力线的密度和通量密度分布进行了理论研究．设火星的磁场由内禀磁场和感应磁场相叠加而成,结合不同的内禀磁矩条件进行了计算．结果表明：（１）随着火心距离的增大,火星磁层中Ｏ＋离子的密度和通量密度沿磁力线都呈现出下降趋势;（２）随着Ｚ坐标的增大,火星磁层中Ｏ＋离子的密度和通量密度先呈现出下降趋势,后又逐渐上升;（３）火星的内禀磁场越强,Ｏ＋离子的密度和通量密度沿磁力线下降得越快;（４）在火星磁尾一定距离处,Ｏ＋离子的密度和通量密度随磁矩的增大而减小．这样,可通过探测火星磁层中离子的密度和通量密度分布来确定火星内禀磁场的强弱  相似文献   

Organics in the solar system     

Sun Kwok 《天文和天体物理学研究(英文版)》2019,(4):1-6

Complex organics are now commonly found in meteorites, comets, asteroids, planetary satellites and interplanetary dust particles. The chemical composition and possible origin of these organics are presented. Specifically, we discuss the possible link between Solar System organics and the complex organics synthesized during the late stages of stellar evolution. Implications of extraterrestrial organics on the origin of life on Earth and the possibility of existence of primordial organics on Earth are also discussed.  相似文献   

云南西双版纳(曼桂)目击陨石的热变质和冲击变质研究     

罗业鑫  陈景有  梁伯健  廖世勇  李晔  李少林  吴蕴华  王英  邓志培  梅苞  徐伟彪 《天文学报》2019,60(5):1-14

曼桂陨石是新近(2018年6月1日)陨落在云南西双版纳地区的目击球粒陨石,其中的主要矿物为橄榄石(Fa_(24.3±0.6))、斜方辉石(Fs_(20.6±0.5)Wo_(0.4±0.2))、长石(An_(11-12)Or_(2-4))、铁镍金属和陨硫铁,次要矿物为铬铁矿、白磷钙矿等.橄榄石和辉石的化学成分表明曼桂陨石属于L型普通球粒陨石.陨石中球粒很少且轮廓不清晰,基质矿物普遍经历过重结晶,重结晶矿物颗粒粒径较大,高钙辉石粒径25–30μm,长石颗粒大多超过50μm,说明该陨石属于6型岩石类型.橄榄石和辉石颗粒中发育有波状消光、嵌晶块状消光现象、平面裂隙和面状变形构造,长石熔长石化并不完全,陨石中观察到宽度不等且纵横交错的冲击熔融脉,表明曼桂普通球粒陨石受到的冲击变质作用可以达到S5级以上.通过熔融脉中的矿物组合推断出熔融脉中矿物经历的压力在15–16 GPa左右.  相似文献   

Spectral heterogeneity on Phobos and Deimos: HiRISE observations and comparisons to Mars Pathfinder results     

N. Thomas  R. Stelter  A. Ivanov  N.T. Bridges  K.E. Herkenhoff  A.S. McEwen 《Planetary and Space Science》2011,59(13):1281-1292

The High-Resolution Imaging Science Experiment (HiRISE) onboard Mars Reconnaissance Orbiter (MRO) has been used to observe Phobos and Deimos at spatial scales of around 6 and 20 m/px, respectively. HiRISE (McEwen et al., JGR, 112, CiteID E05S02, DOI: 10.1029/2005JE002605, 2007) has provided, for the first time, high-resolution colour images of the surfaces of the Martian moons. When processed, by the production of colour ratio images for example, the data show considerable small-scale heterogeneity, which might be attributable to fresh impacts exposing different materials otherwise largely hidden by a homogenous regolith. The bluer material that is draped over the south-eastern rim of the largest crater on Phobos, Stickney, has been perforated by an impact to reveal redder material and must therefore be relatively thin. A fresh impact with dark crater rays has been identified. Previously identified mass-wasting features in Stickney and Limtoc craters stand out strongly in colour. The interior deposits in Stickney appear more inhomogeneous than previously suspected. Several other local colour variations are also evident.Deimos is more uniform in colour but does show some small-scale inhomogeneity. The bright “streamers” (Thomas et al., Icarus, 123, 536–556,1996) are relatively blue. One crater to the south-west of Voltaire and its surroundings appear quite strongly reddened with respect to the rest of the surface. The reddening of the surroundings may be the result of ejecta from this impact.The spectral gradients at optical wavelengths observed for both Phobos and Deimos are quantitatively in good agreement with those found by unresolved photometric observations made by the Imager for Mars Pathfinder (IMP; Thomas et al., JGR, 104, 9055–9068, 1999). The spectral gradients of the blue and red units on Phobos bracket the results from IMP.  相似文献   

Petrography of Yamato 984028 lherzolitic shergottite and its melt vein: Implications for its shock metamorphism and origin of the vein     

Shin Ozawa  Masaaki Miyahara  Eiji Ohtani  Makoto Kimura  Yoshinori Ito 《Polar Science》2011,4(4):550-557

Yamato 984028 (Y984028) is a newly identified lherzolitic shergottite, recovered from the Yamato Mountains, Antarctica, in 1999. As part of a consortium study, we conducted petrographic observations of Y984028 and its melt vein in order to investigate its shock metamorphism. The rock displays the typical non-poikilitic texture of lherzolitic shergottite, characterized by a framework of olivine, minor pyroxene (pigeonite and augite), and interstitial maskelynite. Shock metamorphic features include irregular fractures in olivine and pyroxene, shock-induced twin-lamellae in pyroxene, and the complete conversion of plagioclase to maskelynite, features consistent with those found in other lherzolitic shergottites. The melt vein is composed of coarse mineral fragments (mainly olivine) entrained in a matrix of fine-grained euhedral olivine (with several modes of compositional zoning) and interstitial glassy material. Some coarse olivine fragments consist of an assemblage of fine-grained euhedral to subhedral olivine crystals, suggesting shock-induced fragmentation, recrystallization, and/or a process of sintering. The implication is that the fine-grained olivine crystals in the matrix of the melt vein represent complicated crystallization environments and histories.  相似文献   

Effects of non-carbonaceous meteoritic extracts on the germination, growth and chlorophyll content of edible plants     

Vicente Marcano  Paula Matheus  Nelson Falcon 《Planetary and Space Science》2005,53(12):1263-1279

We have conducted an investigation on the effects that the extracts of a non-carbonaceous meteorite could have on the germination and growth of plants and the ability of non-carbonaceous meteoritic resource to serve as nutrient source for young plants of edible types. Selected plants were two dicotyledons (Lycopersicon esculentum and Daucus carota) and one monocotyledon (Zea mays). Solution cultures were developed using seeds, seedlings and seed-embryos. Meteoritic powder was obtained from the Vigirima mesosiderite, which was analyzed by X-ray diffraction and atomic absorption spectrometry (AAS). Results showed that extracts having variable concentrations of meteoritic matter favored an earlier germination in some plant species but the increase of the concentrations produced a decreased germination. However, total germination rate was higher in the presence of meteoritic extracts than in the presence of controls in the all species. A high metabolic yield in the protein synthesis was seen in dicotyledons utilizing Type-A and B extracts having concentrations of 4.16-8.33×10³ mg l⁻¹. Phaeophytinization index and chlorophyll a/b ratio, suggesting a negative effect of the heavy metals or acidic ions over the photosynthetic activity when extracts having high meteoritic concentrations were utilized. However, a higher chlorophyll (a) production in comparison to that of chlorophyll (b) was seen in extracts (Type-A and -B) with low concentrations of meteoritic matter. On the other hand, Z. mays seed-embryos growing in extracts (Type-D) having 3.53×10⁴ mg l⁻¹ of meteoritic matter showed a protein production (9.81×10⁻² mg protein mg wet wt⁻¹) higher than that observed in seed-embryos coming from extracts having lower concentrations. However, in Murashige medium, the seed-embryos exhibited a enhanced growth and a relatively higher protein production (10.3×10⁻² mg protein mg wet wt.⁻¹). Further, chlorophyll (a+b) synthesis was higher in Murashige medium than in meteoritic extracts but chlorophyll a/b ratio was <1 in all extracts and controls. Our results suggest the usefulness of the non-carbonaceous meteoritic resource as a complementary soil component or fertilizers for culture of edible plants in space settlements and mainly for the production of young plants due to the positive metabolic effects on the chlorophyll synthesis, mitochondrial metabolism and cellular division caused by PO₄³⁻, Fe²⁺, Cu²⁺ and Ca²⁺ ions. Earlier germination responses obtained in the present experiments demonstrated the possibility to utilize germination chambers in space having wet substrates containing meteoritic-powder solutions to obtain a higher number of seedlings in a minimum degree of time. These results also reveal the biological potential of this non-carbonaceous meteoritic matter for the growth of organisms in the early Earth, Mars, and probably in other planetary bodies beyond our Solar system.  相似文献   

Dust Production from the Hypervelocity Impact Disruption of Hydrated Targets     

G. J. Flynn  D. D. Durda  L. E. Sandel  M. M. Strait 《Earth, Moon, and Planets》2005,97(3-4):213-231

More than half of the C-type asteroids, which are the dominant type of asteroid in the outer half of the main belt, show evidence of hydration in their reflectance spectra. In order to understand the collisional evolution of asteroids, the production of interplanetary dust, and to model the infrared signature of small particles in the Solar System it is important to characterize the dust production from primary impact disruption events, and compare the disruption of hydrous and anhydrous targets. We performed impact disruption experiments of three “greenstone” targets, a hydrothermally metamorphosed basalt, and compared the results of these disruptions to our previous disruption experiments on porous, anhydrous basalt targets and to literature data on the disruption of non-porous, anhydrous basalt targets. The greenstone targets were selected because their major hydrous alteration phase is serpentine, the same hydrous alteration phase found in hydrous CM meteorites, like Murchison. The porous, anhydrous basalt targets were selected because their structure, consisting of millimeter-size olivine phenocrysts in a more porous, anhydrous matrix is similar to the structure of anhydrous chondritic meteorites, which consist of millimeter-size olivine chondrules embedded in a more porous, anhydrous matrix. The disruption measurements indicate the threshold collisional specific energy, Q _D^*, is 570 J/kg for the greenstone, which is lower than the literature values for non-porous basalt targets, and significantly lower than the value of 2500 J/kg that we have measured for porous anhydrous basalt targets. We determined the mass-frequency distribution of the debris from the disruption of the greenstone targets, which ranged in mass from 80 to 280 g, over a nine order-of-magnitude mass range, from ~10⁻⁹ g to the mass of the largest fragment. The cumulative mass-frequency distribution from the greenstone targets is fit by two power–law segments, one for masses >10⁻² g, which is significantly steeper than the corresponding segment from the disruption of similar-sized anhydrous basalt, and one in the range from 10⁻⁹ to 10⁻² g, which is significantly flatter than the corresponding segment from the disruption of similar size anhydrous basalt. These hydrous greenstone targets overproduce small fragments (10⁻⁴ to 10⁰ g) compared to anhydrous basalt targets, but underproduce dust-size grains (10⁻⁹ to 10⁻⁴ g) compared to anhydrous basalt targets.  相似文献   

Meteorites from Grove Mountains, Antarctica:An overview     

王道德  林杨挺 《极地研究(英文版)》2003,14(2)

Thirty-two meteorites were collected in Grove Mountains area, Antarctica, by the 15th and 16th Chinese Antarctic Research Expeditions (CHINARE). Petrography and mineral chemistry of these meteorites are reviewed, among which there are one Martian lherzolite, one eucrite, one ungrouped iron meteorite, and six unequili-brated and twenty-three equilibrated ordinary chondrites. An equilibrated ordinary chondrite GRV 98004 ( H5 ) has an unusually low cosmic-ray exposure age. Meteorite concentrating processes in Grove Mountains area are discussed. In addition, future studies on Grove Mountains (GRV) meteorites are proposed.  相似文献   

Near-IR spectral evidence for the presence of iron-poor orthopyroxenes on the surfaces of six M-type asteroids     

Paul S. Hardersen  Michael J. Gaffey  Paul A. Abell 《Icarus》2005,175(1):141-158

The first verifiable near-infrared absorption features in the ∼0.9-μm spectral region are reported for Asteroids 16 Psyche, 69 Hesperia, 110 Lydia, 125 Liberatrix, 201 Penelope, and 216 Kleopatra. These weak features (∼1-3%) are attributed to orthopyroxenes present on the surfaces of these asteroids. 16 Psyche and 125 Liberatrix have full rotational coverage while 69 Hesperia, 110 Lydia, 201 Penelope, and 216 Kleopatra have ∼75% rotational coverage. Qualitative ∼2-μm absorption features are present, but are very weak (<1%). Absorption band positions suggest relatively low abundances of calcium and iron in the pyroxenes. This indicates relatively reducing redox conditions for these asteroids, their parent bodies, and the nebular regions in which they formed. Four potential interpretations for these asteroids include: (1) they are exposed metallic cores or core fragments of differentiated parent bodies with residual orthopyroxene mantle material, (2) they are the result of a smelting-like reaction that converts olivine to pyroxene and metallic iron in the presence of carbon at high temperatures, (3) they are analogs to the primitive metal-rich Bencubbinite meteorites, or (4) they represent metallic surfaces which have accumulated silicate debris from external sources. Of the two original interpretations for the M-asteroids, the enstatite chondrite interpretation (Chapman and Salisbury, 1973, Icarus 19, 507-522; Gaffey and McCord, 1979, Mineralogical and petrological characterizations of asteroids. In: Gehrels T. (Ed.), Asteroids. Univ. of Arizona Press, Tucson, pp. 688-723) can be eliminated for these asteroids because the pyroxene in enstatite chondrites is iron-free and does not exhibit such absorption features. The iron meteorite interpretation remains valid, but with modification. For M-Asteroids 16 Psyche and 216 Kleopatra, these spectral results combined with previous determinations of high radar albedos indicate that these bodies are most probably exposed core fragments of differentiated bodies. M-Asteroids 69 Hesperia, 110 Lydia, 125 Liberatrix, and 201 Penelope exhibit similar spectral features consistent with exposed core fragments, but radar observations would be needed to confirm a high metal abundance. Observations of M-Asteroids 136 Austria and 325 Heidelberga suggest the absence of absorption features in the ∼0.4- to ∼2.5-μm region within the scatter of the data. Verification of the presence or absence of features across the surfaces of these two asteroids requires full rotational coverage. The interpretations for these “featureless” M-asteroids are not well-constrained, but remain consistent with the iron meteorite and enstatite chondrite interpretations.  相似文献   

Exposure ages and radiogenic ages of ureilite(GRV 024516) and ordinary chondrite(GRV 024517) from Antarctica     

王道德  缪秉魁  林杨挺 《极地研究(英文版)》2007,18(1):27-35

The GRV 024516 and GRV 024517 meteorite samples collected from Grove Montains,Antactica are ureilite and H5 ordinary chondrite,respectively.Based on the study of mineralogy-petrology,the cosmic-ray exposure ages and gas retention ages of these two meteorites were determinated and calculated.Their cosmic-ray exposure ages are 33.3 Ma,51.7 Ma,and gas retention ages are 1936.8 Ma and 3720 Ma,respectively.The ureilite contains diamond,graphite and amorphous C,which are mainly carrier of noble gases indicating obviously shock metamorphism effects,which induced 40Ar partial loss.The H5 chondrite indicates thermal metamorphism of parent body,its gas retention age fall the range between 3220 Ma and 4510 Ma of the least shocked H5 chondrites  相似文献