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1.
Tisserand's definition of the “sphere of action” of a planet is based on the equality of tidal vs. gravitational acceleration ratios of the sun and planet. Öpik and others based their relation on equating the differential solar and planetary forces on the particle.Neither expression was formulated to describe the zone of influence surrounding a planet when considering the small but significant (i.e. long-term) perturbative effects of the planets on a particle's orbital elements. For the purpose of determining these effects on interplanetary dust we dervive a zone of influence based on equating the gravitational forces of the sun and planet, and demonstrate its applicability by utilizing the particle's closest approach to the planet as a measure of the zone of influence. 相似文献
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《Icarus》1987,71(1):137-147
Control networks of the five large satellites of Uranus have been established photogrammetrically from pictures taken by the Voyager 2 spacecraft. The control networks cover the illuminated southern hemisphere of each satellite. Coordinates are listed for 103 points on Miranda, 52 points on Ariel, 43 points on Umbriel, 46 points on Titania, and 34 points on Oberon; some points are identified on the U.S. Geological Survey maps of these satellites. Miranda is ellipsoidal in shape with radii of 241, 235 and 232 km. Mean radii are 579 km for Ariel, 586 km for Umbriel, 790 km for Titania, and 762 km for Oberon. 相似文献
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Emel’yanov N. V. Arlot J.-E. Hestroffer D. Varfolomeev M. I. Beskakotov A. S. 《Solar System Research》2022,56(5):308-317
Solar System Research - The article presents new results on motion modeling and creation of ephemeris of satellites of asteroids based on observations. In previous work on the project, ephemeris of... 相似文献
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V.S. Kalantonis E.A. Perdios A.E. Perdiou O. Ragos M.N. Vrahatis 《Astrophysics and Space Science》2003,288(4):479-488
The techniques used for the numerical computation of families of periodic orbits of dynamical systems rely on predictor-corrector
algorithms. These algorithms usually depend on the solution of systems of approximate equations constructed from the periodicity
conditions of these orbits. In this contribution we transform the root finding procedure to an optimization one which is applied
on an objective function based on the exact periodicity conditions. Thus, the determination of periodic solutions and families
of such orbits can be accomplished through unconstrained optimization. In this paper we apply and compare some well-known
minimization methods for the solution of this problem. The obtained results are promising.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
Alan D. Howard 《Icarus》1978,34(3):581-599
The circumpolar stepped topography observed within the Martian polar regions can have originated from one of a limited number of processes, including (i) erosion of resistant layers, (ii) erosion rates inversely proportional to slope gradient, (iii) basal sapping, and (iv) bistable rates of erosion and deposition. The last mechanism appears most likely to operate on the polar escarpments, driven by ablation of volatiles on the dark scarps and deposition on the icy flats. Decreasing albedo and a corresponding increase in radiation input caused by dust accumulations on the ablating layered deposits on steeper slopes provides a metastable erosion rate model sufficient to produce a stepped topography. Wind erosion is presuured later to remove the loose excess residual dust which accumulated during ablation of the scarps. The ablation of the scarps contemporaneously with ice accumulation on the flats implies the layered deposits exposed on the scarps have formed beneath overlying flats, and the observed unconformities within these deposits can due to the exposure of deposits laid down under more than one flat with different gradients. The linearity and mutual parallelism of the scarps is a result of scarp retreat on a regional slope or with a prefered direction of scarf retreat. The spiral arrangement of the scarps is probably due to more rapid retreat of scarps facing slightly west of the equatorward meridian, that is, in the direction of greatest solar and atmospheric warming. The model suggest, but does not prove, that the layered deposits are mostly water ice, with small amounts of codeposited silicate dust and volcanic ash. 相似文献
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Recent probes of the planet Venus reveal a probable surface temperature exceeding 700K and a pressure exceeding 100 atm. A very dusty lower atmosphere may exist which is composed of micron-sized particles kept airborne by mild turbulence and a gentle circulation of deep adiabatic currents. A study of surface conditions responsible for generation and persistence of surface dust clouds is of fundamental importance in the radiative and dynamic properties of the atmosphere. Also spurious radar echoes may be caused by suspended particulate matter, thus explaining the high relief reported by radar altimeters.Equations describing transportation and deposition of dust and sand have been solved for the surface conditions of Venus. It is concluded that the minimum wind velocity for initiating grain movement is about one order of magnitude smaller than on Earth. In addition, this minimum wind velocity occurs for smaller particles on Venus than on Earth. Once the particles are raised, they can be maintained aloft for longer periods of time and over a larger size range on Venus.Surface structures such as ripples evolved from aeolian deposition are likely to be of smaller vertical dimensions but larger horizontally when compared with equivalent structures on Earth. 相似文献
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Several directional discontinuities in the plasma tail of Comet Austin 1982g are apparent on photographs obtained by different observers between 1982 Augut 17.84 and August 21.85. Furthermore, anomalous changes in the orientation of the inner tail axis with respect to the projection on the sky of the prolonged radius vector are noticed. An analysis based on the wind-sock theory of plasma comet tail orientations shows that changes in the azimuthal component of the solar-wind velocity would have produced the observed anomalies. No satellite data on interplanetary conditions were available to check the existence of such a solar-wind event. A type II–IV solar radio event observed on August 17.64, followed by a geomagnetic storm in August 20.67, might denote, however, the existence of a solar flare-generated interplanetary disturbance. 相似文献
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R.D. WolstencroftJ.A. Raven 《Icarus》2002,157(2):535-548
Although there are considerable technical challenges to be overcome during this decade, the prospects for the detection of Earth-like planets (ELPs) orbiting nearby stars are encouraging. If life has developed on some of the ELPs that may be discovered by sophisticated telescope systems, such as the Terrestrial Planet Finder, the detection of photosynthesis is an attractive possibility. Here we discuss the likely preconditions and subsequent events that have led to the occurrence of O2-producing photosynthesis on Earth and then extend this discussion to how this may have occurred on ELPs orbiting in the habitable zone of a variety of main-sequence stars from spectral type F0V to M0V. We point out how the need for liquid water and the need to avoid UV radiation have influenced the evolution of photosynthesis on Earth, how the absorption spectra of the dominant (chlorophyll) photosynthetic pigments may have been determined in natural selection, and how and when the evolution of the ability to use water as an electron donor took place. Models for the photosynthetic productivity of ELPs orbiting at the inner edge of the habitable zone are discussed both from aquatic and land-based photosynthesis, making some allowance for global cloud cover on the ELP. The photosynthetic generation of O2 is greatest on cloud-free planets with hot (e.g., F0V) parent stars, though the advantage over cooler stars depends on the fraction of the planet covered by oceans. The low O2 generation in ELPs orbiting cooler stars is due to the poor match between the parent star's spectral energy distribution and the assumption of terrestrial pigment properties. We discuss the possibility that a three- or four-photon mechanism might operate on such planets (as opposed to the two-photon system on Earth) and how it could influence the spectral properties of the ELP. We also emphasize the role of tectonic and other geological processes as well as biology in determining the O2 level on Earth and on ELPs. 相似文献
10.
Peter Thomas 《Icarus》1979,40(2):223-243
Viking Orbiter images have provided nearly complete coverage of the two satellites of Mars and have been used to construct maps of the surface features of Phobos and Deimos. The satellites have radically different appearances although nearly all features on both objects were formed directly or indirectly by impact cratering. Phobos has an extensive network of linear depressions (grooves) that probably were formed indirectly by the largest impact recorded on Phobos. Deimos lacks grooves as well as the large number of ridges that occur on Phobos. Craters on Deimos have substantial sediment fill; those on Phobos have none. Evidence of downslope movement of debris is prominent on Deimos but is rare on Phobos. Many of the differences between Phobos and Deimos may be caused by modest differences in mechanical properties. However, the lack of a very large crater on Deimos may be responsible for its lack of grooves. 相似文献
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Alvin Seiff Carol R. Stoker John D. Mihalov Christopher P. McKay 《Planetary and Space Science》2005,53(5):594-600
We report scale model laboratory experiments showing how an impact accelerometer on a planetary probe (based on the Huygens probe Phase A configuration) can provide significant information on the mechanical characteristics of the surface. In particular, solid and liquid surfaces can be discriminated. The density of liquids can in principle be determined from the peak deceleration, thereby providing a constraint on composition, although experimental uncertainties present challenges to the accuracy of this method. 相似文献
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使用上海天文台的１．５６ｍ望远镜和Ｓｅｒｉｅｓ２００ＣＣＤ照相机发现ＨａｌｅＢｏｐｐ彗星于１９９６年４月２１日至４月２３日期间有一次爆发,４月２２日彗星星等比前一天增亮了０２等,但一天后其亮度又大致恢复原来的亮度．这段时间内,彗头的半强度处的直径也有相应的变化． 相似文献
14.
This paper presents formulas for the calculation of the refraction anomalies caused by the inclination of atmospheric boundary layers. Anomalies were calculated for a few zenith distances for several different atmospheric models. It was established, that near Earth the atmospheric boundary layers have the global inclination in meridian plane near one minute of arc from North to South. They are calculated with standard deviation ±0.2′–±0.35′. The tilts are decreased gradually with the altitude and equal nearly 0 on the heights 8–10 km. Then direction of inclination is changed on opposite (from South to North) and maximum 1′ reaches on the heights 15–18 km. Next inclinations slowly decrease and equal 0 on the heights 28–30 km. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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N. N. Samus’ O. V. Durlevich A. V. Zharova E. V. Kazarovets N. N. Kireeva E. N. Pastukhova D. B. Williams M. L. Hazen 《Astronomy Letters》2006,32(4):263-273
We present a new electronic version of the third volume of the fourth edition of the General Catalogue of Variable Stars (GCVS) that contains data on 13 855 variables in the constellations Pavo-Vulpecula. The Name Lists of Variable Stars from no. 67 to no. 77 were included in the new version. The main distinctive feature of the new version is that improved J2000.0 equatorial coordinates (including those for 6163 stars corrected for the proper motions) based on the identifications with positional catalogues using finding charts and on our new measurements are presented for 13 812 stars. We searched for a number of stars on original plates from the plate stacks of several observatories and using images from digital sky surveys. Apart from the complete update of the positional information, we made several corrections that were found to be necessary after the publication of the GCVS Volume III (1985) and several corrections of the information about the variability features based on photometry from currently available automatic sky surveys. A number of problem identifications are described in detail. The new version completes our long-term work on the complete revision of the positional information in the GCVS. In the Conclusions, we give a list of references to new Internet resources. 相似文献
16.
Using a volume-limited sample of Main Galaxies from SDSS Data Release 5,we investigate the dependence of galaxy properties on local environment.For each galaxy,a local three-dimensional density is calculated.We find that the galaxy morphological type depends strongly on the local environment:galaxies in dense environments have predominantly early type morphologies.Galaxy colors have only a weak dependence on the environment.This puts an important constraint on the process of galaxy formation. 相似文献
17.
In the present study an investigation of the collision orbits of natural satellites of the Moon (considered to be of finite dimensions) is developed, and the tendency of natural satellites of the Moon to collide on the visible or the far side of the Moon is studied. The collision course of the satellite is studied up to its impact on the lunar surface for perturbations of its initial orbit arbitrarily induced, for example, by the explosion of a meteorite. Several initial conditions regarding the position of the satellite to collide with the Moon on its near (visible) or far (invisible) side is examined in connection to the initial conditions and the direction of the motion of the satellite. The distribution of the lunar craters-originating impact of lunar satellites or celestial bodies which followed a course around the Moon and lost their stability - is examined. First, we consider the planar motion of the natural satellite and its collision on the Moon's surface without the presence of the Earth and Sun. The initial velocities of the satellite are determined in such a way so its impact on the lunar surface takes place on the visible side of the Moon. Then, we continue imparting these velocities to the satellite, but now in the presence of the Earth and Sun; and study the forementioned impacts of the satellites but now in the Earth-Moon-Satellite system influenced also by the Sun. The initial distances of the satellite are taken as the distances which have been used to compute periodic orbits in the planar restricted three-body problem (cf. Gousidou-Koutita, 1980) and its direction takes different angles with the x-axis (Earth-Moon axis). Finally, we summarise the tendency of the satellite's impact on the visible or invisible side of the Moon. 相似文献
18.
The brightness temperature distributions of the solar atmosphere in the polar region at the distances from one to two solar radii during the solar activity minimum are reported. Observations of the maximum phase of the solar eclipse of March 29, 2006 were carried out simultaneously on two sectors of the RATAN-600 radio telescope over a wide range of centimeter waves, 1–31 cm. This study is based on a comparison of models and observations carried out on the northeastern sector of the RATAN-600. 相似文献
19.
Michael D. Moutsoulas 《Earth, Moon, and Planets》1973,8(3):392-430
The measured and calibrated coordinates of selenodetic control points on 35 Pic-du-Midi negatives obtained by the method of star-calibrated lunar photography (cf. Moutsoulas, 1970) are presented in this paper.Paper dedicated to Professor H. C. Urey on the occasion of his 80th birthday on 29 April 1973.Work supported under Contract F 61052-68-C-0002 and Grant AFOSR-72-2261 between the Aerospace Office of Scientific Research, U.S. Air Force, and the University of Manchester in England. 相似文献
20.
John T. Conway 《Monthly notices of the Royal Astronomical Society》2000,316(3):555-558
An infinite family of heterogeneous spheroids has been found for which exact or closed-form solutions for the Newtonian gravitational potential can be given. The family includes both axisymmetric spheroids and spheroids where the matter density varies harmonically with the azimuthal angle. For the axisymmetric family of spheroids, which have no azimuthal dependence of the density, the potential external to the spheroid is of the same form as the potential exterior to a spheroidal homoeoid. It is therefore constant on the surface of the spheroid and on all external spheroidal surfaces confocal with it. The potential is also constant on all internal confocal spheroidal surfaces, with the value on each confocal surface dependent on the density distribution chosen. However, the density is not constant on either concentric or confocal spheroids. These solutions can be considered to be generalizations of analogous spherical solutions given in a companion paper by Conway. For the classical solutions for homogeneous spheroids, the surface is not equipotential, and these are not included within the new family of solutions, except in the special case of a homogeneous sphere. 相似文献