Atmospheric Escape and Evolution of Terrestrial Planets and Satellites

The origin and evolution of Venus’, Earth’s, Mars’ and Titan’s atmospheres are discussed from the time when the active young Sun arrived at the Zero-Age-Main-Sequence. We show that the high EUV flux of the young Sun, depending on the thermospheric composition, the amount of IR-coolers and the mass and size of the planet, could have been responsible that hydrostatic equilibrium was not always maintained and hydrodynamic flow and expansion of the upper atmosphere resulting in adiabatic cooling of the exobase temperature could develop. Furthermore, thermal and various nonthermal atmospheric escape processes influenced the evolution and isotope fractionation of the atmospheres and water inventories of the terrestrial planets and Saturn’s large satellite Titan efficiently.     

Modeling and Simulating Flowing Plasmas and Related Phenomena

Simulation has become a valuable tool that compliments more traditional methods used to understand solar system plasmas and their interactions with planets, moons and comets. The three popular simulation approaches to studying these interactions are presented. Each approach provides valuable insight to these interactions. To date no one approach is capable of simulating the whole interaction region from the collisionless to the collisional regimes. All three approaches are therefore needed. Each approach has several implicit physical assumptions as well as several numerical assumptions depending on the scheme used. The magnetohydrodynamic (MHD), test-particle/Monte-Carlo and hybrid models used in simulating flowing plasmas are described. Special consideration is given to the implicit assumptions underlying each model. Some of the more common numerical methods used to implement each model, the implications of these numerical methods and the resulting limitations of each simulation approach are also discussed.     

Terrestrial Magnetism: Historical Perspectives and Future Prospects

This collection of reviews marks the state of the art of geomagnetic data collection, modelling, and interpretation at a time of unprecedented advances in all 3 facets of the subject. For the first time we have excellent satellite data with the prospect of more to come, vast improvements in laboratory techniques, and opportunities to use large scale computing to model the data. In the past, research has been conducted by the separate disciplines largely in isolation; we can hope the subject has now matured enough for progress to be made by genuine collaboration between theoreticians and experimentalists. The purpose of this chapter is to set the historical setting, and I have chosen a starting date of 1980, when vector satellite data first became available and stimulated many new advances in the subject. We can hope for a similar or better stimulus in the next decade.     

The Geology and Habitability of Terrestrial Planets: Fundamental Requirements for Life

The current approach to the study of the origin of life and to the search for life elsewhere is based on two assumptions. First, life is a purely physical phenomenon closely linked to specific environmental conditions. From this, we hypothesise that when these environmental conditions are met, life will arise and evolve. If these assumptions are valid, the search for life elsewhere should be a matter of mapping what we know about the range of environments in which life can exist, and then simply trying to find these environments elsewhere. Second, life can be clearly distinguished from the non-living world. While a single feature of a living organism left in the rock record is not always sufficient to determine unequivocally whether life was present, life often leaves multiple structural, mineralogical and chemical biomarkers that, in sum, support a conclusion that life was present. Our understanding of the habitats that can sustain or have sustained life has grown tremendously with the characterisation of extremophiles. In this chapter, we highlight the range of environments that are known to harbour life on Earth, describe the environments that existed during the period of time when life originated on Earth, and compare these habitats to the suitable environments that are found elsewhere in our solar system, where life could have arisen and evolved.     

Magnetic Field Topology and Criticality in Geotail Dynamics: Relevance to Substorm Phenomena

Recent observations and analyses seem to suggest that certain dynamical features of the Earth's magnetosphere could resemble the evolution of a complex system near a forced and/or self-organized criticality (FSOC). Here, we review concepts dealing with the phenomenology of criticality and disorder systems in connection with magnetospheric processes. In more detail, we discuss the importance of intermittency, turbulence and local topological disorder in the geomagnetic tail regions, that form a new paradigm for the understanding of the magnetotail dynamics.     

Progress in the Study of Galaxies: Structures,Collective Phenomena and Methods

The review contains the important achievements in dynamics of the galactic disks. Among them there are I. New structures discovered recently: • giant vortices (including giant anticyclone in the Solar vicinity); • slow bar; • inner oscillating structure within spiral arms similar that of enveloped soliton; • chaotic streamlines in the velocity field of the gaseous disk of a real galaxy. II. New collective phenomina discovered recently: • new overreflection instability initiating ‘mini-spiral’ in the innermost central parsec of Galaxy; • large-scale convection caused by nonlinear interaction of density wave with disk gas; • non-kolmogorovian spectrum of weak turbulence corresponding to the observed one in the • Solar vicinity. III. New methods worked out recently: • reconstruction of full three-dimensional vector field of gas velocity from the observed line-of- • sight velocity field; • observational test for verification of the wave-nature of the spiral arms; • observational test to distinguish two types of vertical motions: warp and z-motions in the • density wave; • derivation of correct system of two-dimensional dynamical equations from the initial three- • dimensional one. This revised version was published online in June 2006 with corrections to the Cover Date.     

Planetary Magnetic Fields and Solar Forcing: Implications for Atmospheric Evolution

The solar wind and the solar XUV/EUV radiation constitute a permanent forcing of the upper atmosphere of the planets in our solar system, thereby affecting the habitability and chances for life to emerge on a planet. The forcing is essentially inversely proportional to the square of the distance to the Sun and, therefore, is most important for the innermost planets in our solar system—the Earth-like planets. The effect of these two forcing terms is to ionize, heat, chemically modify, and slowly erode the upper atmosphere throughout the lifetime of a planet. The closer to the Sun, the more efficient are these process. Atmospheric erosion is due to thermal and non-thermal escape. Gravity constitutes the major protection mechanism for thermal escape, while the non-thermal escape caused by the ionizing X-rays and EUV radiation and the solar wind require other means of protection. Ionospheric plasma energization and ion pickup represent two categories of non-thermal escape processes that may bring matter up to high velocities, well beyond escape velocity. These energization processes have now been studied by a number of plasma instruments orbiting Earth, Mars, and Venus for decades. Plasma measurement results therefore constitute the most useful empirical data basis for the subject under discussion. This does not imply that ionospheric plasma energization and ion pickup are the main processes for the atmospheric escape, but they remain processes that can be most easily tested against empirical data. Shielding the upper atmosphere of a planet against solar XUV, EUV, and solar wind forcing requires strong gravity and a strong intrinsic dipole magnetic field. For instance, the strong dipole magnetic field of the Earth provides a “magnetic umbrella”, fending of the solar wind at a distance of 10 Earth radii. Conversely, the lack of a strong intrinsic magnetic field at Mars and Venus means that the solar wind has more direct access to their topside atmosphere, the reason that Mars and Venus, planets lacking strong intrinsic magnetic fields, have so much less water than the Earth? Climatologic and atmospheric loss process over evolutionary timescales of planetary atmospheres can only be understood if one considers the fact that the radiation and plasma environment of the Sun has changed substantially with time. Standard stellar evolutionary models indicate that the Sun after its arrival at the Zero-Age Main Sequence (ZAMS) 4.5 Gyr ago had a total luminosity of ≈70% of the present Sun. This should have led to a much cooler Earth in the past, while geological and fossil evidence indicate otherwise. In addition, observations by various satellites and studies of solar proxies (Sun-like stars with different age) indicate that the young Sun was rotating more than 10 times its present rate and had correspondingly strong dynamo-driven high-energy emissions which resulted in strong X-ray and extreme ultraviolet (XUV) emissions, up to several 100 times stronger than the present Sun. Further, evidence of a much denser early solar wind and the mass loss rate of the young Sun can be determined from collision of ionized stellar winds of the solar proxies, with the partially ionized gas in the interstellar medium. Empirical correlations of stellar mass loss rates with X-ray surface flux values allows one to estimate the solar wind mass flux at earlier times, when the solar wind may have been more than 1000 times more massive. The main conclusions drawn on basis of the Sun-in-time-, and a time-dependent model of plasma energization/escape is that:

1. Solar forcing is effective in removing volatiles, primarily water, from planets,
2. planets orbiting close to the early Sun were subject to a heavy loss of water, the effect being most profound for Venus and Mars, and
3. a persistent planetary magnetic field, like the Earth’s dipole field, provides a shield against solar wind scavenging.

     

Interstellar-Terrestrial Relations: Variable Cosmic Environments, The Dynamic Heliosphere, and Their Imprints on Terrestrial Archives and Climate

In recent years the variability of the cosmic ray flux has become one of the main issues interpreting cosmogenic elements and especially their connection with climate. In this review, an interdisciplinary team of scientists brings together our knowledge of the evolution and modulation of the cosmic ray flux from its origin in the Milky Way, during its propagation through the heliosphere, up to its interaction with the Earth’s magnetosphere, resulting, finally, in the production of cosmogenic isotopes in the Earth’ atmosphere. The interpretation of the cosmogenic isotopes and the cosmic ray – cloud connection are also intensively discussed. Finally, we discuss some open questions.     

Editorial to the Topical Collection on Clusters of Galaxies: Physics and Cosmology

Space Science Reviews -     

Arnab Rai Choudhuri,The Physics of Fluids and Plasmas: An Introduction for Astrophysicists

Space Science Reviews -     

N. Sanchez and A. Zichichi,Current Topics in Astrofundamental Physics: Primordial Cosmology,NATO ASI Series,C: Mathematical and Physical Sciences, #511

Space Science Reviews -