Lower and Upper Ionosphere of Mars

The ionosphere of Mars has been explored mostly with the radio occultation experiment onboard Mariners 6, 7, 9; Mars 2, 3, 4, 6; Viking 1, 2, and more recently on Mars Global Surveyor (MGS) and Mars Express (MEX). In addition to the radio occultation experiment, MEX also carried Mars Advanced Radar for the Subsurface and Ionosphere Sounding (MARSIS) experiment which provided electron density profiles well above the main ionospheric peak. The atmosphere of Mars was measured directly by the neutral mass spectrometer onboard Viking 1 and 2 Landers. Later, an accelerometer and radio occultation experiment on MGS provided large data sets of atmospheric density at various locations in the upper and lower atmospheres of Mars, respectively. In this paper we review results of these upper and lower atmospheric/ionospheric measurements. Results of these measurements have been compared with theoretical models by several workers; therefore, we also review various atmospheric and ionospheric models of Mars.     

Global Muon Detector Network Used for Space Weather Applications

In this work, we summarize the development and current status of the Global Muon Detector Network (GMDN). The GMDN started in 1992 with only two muon detectors. It has consisted of four detectors since the Kuwait-city muon hodoscope detector was installed in March 2006. The present network has a total of 60 directional channels with an improved coverage of the sunward Interplanetary Magnetic Field (IMF) orientation, making it possible to continuously monitor cosmic ray precursors of geomagnetic storms. The data analysis methods developed also permit precise calculation of the three dimensional cosmic ray anisotropy on an hourly basis free from the atmospheric temperature effect and analysis of the cosmic ray precursors free from the diurnal anisotropy of the cosmic ray intensity.     

Searching for Black Holes in Space

Although General Relativity had provided the physical basis of black holes, evidence for their existence had to await the Space Era when X-ray observations first directed the attention of astronomers to the unusual binary stars Cygnus X-1 and A0620-00. Subsequently, a number of faint Ariel 5 and Uhuru X-ray sources, mainly at high Galactic latitude, were found to lie close to bright Seyfert galaxies, suggesting the nuclear activity in AGN might also be driven by accretion in the strong gravity of a black hole. Detection of rapid X-ray variability with EXOSAT later confirmed that the accreting object in an AGN is almost certainly a supermassive black hole.     

Satellite observations of power line harmonic radiation

In-situ spectral observations of power-line harmonic radiation (PLHR) are still quite rare and almost all the detailed characteristics have been derived from studies at Antarctic stations such as Siple and Halley, and their conjugates in North America. Because of the lack of more direct satellite evidence of PLHR and the difficulties in interpretation of morphological studies, such as those of Ariel 3 and 4, there is considerable controversy concerning the relative importance of PLHR and its contribution to wave-particle interactions (WPI) in the magnetosphere. The early Ariel 3 and 4 global surveys indicated that, in terms of true mean wave energy, there is no longitudinal localisation, the contribution of world-wide intense VLF emissions, associated with magnetic storms, being dominant. Also, the most intense wave emission, that of plasmaspheric hiss at ELF (< 1 kHz) exhibits little evidence of localisation. The PLHR phenomenon is most conspicuous by its persistence in quiet times (Kp ≤ 2+) at 45° < Λ < 55° over North America and its conjugate region, even though the less frequent strongest emissions, to which it gives rise in the summer, are located polewards at 3 < L < 5. In the northern winter, when spheric activity over both North America and its conjugate are low, there is a high occurrence of strong discrete emissions, which are more sharply localised than in the summer, on the NE industrial U.S.A. field line. The most recent Ariel 4 studies, particularly on the spheric wavefield over North America (using data from the Appleton Laboratory impulse counters) and on the character of the wavefield over the mainland and over the Atlantic immediately to the east (where the spheric contribution is similar) throw new light on the problem. It appears that the principal role of the PLHR may be to sustain duct structure and multihop propagation which is relatively much rarer over the Atlantic. Typical industrial PLHR consists of a series of narrow pulses at twice the mains frequency. It is suggested that these ‘artificial spherics’ may help to sustain the WPI and multihop duct structure. At L = 4, Yoshida et al. (1980) have shown that there is a strong, sharp maximum for WPIs originating in spherics, at f ? 3 kHz, in good agreement with Siple observations.     

Dynamic phenomena in the visible layers of sunspots

The empirical properties of the various dynamic phenomena are reviewed and interrelated with emphasis on recent observational results. The topics covered are:

1. Introduction
2. Aperiodic Phenomena
3. Externally Driven Phenomena
4. Umbral Flares
5. Inverse Evershed Flow
6. Internally Driven Phenomena
7. Penumbra
8. Penumbral Grains
9. Evershed Flow
10. Umbra
11. Umbral Dots
12. Inhomogeneity of the Umbral Magnetic Field
13. Umbral Turbulence
14. Oscillations and Waves
15. Chromosphere
16. Umbra: Oscillations and Flashes
17. Penumbra: Running Waves and Dark Puffs
18. Photosphere
19. Overview

It is proposed from the observations that umbral dots and penumbral grains are essentially the same phenomenon, and that the observational goal of highest priority with respect to both the origin of the periodic phenomena and the problem of the missing heat flux is to better determine the nature of these elementary bright features.     

A strategy for investigation of the outer solar system

The requirements of systematic exploration of the outer solar system have been intensively studied by a Science Advisory Group (SAG) of consulting scientists for the National Aeronautics and Space Administration (NASA). Comets and Asteroids were excluded from this study, as a separate group is planning missions to these bodies. This paper and accompanying articles on specific related scientific subjects written by members of the SAG, summarize the findings and recommendations of this group. These recommendations should not be interpreted as official NASA policy. Following some general introductory remarks, a brief sketch is given of the development and current status of scientific missions to the inner planets by the U.S. and the U.S.S.R. With this perspective, the development of the U.S. program for investigation of the outer solar system is described. The scientific focus of outer solar system exploration has been studied in detail. The relationship of the outer planetary bodies to one another and to the inner planets, as parts in a unified solar system evolved from a primitive solar nebula, is emphasized. Deductions from outer solar system investigations regarding the conditions of the solar nebula at the time of planetary formation have been considered. Investigations have been proposed that are relevant to studies of the atmospheric structure and dynamics, internal structure of the planets, satellite composition and morphology, and planetary and interplanetary fields and energetic particles. The mission type and sequence required to conduct a systematic exploration of the outer solar system has been developed. Technological rationales for the suggested missions are discussed in general terms. The existing NASA program for outer solar system exploration is comprised of four missions:

1. Pioneer 10 fly-by mission to Jupiter and beyond, currently underway, with launch on 3 March 1972;
2. Pioneer G, intended for a similar mission with planned launch 2–22 April 1973; and
3. Two Mariner Jupiter/Saturn fly-bys in 1977, with experiment selection scheduled for late 1972 and detailed engineering design during 1972–74.

The Science Advisory Group advocates that detailed mission planning be undertaken on the following additional missions for launches during the late 1970's and early 1980's. Together with existing plans, these would provide a balanced, effective exploration program.

1. 1976 Pioneer Jupiter/Out-of-Ecliptic (One Mission)
2. 1979 Mariner Jupiter/Uranus Fly-bys (Two Missions)
3. 1979 Pioneer Entry Probe to Saturn 1980 Pioneer Entry Probe to Uranus via Saturn Fly-by (Three Missions)
4. 1981/1982 Mariner Jupiter Orbiter (Two Missions).

     

Voyager mission description

The Voyager Project, managed by the Jet Propulsion Laboratory, involves the lauching of two advanced spacecraft to explore the Jovian and Saturnian systems, as well as interplanetary space. The one-month lauch period opens on August 20, 1977, with arrivals at Jupiter in March and July of 1979, and at Saturn in November of 1980 and August of 1981. Gravity-assist swingbys of Jupiter are utilized in order to reduce the lauch energy demands needed to reach Saturn. In addition, a gravity-assist targeting option at Saturn will be maintained on the second-arriving Voyager for a possible continuation on to Uranus, with arrival in January of 1986. Flight through the Jovian and Saturnian systems will achieve close to moderate flyby encounters with several of the natural satellites, including special flyby geometry conditions for Io and Titan, as well as an Earth occultation of the spacecraft's radio signal by the rings of Saturn. The purpose of this paper is to describe the Voyager mission characteristics in order to establish a framework upon which to better understand the objectives and goals of the eleven scientific investigations which are described in subsequent papers.     

Solar wind interaction with comets

The planned missions to Comet Halley, which will arrive at the nearest space of the Sun in 1986, have recently revived interest in studying solar wind interaction with comets. Several unsolved problems exist and the most urgent of them are as follows:

1. The character of the solar wind interaction with comets: bow shocks and contact surface formation near comets; similarities and differences of solar- wind interaction with comets and with Venus. The differences are probably associated with a great extension of neutral atmospheres of comets (due to a practical lack of cometary gravitation) and the ‘loading’ of the solar wind flux by cometary ions during the interaction.
2. The anomalous ionization in cometary heads.
3. The problem of the anamalously high accelerations of ions in the plasma tails of comets.
4. The variability of plasma structures observed in cometary tails.

     

Observational Appearance of Black Holes in X-Ray Binaries and AGN

Accretion onto black holes powers most luminous compact sources in the Universe. Black holes are found with masses extending over an extraordinary broad dynamic range, from several to a few billion times the mass of the Sun. Depending on their position on the mass scale, they may manifest themselves as X-ray binaries or active galactic nuclei. X-ray binaries harbor stellar mass black holes—endpoints of the evolution of massive stars. They have been studied by X-ray astronomy since its inception in the early 60-ies, however, the enigma of the most luminous of them—ultra-luminous X-ray sources, still remains unsolved. Supermassive black holes, lurking at the centers of galaxies, are up to hundreds of millions times more massive and give rise to the wide variety of different phenomena collectively termed “Active Galactic Nuclei”. The most luminous of them reach the Eddington luminosity limit for a few billions solar masses object and are found at redshifts as high as z≥5–7. Accretion onto supermassive black holes in AGN and stellar- and (possibly) intermediate mass black holes in X-ray binaries and ultra-luminous X-ray sources in star-forming galaxies can explain most, if not all, of the observed brightness of the cosmic X-ray background radiation. Despite the vast difference in the mass scale, accretion in X-ray binaries and AGN is governed by the same physical laws, so a degree of quantitative analogy among them is expected. Indeed, all luminous black holes are successfully described by the standard Shakura-Sunyaev theory of accretion disks, while the output of low-luminosity accreting black holes in the form of mechanical and radiative power of the associated jets obeys to a unified scaling relation, termed as the “fundamental plane of black holes”. From that standpoint, in this review we discuss formation of radiation in X-ray binaries and AGN, emphasizing their main similarities and differences, and examine our current knowledge of the demographics of stellar mass and supermassive black holes.     

Cosmic Rays,Clouds, and Climate

A correlation between a global average of low cloud cover and the flux of cosmic rays incident in the atmosphere has been observed during the last solar cycle. The ionising potential of Earth bound cosmic rays are modulated by the state of the heliosphere, while clouds play an important role in the Earth's radiation budget through trapping outgoing radiation and reflecting incoming radiation. If a physical link between these two features can be established, it would provide a mechanism linking solar activity and Earth's climate. Recent satellite observations have further revealed a correlation between cosmic ray flux and low cloud top temperature. The temperature of a cloud depends on the radiation properties determined by its droplet distribution. Low clouds are warm (>273K) and therefore consist of liquid water droplets. At typical atmospheric supersaturations (1%) a liquid cloud drop will only form in the presence of an aerosol, which acts as a condensation site. The droplet distribution of a cloud will then depend on the number of aerosols activated as cloud condensation nuclei (CCN) and the level of super saturation. Based on observational evidence it is argued that a mechanism to explain the cosmic ray-cloud link might be found through the role of atmospheric ionisation in aerosol production and/or growth. Observations of local aerosol increases in low cloud due to ship exhaust indicate that a small perturbation in atmospheric aerosol can have a major impact on low cloud radiative properties. Thus, a moderate influence on atmospheric aerosol distributions from cosmic ray ionisation would have a strong influence on the Earth's radiation budget. Historical evidence over the past 1000 years indicates that changes in climate have occurred in accord with variability in cosmic ray intensities. Such changes are in agreement with the sign of cloud radiative forcing associated with cosmic ray variability as estimated from satellite observations.     

Earth-moon libration points: Theory,existence and applications

The availability of reliable satellites and space probes makes it timely to review our state of knowledge in detail on all aspects of our solar system so that these new tools can be used to maxi-mum advantage in scientific exploration and technical use.Earth-Moon libration points have been of theoretical interest as a concrete example in the three body problem. In analogy with the Trojan Asteroids they may also be collection points for dust or particles or other small bodies which are shown to be of geophysical interest. Finally, they may find use in applications where relatively long time stationary behavior relative to the Earth and the Moon is desirable; for example: for long term Solar observation or as a communication link.The leading question of interest at the present is confirmation of reported ground observations on dust clouds in the vicinity of the stable points through satellite based observations.The Authors are indebted to the Space Sciences Board of the U.S. National Academy of Sciences for permission to use background material of the Space Research Summer Study 1965.     

Venus Atmospheric Thermal Structure and Radiative Balance

From the discovery that Venus has an atmosphere during the 1761 transit by M. Lomonosov to the current exploration of the planet by the Akatsuki orbiter, we continue to learn about the planet’s extreme climate and weather. This chapter attempts to provide a comprehensive but by no means exhaustive review of the results of the atmospheric thermal structure and radiative balance since the earlier works published in Venus and Venus II books from recent spacecraft and Earth based investigations and summarizes the gaps in our current knowledge. There have been no in-situ measurements of the deep Venus atmosphere since the flights of the two VeGa balloons and landers in 1985 (Sagdeev et al., Science 231:1411–1414, 1986). Thus, most of the new information about the atmospheric thermal structure has come from different remote sensing (Earth based and spacecraft) techniques using occultations (solar infrared, stellar ultraviolet and orbiter radio occultations), spectroscopy and microwave, short wave and thermal infrared emissions. The results are restricted to altitudes higher than about 40 km, except for one investigation of the near surface static stability inferred by Meadows and Crisp (J. Geophys. Res. 101:4595–4622, 1996) from 1 \(\upmu\)m observations from Earth. Little information about the lower atmospheric structure is possible below about 40 km altitude from radio occultations due to large bending angles. The gaps in our knowledge include spectral albedo variations over time, vertical variation of the bulk composition of the atmosphere (mean molecular weight), the identity, properties and abundances of absorbers of incident solar radiation in the clouds. The causes of opacity variations in the nightside cloud cover and vertical gradients in the deep atmosphere bulk composition and its impact on static stability are also in need of critical studies. The knowledge gaps and questions about Venus and its atmosphere provide the incentive for obtaining the necessary measurements to understand the planet, which can provide some clues to learn about terrestrial exoplanets.     

The local bubble

Recently, observations with the rosat PSPC instrument and the spectrometers onboard the euve satellite have given new detailed information on the structure and physical conditions of the Local Bubble. From the early rocket experiments, and in particular from the WISCONSIN Survey, the existence of a diffuse hot gas in the vicinity of the solar system, extending out to about 100 pc, has been inferred in order to explain the emission below 0.3 keV. The higher angular resolution and sensitivity of rosat made it possible to use diffuse neutral clouds as targets for shadowing the soft X-ray background. Thus, in some directions, more than half of the flux in the 0.25 keV band appears to come from outside the Local Bubble. Further, measurements of the diffuse EUV in the LISM, show surprisingly few emission lines. These findings are in conflict with the standard LHB model, which assumes a local hot (T 10⁶ K) plasma in CIE. Model calculations, based on the non-equilibrium cooling of an expanding plasma, show a promising way of reconciling all available observations. Thus the present temperature within the LB may be as low as 4 × 10⁴ K and its number density as large as 2 × 10^–2 cm ^–3, giving a total pressure that is roughly in agreement with the Local Cloud.Abbreviations CIE collisional ionization equilibrium - ISM Interstellar Medium - LHB Local Hot Bubble - LB Local Bubble - LISM Local ISM - SB superbubble - SXR soft X-ray - SXRB SXR Background - VLISM Very Local ISM Heisenberg Fellow     

Clouds and Diffuse Baryonic Dark Matter

The nature of the dark matter in the halo of our galaxy is still largely unknown. The microlensing events found so far towards the Large Magellanic Cloud suggest that at most about 20% of the halo dark matter is in form of MACHOs (Massive Astrophysical Compact Halo Objects). The dark matter could also, at least partially, be made of cold molecular clouds (mainly H₂). We proposed a model for baryonic dark matter, according to which dark clusters of brown dwarfs and cold self-gravitating H₂ clouds populate the outer galactic halo. A signature would be a diffuse -ray emission from the galactic halo. Basically, cosmic-ray protons in the galactic halo scatter on the clouds clumped into dark clusters, giving rise to a -ray flux. An analysis of EGRET data has led to the discovery of a statistically significant diffuse -ray emission from the galactic halo, which turns out to be in remarkably good agreement with our prediction.