Geophysical Circumstances Of The 1908 Tunguska Event In Siberia,Russia

On the morning of June 30, 1908 a remarkable naturalphenomenon took place in the region to the north and north-west of Lake Baikal in Russia, which is now usually known as the Tunguska event. Despite the fact that a dozen explanations or more have been put forward to explain this event, its origin is still questionable.In this work geophysical circumstances of the Tunguskaevent are investigated. The research reveals that the event took place during a strong upsurge of tectonic activity in the Tunguska event region, and there were some peculiarities in tectonic activity even on larger scales. Also the event occurred during a change from a long period of "good" weather to a 'bad' one in the region. And there were also peculiarities in the atmosphere on larger scales at those times.In the author's opinion, this suggests that the Tunguskaevent was of geophysical origin. On much smaller scales similar geophysical events occur rather often.     

Insights into the petrogenetic history of the Northwest Africa 7635 augite-rich shergottite

The petrogenesis of the Northwest Africa (NWA) 7635 Martian meteorite involved the entrainment of xenocrystic olivine grains into a relatively magnesian and oxidized melt, followed by a redox-dependent reaction between olivine and melt that resulted in the crystallization of orthopyroxene and magnetite. Subsequent crystallization of the melt began with augite, plagioclase, and magnetite phenocrysts, and was followed by crystallization of augite, plagioclase, magnetite, ilmenite, and pyrrhotite in the groundmass, which took place under more rapid conditions of cooling, as reflected in the groundmass grain size. The petrogenetic history of NWA 7635 is similar in many ways to that of NWA 8159; this observation, coupled with similarities in geochemical and isotopic characteristics from other studies, suggests that the parent melts of the two rocks—as represented by all minerals except the xenocrystic olivine—were one and the same. The main distinctions between the two rocks are that their parent melts entrained xenocrystic olivine of different composition, and the cooling rate of the groundmass of NWA 7635 was more rapid than that of NWA 8159. The conclusion that the redox reaction took place between olivine and melt is in contrast to other work that suggests the reaction took place in the subsolidus, and has implications for the nature of the reaction in both NWA 7635 and NWA 8159.     

Atmospheric ionization and cosmic rays: studies and measurements before 1912

The discovery of cosmic rays, a milestone in science, was based on the work by scientists in Europe and the New World and took place during a period characterized by nationalism and lack of communication. Many scientists that took part in this research a century ago were intrigued by the penetrating radiation and tried to understand the origin of it. Several important contributions to the discovery of the origin of cosmic rays have been forgotten; historical, political and personal facts might have contributed to their substantial disappearance from the history of science.     

Quasi-Simultaneous Flux Emergence in the Events of October – November 2003

From late October to the beginning of November 2003, a series of intense solar eruptive events took place on the Sun. More than six active regions (ARs), including three large ARs (NOAA numbers AR 10484, AR 10486, and AR 10488), were involved in the activity. Among the six ARs, four of them bear obviously quasi-simultaneous emergence of magnetic flux. Based on the global Hα and SOHO/EIT EUV observations, we found that a very long filament channel went through the six ARs. This implies that there is a magnetic connection among these ARs. The idea of large-scale magnetic connectivity among the ARs is supported by the consistency of the same chirality in the three major ARs and in their associated magnetic clouds. Although the detailed mechanisms for the quasi-simultaneous flux emergence and the large-scale flux system formation need to be extensively investigated, the observations provide new clues in studying the global solar activity.     

Phyllosilicates in the matrix of the unique carbonaceous chondrite Lewis Cliff 85332 and possible implications for the aqueous alteration of CI chondrites

Abstract— The fine-grained matrix of the unique, unequilibrated carbonaceous chondrite Lewis Cliff (LEW) 85332 has been studied by scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and transmission electron microscopy (TEM). Compositionally, LEW 85332 has a matrix that is more Fe-rich than typical CI chondrites but has elemental abundance ratios that appear to be closer to CI matrices than to CM or CR chondrites. The mineralogy of the matrix is dominated by phyllosilicate phases that are predominantly interlayered Fe-rich serpentine/saponite; anhydrous silicate phases such as olivine and pyroxene are rare. Minor magnetite, troilite and ferrihydrite also occur associated with the phyllosilicates. Despite the high degree of weathering in LEW 85332, the phyllosilicates appear to have an extraterrestrial origin, but the highly variable Mg/Fe ratios of saponite may be the result of partial terrestrial oxidation of Fe-rich saponite to a more Mg-rich saponite and ferrihydrite. Alternatively, some of the ferrihydrite may have formed as a result of terrestrial weathering of Fe-Ni metal. The compositional and mineralogical data suggest that the matrix of LEW 85332 may represent a very early stage in the type of aqueous alteration experienced by the CI chondrites, although it is improbable that LEW 85332 was a precursor to the CI chondrites because of its high abundance of chondrules. The absence of carbonates, the high-Fe content of the matrix and phyllosilicate phases and relatively low abundance of magnetite all indicate that the degree of oxidation and leaching of LEW 85332 matrix was significantly less than that experienced by the CI chondrites. The absence of clear evidence for alteration of chondrules suggests that either the formation of the hydrous phases in the matrix occurred prior to accretion or that alteration occurred on a parent body and involved limited amounts of fluid, such that the reactions took place preferentially and exclusively within the fine-grained (anhydrous?) matrix materials.     

Classical symbiotic star Z And during the recent activity period

The results of study of the classical symbiotic star Z And during the recent activity period that began in 2000 are presented. Up to now series of six outbursts took place. Comparison of observational data with the results of gasdynamic modeling allow us to suggest the possible scenario for activity in this system describing all stages of an outburst development—from the mechanism of transition to the outburst and outburst development to the behavior of the system during all the activity period. Particularly, the proposed scenario explains the principal difference between outbursts—the presence of high-velocity bipolar collimated optical outflows in strong recurring outbursts. We have not found contradictions with the available data for previous outbursts of Z And. We assume that the proposed scenario could be also typical for other classic symbiotic stars. In order to check and improve our model additional observations are highly desirable and the UV spectral range could provide us with very useful data.     

The petrography,mineralogy and origins of calcium sulphate within the Cold Bokkeveld CM carbonaceous chondrite

Abstract— A detailed scanning and transmission electron microscopy study of Cold Bokkeveld has shown that calcium sulphate is widespread, occluding ～30 μm wide matrix-cutting fractures in addition to μm-sized veins and irregular dissolution pores within calcitized chondrules, matrix calcite grains and Ca- and Al-rich inclusions (CAI). The majority of calcium sulphate crystals have fibrous habits, especially those which have grown within straight-sided fractures and veins. Mineralogically, the calcium sulphate is composed of a fine-scale mixture of hemihydrate and anhydrite which have probably formed by the dehydration of primary gypsum during sample preparation. In all contexts, calcium sulphate precipitation was the last identifiable diagenetic event in the pre-terrestrial history of Cold Bokkeveld and followed pervasive aqueous alteration of the meteorite matrix to phyllosilicates. The fibrous fracture- and vein-filling calcium sulphates are morphologically similar to a terrestrial form of gypsum termed “satinspar” and so may have formed in a similar manner by precipitation from supersaturated aqueous solutions during fracture and vein dilation. The aqueous solutions were most probably generated by melting of water ice due to internal heating and/or post-accretional impact heating of the parent body. Although impact-produced fractures and veins may have provided conduits for fluid advection, the dissolution of calcite, alteration of metal sulphides and precipitation of gypsum probably took place when aqueous solutions were more-or-less static. Despite their similarity to late-stage mineralized fractures in CI meteorites, the calcium sulphate-filled fractures in Cold Bokkeveld probably do not have any significance regarding a shared CM-CI parent body.     

Spectroscopic Coronal Observations During the Total Solar Eclipse of 11 July 2010

The flash spectra of the solar chromosphere and corona were measured with a slitless spectrograph before, after, and during the totality of the solar eclipse of 11 July 2010, at Easter Island, Chile. This eclipse took place at the beginning of Solar Cycle 24, after an extended minimum of solar activity. The spectra taken during the eclipse show a different intensity ratio of the red and green coronal lines compared with those taken during the total solar eclipse of 1 August 2008, which took place toward the end of Solar Cycle 23. The characteristic coronal emission line of forbidden Fe xiv (5303 Å) was observed on the east and west solar limbs in four areas relatively symmetrically located with respect to the solar rotation axis. Subtraction of the continuum flash-spectrum background led to the identification of several extremely weak emission lines, including forbidden Ca xv (5694 Å), which is normally detected only in regions of very high excitation, e.g., during flares or above large sunspots. The height of the chromosphere was measured spectrophotometrically, using spectral lines from light elements and compared with the equivalent height of the lower chromosphere measured using spectral lines from heavy elements.     

Intense Geomagnetic Storms Associated with Coronal Holes Under the Weak Solar-Wind Conditions of Cycle 24

The activity of Solar Cycle 24 has been extraordinarily low. The yearly averaged solar-wind speed is also lower in Cycle 24 than in Cycles 22 and 23. The yearly averaged speed in the rising phase of Cycle 21 is as low as that of Cycle 24, although the solar activity of Cycle 21 is higher than that of Cycle 24. The relationship between the solar-wind temperature and its speed is preserved under the solar-wind conditions of Cycle 24. Previous studies have shown that only a few percent of intense geomagnetic storms (minimum \(\mathrm{Dst} < -100\) nT) were caused by high-speed solar-wind flows from coronal holes. We identify two geomagnetic storms associated with coronal holes within the 19 intense geomagnetic storms that took place in Cycle 24.     

Offshore evidence for Neogene uplift in central West Greenland

Multi-channel seismic lines off southern and central West Greenland show a >3-km-thick sedimentary section of mid-Eocene and younger age that dips seaward and is truncated either at the seabed or by an erosional unconformity a short distance below the seabed. This pattern indicates that there has been uplift and erosion of the section and probably of the nearby landmass. The timing of the uplift is not well constrained by borehole data, but certainly took place after the early Eocene, probably during the Neogene and possibly as late as the onset of glaciation in West Greenland in the early Pliocene. The uplift took place substantially later than the cessation of magmatism in the early Eocene and the abrupt slowing or cessation of sea-floor spreading in the Labrador Sea between Chrons 20 and 13 (middle–late Eocene). This means that, whatever the cause of the uplift, it is unlikely to be directly related to processes either of magmatic emplacement or sea-floor spreading.     

Cover

Brecciated and hydrothermally altered orthogneiss‐amphibolite complex in the Maniitsoq structure, West Greenland. Inset: variably hydrothermally altered zircon with reset U‐Pb systematics, yielding a hydrothermal age of 3000.9 ± 1.9 Ma. The hydrothermal alteration of regional extent took place at upper amphibolite facies, and is interpreted as due to infl ux of (sea?) water and development of a crustal‐scale hydrothermal convection cell in a now deeply exhumed Archaean impact structure. A. Scherstén and A. A. Garde discuss the details in their paper on pp. 1472–1498. (Images courtesy of Adam Garde and Leif Johansson.)     

Comments on the course of solar activity during the declining phase of solar cycle 20 (1970–74)

In the declining phase of solar cycle 20 (1970–74) three pulses of activity occurred and resulted in two well defined ‘stillstands’ in the smoothed means of sunspot, 2800 MHz, and calcium plage data. Marked diminutions in spot and 2800 MHz flux took place in 1970 and 1971, respectively, and were accompanied by concomitant decreases in flare-occurrence. Studies of the latitude distribution of spots and flares show the extent of the dominance of the northern hemisphere in cycle 20 and the marked phase shift between northern and southern hemispheres. In the years studied, the longitudes of centers of activity clustered in identifiable zones or hemispheres for relatively long intervals of time. From mid-1973 to mid-1974 the Sun had a relatively inactive hemisphere centered on ～0° longitude. The relationship of certain well defined ‘coronal holes’ to this inactive hemisphere of the chromosphere is noted. The first two spot groups of the new cycle formed in November 1974 and January 1975 in the longitude zone associated with relatively high levels of old cycle activity, a repetition of the pattern observed in 1963–64.     

Petrogenesis of the EET 92023 achondrite and implications for early impact events

We report petrology and geochemistry of an achondrite EET 92023 and compare it with normal and anomalous eucrites. EET 92023 is an unbrecciated achondrite and shows a granular texture mainly composed of low‐Ca pyroxene and plagioclase, petrologically similar to normal cumulate eucrites such as Moore County. However, this rock contains a significant amount of kamacite and taenite not common in unbrecciated, crystalline eucrites. EET 92023 contains a significant amount of platinum group elements (PGEs) (ca. 10% of CI), several orders of magnitude higher than those of monomict eucrites. We suggest that the metallic phases carrying PGEs were incorporated by a projectile during or before igneous crystallization and thermal metamorphism. The projectile was likely to be an iron meteorite rather than chondritic materials, as indicated by the lack of olivine and the presence of free silica. Therefore, the oxygen isotopic signature is indigenous, rather than due to contamination of the projectile material with different oxygen isotopic compositions. A significant thermal event involving partial melting and metamorphism after the impact event indicates that EET 92023 records early impact events which took place shortly after the crust formation on a differentiated protoplanet when the crust was still hot.     

Magnetic field changes associated with a sub-flare and surge

A sub-flare and surge were observed on June 13, 1990, with the Marshall Space Flight Center vector magnetograph and coaligned H telescope. This activity occurred at the site of a parasitic polarity near a large, mature sunspot. Analysis of the vector magnetic field showed that while flux emergence and other field changes occurred sporadically throughout a period of 4 days, the sub-flare and surge only took place after an increase in magnetic shear in the field of the parasitic polarity. This event also provided an example of relaxation of magnetic shear following the flare and surging.     

Measurement and analysis of magnetic field variation during a class 2b flare

We report a digital analysis of high-time-resolution videomagnetograms taken during a class 2b flare that occurred at 60° east. The data were obtained at the Big Bear Observatory and calibrated by a Mt. Wilson magnetogram. Changes of weak magnetic fields (less than 100 G) with an amplitude from 30 to 100% have been detected over 55% of the optical flare region, apparently taking place at the initial phase of the flare. Statistical considerations suggest a real flare association with most of these changes.H observations show that large changes took place over the footpoints of heavily inclined structures like penumbral fibrils, while smaller changes took place over the plage region. An apparent polarity reversal was found at the feet of erupted fibrils.Based on force-free field calculations these changes can be reasonably explained as a transformation of the current-carrying fields to potential fields which produced large changes in the field line inclination and rotation.Visiting Associate, Summer 1977.     

Ceres’ spectral link to carbonaceous chondrites—Analysis of the dark background materials

Ceres’ surface has commonly been linked with carbonaceous chondrites (CCs) by ground‐based telescopic observations, because of its low albedo, flat to red‐sloped spectra in the visible and near‐infrared (VIS/NIR) wavelength region, and the absence of distinct absorption bands, though no currently known meteorites provide complete spectral matches to Ceres. Spatially resolved data of the Dawn Framing Camera (FC) reveal a generally dark surface covered with bright spots exhibiting reflectance values several times higher than Ceres’ background. In this work, we investigated FC data from High Altitude Mapping Orbit (HAMO) and Ceres eXtended Juling (CXJ) orbit (~140 m/pixel) for global spectral variations. We found that the cerean surface mainly differs by spectral slope over the whole FC wavelength region (0.4–1.0 μm). Areas exhibiting slopes ?1 constitute only ~3% of the cerean surface and mainly occur in the bright material in and around young craters, whereas slopes ≥?10% μm^?1 occur on more than 90% of the cerean surface; the latter being denoted as Ceres’ background material in this work. FC and Visible and Infrared Spectrometer (VIR) spectra of this background material were compared to the suite of CCs spectrally investigated so far regarding their VIS/NIR region and 2.7 μm absorption, as well as their reflectance at 0.653 μm. This resulted in a good match to heated CI Ivuna (heated to 200–300 °C) and a better match for CM1 meteorites, especially Moapa Valley. This possibly indicates that the alteration of CM2 to CM1 took place on Ceres.     

Chocolate tablet aspects of tectonics of Meshkenet Tessera on Venus

The intrablock deformation of Meshkenet Tessera on Venus is mostly due to responses of the uppermost surface bedrock to tensional stresses. It is found that complex deformation structures within the highland blocks resemble those of formed in chocolate tablet boudinaging which has taken place after original parallel faulting and bar-like crustal block formation. The high-angle tessera structures with varying cross-cutting relations define styles and locations of multiphase deformation most evidently related to local relaxation of tessera topography. Series of progressive or superposed fracturing events with alternating fault directions took place at high angles during this relaxational deformation. Compressional ridges often surround these tesserae.     

HaleBopp彗星的爆发活动

９９６ 年９ 月至１１ 月间,对ＨａｌｅＢｏｐｐ 彗星进行了照相和光电观测．给出观测结果,包括几次爆发和可能的爆发活动     

Identification of a new outflow channel on Mars in Syrtis Major Planum using HRSC/MEx data

Syrtis Major Planum is a volcanic plain dominated by lava flows. High resolution stereo camera (HRSC) images of the northern Syrtis Major region display erosional features such as grooves, teardrop-shaped islands and valleys. These landforms are characteristics of outflow channels seen on Mars, therefore implying that a flood event took place in this region. The flow of 100 km long and a few kilometer wide followed the local slopes in most locations. Maximum flood discharges estimated from images and topography vary from about 0.3×10⁶ to 8×10⁶ m³/s, and therefore are in the range of terrestrial mega-floods in the Scablands or Lake Bonneville. In North Syrtis Major, the relationships with surrounding lava flows and the timing of the flood coeval to Syrtis Major volcanic activity suggest that it could be related to the subsurface water discharge mobilized by the volcanic activity. The proximity of Noachian age basement rocks 20 km away from the flood and below lava flows might have played a role in its formation and water presence.     

The validity of the continuum limit in the gravitational N-body problem

This paper attempts to give quantitative as well as qualitative answers to the question of the analogy between smooth potentials and N-body systems. A number of simulations were performed in both integrable and nonintegrable smooth environments and their frozen N-body analogues, and comparisons were made using a number of different tools. The comparisons took place on both statistical and pointwise levels. The results of this study suggest that microscopic chaos associated with discreteness effects is always present in N-body configurations. This chaos is different from the macroscopic chaos which is associated with the bulk potential and persists even for very large N. Although the Lyapunov exponents of orbits evolving in N-body environments do not decrease as N increases, comparisons associated with the statistical properties, as well as with the power spectra of the orbits, affirm the existence of the continuum limit.