共查询到20条相似文献，搜索用时 593 毫秒
1.
Everett K. Gibson Jr. 《Earth, Moon, and Planets》1975,13(1-3):321-326
The abundances and distributions of carbon, nitrogen, and sulfur in lunar soils are reviewed. Carbon and nitrogen have a predominantly extra-lunar origin in lunar soils and breccias, while sulfur is mostly indigeneous to the Moon. The lunar processes which effect the movement, distribution, and evolution of carbon, nitrogen, and sulfur, along with the volatile alkali elements sodium, potassium, and rubidium during regolith processes are discussed. Possible mechanisms which may result in the addition to or loss from the Moon of these volatile elements are considered. 相似文献
2.
Numerous U and V magnitude measurements were performed for the nucleus of the Seyfert galaxy NGC 4151 at the Crimean Laboratory of the SAI (Moscow University) in 1994–2005. Adding them to the previous data for 1968–1997 has led to a substantial increase in the confidence level of the light variations in NGC 4151 with a stable period of P G = 160.0108(7) min and a mean amplitude of 0.007 U mag (in the “active” state of the nucleus). The period of NGC 4151 agrees well with the period of 160.0101(15) min found previously in the oscillations of the Sun. It is treated as the period of a “coherent cosmic oscillation” independent of redshift z or as the period of “free cosmic vibrations” of the hydrogen atom, the main element of the Universe. The period and initial phase of the P G oscillation have been constant for 38 years of NGC 4151 observations. The new astrophysical phenomenon appears to be closely related to the quantum nonlocality of photons and is of particular interest in physics and cosmology. 相似文献
3.
We analyse the angular momentum evolution from the red giant branch (RGB) to the horizontal branch (HB) and along the HB. Using rotation velocities for stars in the globular cluster M13, we find that the required angular momentum for the fast rotators is up to 1–3 orders of magnitude (depending on some assumptions) larger than that of the Sun. Planets of masses up to 5 times Jupiter's mass and up to an initial orbital separation of ~2 au are sufficient to spin-up the RGB progenitors of most of these fast rotators. Other stars have been spun-up by brown dwarfs or low-mass main-sequence stars. Our results show that the fast rotating HB stars have been probably spun-up by planets, brown dwarfs or low-mass main-sequence stars while they evolved on the RGB. We argue that the angular momentum considerations presented in this paper further support the 'planet second parameter' model. In this model, the 'second parameter' process, which determines the distribution of stars on the HB, is interaction with low-mass companions, in most cases with gas-giant planets, and in a minority of cases with brown dwarfs or low-mass main-sequence stars. The masses and initial orbital separations of the planets (or brown dwarfs or low-mass main-sequence stars) form a rich spectrum of different physical parameters, which manifests itself in the rich varieties of HB morphologies observed in the different globular clusters. 相似文献
4.
The extinction of light caused by the presence of dust along the IC 1318 nebular complex has been investigated by comparing optical (H) data of high photometric accuracy and radio data of the same angular resolution. The role of the detected dust condensations in the formation of stars has also been discussed. 相似文献
5.
T. H. Burbine P. C. Buchanan R. P. Binzel S. J. Bus T. Hiroi J. L. Hinrichs A. Meibom T. J. Mccoy 《Meteoritics & planetary science》2001,36(6):761-781
Abstract— Spectra of asteroid 4 Vesta and 21 small (estimated diameters less than 10 km) asteroids with Vesta‐like spectral properties (Vestoids) were measured at visible and near‐infrared wavelengths (～0.44 to ～1.65 μm). All of the measured small asteroids (except for 2579 Spartacus) have reflectance spectra consistent with surface compositions similar to eucrites and howardites and consistent with all being derived from Vesta. None of the observed asteroids have spectra similar to diogenites. We find no spectral distinction between the 15 objects tabulated as members of the Vesta dynamical family and 6 of the 7 sampled “non‐family” members that reside just outside the semi‐major axis (a), eccentricity (e), and inclination (i) region of the family. The spectral consistency and close orbital (a‐e‐i) match of these “non‐family” objects to Vesta and the Vesta family imply that the true bounds of the family extend beyond the subjective cut‐off for membership. Asteroid 2579 Spartacus has a spectrum consistent with a mixture of eucritic material and olivine. Spartacus could contain olivine‐rich material from Vesta's mantle or may be unrelated to Vesta altogether. Laboratory measurements of the spectra of eucrites show that samples having nearly identical compositions can display a wide range of spectral slopes. Finer particle sizes lead to an increase in the slope, which is usually referred to as reddening. This range of spectral variation for the best‐known meteoritic analogs to the Vestoids, regardless of whether they are actually related to each other, suggests that the extremely red spectral slopes for some Vestoids can be explained by very fine‐grained eucritic material on their surfaces. 相似文献
6.
David Parry Rubincam 《Icarus》2006,184(2):532-542
Saturn's icy ring particles, with their low thermal conductivity, are almost ideal for the operation of the Yarkovsky effects (photon thrust due to temperature gradients across the ring particles). An extremely simple case of the Yarkovsky effects is examined here, in which orbital evolution is computed as though each particle travels around Saturn alone in a circular orbit, so that there are no collisions, shadowing, or irradiance from other particles; nor are resonances, tumbling, or micrometeoroid erosion considered. The orbital evolution for random spin orientations appears to be a competition between two effects: the seasonal Yarkovsky effect, which makes orbits contract, and the Yarkovsky-Schach effect, which makes orbits expand. There are values of the far infrared and visible particle albedos for which (working radially out from the planet) the along-track particle acceleration S is negative, then positive, and then negative again; the region for which S>0 is interpreted as a region where stable rings are possible. Typical timescales for centimeter-sized particles to travel half a Saturn radius are 107-108 yr. Collisions, shadowing, and resonances may lengthen the timescales, perhaps considerably. It is speculated here that the C ring may be depleted of particles because of the seasonal Yarkovsky effect, and small particles that are present in the C ring ultimately fall on Saturn, possibly creating a “Ring of Fire” as they enter the planet's atmosphere. 相似文献
7.
Scot C.R. Rafkin 《Planetary and Space Science》2012,60(1):147-154
A review of non-local, deep transport mechanisms in the atmosphere of Earth provides a good foundation for examining whether similar mechanisms are operating in the atmospheres of Mars and Titan. On Earth, deep convective clouds in the tropics constitute the upward branch of the Hadley Cell and provide a conduit through which energy, moisture, momentum, aerosols, and chemical species are moved from the boundary layer to the upper troposphere and lower stratosphere. This transport produces mid-tropospheric minima in quantities such as water vapor and moist static energy and maxima where the clouds detrain. Analogs to this terrestrial transport are found in the strong and deep thermal circulations associated with topography on Mars and with Mars dust storms. Observations of elevated dust layers on Mars further support the notion that non-local deep transport is an important mechanism in the atmosphere of Mars. On Titan, the presence of deep convective clouds almost assures that non-local, deep transport is occurring and these clouds may play a role in global cycling of energy, momentum, and methane. Based on the potential importance of non-local deep transport in Earth's atmosphere and supported by evidence for such transport in the atmospheres of Mars and Titan, greater attention to this mechanism in extraterrestrial atmospheres is warranted. 相似文献
8.
Abstract— There are a variety of isotopic data for meteorites which suggest that the protostellar nebula existed and was involved in making planetary materials for some 107 yr or more. Many cosmochemists, however, advocate alternative interpretations of such data in order to comply with a perceived constraint, from theoretical considerations, that the nebula existed only for a much shorter time, usually stated as ≤ 106 yr. In this paper, we review evidence relevant to solar nebula duration which is available through three different disciplines: theoretical modelling of star formation, isotopic data from meteorites, and astronomical observations of T Tauri stars. Theoretical models based on observations of present star-forming regions indicate that stars like the Sun form by dynamical gravitational collapse of dense cores of cold molecular clouds in the interstellar medium. The collapse to a star and disk occurs rapidly, on a time scale of the order 105 yr. Disks evolve by dissipating energy while redistributing angular momentum, but it is difficult to predict the rate of evolution, particularly for low mass (compared to the star) disks which nonetheless still contain enough material to account for the observed planetary system. There is no compelling evidence, from available theories of disk structure and evolution, that the solar nebula must have evolved rapidly and could not have persisted for more than 1 Ma. In considering chronologically relevant isotopic data for meteorites, we focus on three methodologies: absolute ages by U-Pb/Pb-Pb, and relative ages by short-lived radionuclides (especially 26Al) and by evolution of 87Sr/86Sr. Two kinds of meteoritic materials-refractory inclusions such as CAIs and differentiated meteorites (eucrites and angrites)—appear to have experienced potentially dateable nebular events. In both cases, the most straightforward interpretations of the available data indicate nebular events spanning several Ma. We also consider alternative interpretations, particularly the hypothesis of radically heterogeneous distribution of 26Al, which would avoid these chronological interpretations. The principal impetus for such alternative interpretations seems to be precisely the obviation of the chronological interpretation (i.e., the presumption rather than the inference of a short (≤1 Ma) lifetime of the nebula). Astronomical observations of T Tauri stars indicate that the presence of dusty disks is a common if not universal feature, that the disks are massive enough to accomodate a planetary system such as ours, and that at least some persist for 107 yr or more. The results are consistent with the time scales inferred from the meteorite isotopic data. They cannot be considered conclusive with regard to solar nebula time scales, however, in part because it is difficult to relate disk observations to processes that affect meteorites, and in part because the ages assigned for these stars could be wrong by a factor of several in either direction. We conclude that the balance of available evidence favors the view that the nebula existed and was active for at least several Ma. However, because the evidence is not definitive, it is important that the issue be perceived to be an open question, whose answer should be sought rather than presumed. 相似文献
9.
In a previous paper Lyttleton (1976) has shown that the apparent secular accelerations of the Sun and Moon, as given by de Sitter, can be largely explained if the Earth is contracting at the rate required by the phase-change hypothesis for the nature of the core. More reliable values for these accelerations have since become available which warrant a redetermination of the various effects concerned on the basis of constantG, and this is first carried out in the present paper. The lunar tidal couple, which is the same whetherG is changing or not, is found to be (4.74±0.38)×1023 cgs, about three-quarters that yielded by the de Sitter values, while within the theory the Moon would take correspondingly longer to reach close proximity to the Earth at about 1.5×109 years ago.The more accurate values of the accelerations enable examination to be made of the effects that a decreasingG would have, and it is shown that a valueG/G=–3×10–11 yr–1 can be weakly satisfied compared with the close agreement found on the basis of constantG, while a value as large numerically asG/G=–6×10–11 yr–1 seems to be definitely ruled out. On the iron-core model, an intrinsic positive component of acceleration of the angular velocity cannot be reconciled at all with the secular accelerations even for constantG, and far less so ifG is decreasing at a rate suggested by any recent cosmological theory.ItG=0, the amount of contraction available for mountain-building would correspond to a reduction of surface area of about 49×106 km2 and a volume to be redistributed of 160×109 km3 if the time of collapse were 2.5×109 years ago. For earlier times, the values are only slightly reduced. IfG/G=–3×10–11 yr–1, the corresponding values are 44×106 km2 and 138×109 km3 for collapse at –2.5×109 yr, and not importantly smaller at 38×106 km2 and 122×109 km3 for collapse at –4.5×109 yr. Any of these values would suffice to account in order of magnitude for all the eras of mountain-building. An intense brief period of mountain-building on an immense scale would result from the Ramsey-collapse at whatever time past it may have occurred. 相似文献
10.
Mineralogy,petrology, and distribution of meteorites at the Whitecourt crater,Alberta, Canada 
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下载免费PDF全文 The Whitecourt meteorite impact crater, Alberta, Canada is a rare example of a well‐preserved small impact structure, with which thousands of meteorite fragments are associated. As such, this crater represents a unique opportunity to investigate the effect of a low‐energy impact event on an impacting iron bolide. Excellent documentation of meteorite fragment locations and characteristics has generated a detailed distribution map of both shrapnel and regmaglypted meteorite types. The meteorites' distribution, and internal and external characteristics support a low‐altitude breakup of the impactor which caused atmospherically ablated (regmaglypted) meteorites to fall close to the crater and avoid impact‐related deformation. In contrast, shrapnel fragments sustained deformation at macro‐ and microscales resulting from the catastrophic disruption of the impactor. The impactor was significantly fragmented along pre‐existing planes of weakness, including kamacite lamellae and inclusions, resulting in a bias toward low‐mass (<100 g) fragments. Meteorite mineralogy was investigated and the accessory minerals were found to be dominated by sulfides and phosphides with rare carlsbergite, consistent with other low‐Ni IIIAB iron meteorites. Considerations of the total mass of meteoritic material recovered at the site relative to the probable fraction of the impactor that was preserved based on modeling suggests that the crater was formed by a higher velocity, lower mass impactor than previously inferred. 相似文献
11.
P. J. McGough 《Meteoritics & planetary science》1944,3(10):143-147
The following four additional references on the history of the Tucson, Arizona, meteorites, the so-called “Irwin-Ainsa” and “Carleton” irons, have all been taken from an old Tucson newspaper, the Arizona Citizen, of dates January 15, April 1, and April 8, 1876. These references, which supplement those contained in the article that appeared in C.S.R.M., 3 , 108–19; P. A., 51 , 511–18, 563–7, 1943, will serve to complete the colorful record of the early history of the two well-known Tucson irons. 相似文献
12.
H.J. Melosh 《Icarus》1984,59(2):234-260
Recent discoveries suggest that some meteorites have originated from major planets or satellites. Although it has been suggested that a large primary impact event might eject rock fragments as secondaries, it was previously supposed that material ejected at several kilometers per second would be highly shocked or perhaps melted. It is shown that a small amount of material (0.01 to 0.05 projectile mass) may be ejected at high velocity shock pressures. The approach utilizes observations of stress-wave propagation from large underground explosions to predict stresses and particle velocities in the near-surface environment. The largest fragments ejected at any velocity are spalls that originate from the target planet's surface. The spall size is proportional to the radius of the primary impactor and the target tensile strength and inversely proportional to ejection velocity. The shock level in the spalls is low, typically half of the dynamic crushing strength of the rock. The model also predicts the aspect ratio of the spalled fragments, the angle of ejection, and the sizes and shock level of other fragments originating deeper in the target. Comparison with data from laboratory experiments, the Ries Crater, and secondary crater sizes shows generally good agreement, although the observed fragment size at ejection velocities greater than 1 km/sec is considerably smaller than the simple version of the theory predicts. The theory indicates that although significant masses of solid material could be ejected from the Moon or Mars by large meteorite impacts, the fragments ejected from ca. 30-km-diameter craters are at most a few tens of meters in diameter if the most optimistic assumptions are made. The maximum fragment diameter is more likely to be about a meter. This theory, however, applies rigorously only up to ejection velocities of ca 1 km/sec. Further numerical extensions are necessary before film conclusions can be drawn, especially for Martian ejecta. 相似文献
13.
The advent of three-dimensional, electromagnetic, and fully relativistic particle simulations allows a detailed study of a magnetized, rotating plasma, galaxy model. When two such models are simulated, an interaction yielding results resembling observational data from double radio sources, including the emission of synchrotron radiation, are obtained. Simulation derived morphologies, radiation intensities, frequency spectra, and isophote patterns are directly compared to observations. The constituent plasma parameters associated with the source Cygnus A are found to ben e =1.8×10?3 cm?3,T=2.8 keV,B=20–30 gamma, with a small population of electrons accelerated to GeV energies by a rotation induced electric field. The results of these simulations, involving a computational resource of five CDC 7600 and five Cray-1 computers, strongly supports an inhomogeneous version of the Klein world model. 相似文献
14.
F. W. Stecker 《Astrophysics and Space Science》1973,20(1):47-57
The production of ultrahigh energy photons, electrons and neutrinos as the decay products of pions produced in photomeson interactions between cosmic-ray nucleons and the blackbody microwave background is discussed in terms of the resultant energy spectra of these particles. Simple asymptotic formulas are given for calculating the ultrahigh energy photon spectrum predicted for the universal cosmic-ray hypothesis and the resulting spectra are compared with those obtained previously by numerical means using a different propagation equation for the photons. Approximate analytic solutions for the photon spectra are given in terms of simple power-law energy functions and slowly varying logarithmic functions. These can be used to estimate ultrahigh energy photon fluxes for various astrophysical parameters. The generic relation between the various secondary components is then discussed in terms of their astrophysical implications which are summarized in the conclusion. 相似文献
15.
Philip A. Isenberg 《Solar physics》1976,50(1):49-63
The boundary between the umbra and penumbra of a sunspot is consistently observed to be very sharp, on the order of 500 km. Approximating the sunspot as a static region in a homogeneous medium with a radiative surface, temperature distributions resulting from a variety of convective motions exterior to the sunspot are calculated. The calculations suggest that, for the exterior convection to produce the observed boundary, the maximum depth of the region of inhibited convection below a sunspot umbra is on the order of 103 km. 相似文献
16.
Abstract— The Carcote meteorite, detected in 1888 in the northern Chilean Andes, is a brecciated, weakly shocked H5 chondrite. It contains a few barred olivine chondrules and, even more rarely, fan-shaped or granular orthopyroxene chondrules. The chondrules are situated in a fine-grained matrix that consists predominantly of olivine and orthopyroxene with accessory clinopyroxene, troilite, chromite, merrillite, and plagioclase. The metal phase is mainly kamacite with subordinate taenite and traces of native Cu. In its bulk rock composition, Carcote compares well with other H5 chondrites so far analysed, except for a distinctly higher C content. Microprobe analyses revealed the following mineral compositions: olivine (Fa16.5–20), orthopyroxene (Fs14–17.5), diopsidic clinopyroxene (FS6–7), plagioclase (An15–20). Troilite is stoichimetric FeS with traces of Ni and Cr; chromite has Cr/(Cr + Al) of 0.86, Fe2+/(Fe2+ + Mg) of 0.80-0.88 and contains considerable amounts of Ti, Mn, and Zn. Merrillite is close to the theoretical formula Ca18(Mg, Fe)2Na2(PO4)14, although with a Na deficiency not compensated for by excess Ca; the Mg/(Mg + Fe2+) ratio of the Carcote merrilite is 0.93-0.95. Kamacite and taenite have Ni contents of 5.6–7.2 and 17.1–23.4 wt%, respectively. Native Cu contains about 3.1–3.3 wt% Fe and 1.6 wt% Ni. Application of different geothermometers to the Carcote H5 chondrite yielded apparently inconsistent results. The highest temperature range of 850–950 °C (at 1 bar) is derived from the Ca-in-opx thermometer. From the cpx-opx solvus geothermometers and the two-pyroxene Fe-Mg exchange geothermometer, a lower temperature range of 750–840 °C is estimated, whereas lower and more variable temperatures of 630–770 °C are obtained from the Ca-in-olivine geothermometer. Recent calibrations of the olivine-spinel geothermometer yielded a still lower temperature range of 570–670 °C, which fits well to the temperature information derived from the Ni distribution between kamacite and taenite. Judging from crystal chemical considerations, we assume that these different temperatures reflect the closure of different exchange equilibria during cooling of the meteorite parent body. 相似文献
17.
Henri E. Mitler 《Astrophysics and Space Science》1972,17(1):186-218
The production of deuterium, He3, lithium, beryllium, and boron by galactic cosmic rays in the interstellar medium, over the life of the Galaxy, is calculated. It is found that high-energy - reactions contribute in an essential way to the observed lithium. When allowance is made for the interchange of material between stars and the interstellar gas and for the change of cosmic-ray intensity with time, the Li6, Be9, and boron produced turn out to be ample to explain the observed abundances, and with remarkable internal consistency. Deuterium and He3 arenot produced in significant amounts, nor Li7 in sufficient amount, however. To explain the Li7/Li6 ratio measured terrestrially and in chondritic meteorites, we invoke cosmological production of Li7. This implies the production of deuterium, He3, and He4 as well, in amounts consistent with observation. The theory in its present form cannot explain a solar-system Li7/Li6 ratio of 12and stellar ratios as low as 3, but additional processes can be adduced to reconcile them. The consistency of the numbers when cosmological production is included lends additional support to the big-bang hypothesis. An incidental result is that the mean luminosity of the Galaxy over its lifetime has been about 3 times its present luminosity. 相似文献
18.
《Icarus》1987,71(2):250-256
Estimates of the total inventory of the volatile elements C, H, O, and N on Mars, based upon atmospheric gas tracers, vary by a factor of 25 among different authors. Accretion of comets as the source of volatiles can account for less than 5% of the actual inventory, assuming the chondritic S/Cl abundance ratio in comets and a Martian outgassing ratio for these two elements no lower than for the estimated excess volatile inventory on Earth. Sulfate salt formation with the igneous minerals in the regolith can be a major sink for H2O, but first will recycle C and N incorporated in carbonate and nitrate minerals back to the atmosphere. Extrusive and shallow intrusive volcanism, at a persistent but decreasing rate, can interfere with this volatile recycling by irreversibly masking much of the incorporated inventory, resulting in the inevitable evolution to a relatively volatile-poor environment at the outermost, observable surface of Mars. 相似文献
19.
Anthony L. Turkevich 《Earth, Moon, and Planets》1972,5(3-4):411-421
The principal chemical element composition and inferred mineralogy of the powdered lunar surface material at seven mare and one terra sites on the Moon are compared. The mare compositions are all similar to one another and comparable to those of terrestrial ocean ridge basalts except in having higher titanium and much lower sodium contents than the latter. These analyses suggest that most, if not all, lunar maria have this chemical composition and are derived from rocks with an average density of 3.19 g cm–3. Mare Tranquillitatis differs from the other maria in having twice the titanium content of the others.The chemical composition of the single highland site studied (Surveyor 7) is distinctly different from that of any of the maria in having much lower amounts of titanium and iron and larger amounts of aluminium and calcium. Confirmation of these general characteristics of lunar highland material has come from recent observations by the Apollo 15 Orbiter. The inferred mineralogy is 45 mole percent high anorthite plagioclase and the parent rocks have an estimated density of 2.94 g cm–3. The Surveyor 7 chemical composition is the principal contributor to present estimates of the overall chemical composition of the lunar surface.Presented at the NATO Advanced Study Institute on Lunar Studies, Patras, Greece, September 14–25, 1971. This paper is an expanded and updated version of a paper presented at the Apollo 12 Lunar Science Conference, Houston, Texas, January 11–14, 1971, and published in the Proceedings of this Conference (Turkevich, 1971). 相似文献