The solar wind in the outer solar system

The properties of the solar wind including magnetic fields, plasma, and plasma waves are briefly reviewed with emphasis on conditions near and beyond the orbit of Jupiter. An extrapolation of the steady-state wind to large distances, evolution of disturbances and structure, modulation of cosmic rays, interactions with planetary bodies (bow shocks and magnetosheaths), and interactions with interstellar neutral helium and hydrogen are briefly discussed. Some comments on instrumentation requirements to observationally define the above phenomena are also included.This is one of the publications by the Science Advisory Group.     

Radio physics of the outer solar system

The remote sensing of low frequency nonthermal radio emission is the astronomy of field and particle phenomena. Observations conducted from space lead to information about the composition and dynamic processes occurring in planetary magnetospheres as well as within the interplanetary and interstellar medium. The potential of this technique is demonstrated by considering observations obtained from Earth orbit missions.This is one of the publications by the Science Advisory Group.     

Planetary magnetism in the outer solar system

A brief review of the salient considerations which apply to the existence of magnetic fields in connection with planetary and subplanetary objects in the outer solar system is given. Consideration is given to internal dynamo fields, fields which might originate from interaction with the solar wind or magnetospheres (externally driven dynamos) and lastly fossil magnetic fields such as have been discovered on the Moon. Where possible, connection is made between magnetism, means of detection, and internal body properties.This is one of the publications by the Science Advisory Group.     

Fields and plasmas in the outer solar system

The most significant information about fields and plasmas in the outer solar system, based on observations by Pioneer 10 and 11 investigations, is reviewed. The characteristic evolution of solar wind streams beyond 1 AU has been observed. The region within which the velocity increases continuously near 1 AU is replaced at larger distances by a thick interaction region with abrupt jumps in the solar wind speed at the leading and trailing edges. These abrupt increases, accompanied by corresponding jumps in the field magnitude and in the solar wind density and temperature, consist typically of a forward and a reverse shock. The existence of two distinct corotating regions, separated by sharp boundaries, is a characteristic feature of the interplanetary medium in the outer solar system. Within the interaction regions, compression effects are dominant and the field strength, plasma density, plasma temperature and the level of fluctuations are enhanced. Within the intervening quiet regions, rarefaction effects dominate and the field magnitude, solar wind density and fluctuation level are very low. These changes in the structure of interplanetary space have significant consequences for the many energetic particles propagating through the medium. The interaction regions control the access to the inner solar system of relativistic electrons from Jupiter's magnetosphere. The interaction regions and shocks appear to be associated with an acceleration of solar protons to MeV energies. Flare-generated shocks are observed to be propagating through the outer solar system with constant speed, implying that the previously recognized deceleration of flare shocks takes place principally near the Sun. Radial gradients in the solar wind and interplanetary field parameters have been determined. The solar wind speed is nearly constant between 1 and 5 AU with only a slight deceleration of 30 km s⁺¹ on the average. The proton flux follows an r ⁺² dependence reasonably well, however, the proton density shows a larger departure from this dependence. The proton temperature decreases steadily from 1 to 5 AU and the solar wind protons are slightly hotter than anticipated for an adiabatic expansion. The radial component of the interplanetary field falls off like r ⁺² and, on the average, the magnitude and spiral angle also agree reasonably well with theory. However, there is evidence, principally within quiet regions, of a significant departure of the azimuthal field component and the field magnitude from simple theoretical models. Pioneer 11 has obtained information up to heliographic latitudes of 16°. Observations of the interplanetary sector structure show that the polarity of the field becomes gradually more positive, corresponding to outward-directed fields at the Sun, and at the highest latitudes the sector structure disappears. These results confirm a prior suspicion that magnetic sectors are associated with an interplanetary current sheet surrounding the Sun which is inclined slightly to the solar equator.Proceedings of the Symposium on Solar Terrestrial Physics held in Innsbruck, May–June 1978.     

Mission building blocks for outer solar system exploration

Summary A meaningful outer-planet exploration program can be conducted within expected economic constraints. The spacecraft needed can be developed in an evolutionary manner from the existing Pioneer and Mariner families. Advanced propulsion capability may reduce the costs associated with constrained weight margins and long trip times.This is one of the publications by the Science Advisory Group.     

Electrodynamics of the outer solar atmosphere

The structure of the outer solar atmosphere and its magnetic coupling to the photospheric motions indicate the existence of large-scale current systems. The heating and the dynamics of coronal structures is therefore governed by electrodynamic coupling of these structures to the underlying photosphere. In a structured corona, the heating is enhanced because of several processes such as resonance absorption of Alfvénic surface waves, anomalous Joule heating, reconnection and the related topological dissipation. The global thermal and dynamic behaviour of coronal structures can be fruitfully described in terms of equivalent electrodynamic circuits, taking into account the paramount role of the photospheric boundaries. Coronal current systems may be stable, as in the case of coronal loops, but occassionally they show catastrophic behaviour if the current intensity surpasses a critical threshold.     

Chemistry of the solar nebula

The composition, mineralogy and texture of chondritic meteorites suggest they are relatively unaltered relicts of the condensation and accretion processes which took place in the primitive solar nebula. Chondrites thus are thought to contain a unique record of the physico-chemical conditions which prevailed at the time and place (asteroid belt) of their origin. Elemental abundance patterns are an important clue to the events and processes. Most elements can be placed in one of four groups according to their observed fractionation behavior in chondritic material: refractory, siderophile, normally depleted and strongly depleted. This grouping can be explained in terms of four events which presumably took place during cooling, condensation and accretion in the nebula. In order of inferred occurrence these are: (1) partial loss of the initial condensates rich in refractory elements at T > 1300K, (2) partial loss of metallic Fe-Ni grains, perhaps because they were magnetic, at 1000 to 700K, (3) partial remelting and outgassing of the condensate (chondrule formation) at 600 to 350K, and (4) accretion, when the P-T conditions controlled the volatile content (500 to 350K). Total gas pressure at the time and place of accretion is estimated to fall between 10^-–6 and 10^–-4 atm.Contribution No. 80, Center for Meteorite Studies.     

Communicating across the solar system

The next chapter in our ongoing quest for discovery began in the last half of the 20th century, with the initiation of robotic exploration of our solar system. In less than fifty years, we have broken free of Earth's gravity and flown spacecraft to every planet in the solar system except Pluto. The ultimate goal of this exploration is to establish a virtual (and, perhaps, someday, an actual) human presence throughout the solar system. Clearly, communications is one of the central elements of creating such a virtual presence, and also one of the biggest technical challenges in planetary exploration. Transmit performance is characterized by the product of antenna gain and transmitter power, while receive performance scales with the ratio of aperture effective area to system noise temperature. A number of key communications technology advances have enabled our planetary exploration to date, and future technology will open the door to new vistas in space exploration     

Minor objects in the solar system

The present status of theory and experiment relating to interplanetary bodies larger than molecules but smaller than asteroids is reviewed. The dynamics, nature, and origins of these objects are considered. The evidences from rocket and spacecraft measurements, meteor observations, terrestrial accretion and light-scattering phenomena are presented. The various lines of research are leading to a better understanding of these bodies, but there are many uncertainties to be resolved.This article was written independently but with approval of the National Aeronautics and Space Administration. The views or conclusions contained herein should not be interpreted as representing the official opinion of NASA.     

Supernovae and the origin of the solar system

This review concentrates on recent ideas involving a relationship between the early solar system and supernova explosions. It summarizes briefly the data that has helped inspire those ideas. Because the true relationship is still unknown and generates controversy, the distinct ideas are introduced singly in the historical context of their origins, and the active sense of surprise and controversy is visible. Quotations from pivotal papers are used as part of the exposition. The subject involves equally the isotopic anomalies detected in meteorites and the dynamic events of galactic evolution, nucleosynthesis, and protosolar collapse. Whatever the correct situation is, new connections have been found between the origin of the elements and the formation of the solar system. The objective of this review is to enable interested space scientists to quickly identify the competing points of view and the experiments and theories that have led to them.     

Abundances of the elements in the solar system

The present status of abundance information for elements in meteorites and in the Sun is reviewed, and a new table of abundances of the elements, which should be characteristic of the primitive solar nebula, is compiled and presented. Special attention is called to the elemental abundances in the silicon-to-calcium region, where many of the abundances are rather poorly determined, and where these abundances have an impact on theories of nucleosynthesis of the elements. To each elemental isotope is assigned a mechanism of nucleosynthesis which may have been responsible for production of most of that isotope, and brief comments are made concerning the present status of understanding of the different mechanisms of nucleosynthesis.This paper not presented at the Symposium on Cosmochemistry.     

Unmanned scientific exploration throughout the solar system

Velocity requirements for scientific probe vehicles operating throughout the entire solar system are presented. Both direct flights and those using planetary swingby modes are considered. Launch-vehicle and payload sizes necessary to perform useful scientific missions are examined. Scientific investigation of the solar system is shown to be much less difficult than is commonly believed.     

Global energy regulation in the solar wind-magnetosphere-ionosphere system

Some basic concepts which are essential in the understanding of global energy regulation in the solar wind-magnetosphere-ionosphere system are introduced. The importance of line-tying concept is particularly emphasized in connection with the solar wind enetry, energy release in the magnetopshere and energy dissipation in the ionosphere.     

Large-signal stability analysis of solar array power system

A large-signal stability analysis of the solar array regulator system is performed to facilitate the design and analysis of a low-earth-orbit (LEO) satellite power system. The effective load characteristics of various control methods in the solar array regulator system, such as the constant power load, variable power load, constant voltage load, constant current load, and constant resistive load, are classified to analyze the large-signal stability. Then, using the state plane analysis technique, the large-signal behavior of the solar array system is portrayed and the stability of various equilibrium points is analyzed. Thus, this approach can be contributed to organize the optimal controller structure of the system by representing the relationship between the control method of the solar array regulator and the large-signal stability. For the verification of the proposed large-signal analysis, a solar array regulator system that consists of two 100 W parallel module buck converters has been built and tested using a real 200 W solar array.     

Formation of the outer planets

A discussion is given of a number of physical processes which were probably important during the formation of the outer planets if these formed from a gaseous solar nebula in which magnetic effects were not important. Arguments are given that large-scale gravitational instabilities in the solar nebula did not occur. Qualitative consideration is given to the conditions in which dynamical capture of gas onto a planetary core may take place; this may have played a major role in the formation of Jupiter and Saturn. Because of the great difficulty of fractionating hydrogen from helium in the assembly of the outer planets, it is argued that a new approach should be made to the construction of planetary models. Conditions which may lead to the formation of the regular satellite systems are discussed, and the associated problem of removal of primordial angular momentum from Jupiter, Saturn, and Uranus.This is one of the publications by the Science Advisory Group.