Mikhail Ya. Marov

The Structure of the Universe

The view of the universe reveals a hierarchical system of structures. Stars are grouped in giant star clusters: galaxies, involving the most prominent star formation regions in their molecular clouds, and stellar associations such as open and globular clusters. A galaxy is a massive, gravitationally bound system consisting of stars, stellar remnants, an interstellar medium of gas and dust, and dark matter. Galaxies form clusters of progressively growing size, while galactic clusters form much larger superclusters of galaxies which are not uniformly distributed in the universe. This nonuniform distribution of clusters of galaxies forms a more ordered structure composed of walls and voids, which is called the Cosmic Web and is regarded as the remnants of fluctuations in the matter of the expanding universe after its origin (the Big Bang).

The Terrestrial Planets

The terrestrial planets (Mercury, Venus, Earth, and Mars), also called the inner planets, occupy the region within 1.5 AU from the Sun. They exhibit manifold properties of their surface landforms, geology, interiors, and atmospheric features. The Earth possesses a unique nature; the natural conditions of our neighbors Venus and Mars are completely different. These two planets serve as two extreme models of the Earth’s evolution. Plausible scenarios of how these planets evolved and came to their modern natural conditions are discussed in detail.

The Solar System

The solar system is the space environment closest to our home planet Earth and is the most important in terms of human habitation. The solar system family includes the major planets with their satellites as well as numerous small bodies (asteroids, comets, meteoroids, and interplanetary dust). The major planets fall into two categories: terrestrial solid planets and giant gaseous-icy planets. Nearly all the satellites in the solar system belong to the giant planets, which also have systems of rings. The numerous small bodies are regarded as remnants of the solar system formation that have preserved pristine matter. The remarkable properties of the solar system dynamics involving different types of orbital and rotational resonances, migration of the small bodies, and collisional interactions with major planets throughout the solar system history have important implications for its evolution.

Planetary Systems: Origin and Evolution

The scenario for the origin and evolution of planetary systems (and in particular, the solar system) is based on fundamental theoretical concepts and astrophysical data involving the process of star formation. Mechanical and cosmochemical properties of the solar system through radioisotope dating place important constraints on such a scenario. The sequence of events includes formation of a protoplanetary gas-dust accretion disk around a parent star from a primordial nebula, followed by disk instability and fragmentation into the first solid bodies (planetesimals), and their collisional interactions giving rise eventually to planets.

The Giant Planets

The giant planets (Jupiter, Saturn, Uranus, and Neptune), also called the outer planets, are located between 5 and 30 AU from the Sun. They are large bodies, notably exceeding the terrestrial planets in size. Jupiter and Saturn are composed mostly of hydrogen-helium gases, whereas Uranus and Neptune consist of hydrogen-bearing compounds (e.g., methane, ammonia, and water) exhibiting ice properties under high pressure in their interiors. The giant planets have no solid surface and have experienced only limited evolution since their origin. They have very rich systems of satellites and rings.

The Sun and Heliosphere

The Sun is our star. It provides the energy that makes life’s existence on Earth possible. The main zones of the observed Sun are the photosphere, chromosphere, and corona. Their composition, structure, and peculiarities are intrinsically related with the interior where nuclear fusion occurs. Solar activity includes an 11-year solar cycle and different phenomena caused by disturbances in the chromosphere/corona. The solar wind is a plasma flowing out permanently from the Sun. It fills up the region called the heliosphere, which surrounds the Sun and expands to a huge distance where its outer boundary interacts with the interstellar medium. Important phenomena within the heliosphere are solar wind interactions with the planets and small bodies, particularly interactions with the Earth’s upper atmosphere and magnetosphere, which protect the biosphere from harmful solar electromagnetic and corpuscular radiation.

Stars: Birth, Lifetime, and Death

Stars are born of gas and dust in the interstellar medium and evolve throughout their lifetimes from early to final stages. They are massive luminous spheres of plasma composed of the most abundant elements in space—hydrogen and helium—held together by their own gravity. The evolution of the various types of stars is traced along the Hertzsprung-Russell diagram. The life cycle of a star, from birth in the giant molecular clouds, through active phase involving nuclear fusion as an energy source, and ultimate death, principally depends on its mass. The final stages of low-mass and high-mass stars are also different: low-mass stars die forming a red giant and then a white dwarf, while high-mass stars explode as supernovae, leaving behind a neutron star or black hole.

Cosmology: The Origin and Fate of the Universe

Cosmology is the study of the origin and fate of the universe. We address the current model of the origin of the universe focusing on the Big Bang theory and evidence in support of the model. The scenario of the ultimate fate of the universe based on its total mass estimate with the involvement of dark matter and dark energy is also discussed. Finally, modern physical theories including the standard model with the basics of elementary particle physics and symmetry principles (and their violation), superstring (M) theory, the multiverse, and wormholes are addressed.

Astrobiology: Basic Concepts

Astrobiology is a challenging interdisciplinary field of contemporary science which appeared in the second half of the last century and stimulated a better understanding of the frontiers of biology. Astrobiology aims to answer the fundamental questions: Is there life beyond Earth? Which distinctive features could it acquire? How did it adapt to various natural environments and to which extremes did it evolve? Did it possibly evolve to the level of intellectual capacity and a technological ability to communicate? This field is rooted in the synergy between astrophysics and biology and is intimately related with planetary sciences, in particular with planetary systems formation and evolution. It is also closely linked to basic philosophical concepts.

Differential Models for the Closure of Turbulently Averaged Hydrodynamic Equations for a Chemically Active Continuous Medium

The problem of constructing semiempirical second-approximation turbulence models for a multicomponent chemically active gas mixture with a variable density and variable thermophysical properties is addressed. The set of closing differential transfer equations for the various one-point (one-time) second correlation moments of the fluctuating thermohydrodynamic parameters appearing in the averaged hydrodynamic equations of mean motion for a reacting mixture is derived. The closure problem for a chemically active medium is generally greatly complicated due to the necessity of averaging the nonlinear “source terms” of substance production in chemical reactions with an exponential behavior. Therefore, we propose an original procedure for averaging the rates of chemical reactions of any order and outline a scheme for semiempirical modeling of these additional correlations. Approximating expressions containing universal empirical coefficients that need not be chosen again for each new flow are used in modeling the third-order correlations in the transfer equations. It should be emphasized that although these additional equations are semiempirical, the invariant models of fully developed turbulence in chemically active gases based on them are fairly flexible. In particular, they allow the influence of the mechanisms of convection, diffusion, formation, redistribution, and dissipation of stochastic turbulent characteristics for the field of fluctuating thermohydrodynamic parameters on the spatiotemporal distribution of averaged thermohydrodynamic parameters for the medium to be taken into account. Basically, the approach we developed is widely used in numerical simulations of real reacting turbulized fluid flows with a significant influence of the flow prehistory on the turbulence characteristics at a point. On the other hand, it is used to derive more accurate algebraic relations for the turbulent transport coefficients in multicomponent shear mixture flows (and as applied to the specificity of modeling natural media), which is embodied in this chapter of the book.