Solar Systems

Long before spacecraft encounters, celestial mechanics had been employed to determine the masses of those planets that possess moons. With the exceptions of Mercury and Venus, for which the arguments were more indirect, the masses of all the planets are now known from satellite observations. Detailed examination of the periodicities of their moons also reveals that they interact through resonant orbits, which causes the structuring of the radial distribution of the planetary satellite systems. Detailed observations of satellite motion also permit the determination of internal mass distribution and oblateness for most of the planets. These determinations have been augmented for the outer planets by direct flybys with the Voyager 1 and 2 spacecraft. Finally, mutual phenomena of the moons of several of the major planets provide the determination of satellite masses through the solution of the motion under mutual perturbations for the satellite systems. 

The evolution of cometary orbits—especially Comet Halley for which there is a significant historical record— shows evidence for nongravitational forces. These are presumed to arise from the mass loss from the comet produced by interaction with the solar wind and radiation-induced outgassing. The change in the mass of the comet carries angular momentum because of the finite escape velocity for 

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In fact, even in the solar system, despite the relative strengths of planetary attraction, there are constituents, the asteroids, with very irregular, chaotic behaviour. The issue of chaotic motion in molecules is an issue that will appear later with great salience.)... 

Percentage of meteorites seen to fall. Chondrites. Over 90% of meteorites that are observed to fall out of the sky are classified as chondrites, samples that are distinguished from terrestrial rocks in many ways (3). One of the most fundamental is age. Like most meteorites, chondrites have formation ages close to 4.55 Gyr. Elemental composition is also a property that distinguishes chondrites from all other terrestrial and extraterrestrial samples. Chondrites basically have undifferentiated elemental compositions for most nonvolatile elements and match solar abundances except for moderately volatile elements. The most compositionaHy primitive chondrites are members of the type 1 carbonaceous (Cl) class. The analyses of the small number of existing samples of this rare class most closely match estimates of solar compositions (5) and in fact are primary source solar or cosmic abundances data for the elements that cannot be accurately determined by analysis of lines in the solar spectmm (Table 2). Table 2. Solar System Abundances of the Elements ... 

Element Solar system Mean CI chondrite, ppb Orgued, ppb Element Solar system Mean CI chondrite, ppb Orgued, ppb... 

S. R. Taylor, Solar System Evolution, Cambridge University Press, Cambridge, UK, 1992. 

Earth to space (sateUite) to earth communication links are relatively insensitive to ionospheric disturbances. Communications between earth and manned space vehicles are barely affected by plasmas when the spaceships are well away from the atmosphere, eg, in orbit or in a translunar trajectory. However, during reentry of a spaceship, a low temperature plasma forms around the vehicle and intermpts the communication links to it (183). Plasmas are incidental to the performance of modem rockets used to explore the solar system. 

Most schemes that have been proposed to propel starships involve plasmas. Schemes differ both in the selection of matter for propulsion and the way it is energi2ed for ejection. Some proposals involve onboard storage of mass to be ejected, as in modem rockets, and others consider acquisition of matter from space or the picking up of pellets, and their momentum, which are accelerated from within the solar system (184,185). Energy acquisition from earth-based lasers also has been considered, but most interstellar propulsion ideas involve nuclear fusion energy both magnetic, ie, mirror and toroidal, and inertial, ie, laser and ion-beam, fusion schemes have been considered (186—190). 

J. L. Burch and J. H. Waite, Jr., eds., Solar System Plasma in Space and Time, American Geophysical Union, Washiagton, D.C., 1994. 

Resource pessimists counter that this process cannot proceed forever because the eternal persistence of demand for any given commodity that is destroyed by use must inevitably lead to its depletion. I lowever, the eternal persistence assumption is not necessarily correct. The life of a solar system apparently is long but finite. Energy sources such as nuclear fusion and solar energy in time could replace more limited resources such as oil and natural gas. Already, oil, gas, nuclear power, and coal from better sources have displaced traditional sources of coal in, for example, Britain, Germany, Japan, and France. 

Th ese manufactured light sources are, perhaps ironically, largely dependent on the Sun. The radiant energy from the Sun has been stored in the fossilized remains of billions of creatures over millions of years and is used to power the electric light sources created by modern humans. The power generated by hydroelectric sources also is a result of solar evaporation and subsequent rainfall. Only nuclear reactors provide power independent of the Sun, which is, of course, the largest nuclear reactor in the solar system. 

Book II investigates the dynamical conditions of fluid motion. Book III displays the law of gi avitatioii at work in the solar system. It is demonstrated from the revolutions of the six known planets, including Earth, and their satellites, though Newton could never quite perfect the difficult theory of the Moon s motion. It is also demonstrated from the motions of comets. The gravitational forces of the heavenly bodies are used to calculate their relative masses. The tidal ebb and flow and the precession of the equinoxes is explained m terms of the forces exerted by the Sun and Moon. These demonstrations are carried out with precise calculations. 

It is estimated that the earth s age is in the neighborhood of 4 to 7 billion years. These estimates are basically derived from carbon-14, potassium-40, uranium-235, and uranium-238 dating of earth rocks and meteorites. The meteorites give important data as to the age of our solar system. Geologic time is felt to be represented by the presence of rock intervals in the geologic column (layers of rock formations in vertical depth) or by the absence of equivalent rocks in correlative columns in adjacent locations [25,26]. The two basic factors that are used to determine geologic time are ... 

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