共查询到20条相似文献，搜索用时 15 毫秒
1.
The problem of electromagnetic perturbations of charged dust particle orbits in interplanetary space has been re-examined in the light of our better understanding of the large scale spatial and temporal interplanetary plasma and field topology. Using both analytical and numerical solutions for particle propagation it was shown that: (1) stochastic variations induced by electromagnetic forces are unimportant for the zodiacal dust cloud except for the lowest masses, (2) systemetic variations in orbit inclinations are unimportant if orbital radii are larger than 10 a.u. This is due to the solar cycle variation in magnetic polarity which tends to cancel out systematic effects, (3) systematic variations in orbital parameters (inclination, longitude of ascending node, longitude of perihel) induced by electromagnetic forces inside 1 a.u. tend to shift the plane of symmetry of the zodiacal dust cloud somewhat towards the solar magnetic equatorial plane, (4) inside 0.3 a.u. there is a possibility that dust particles may enter a region of “magnetically resonant” orbits for some time. Changes in orbit parameters are then correspondingly enhanced, (5) the observed similarity of the plane of symmetry of zodiacal light with the solar equatorial plane may be the effect of the interaction of charged interplanetary dust particles with the interplanetary magnetic field. Numerical orbit calculation of dust particles show that one of the results of this interaction is the rotation of the orbit plane about the solar rotational axis. 相似文献
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Shear and compressional dust Alfvén solitons in a magnetized plasma medium of opposite polarity dust
A. A. Mamun 《Astrophysics and Space Science》2014,351(1):173-179
Shear and compressional dust Alfvén solitons propagating in a medium of opposite polarity magnetized dust fluids have been theoretically studied by using the reductive perturbation method. The derivative nonlinear Shrödinger (DNLS) and Korteweg-de Vries (K-dV) equations, and their stationary solitonic solutions have been derived to identify the basic properties of shear and compressional dust Alfvén solitons. It is found that the opposite polarity dust medium under consideration supports the shear and compressional dust Alfvén solitons having new features with new (slow) time and (large) length scales. The basic features (amplitude and width) of the shear dust Alfvén solitons are found to be significantly different from those of the compressional ones. The importance of our results in understanding the nonlinear (localized) electromagnetic wave phenomena in space environments and laboratory devices is briefly discussed. 相似文献
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《Planetary and Space Science》1999,47(3-4):363-383
The Ulysses spacecraft is orbiting the Sun on a highly inclined ellipse (i = 79°). After its Jupiter flyby in 1992 at a heliocentric distance of 5.4 AU, the spacecraftreapproached the inner solar system, flew over the Suns south polar region in September 1994,crossed the ecliptic plane at a distance of 1.3 AU in March 1995, and flew over the Suns northpolar region in July 1995. We report on dust impact data obtained with the dust detector onboardUlysses between January 1993 and December 1995. We publish and analyse the complete dataset of 509 recorded impacts of dust particles with masses between 10−16 g–10−7 g. Together with 968 dust impacts from launch until the end of 1992 published earlier (Grün et al., 1995c), information about 1477 particles detected with theUlysses sensor between October 1990 and December 1995 is now available. The impact ratemeasured between 1993 and 1995 stayed relatively constant at about 0.4 impacts per day andvaried by less than a factor of ten. Most of the impacts recorded outside about 3.5 AU arecompatible with particles of interstellar origin. Two populations of interplanetary particles havebeen recognized: big micrometer-sized particles close to the ecliptic plane and smallsub-micrometer-sized particles at high ecliptic latitudes. The observed impact rate is comparedwith a model for the flux of interstellar dust particles which gives relatively good agreement withthe observed impact rate. No change in the instruments noise characteristics or degradation of thechanneltron could be revealed during the three-year period. 相似文献
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The currently available infrared data on scattered light from the dust comae of ernis and Bowell set stringent upper limits to the contribution of icy grains. For Comet ernis the data is consistent with only a 10% mass fraction of water-ice included within silicate-organic-carbon grains of scale radius 15 microns, while for Comet Bowell there is no evidence for any ice component. A coma of small (10–100m) organic grains containing a fraction of OH-bearing molecules that evaporate over weeks at 5 AU and leave an absorptive carbonaceous grain residue is the simplest model for Comet Bowell. 相似文献
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Infrared spectra obtained from the Mariner 9 spacecraft during the 1971–1972 dust storm are used to derive information on the composition and particle size distribution of the dust and to study the time evolution of the storm. The dust is not composed of pure granite, basalt, basaltic glass, obsidian, quartz, andesite, or montmorillonite. The infrared spectra suggest that the dust is a mixture of materials, dominated by igneous silicates with >62;60% SiO2, or weathering products such as clay minerals, but the dust could possibly have a significant component of lower SiO2 materials such as basalt. Substantial quantities of carbonates, nitrates, or carbon suboxide are excluded from the mixture. All infrared, visible, and ultraviolet data on the Martian surface composition seem consistent with a mixture of basalt and clay minerals or high SiO2 igneous rocks, with a surface patina of oxides of iron. For all candidate compositions, the data are best matched with a size distribution that approximates a differential power law function of slope ?4. This size distribution is quite similar to terrestial size distributions in regions remote from sources of dust. The relative abundance of particles between 1- and 10-μm radius did not change during the Mariner 9 mission; thus suspended particles did not experience Stokes-Cunningham fallout but instead were supported by turbulence with an eddy diffusion coefficient, . The aerosol optical depth, standardized to 0.3-μm wavelength, varied from about 1.5 early in the mission to about 0.2 at Orbit 200. 相似文献
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Yu. N. Mishurov I. A. Acharova M. G. Shevchenko D. A. Tyshlangov 《Astrophysical Bulletin》2014,69(1):21-26
A new mechanism of sweeping out of dust grains beyond galactic disks both in the radial direction along the galactic plane and in the vertical, cross-disk direction is proposed. The mechanism is driven by the interaction of dust grains with the bisymmetric nonstationary magnetic field of the galaxy, whose lines are curved and corotate with the stellar spiral density wave responsible for the arms. We attribute the radial transfer of interstellar dust grains in the plane of galactic disks to the fact that charged dust grains are “glued” to magnetic field lines and are therefore pushed outward because of the rotation of magnetic field lines and their tilt with respect to the radial direction parallel to the disk plane. In addition, dust is swept out vertically in the cross-disk direction because of the drift motion in crossed magnetic and gravitational fields (both are parallel to the galactic plane). Numerical computations of the motion of dust grains in real magneto-gravitational fields with the allowance for the drag force from interstellar gas show that the time scale of dust grain transport beyond galactic disks is on the order of 1 Gyr or shorter. 相似文献
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William M. Farrell Jan-Erik Wahlund Michiko Morooka Donald A. Gurnett William S. Kurth Robert J. MacDowall 《Icarus》2012,219(1):498-501
As the saturnian magnetoplasma sweeps past Enceladus, it experiences both a decrease in electron content and sharp slowdown in the northern hemisphere region within ～5 Enceladus Radii (Re). This slowdown is observed by Cassini in regions not obviously associated with the southern directed plume-originating ions. We suggest herein that the decrease in northern hemisphere electron content and plasma slowdown could both be related to the presence of fine dust grains that are being accelerated by the Lorentz force created within the saturnian magnetic field system. 相似文献
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Corrado Massa 《Astrophysics and Space Science》2008,317(1-2):139-141
We find that Einstein’s like field equations with coordinate-dependent cosmological “constant” Λ(x i ) imply a non geodesic law of motion for test particles moving in a continuous distribution of incoherent matter (“dust”). The deviation from the geodesic law depends on the derivatives ?Λ/? x i and, in the weak field approximation, causes an anomalous acceleration A～(Vc 2/γ ρ)?Λ/? t+(c 4/γ ρ)?Λ/? r where V=dr/dt, c=the speed of light, γ=8π G with G=the gravitational coupling, ρ=the mass density of the cloud, r and t are the radial and time coordinate respectively. Reasonable assumptions on Λ=Λ(t) give A<10?8 cm/s2 when ρ>10?29 g/cm3 i.e. in all known astrophysical systems. A possible connection with the anomalous Pioneer acceleration is shortly discussed in the case of a cosmological “constant” coupled to matter. 相似文献
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《Planetary and Space Science》1999,47(8-9):1029-1050
We predict the amount of cometary, interplanetary, and interstellar cosmic dust that is to be measured by the Cometary and Interstellar Dust Analyzer (CIDA) and the aerogel collector on board the Stardust spacecraft during its fly-by of comet P⧸Wild 2 and during the interplanetary cruise phase. We give the dust flux on the spacecraft during the encounter with the comet using both, a radially symmetric and an axially symmetric coma model. At closest approach, we predict a total dust flux of 1060 m−2 s−1 for the radially symmetric case and 1065 m−2 s−1 for the axially symmetric case. This prediction is based on an observation of the comet at a heliocentric distance of 1.7 AU. We reproduce the measurements of the Giotto and VEGA missions to comet P⧸Halley using the same model as for the Stardust predictions. The planned measurements of interstellar dust by Stardust have been triggered by the discovery of interstellar dust impacts in the data collected by the Ulysses and Galileo dust detector. Using the Ulysses and Galileo measurements we predict that 25 interstellar particles, mainly with masses of about 10−12 g, will hit the target of the CIDA experiment. The interstellar side of the aerogel collector will contain 120 interstellar particles, 40 of which with sizes greater than 1 μm. Furthermore, we investigate the contamination of the CIDA and collector measurements by interplanetary particles during the cruise phase. 相似文献
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Malte Willmes Dennis Reiss Harald Hiesinger Michael Zanetti 《Planetary and Space Science》2012,60(1):199-206
The mid- and high-latitudes of Mars are covered by a smooth young mantle that is interpreted as an atmospherically derived air-fall deposit of ice and dust related to recent climate changes. In order to determine relative and absolute ages of this surface unit within the southern hemisphere, a systematic survey of all available HiRISE and CTX images in the Malea Planum region from 55–60°S latitude and 50–70°E longitude was performed and the distribution and the morphology of small impact craters on the mantle deposit were investigated. Using crater size-frequency measurements, we derived absolute model ages of ～3–5 Ma for the surface of the mantle, immediately south of the Hellas basin rim. Morphologic observations of the mantle, its fresh appearance, very low number of craters, and superposition on older units support this very young Amazonian age. Nearly all observed craters on the smooth mantle in Malea Planum are small and show signs of erosion, evidence for the ongoing modification of the ice–dust mantle. However, this modification has not been strong enough to reset the surface age. Compared to the ice–dust mantle at higher latitudes in the northern and southern hemisphere, the surface of the mantle in Malea Planum is older and thus has been relatively stable during obliquity changes in the last ～3–5 Ma. This is consistent with the hypothesis that the ice–dust mantle is a complex surface deposit of different layers, that shows a strong latitude dependence in morphology and has been deposited and degraded at different times in martian history. 相似文献
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A continuity equation is developed to model the evolution of a swarm of self-propelled ‘smart dust’ devices in heliocentric orbit driven by solar radiation pressure. These devices are assumed to be MEMs-scale (micro-electromechanical systems) with a large area-to-mass ratio. For large numbers of devices it will be assumed that a continuum approximation can be used to model their orbit evolution. The families of closed-form solutions to the resulting swarm continuity equation then represent the evolution of the number density of devices as a function of both position and time from a set of initial data. Forcing terms are also considered which model swarm sources and sinks (device deposition and device failure). The closed-form solutions presented for the swarm number density provide insights into the behaviour of swarms of self-propelled ‘smart dust’ devices an can form the basis of more complex mission design methodologies. 相似文献
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N. R. Tanvir A. J. Levan E. Rol R. L. C. Starling J. Gorosabel R. S. Priddey D. Malesani P. Jakobsson P. T. O'Brien A. O. Jaunsen J. Hjorth J. P. U. Fynbo A. Melandri A. Gomboc B. Milvang-Jensen A. S. Fruchter M. Jarvis C. A. C. Fernandes T. Wold 《Monthly notices of the Royal Astronomical Society》2008,388(4):1743-1750
Gamma-ray bursts (GRBs) are powerful probes of the early Universe, but locating and identifying very distant GRBs remain challenging. We report here the discovery of the K -band afterglow of Swift GRB 060923A, imaged within the first hour post-burst, and the faintest so far found. It was not detected in any bluer bands to deep limits, making it a candidate very high- z burst ( z ≳ 11) . However, our later-time optical imaging and spectroscopy reveal a faint galaxy coincident with the GRB position which, if it is the host, implies a more moderate redshift (most likely z ≲ 2.8 ) and therefore that dust is the likely cause of the very red-afterglow colour. This being the case, it is one of the few instances so far found of a GRB afterglow with high-dust extinction. 相似文献
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《New Astronomy》2004,9(1):33-42
We obtained low resolution (R=100) mid-infrared (8–13 μm wavelengths) spectra of 8 nearby young main sequence stars with the Keck 1 telescope and Long-Wavelength Spectrometer (LWS) to search for 10 μm silicate (Si–O stretch) emission from circumstellar dust. No stars exhibited readily apparent emission: Spectra were then analyzed by least-squares fitting of a template based on a spectrum of Comet Hale-Bopp. Using this technique, we were able to constrain the level of silicate emission to a threshold 10 times below what was previously possible from space. We found one star, HD 17925, with a spectrum statistically different from its calibrator and consistent with a silicate emission peak of 7% of the photosphere at a wavelength of 10 μm. Excess emission at 60 μm from this star has already been reported. 相似文献
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《Planetary and Space Science》1999,47(6-7):781-785
Amorphous silicate dust grains have been produced in the laboratory by means of laser ablation of solid targets in different ambient atmospheres. In this work we show that, if the condensation occurs in the presence of hydrogen, the spectra of silicate grains, together with the characteristic 10 and 20 μm features, exhibit an absorption band around 4.6 μm. Such features, absent in the spectra of the same silicate grains produced in an oxygen atmosphere, may be attributed to a fundamental stretching vibration of –SiH functional groups bound into the grains or on their surface.Based on the cosmic abundance of the elements, silicates are expected to condense in the atmospheres of oxygen-rich stars where hydrogen is also abundant. This means that –SiH functional groups may be present also in the circumstellar and interstellar silicate dust grains. An absorption feature at 4.6 μm has already been observed in the absorbing dust of several protostellar embedded sources. The observation of a similar feature in comets can give important information on the origin and evolution of cometary material. © 1999 Elsevier Science Ltd. All rights reserved. 相似文献
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Bogdan Wszolek Konrad Rudnicki Silvia Masi Paolo De Bernardis Antonio Salvi 《Astrophysics and Space Science》1989,152(1):29-34
We used theIRAS All Sky Maps in order to search for infrared emission in the direction of the Okroy Cloud (R.A.=12h50m, =22°). An enhancement of 100 m diffuse emission is evident in such a region, with an anomalous value of the ratioI
v (100 m)/A
v
; hydrogen 21 cm emission is also present with low radial speed, thus suggesting that the cloud could be a satellite of our Galaxy. 相似文献
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Based on recent evidence that oxide grains condensed from a plasma will contain oxygen that is mass‐independently fractionated compared to the initial composition of the vapor, we present a first attempt to evaluate the potential magnitude of this effect on dust in the primitive solar nebula. This assessment relies on previous studies of nebular lightning to provide reasonable ranges of physical parameters to form a very simple model to evaluate the plausibility that lightning could affect a significant fraction of nebular dust and that such effects could cause a significant change in the oxygen isotopic composition of solids in the solar nebula over time. If only a small fraction of the accretion energy is dissipated as lightning over the volume of the inner solar nebula, then a large fraction of nebular dust will be exposed to lightning. If the temperature of such bolts is a few percent of the temperatures measured in terrestrial discharges, then dust will vaporize and recondense in an ionized environment. Finally, if only a small average decrease is assumed in the 16O content of freshly condensed dust, then over the last 5 Myr of nebular accretion the average Δ17O of the dust could increase by more than 30 per mil. We conclude that it is possible that the measured “slope 1” oxygen isotope line measured in meteorites and their components represents a time‐evolution sequence of nebular dust over the last several million years of nebular evolution where 16O‐rich materials formed first, then escaped further processing as the average isotopic composition of the dust gradually became increasingly depleted in 16O. 相似文献