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1.
Using Magellan radar images of the Venera and Vega landing-site regions, we carried out a photogeologic analysis and mapping of these regions, the soil composition of which was earlier analyzed by the spacecraft of these series. All these landing-site regions are shown to possess a similar set of geologic situations, which are typical of the planet as a whole, and a similar sequence of geologic evolution. Judging by the results of mapping, a geochemically advanced material analyzed at the Venera-8 landing site appears to be a complex of shield plains (Psh). Tholeiitic compositions obtained by Venera-9/10 and Vega-1/2 probably represent the unit of plains with wrinkle ridges (Pwr), which is most common on Venus. The material of tholeiitic composition analyzed by Venera-14 is likely to be the unit of relatively young lobate plains (Pl). 相似文献
2.
L. V. Ksanfomality 《Solar System Research》2012,46(5):364-373
Data on the results of the analysis of the content of re-processed panorama of the VENERA-9 lander are presented. The panorama was transmitted historically for the first time from the surface of Venus in 1975. The low noise of the VENERA-9 data allowed allocating a large object of an unusual regular structure. Earlier, its fuzzy image was repeatedly cited in the literature being interpreted as a ??strange stone??. The complex shape and its other features suggest that the object may be a real habitant of the planet. It is not excluded that another similar object observed was damaged during the VENERA-9 landing. From the evidence of its movement and position of some other similar objects it is concluded that because of the limited energy capacity, the physical action of the Venusian fauna may be much slower than that of the Earth fauna. Another question considered is what sources of energy could be used by life in the conditions of the high temperature oxygenless atmosphere of the planet. It is natural to assume that, like on Earth, the Venusian fauna is heterotrophic and should be based on hypothetical flora, using photosynthesis (based on an unknown high temperature biophysical mechanism). 相似文献
3.
This paper and subsequent Paper II are an investigation of the annihilation line formation in gamma-ray bursts based on the assumption of positron production in a strong magnetic field (because of one-photon absorption of hard gamma-quanta radiated in the neutron star hot polar spot). We discuss a two-photon annihilation line in this paper. It is shown that if the star magnetic field is greater than 3×1012 G, the relative flux in the line depends solely on the hardness of the continuum and is, as a rule, less than or about 10–20% of the total flux. This is consistent with the spectral data recorded by ‘Venera-11’ and ‘Venera-12’ space probes. The annihilation region formation above the hot polar spot is discussed, and positron density and annihilation region dimensions are estimated. 相似文献
4.
Don P. Mitchell 《Solar System Research》2012,46(5):382-384
Some anomalies in the video images from Venera-13 are explained as possible artifacts of the telemetry system. One anomaly may be a shadow caused by a change in the distribution of illumination. 相似文献
5.
Dark matter is explained within our scenario of the formation of the universe from the decay of macroscopic superstrings. The observed increase of the fraction of dark matter with the hierarchical rank of astronomical objects is explained by assuming that about 90% of superstrings of each rank decay into unbound fragments. The dark matter consists essentially of asteroids and smaller objects which are not bound to stars. 相似文献
6.
Maria Eugenia VARELA Paul SYLVESTER Almut ENGLER Gero KURAT 《Meteoritics & planetary science》2012,47(10):1537-1557
Abstract– Nineteen nonporphyritic pyroxene and pyroxene/olivine chondrules, chondrule fragments, and irregular objects were studied from two equilibrated chondrites, the ordinary (L/LL5) Knyahinya chondrite and the Rumuruti type (R4) Ouzina chondrite. Major element contents for almost all objects in the chondrites are disturbed from their chondritic ratios, most probably during metamorphic re‐equilibration. However, the volatile elements (Na2O + K2O) in Ouzina scatter around the CI line, probably the result of being generated and/or processed in different environments as compared with those for Knyahinya. All studied objects from Knyahinya and Ouzina possess systematically fractionated trace element abundances. Depletion of LREE with respect to HREE and ultra‐refractory HFSE documents variable degrees of LREE transport into an external mineral sink and restricted mobility of most of the HREE and HFSE. Moderately volatile elements preserve volatility‐controlled abundances. Strongly fractionated Rb/Cs ratios (up to 10× CI) in all studied objects suggest restricted mobility of the large Cs ion. All studied objects sampled and preserved Y and Ho in solar proportions, a feature that they share with the nonporphyritic chondrules of unequilibrated ordinary chondrites. 相似文献
7.
Vincenzo Zappalà Franco Scaltriti Paolo Farinella Paolo Paolicchi 《Earth, Moon, and Planets》1980,22(2):153-162
Recent occultation data and an analysis of some photometric lightcurves have shown the possible existence of asteroidal binary systems.A simple geometrical model taking into account mutual shadowing effects shows some peculiar features of the lightcurve which can be recovered in several previously observed objects; therefore the hypothesis of a relatively high frequency of binary asteroids should be seriously considered.On the other hand, while the rotational period distribution of large asteroids (D>200 km) is sharply peaked at about 5–8 hours, the surprisingly higher dispersion towards longer periods for intermediate size objects (50<D<150 km) could be connected with a larger probability of binary nature within this class.From a theoretical point of view, the collisional fragmentation of asteroids could originate gravitationally bound fragments, with a tidal transfer of rotational into orbital angular momentum, causing a rapid synchronization of the system. This kind of processes could more easily occur for intermediate objects since: (a) for large ones, very massive colliding bodies are needed for fragmentation, that means a very rare event; (b) for smaller asteroids, solid state interactions are stronger than the gravitational ones, so that a breakage probably causes a complete disruption of the gravitational binding. Further collisional events could disintegrate some systems, so that the present frequency of binary asteroids could be lower than that of the objects whose rotational period was increased by such processes.Paper presented at the European Workshop on Planetary Sciences, organised by the Laboratorio di Astrofisica Spaziale di Frascati, and held between April 23–27, 1979, at the Accademia Nazionale del Lincei in Rome, Italy. 相似文献
8.
Conclusions Since there is sufficiently detailed information on the observed galaxies listed in the notes to Table 1, we briefly summarize the main results.From the observations of 94 objects, emission lines are discovered in 64; in one, Markaryan 396, hydrogen absorption lines are observed (this is a white dwarf, probably type DA, and possibly a weak radio source [23]). In the red region there are no lines detected in the objects Markaryan 422(3), 425(3), 431(4), 433(3), 616(3), 621(5), 643(4), 655(5), 656(4), and 658(3); the number of spectrograms is indicated in parentheses; it is possible that Markaryan 643 is a galactic cluster.The objects Markaryan 595, 609, 622, 688, 699, and 700 have broad, hydrogen emission lines and can be attributed to the Seyfert class of galaxies. Markaryan 609, 622, and 699, plus, probably, Markaryan 423, possess moderate Seyfert characteristics. Furthermore, in Markaryan 414, 584, 612, 617, 646, 670, 684, and 693 broad emission lines are observed or suspected. Markaryan 586 is probably similar to a QSO. Further observations are advisable for all these objects.In conclusion, the authors express their gratitude to A. L. Shcherbanovskii for help in the treatment of the spectrograms on the M-222 computer.Institute of Astrophysics, Academy of Sciences of the Kazakh SSR. Special Astrophysical Observatory, Academy of Sciences of the USSR. Translated from Astrofizika, Vol. 12, No. 4, pp. 665–682, October–December, 1976. 相似文献
9.
Cassini UVIS star occultations by the F ring detect 13 events ranging from 27 m to 9 km in width. We interpret these structures as likely temporary aggregations of multiple smaller objects, which result from the balance between fragmentation and accretion processes. One of these features was simultaneously observed by VIMS. There is evidence that this feature is elongated in azimuth. Some features show sharp edges. At least one F ring object is opaque and may be a “moonlet.” This possible moonlet provides evidence for larger objects embedded in Saturn's F ring, which were predicted as the sources of the F ring material by Cuzzi and Burns [Cuzzi, J.N., Burns, J.A., 1988. Icarus 74, 284-324], and as an outcome of tidally modified accretion by Barbara and Esposito [Barbara, J.M., Esposito, L.W., 2002. Icarus 160, 161-171]. We see too few events to confirm the bi-modal distribution which Barbara and Esposito [Barbara, J.M., Esposito, L.W., 2002. Icarus 160, 161-171] predict. These F ring structures and other youthful features detected by Cassini may result from ongoing destruction of small parent bodies in the rings and subsequent aggregation of the fragments. If so, the temporary aggregates are 10 times more abundant than the solid objects. If recycling by re-accretion is significant, the rings could be quite ancient, and likely to persist far into the future. 相似文献
10.
11.
I.L. Bertaux J. Blamont M. Marcelin V.G. Kurt N.N. Romanova A.S. Smirnov 《Planetary and Space Science》1978,26(9):817-831
The dayside hydrogen exosphere was observed in October–November 1975 with a Lymanalpha photometer carried on board Venera-9 and 10. In addition to intensity measurements, the use of a hydrogen cell allowed for the first time linewidth measurements. Both intensity and linewidth measurements below 1500 km of altitude are well fitted by a single exospheric component (Tc = 500 ± 100 K, nc = 1.5 × 104 atom cm?3at 250 km). Above 3000 km, the measured linewidth increased sharply, to decrease again above 4500 km. This feature is interpreted as the signature of an additional population of “hot” atoms circulating on satellite orbits, created just behind the bow-shock by charge-exchange collisions (with an efficiency of 4%) between the neutral atoms and the solar wind protons, which became turbulent after bow-shock crossing. The density ratio of “hot” to standard population is of the order of 10% around 3500 km of altitude. 相似文献
12.
This paper investigates the physics of meteoroid breakup in the atmosphere and its implications for the observed features of strewn fields. There are several effects which cause dispersion of the meteoroid fragments: gravity, differential lift of the fragments, bow shock interaction just after breakup, centripetal separation by a rotating meteoroid, and possibly a dynamical transverse separation resulting from the crushing deceleration in the atmosphere. Of these, we show that gravity alone can produce the common pattern in which the largest crater occurs at the downrange end of the scatter ellipse. The average lift-to-drag ratio of the tumbling fragments must be less than about 10?3, otherwise small fragments would produce small craters downrange of the main crater, and this is not generally observed. The cross-range dispersion is probably due to the combined effects of bow shock interaction, crushing deceleration, and possibly spinning of the meteoroid. A number of terrestrial strewn fields are discussed in the light of these ideas, which are formulated quantitatively for a range of meteoroid velocities, entry angles, and crushing strengths. It is found that when the crater size exceeds about 1 km, the separation between the fragments upon landing is a fraction of their own diameter, so that the crater formed by such a fragmented meteoroid is almost indistinguishable from that formed by a solid body of the same total mass and velocity. 相似文献
13.
研究了环绕致密天体的吸积盘的稳定性质和振动模式。特别关注了在热致和粘滞扰动作用下稳定的对流起支配作用的盘外流。还研究了相对论性吸积盘的振动模式。一些在盘内的捕获的 ,非衰减的模式也许可以用来解释X射线双星和活动星系核中所观测到的准周期振动。 相似文献
14.
We have obtained deep 6, 20 and 90 cm observation of two of the richest globular clusters in the galaxy, Terzan 5 and Liller
1. In addition to the well known eclipsing pulsar, PSR1744-24A, our 20 cm image of Terzan 5 displays numerous point sources
within 30″, or 4 core radii of the cluster center. The density of these objects rises rapidly toward the core, where an elongated
region of emission is found. This feature may be due to the presence of a higher density of point sources than can be resolved
by the 1″ resolution of our data. Observations at 6 and 90 cm show that the brightest individual sources, as well as the extended
emission, possess the steep spectra expected of pulsars. Furthermore, we find that the strength of the sources in the 20 cm
image agrees well with the standard pulsar luminosity function. The total luminosity and number of objects observed in Terzan
5 suggest that this cluster may contain 100 pulsars — probably more than any other Galactic cluster. Although we do not resolve
individual sources in Liller 1, comparison of our images with other observations suggests that we are again observing the
sum of emission from a number of objects. The 90 cm flux densities of Terzan 5 and Liller 1 are 35 and 9 mJy, respectively,
implying that a number of bright pulsars in these clusters have been hidden from pulsed searches, perhaps by a combination
of dispersion smearing, scattering and doppler broadening. 相似文献
15.
George W. Wetherill 《Meteoritics & planetary science》1985,20(1):1-22
The orbital evolution of asteroidal fragments with diameters ranging from 10 cm to 20 km, injected into the 3:1 Kirkwood gap at 2.50 A.U., has been investigated using Monte Carlo techniques. It is assumed that this material can become Earth-crossing on a time scale of 106 years, as a result of a chaotic zone discovered by Wisdom, associated with the 3:1 resonance. This phenomenon, as well as close encounter planetary perturbations, the v6 secular resonance, and the ablative effects of the Earth's atmosphere are included in the determination of the orbital characteristics of meteorites impacting the Earth derived by fragmentation of this asteroidal material. It is found that the predicted meteorite orbits closely match those found for observed ordinary chondrites, and the total flux is in approximate agreement with the observed fall rate of ordinary chondrites. About 10% of the predicted impacting bodies are meteorite-size bodies originating directly from the asteroid belt. The remainder are obtained by subsequent fragmentation of larger (～1 m to 20 km diameter) Earth-crossing asteroidal fragments. The largest of these fragments are observable as Apollo-Amor objects. Thus the apparent paradox between the orbital characteristics of observed ordinary chondrites and those predicted from Apollo object sources is reconciled. Both appear to be complementary aspects of the same phenomena. No other asteroidal resonance is found to be satisfactory as a source of ordinary chondrites. These meteorites are therefore most likely to be derived from S asteroids in this limited region of the asteroidal belt, the largest of which are 11 Parthenope, 17 Thetis, and 29 Amphitrite. 相似文献
16.
During the decay of solar cosmic-ray events cosmic-rays with kinetic energies of about 1 MeV are convected outward with the solar wind. It is shown that, with currently available observations it should be possible to demonstrate directly the energy losses which are occurring. Observations from two spacecraft on the same heliocentric radial line are required. In this paper observations from Venera-4 and Imp-F have been used. A simple and direct demonstration would be provided by the observation of nearly mono-energetic pulses convected between the two spacecraft, but no such pulses were found to be present. A second method depends upon observing the ratio of the integral fluxes at the two spacecraft and comparing this with the value predicted by theory. The relevant theoretical analysis has been given. It is shown that in order to discriminate between energy-loss processes the spacecraft must be well separated. For spacecraft at Earth's orbit and the orbit of Venus the integral-flux ratio predicted with energy loss due to adiabatic deceleration is a factor of three higher than that predicted with no energy loss. Comparisons of integral-flux ratios for two events observed on spacecraft separated by approximately 0.1 AU gave inconclusive results. In view of the importance of energy-loss processes in the propagation of cosmic rays it is suggested that others with access to relevant data might continue this investigation. 相似文献
17.
Abstract— We measured the sizes and textural types of 719 intact chondrules and 1322 chondrule fragments in thin sections of Semarkona (LL3.0), Bishunpur (LL3.1), Krymka (LL3.1), Piancaldoli (LL3.4) and Lewis Cliff 88175 (LL3.8). The mean apparent diameter of chondrules in these LL3 chondrites is 0.80 φ units or 570 μm, much smaller than the previous rough estimate of ～900 μm. Chondrule fragments in the five LL3 chondrites have a mean apparent cross‐section of 1.60 φ units or 330 μm. The smallest fragments are isolated olivine and pyroxene grains; these are probably phenocrysts liberated from disrupted porphyritic chondrules. All five LL3 chondrites have fragment/ chondrule number ratios exceeding unity, suggesting that substantial numbers of the chondrules in these rocks were shattered. Most fragmentation probably occurred on the parent asteroid. Porphyritic chondrules (porphyritic olivine + porphyritic pyroxene + porphyritic olivine‐pyroxene) are more readily broken than droplet chondrules (barred olivine + radial pyroxene + cryptocrystalline). The porphyritic fragment/chondrule number ratio (2.0) appreciably exceeds that of droplet‐textured objects (0.9). Intact droplet chondrules have a larger mean size than intact porphyritic chondrules, implying that large porphyritic chondrules are fragmented preferentially. This is consistent with the relatively low percentage of porphyritic chondrules within the set of the largest chondrules (57%) compared to that within the set of the smallest chondrules (81%). Differences in mean size among chondrule textural types may be due mainly to parent‐body chondrule‐fragmentation events and not to chondrule‐formation processes in the solar nebula. 相似文献
18.
We investigate the flux of main-belt asteroid fragments into resonant orbits converting them into near-Earth asteroids (NEAs), and the variability of this flux due to chance interasteroidal collisions. A numerical model is used, based on collisional physics consistent with the results of laboratory impact experiments. The assumed main-belt asteroid size distribution is derived from that of known asteroids extrapolated down to sizes of ≈ 40 cm, modified in such a way to yield a quasi-stationary fragment production rate over times ≈ 100 Myr. The results show that the asteroid belt can supply a few hundred km-sized NEAs per year, well enough to sustain the current population of such bodies. On the other hand, if our collisional physics is correct, the number of existing 10-km objects implies that these objects either have very long-lived orbits, or must come from a different source (i.e., comets). Our model predicts that the fragments supplied from the asteroid belt have initially a power-law size distribution somewhat steeper than the observed one, suggesting preferential removal of small objects. The component of the NEA population with dynamical lifetimes shorter than or of the order of 1 Myr can vary by a factor reaching up to a few tens, due to single large-scale collisions in the main belt; these fluctuations are enhanced for smaller bodies and faster evolutionary time scales. As a consequence, the Earth's cratering rate can also change by about an order of magnitude over the 0.1 to 1 Myr time scales. Despite these sporadic spikes, when averaged over times of 10 Myr or longer the fluctuations are unlikely to exceed a factor two. 相似文献
19.
Boris Shustov 《Astrophysics and Space Science》2009,320(1-3):55-59
Two mechanisms of mass loss: galactic wind accompanied by the expulsion of supershell remnants and dust expelling from galaxies are briefly considered. Theoretically estimated parameters of the supershell fragments are similar to those of observed objects in vicinity of the Milky Way: small HI clouds and OIV structures observed with FUSE. Dust expelling brings dust in the IGM, and thus the analysis of intergalactic extinction curve will reveal a nature of the intergalactic dust. Evaporation of circumgalactic dust will change the chemical composition of gaseous galactic coronae. Ultraviolet observatories will have a significant impact on studies of these processes. Some prospects of such observations are outlined. 相似文献
20.
《Icarus》1987,69(1):33-50
Spectrophotometric data on groups of asteroids in different types of orbits reveal different distributions of spectral properties, depending on whether the orbits are cometary or noncometary. In a list of 10 asteroids frequently suggested on purely dynamical grounds to be extinct or dormant comets, all have properties suggestive of spectral classes D, P, or C. Preliminary IRAS albedo results support this. Objects in these classes are very dark, reddish-black to neutral-black, and prevalent among the Trojans and outer belt. Two comets observed at low activity (visible nuclei) also have properties more consistent with D asteroids than any other class (very low reported geometric albedos of 0.02 and red colors). Consistent with these results are very low albedos reported for materials in more than a dozen comets; they average 0.05. Also, sampled cometary dust particles appear to consist of dark carbonaceous materials. Dramatically different are a control group of 13 Aten/Apollo/Amor objects selected from noncometary orbits. Most are in moderate-albedo classes: 8 or 9 appear to be of class S, and only 1 is in a low-albedo class (C). These are probably mostly objects perturbed out of the inner asteroid belt. The preponderence of S's in the noncometary group, together with the preponderence of ordinary chondrites among meteorites, may be evidence that such meteorites came from S asteroids. The data indicate that extinct, dormant, inactive, and minimally active comet nuclei have low albedos (pv=a few percent) and very red to moderately red colors. As a group, their spectra are more similar to those of outer Solar System asteroids of classes D, P, and C, than to those of inner belt classes, though the observations are frequently not yet complete enough to assign definitively a spectral class. The results, taken together, support the view that dynamically identified “extinct comet candidates” are indeed outer Solar System objects probably of cometary origin. The results also support a scenario of Solar System formation in which dark carbonaceous dust dominated the spectrophotometric properties of planetesimals formed from about 2.7 AU out to at least the Trojan region at 5.2 AU. From 2.7 to at least 5.2 AU, and from class C to class D, the color of this dust reddens, apparently due to increasing amounts of red organic condensates. Comets are probably also colored to different degrees, by dust of this type, and may in some cases be even redder than D asteroids. 相似文献