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望远镜发明之后,由于伽利略立刻就用它看到了金星的盈亏、木星的卫星,于是人们对太阳系天体的观测投入了极大的热情,因为那时,人们心目中的宇宙主要是太阳系。到19世纪末,天文学家不但对太阳系天体的运行规律基本做到了如指掌,而且对行星的表面性质、结构,以及它们的卫星、光环都有了越来越多的了解,小行星的发现,对彗星 相似文献
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我们所在的太阳系,是银河系中一个典型的行星系。它以太阳为中心,包括八颗行星,即水星、金星、地球、火星、木星、土星、天王星和海王星;有至少167颗已知的卫星;一些矮行星（包括类冥天体）：还有大量的、难以计数的太阳系小天体。太阳拥有太阳系内已知质量的99．86％,并以引力主宰着太阳系;木星和土星是太阳系内最大的两颗行星,它们占了剩余质量的90％以上。 相似文献
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目前已发现了285颗围绕太阳系八大行星公转的卫星, 它们的轨道和物理性质呈现了丰富多样性. 目前为止, 几乎所有的卫星研究工作都基于单个卫星系统或者卫星群, 似乎缺少统一的研究. 提出了一个新的与行星性质无关、只与恒星半径有关的轨道参数n, 定义为以太阳半径为单位的轨道半长轴的自然对数. 不同行星的卫星的n值都存在双极分布, 绝大部分卫星在$n\gtrsim2$区间, 其次在$n\lesssim-1$区间, 位于中间区域的行星则很少. 从卫星物理参数和轨道参数与n的关系中发现, 分属六大行星的卫星有明显的共同特征. 首先, 轨道偏心率和轨道倾角偏大的卫星的n值都在3.5左右, 它们都是巨行星的不规则卫星. 其次, n值在-1和1之间的卫星绝大部分体积大、质量大、反照率高、自转速度慢. 从文献中找到11颗系外卫星候选体, 获得了它们轨道n值和卫星质量, 发现后者也是在-1< n< 1区间最大,其他区间偏小.这些统一的 规律暗示,太阳系内不同行星的卫星形成机制以及太阳系外卫星的形成机制可能一样或类似. 相似文献
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薛善夫 《中国天文和天体物理学报》1984,(2)
根据角动量守恒定律,笔者通过计算,定量的论证了行量、卫星是经过星云环形成的。在此基础上,进一步探讨了星云环的分布和行星、卫星质量分布的对应关系,得出了星去环形成的一个明显特征——级式分裂.这对行星、卫星的形成过程及其质量分布的规律性是一个新的认识,并为今后寻找太阳系新的天体以及分析宇宙飞行的安全性区域提出几点粗浅看法. 相似文献
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根据太阳系行星物质的主要性态和大小,人们通常将其分成行星（包括类地行星和类木行星）、卫星、小行星、彗星和流星体。类地行星包括水星、金星、地球和火星;类木行星包括木星、土星、天王星和海王星;质量较大的小行星和卫星的内部结构与类地行星相似,质量较小的小行星和卫星以及流星体主要由岩石和金属组成;彗星是含有太阳系形成时期物质且没有经过太多物理和化学演化的冰态小天体。 相似文献
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小行星是太阳系形成之初的原始产物,是围绕太阳运行的岩石或金属天体,但体积和质量比行星小得多,尺寸差别也很大--大至直径可达上千千米的小行星谷神星（2006年国际天文学会将其归类为矮行星）,小至几十米甚至几米的石块。 相似文献
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We have examined a wide range of physical, chemical, and thermal models of the atmosphere of Uranus. In that model, which we believe maximizes favorable conditions for the support of life [Weidenschilling and Lewis, Icarus20, 465–476 (1973)], we find the probability of growth of a contaminant terrestrial microorganisms to be nil. If, as is likely, conditions are even more extreme on Neptune, the probability of contamination of both of the outer planets Uranus and Neptune is nil. The Wiedenschilling and Lewis model guarantees the presence of water droplets through the temperature range 0 to 100°C; other published models add water liquid at higher temperatures or fail to provide liquid water at all within this temperature range. In this model the heavy elements (C, N, O, etc.) are enhanced in Uranus by a factor sufficient to form a deep massive cloud layer of aqueous ammonia solution droplets. We can estimate the probability of growth with respect to the following factors: the presence of stable liquid water, convection of parcels of atmosphere to lethally hot depths, solar energy sources reaching the water layer, organic molecular production by solar ultraviolet light, ammonia concentration at the water cloud level, ionic species distribution, and concentrations at the water cloud level. The evaluation of these factors suggests that most terrestrial life as we know it would be excluded on the basis of any one of them. We know of no organism that would be adapted to all the stringent Uranus conditions simultaneously. The discovery of even a single species of Earth organism that can survive or grow under allowable outer planetary conditions would establish new principles in biology.Titan, the methane-rich moon of Saturn, may be more hospitable for terrestrial organisms than any of the other objects of the outer solar system. Even there we see formidable barriers to the growth of an Earth organism in Titan's atmosphere. We recognize that revision of our views concerning Titan must occur as more is learned about this satellite.We advocate the abandonment, in principle, of the probabilistic approach to the estimation of growth of terrestrial organisms on spacecraft, planets, and satellites in the solar system. We do not support an approach which estimates probabilities of qualitatively unknown phenomena. We recommend a strategy which involves identification and intensive study of those organisms most likely to thrive under known conditions for each of the planets respectively. (Unknown environmental conditions may be allowed to vary optimally.) Some explicit areas for Earth-based experimentation are indicated. 相似文献
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Daniel R. Wells 《Astrophysics and Space Science》1995,227(1-2):255-263
It has been shown in detail by Wells (Wells, 1986) that the Bode numbers and measured velocity ratios of the planets are accurately predicted by the eigenvalues of the Euler-Lagrange equations resulting from the variation of the free energy of the generic plasma that formed the Sun and planets. This theory is reviewed and extended to show that the equations make accurate predictions for all the major planets out to and including Pluto. The semimajor axes and velocity ratios of Pluto and Neptune are predicted exactly. The Bode numbers are shown in Table I to correspond to the roots of the first-order Bessel functions. The extrema of the roots of the zeroth-order Bessel function predict the ratios of the measured planetary velocities almost without error for the outer planets. Both sets of roots correspond to the same eigenvalue solution of the forcefree equation. The eigenvalues are set by the initial energy input to the plasma nebula. Both the Titius-Bode series and Kepler's harmonic law are predicted by the relaxed state solution of the free-energy equation for the generic plasma that formed the Sun and planets. Newton's law of gravitation is not used in the calculations. The solution makes exact predictions for the outer planets where the Titius-Bode series fails completely.The work of Arp (Arp, 1985) adds to the growing body of observable evidence of objects which appear to be attached to galaxies or galaxy systems but display red shifts, sometimes quite large, differing from those of the associated galaxies. Adding to the mystery and confusion are a series of objects that have quantized red shifts.It is widely recognized that the history of these objects involves extremely high energy processes. The solutions of the equations of the relaxed state of the resulting high energy plasmas is discussed and it is shown that the predictions of red shift frequencies are quantized and agree numerically with many of the quantized shifts reported by Arp and Sulentic. 相似文献
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Connecting atmospheric science and atmospheric models for aerocapture at Titan and the outer planets
Many atmospheric measurement systems, such as the sounding instruments on Voyager, gather atmospheric information in the form of temperature versus pressure level. In these terms, there is considerable consistency among the mean atmospheric profiles of the outer planets Jupiter through Neptune, including Titan. On a given planet or on Titan, the range of variability of temperature versus pressure level due to seasonal, latitudinal, and diurnal variations is also not large. However, many engineering needs for atmospheric models relate not to temperature versus pressure level but atmospheric density versus geometric altitude. This need is especially true for design and analysis of aerocapture systems. Drag force available for aerocapture is directly proportional to atmospheric density. Available aerocapture “corridor width” (allowable range of atmospheric entry angle) also depends on height rate of change of atmospheric density, as characterized by density scale height. Characteristics of hydrostatics and the gas law equation mean that relatively small systematic differences in temperature versus pressure profiles can integrate at high altitudes to very large differences in density versus altitude profiles. Thus, a given periapsis density required to accomplish successful aerocapture can occur at substantially different altitudes (∼150-300 km) on the various outer planets, and significantly different density scale heights (∼20-50 km) can occur at these periapsis altitudes. This paper will illustrate these effects and discuss implications for improvements in atmospheric measurements to yield significant impact on design of aerocapture systems for future missions to Titan and the outer planets. Relatively small-scale atmospheric perturbations, such as gravity waves, tides, and other atmospheric variations can also have significant effect on design details for aerocapture guidance and control systems. This paper will discuss benefits that would result from improved understanding of Titan and outer planetary atmospheric perturbation characteristics. Details of recent engineering-level atmospheric models for Titan and Neptune will be presented, and effects of present and future levels of atmospheric uncertainty and variability characteristics will be examined. 相似文献
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The transmission of light through a planetary atmosphere can be studied as a function of altitude and wavelength using stellar or solar occultations, giving often unique constraints on the atmospheric composition. For exoplanets, a transit yields a limb-integrated, wavelength-dependent transmission spectrum of an atmosphere. When scattering haze and/or cloud particles are present in the planetary atmosphere, the amount of transmitted flux not only depends on the total optical thickness of the slant light path that is probed, but also on the amount of forward-scattering by the scattering particles. Here, we present results of calculations with a three-dimensional Monte Carlo code that simulates the transmitted flux during occultations or transits. For isotropically scattering particles, like gas molecules, the transmitted flux appears to be well-described by the total atmospheric optical thickness. Strongly forward-scattering particles, however, such as commonly found in atmospheres of Solar System planets, can increase the transmitted flux significantly. For exoplanets, such added flux can decrease the apparent radius of the planet by several scale heights, which is comparable to predicted and measured features in exoplanet transit spectra. We performed detailed calculations for Titan’s atmosphere between 2.0 and 2.8 μm and show that haze and gas abundances will be underestimated by about 8% if forward-scattering is ignored in the retrievals. At shorter wavelengths, errors in the gas and haze abundances and in the spectral slope of the haze particles can be several tens of percent, also for other Solar System planetary atmospheres. We also find that the contribution of forward-scattering can be fairly well described by modelling the atmosphere as a plane-parallel slab. This potentially reduces the need for a full three-dimensional Monte Carlo code for calculating transmission spectra of atmospheres that contain forward-scattering particles. 相似文献
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L. V. Ksanfomality 《Astronomy Letters》2007,33(7):488-497
Analysis of the data obtained during transits of low-orbit extrasolar planets across the stellar disk yields different estimates of their atmospheric loss rates. Experimental data point to the probable existence of several distinct subtypes of extrasolar giant planets, including “hot Jupiters” of low density (HD 209458b), with massive cores composed of heavy elements (HD 149026b), and others. We show that the expected hot-Jupiter mass losses due to atmospheric escape on a cosmogonic time scale do not exceed a few percent, while the losses through Jeans dissipation are negligible. We also argue that low-orbit giant planets should have a strong magnetic field that interacts with circumstellar plasma with the planet’s supersonic orbital velocity. The magnetic field properties can be used to search for extrasolar planets. 相似文献
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The Chree superposition analysis of the luminosities of the planets Jupiter, Saturn, Uranus and Neptune indicates a correlation between solar activity and planetary luminosity. The variations of the solar constant in the visible range are considered to be too small to explain the observed changes in brightness. The interaction of solar extreme ultraviolet or solar wind particles with the atmospheres of these planets is probably responsible for the increased albedo during periods of high solar activity. 相似文献
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Gunnar Fjeldbo 《Planetary and Space Science》1973,21(9):1533-1547
Spacecraft radio occultation measurements planned for outer planet missions may yield profiles in height of atmospheric refractivity and microwave loss above the super-refractive regions of the giant planets. In a planetary ionosphere, the refractivity determines the electron number density distribution. At lower levels, the loss and the refractivity may be used to study the density, pressure, temperature and composition of the atmosphere. In order to maximize the scientific yield of outer planet occultation experiments, it is necessary to consider the effects of atmospheric refraction, multipath propagation, navigation errors and spacecraft accelerations in the design of the radio system and the spacecraft attitude control system. 相似文献
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The velocity distribution function of a minor gaseous constituent escaping from a planetary atmosphere is perturbed from the equilibrium Maxwell-Boltzmann distribution function, There is a depletion in the high energy portion of the distribution function. The escape flux is consequently somewhat less than the Jeans flux obtained assuming complete equilibrium. The non-Maxwellian velocity distribution function for an escaping constituent is calculated with a Boltzmann equation modified by the addition of an isotropic sink term. The effects due to diffusion of particles and heat conduction are neglected. A discrete ordinate method which requires little computational time is employed in the solution of the Boltzmann equation. The corrections to the Jeans flux calculated in this way are compared with the results obtained with the Monte-Carlo techniques. The corrections for the escape of H and He from Earth, H from Mars and H2 from Titan are calculated. The reductions in the Jeans flux are largest for a light escaping gas and for small escape parameters. The depletion of fast particles also results in the cooling of the minor component below the temperature of the background gas. This effect is also studied for the escape of H from Earth. 相似文献
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Peter H. Stone 《Icarus》1975,24(3):292-298
Current knowledge of the atmosphere of Uranus is reviewed and specific objectives are suggested for satellite missions to Uranus. The anomalous composition of Uranus makes determinations of its atmospheric composition particularly valuable for testing theories of solar system evolution. The weakness of its atmospheric heating makes the determination of its atmospheric structure and dynamics particularly valuable for testing theories of atmospheric behavior. The large axial inclination of Uranus implies an anomalous latitudinal variation of temperature and dynamics different from that of the other planets. 相似文献
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A combined fluid/kinetic model is developed to calculate thermally driven escape of N2 from Pluto’s atmosphere for two solar heating conditions: no heating above 1450 km and solar minimum heating conditions. In the combined model, one-dimensional fluid equations are applied for the dense part of the atmosphere, while the exobase region is described by a kinetic model and calculated by the direct simulation Monte Carlo method. Fluid and kinetic parts of the model are iteratively solved in order to maintain constant total mass and energy fluxes through the simulation region. Although the atmosphere was found to be highly extended, with an exobase altitude at ～6000 km at solar minimum, the outflow remained subsonic and the escape rate was within a factor of two of the Jeans rate for the exobase temperatures determined. This picture is drastically different from recent predictions obtained solely using a fluid model which, in itself, requires assumptions about atmospheric density, flow velocity and energy flux carried away by escaping molecules at infinity. Gas temperature, density, velocity and heat flux versus radial distance are consistent between the hydrodynamic and kinetic model up to the exobase, only when the energy flux across the lower boundary and escape rate used to solve the hydrodynamic equations is obtained from the kinetic model. This limits the applicability of fluid models to atmospheric escape problems. Finally, the recent discovery of CO at high altitudes, the effect of Charon and the conditions at the New Horizon encounter are briefly considered. 相似文献