Solar System Feature

The presence of water as solid, liquid, and gas is a feature that makes Earth unique in the solar system and that makes life possible as we know it. The transport of water and the energy exchanged as it is converted from one state to another are important drivers in our weather and climate. One of the key missions is to develop a better understanding of the global water cycle at a variety of scales so that we can improve model forecasts of climate trends,... 

Within the solar system the observable changes are of a different kind, best described as chemical change. The most striking common feature of those chemical reactions driven by solar energy is their cyclic nature, linked to planetary motion. All phenomena, collectively known as life, or growth, are of this type. Their essential characteristic is a state far from equilibrium. For a life process, equilibrium is synonymous with death and chemical change after death is a rapid slide towards equilibrium. The most advanced chemical theories deal with these posthumous effects and related reactions only, albeit rather superficially. A fundamental theory to predict conditions for the onset of elementary chemical change is not available. 

Inclusions of the CV3 led to the search for isotopic signatures of individual nucleosynthetic processes, or at least for components closer to the original signature than average solar compositions. They have also begun to demonstrate the isotopic variability of matter emerging from these processes in agreement with astrophysical and astronomical expectations. The principal features of inclusions are an up to 4% 0 enriched reservoir in the early solar system, variations in a component produced in a nuclear neutron-rich statistical equilibrium, and variations in the contribution of p- and r-process products to the heavy elements. 

Fig. 4.1. Abundance table of elements in the Solar System. The main features of the abundance distribution are as follows (1) the hydrogen (Z = 1) peak, shouldered by helium (Z = 2) the precipitous gorge separating helium and carbon (Z = 6) ...

There are several basic features to note about the chemical abundances of the solar system. First, the Sun, and thus the solar system, consists dominantly of hydrogen and helium, with these two elements making up >98% of the mass of the solar system. Outside of the Sun, hydrogen and helium are found primarily in the gas-giant planets. 

The solar system abundances of the elements are the result of the Big Bang, which produced hydrogen and helium, 7.5 billion years of stellar nucleosynthesis, which produced most of the rest of the elements, and the physical processes that mixed the materials together to form the Sun s parent molecular cloud. The unique features of the solar system composition may also reflect the stochastic events that occurred in the region where the Sun formed just prior to solar system formation. 

Table II summarizes some of the features of the radioactive fallout processes in geophysical and astronomical settings. It seems that similarities do exist between the processes of formation of single particles from nuclear explosions and formation of the solar system from the debris of supernova explosion. We may be able to learn much more about the origin of the earth, by further investigating the process of radioactive fallout from the nuclear weapons tests.

The search for signs of life, present or past, is an important goal of NASA s robotic solar system exploration programs and, ultimately, for its astronomical programs designed to probe the gross characteristics of extrasolar planetary systems. To date, that search has been governed by a model of life that is based on the life that we know on Earth—terran life. Several features of terran life have attracted particular focus ... 

There is convincing observational evidence that the placental interstellar medium (ISM) from which the solar system originated was a dense molecular cloud (Wasserburg et al., 1982 1979). In fact, the recent evidence of the presence of short-lived nuclei in meteorites requires that the free-fall time scale for gravitational collapse (tft) be less than or comparable to the mean lifetime of Al ( 10 yrs), i.e. ttt 4.10 / /n < 10 yrs, which requires nn lOVcc, a value typical of molecular clouds. Since molecular clouds are observed to be a major feature in our galaxy, they constitute a most reliable starting point for the processes that will eventually lead to the formation of stars and planetary systems (Falk and... 

Recently, theorists seem to have come to grips with all the factors needed to account for the principal features of CRE age distributions. A decade ago, in the reigning view, the Earth competed for meteoroids against collisional destruction and ejection from the solar system or incineration by the Sun (Greenberg and Nolan, 1989). Earth capture depended on injection of the meteoroid into an orbit close to or in a chaotic resonance in the inner main belt ... 

The primary feature of the main asteroid belt is its great depletion in mass relative to other regions of the planetary system. The present mass of the main belt is 5 X 10 m , which represents 0.1 -0.01 % of the solid mass that existed at the time planetesimals were forming. There are several ways the main asteroid belt could have lost most of its primordial mass. Substantial loss by collisional erosion appears to be mled out by the preservation of asteroid Vesta s basaltic cmst, which formed in the first few million years of the solar system (Davis et al., 1994). More plausible models are based on the existence of orbital resonances associated with the giant planets. 

---