Effects of a close encounter with Jupiter on different populations of planet-crossing objects

The evolutions of different planet-crossing populations due to a close encounter with Jupiter are examined and the implications on materials displacement throughout the solar system are discussed. The effects of the encounter are shown to be very important for those planet-crossers that could be responsible of planets surface cratering.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.     

Stability of the solar system

If the solar system is considered as a mechanical clockwork consisting of its present members which attract each other as mass-points, the extent of its present approach to secular stability (i.e., the state of minimum potential energy) — manifested by the existence of a number of nearcommensurabilities of the present orbital periods, not only of the planets, but also of their satellites —could not have been attained in a time-span of 4.6×10⁹ yr of its age by gravitational perturbations alone.The existence of such commensurabilities — striking in many instances— could then be understood only on the assumption that either (a) the solar system was actually born with the present 2-, 3- and 4-term couplings between the orbital period of the planets already built-in from the outset (which is improbable on any known grounds); or (b) that these couplings — in particular, the 25 Jupiter-Saturn commensurability — have arisen as a result of tidal interaction between proto-planetary globes of much larger dimensions than these planets possess today. For the present dimensions and mutual distances of these planets, their tidal interaction in 10⁹ yr would exert but negligible effects; and during that time neither their masses, nor the scale of the solar system underwent any essential change.Therefore, a hypothesis is proposed that the situation now obtaining had its origin in the early days of the formation of the solar system, when the planetary globes — in particular, those of Jupiter and Saturn (now in the terminal stage of Kelvin contraction) — were very much larger than they are today; and when, as a result, the tidal coupling between them operated at a much higher rate than at the present time.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.     

Dynamics,interrelations and evolution of the systems of asteroids and comets

The dynamics of larger interplanetary bodies is reviewed, with emphasis on evolutionary problems, interrelations, and open questions. Observational biases distinguishing the sample of known objects from the whole population are briefly discussed. A schematic division of the solar system into zones with different regimes of motion, and a rough taxonomy of orbit types are attempted. The role of individual major planets in controlling the dynamical evolution of interplanetary objects, in particular by stabilizing resonances and destabilizing close encounters, is compared. There are significant evolution asymmetries due to boundary conditions and preferential evolutionary paths; individual major displacements in the phase space of orbital elements conserve the Tisserand invariant with respect to the planet responsible, thus favouring certain evolutionary sequences against others. Very limited lifetimes of some orbit types imply a long-term balance between source and sink, and require a continuous supply of objects from other types of orbits. In this respect, the ultimate fate of extinct comets is of particular interest. Under very specific conditions, nongravitational effects of mass loss can result in stabilization of a formerly unstable orbit. Since the dividing line between the two basic interplanetary populations distinguished by origin and composition — the asteroids and the comets — is essentially that between stable and unstable motion, orbital data can be used to specify which of the known asteroid-like objects may be devolatilized cometary nuclei.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.     

The Genesis solar wind sample return mission: Past,present, and future

The Genesis Discovery mission returned solar matter in the form of the solar wind with the goal of obtaining precise solar isotopic abundances (for the first time) and greatly improved elemental abundances. Measurements of the light noble gases in regime samples demonstrate that isotopes are fractionated in the solar wind relative to the solar photosphere. Theory is required for correction. Measurement of the solar wind O and N isotopes shows that these are very different from any inner solar system materials. The solar O isotopic composition is consistent with photochemical self‐shielding. For unknown reasons, the solar N isotopic composition is much lighter than essentially all other known solar system materials, except the atmosphere of Jupiter. Ne depth profiling on Genesis materials has demonstrated that Ne isotopic variations in lunar samples are due to isotopic fractionation during implantation without appealing to higher energy solar particles. Genesis provides a precise measurement of the isotopic differences of Ar between the solar wind and the terrestrial atmosphere. The Genesis isotopic compositions of Kr and Xe agree with data from lunar ilmenite separates, showing that lunar processes have not affected the ilmenite data and that solar wind composition has not changed on 100 Ma time scales. Relative to Genesis solar wind, ArKrXe in Q (the chondrite noble gas carrier) and the terrestrial atmosphere show relatively large light isotope depletions.     

Solar cycle variation of large-scale coronal structures

A green line intensity variation is associated with the interplanetary and photospheric magnetic sector structure. This effect depends on the solar cycle and occurs with the same amplitude in the latitude range 60° N–60° S. Extended longitudinal coronal structures are suggested, which indicate the existence of closed magnetic field lines over the neutral line, separating adjacent regions of opposite polarities on the photospheric surface.Supported by an ESRO/NASA fellowhip.On leave from Torino University, Italy; now at Istituto di Fisica, Universita di Torino, Italy.     

Numerical integration methods in dynamical astronomy

We review what kinds of numerical integrators are used by astronomers in the field of dynamical astronomy and to what problems they are applied. This review is based on the questionaires distributed mainly to the members of IAU Commission 7 (Celestial Mechanics). Because of the restriction to the Commission 7 members, the answers are mainly from astronomers in the solar system dynamics and problems mentioned in the answers are also related to celestial bodies in the solar system. Other than above, two questions, how to check the precision or accuracy of numerically integrated results and how to treat a close approach, are also surveyed. The problem of the suitable choice of a numerical integrator from various numerical integrators is out of the scope of this review, and it depends strongly on the dynamical nature of a particular dynamical system and the required accuracy.     

太阳大气等离子体的电流研究

该文讨论了太阳大气等离子体中电流的成因和对各种爆发活动的作用和影响,对目前的研究现状和存在的问题进行了分析讨论,指出虽然磁场是太阳物理观测和研究的关键要素,但是电流也是理解能量的传输与耗散、不稳定性的驱动和激发、等离子体的加热和粒子加速等太阳物理过程的重要概念.该文还提出了一个定性的改进电路模型,认为电流主要产生于太阳内部的发电机过程,同时电路在日冕部分的环形磁场位型也将产生部分新经典电流,通过磁通量管流入太阳大气,并在日冕区域通过磁场重联等过程释放能量.对该模型尚待解决的问题也进行了简单讨论.     

On sheared magnetic field structures containing neutral points

This paper discusses the occurence of current sheets near the separatrix in sheared magnetic field structures containing an x-type neutral point, as suggested by a number of previous authors. Our approach is based on selfconsistent theory. In analogy to the theory of quasistatic convection by Grad, we interpret the break-down of the quasistatic theory near the separatrix as evidence for the occurence of a boundary layer. In particular, this picture suggests large (however integrable) current sheets, with the current flowing parallel to the poloidal magnetic field. This concept is also tested by numerical computations. Here the discretization procedure simulates those physical effects that in a real case would keep the current from becoming infinitely large. The results fully confirm the formation of current sheets. Our findings have potential applications to energy storage for solar flares and to the heating of the solar corona.     

Automatic guiding of the primary image of solar Gregory telescopes

The primary image reflected from the field stop of solar Gregory telescopes is used for automatic guiding. This new system avoids temporal varying influences from the bending of the telescope tube by the main mirror's gravity and from offsets between the telescope and a separate guiding refractor. The required stiffness of the guider mechanics and the small areas of the sensors demand small f numbers for the guider optics, which cause problems with the image quality and with heat. Problems also arise from the pinhole in the telescope's field stop which is imaged as a dark dot on the sensor. Pointing errors introduced by the telescope affect shifts of the solar image on the sensor. These are numerically determined by Fourier methods which are found to be less sensitive to noise than profile centering methods. Several types of guiders are tested, the final equipment, now installed at the Gregory telescopes at Tenerife and at Locarno, is described.     

Tidal-friction theory of the Earth-Moon system

The standard discussion of tidal friction in the Earth-Moon system has been that given by Jeffreys in successive editions ofThe Earth over the past several decades. It is herein shown to contain several erros vitiating its results. The dynamical equation utilised for finding the rate of change of angular velocity of the Earth fails to take account of the fact that the moment of inertia of the Earth may be changing with time, and all subsequent equations which depend on this are incorrect as a result. Simple equations have been left unsolved that ought to have been solved, and the alleged numerical conclusions in no way follow from the values set down initially for the observed apparent secular accelerations of the Moon and Sun.The revised dynamical equations are shown to enable the lunar and solar tidal couples to conform to theory, and may imply that the moment of inertia of the Earth is decreasing at a non-negligible rate. Recognition of this is the key to the whole problem. The only available hypothesis providing adequate contraction is that following from the phase-change theory of the nature of the terrestrial core, and the value of the rate of decrease of moment of inertia calculated from this is in close agreement with that implied by modern improved values of the secular accelerations.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.     

太阳活动极大和极小期太阳磁场周期变化研究

利用Wilcox天文台1975年到2010年间的太阳磁场数据,分析了太阳平均磁场在太阳活动极大和极小时期的短时周期性.结果显示太阳磁场主要具有9 d、13.5 d、27 d左右的周期.在太阳活动极大时期,27 d左右周期最为显著,而在太阳活动极小时期最显著的周期为13.5 d左右(1984～1986年间的太阳活动极小时期除外).这些结果说明太阳的活动区域在活动极大和极小时期具有明显不同的分布.     

Formation of the sodium clouds and the regolith on Io by micrometeoroid impacts

The effects of the amount of sodium ions, their solar angles correlation, temperature and velocities, have been explained as consequences of the almost full penetration of the second mode of micrometeorite fluxes (M>10^–8 g) across the Io atmosphere to its surface, whereas volcanism may satisfy only the amount of sodium.Conclusions about the formation of fine grains on the Io surface, unflooded by lava, are presented. Due to its large specific surface (m² g^–1) the interaction of this topsoil and the Io atmosphere is no less important than the lava-atmosphere interaction.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.From September 1979.     

New views of the lunar plasma environment

A rich set of new measurements has greatly expanded our understanding of the Moon–plasma interaction over the last sixteen years, and helped demonstrate the fundamentally kinetic nature of many aspects thereof. Photon and charged particle impacts act to charge the lunar surface, forming thin Debye-scale plasma sheaths above both sunlit and shadowed hemispheres. These impacts also produce photoelectrons and secondary electrons from the surface, as well as ions from the surface and exosphere, all of which in turn feed back into the plasma environment. The solar wind interacts with sub-ion-inertial-scale crustal magnetic fields to form what may be the smallest magnetospheres in the solar system. Proton gyro-motion, solar wind pickup of protons scattered from the dayside surface, and plasma expansion into vacuum each affect the dynamics and structure of different portions of the lunar plasma wake. The Moon provides us with a basic plasma physics laboratory for the study of fundamental processes, some of which we cannot easily observe elsewhere. At the same time, the Moon provides us with a test bed for the study of processes that also operate at many other solar system bodies. We have learned much about the Moon–plasma interaction, with implications for other space and planetary environments. However, many fundamental problems remain unsolved, including the details of the coupling between various parts of the plasma environment, as well as between plasma and the surface, neutral exosphere, and dust. In this paper, we describe our current understanding of the lunar plasma environment, including illustrative new results from Lunar Prospector and Kaguya, and outstanding unsolved problems.     

The polarization-free approximation

The development of effective iterative methods capable of accurately solving NLTE Stokes transfer problems is of considerable importance for the investigation of solar and stellar magnetic fields. After briefly indicating the iterative approach which is being presently pursued for the exact solution of such problems, the particular regime where polarization signals can only be due to the Zeeman effect is considered in some detail. By means of NLTE Stokes transfer calculations for a two-level atomic model it is first shown that the currently-used field-free approximation (Rees, 1969) cannot be safely applied in the presence of magnetic field gradients. Such gradients lead to changes in the shape and width of the line profiles and they can produce non-negligible effects on the atomic level populations and line source functions. A new approximate method is then proposed, which does not require the actual solution of the Stokes vector transfer equation and is practically as fast as the field-free one. This polarization-free approximation provides a fairly good account of the effects of homogeneous and inhomogeneous magnetic fields on the statistical equilibrium and is very easy to implement in any existing non-magnetic, multi-level transfer code.On leave from the Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze, Largo E. Fermi 5, I-50125 Firenze, Italia     

Accretion and Early History of Planetesimals and Planets: The Noble Gas Record

Some of the distinct noble gas “components” in meteorites represent a record of processes during and even before solar system formation. This record is difficult to interpret. Often, one of the major problems is to recognize whether a certain noble gas elemental and isotopic pattern has been established in a presolar epoch, later in the solar accretion disk, during meteorite parent body formation or finally as a result of metamorphism on a parent body. It would also appear that noble gases are a preferred tool to deduce the types of matter from which the Earth and other planets accreted—if the respective parent materials are present in our extraterrestrial sample collections at all. However, also this issue is unsettled. Noble gas isotopes originating from the decay of radioactive precursors allow us to study the early and later degassing history of terrestrial planets, although the interpretation often remains model-dependent. This contribution briefly reviews some of the fundamental aspects of the noble gas record in meteorites and planets.     

Ozone and temperature fluctuations in the strato-mesosphere with solar activity

The response of the stratosphere and lower mesosphere to quasi-eleven-year solar activity cycle (indicated by sunspot variations) is studied by using temperature data obtained from rockets which are mostly based on datasonde system throughout the decade 1969–1978. It is suggested that the solar trace is evident at wintertime in the strato-mesosphere over low and middle latitudes. At summertime in the lower mesosphere over high latitudes the solar trace is absent. During springtime the solar signal appears over low latitudes and diminishes to the middle and high latitudes. The reverse occurs at falltime. The observed stratospheric temperature and ozone variations during the solar activity cycle are possibly within model calculations of UV and solar particle enhancements at solar maximum.     

Glaciopanspermia: Seeding the terrestrial planets with life?

The question whether life originated on Earth or elsewhere in the solar system has no obvious answer, since Earth was sterilized by the Moon-forming impact and possibly also during the LHB, about 700 Ma after the formation of the solar system. Seeding by lithopanspermia has to be considered. Possible sources of life include Earth itself, Mars, Venus (if it had a more benign climate than today) and icy bodies of the solar system. The first step of lithopanspermia is the ejection of fragments of the surface into space, which requires achieving at least escape velocity. As the velocity distribution of impact ejecta falls off steeply, attention is drawn to bodies with lower escape velocities. Ceres has had, or still has, an ocean more than 100 km deep, with hydrothermal activity at its rocky core. The possible presence of life, its relative closeness to the terrestrial planets and Ceres' low escape velocity of 510 m/s suggest that Ceres could well be a parent body for life in the solar system.Icy impact ejecta - hence glaciopanspermia - from Ceres will be subject to evaporation of volatiles. Spores may be loosened by evaporation and enter the atmospheres of the terrestrial planets as micrometeorites.The seeding of the terrestrial planets from Ceres would result in (1) detection of life in the crustal layers of Ceres; (2) a commonality of Cerean life with Terran and possible Martian and Venusian life and (3) biomarkers of Cerean life, which might be found in the ice at the Moon's poles and on the surface of other main belt asteroids.     

Certain problems of solar and heliospheric physics in the light of novel satellite data

Recent satellite data have given a better insight into the possible nature of extremely strong disturbances on the Sun and in the heliosphere by relating them to processes in the solar interior. The energy, momentum, and mass transfer on various spatiotemporal scales are organized in the Sun into a hierarchy of coupled nonlinear processes. Confirmation has been given to the fact that coronal mass ejections and solar flares are not linked causally but merely reflect the existence of two channels of free-energy dissipation in the solar atmosphere in the form of plasma motion and plasma emission; their relative role can be described by a corresponding nondimensional parameter. Information on the global asymmetry of the solar emission and active processes has been gained. A great diversity in the geometry of eruptive events (not necessarily associated with magnetic reconnection) has been revealed. In our opinion, the basic unresolved problems in the investigation of solar activity dictate the necessity of carrying out more accurate, absolutely calibrated measurements of the whitelight solar emission at appropriately high spatiotemporal resolutions. The development of direct and indirect techniques of measuring the electric fields and currents with the aim of reconstructing the solar and heliospheric current system remains a challenging task.     

First Results from SWAN Lyman α solar wind mapper on SOHO

After one year of almost flawless operation on board the SOHO spacecraft poised at L1 Lagrange point, we report the main features of SWAN observations. SWAN is mainly dedicated to the monitoring of the latitude distribution of the solar wind by the Lα method. Maps of sky Lα emissions were recorded througout the year. The region of maximum emission, located in the upwind hemisphere, deviates strongly from the pattern that could be expected from a solar wind constant with latitude. It is divided into two lobes by a depression aligned with the solar equatorial plane called the Lyα groove already noted in 1976 Prognoz data. The north lobe is much brighter than the south lobe. These two characteristics can be explained qualitatively by an enhanced ionization along the neutral sheet where the slow solar wind is concentrated, which results from the higher low-latitude solar wind mass flux as measured by Ulysses. The groove is the direct imprint on the sky of the enhanced carving by the slow solar wind, at this time of solar minimum, when the tilt angle of the neutral sheet is small. The question is still pending to predict what will happen with the ascending phase of the solar cycle. Observations of comets are briefly mentioned, with the ability of SWAN to monitor the H₂O production of many comets. Operations of the instrument are briefly described, including some instrumental problems which could be solved by software modifications sent to the instrument. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004979605559     

Periodic Variability of Visual Sporadic Meteor Rates

A long-term variability of visual sporadic meteor hourly rates is studied in the period between 1984 and 2006. The present analysis involves four particular periods of visual sporadic meteor activity in January, March, July and September over two solar cycles, and the results reveal that the observed visual sporadic meteor rates vary periodically in the course of the solar cycle. It is found that the highest sporadic meteor rates are observed in the years near solar activity maxima, and their variability directly correlates with solar activity expressed by International sunspot numbers.