Ionospheric and field-aligned current systems in the auroral zone: a concise review

During the last few years our knowledge about the real three-dimensional current flow in the auroral zone has been significantly increased due to new improved measurements, especially those made by ground-based magnetometer networks, coherent and incoherent auroral radars, sounding rockets and low-altitude satellites. Combination of two or even more of those data sets (e.g. electron densities and electric and magnetic fields) allowed for a rather accurate determination of the distribution of Hall, Pedersen and Birkeland currents in the auroral zone. In this review an attempt is made to summarize the present knowledge about the distribution of conductivity, electric field and current flow in the auroral zone as well for the large-scale electrojet systems as for the comparatively smaller current systems associated with quiet and active aurora, i.e. discrete arcs, auroral break-ups, westward travelling surges and omega bands.     

Hypersaline microbial systems of sabkhas: examples of life's survival in "extreme" conditions

Life and living systems need several important factors to establish themselves and to have a continued tradition. In this article the nature of the borderline situation for microbial life under heavy salt stress is analyzed and discussed using the example of biofilms and microbial mats of sabkha systems of the Red Sea. Important factors ruling such environments are described, and include the following: (1) Microbial life is better suited for survival in extremely changing and only sporadically water-supplied environments than are larger organisms (including humans). (2) Microbial life shows extremely poikilophilic adaptation patterns to conditions that deviate significantly from conditions normal for life processes on Earth today. (3) Microbial life adapts itself to such extremely changing and only ephemerally supportive conditions by the capacity of extreme changes (a) in morphology (pleomorphy), (b) in metabolic patterns (poikilotrophy), (c) in survival strategies (poikilophily), and (d) by trapping and enclosing all necessary sources of energy matter in an inwardly oriented diffusive cycle. All this is achieved without any serious attempt at escaping from the extreme and extremely changing conditions. Furthermore, these salt swamp systems are geophysiological generators of energy and material reservoirs recycled over a geological time scale. Neither energy nor material is wasted for propagation by spore formation. This capacity is summarized as poikilophilic and poikilotroph behavior of biofilm or microbial mat communities in salt and irradiationstressed environmental conditions of the sabkha or salt desert type. We use mainly cyanobacteria as an example, although other bacteria and even eukaryotic fungi may exhibit the same potential of living and surviving under conditions usually not suitable for life on Earth. It may, however, be postulated that such poikilophilic organisms are the true candidates for life support and survival under conditions never recorded on Planet Earth. Mars and some planets of other suns may be good candidates to search for life under conditions normally not thought to be favorable for the maintenance of life.     

Erdbeobachtende missionen—Anforderungen und konzepte

(Earth Observation Missions—Requirements and Concepts)—Ten years ago, on 23 July 1972. NASA launched the first satellite specifically designed for Earth observation. With Landsat 1 the importance and attractiveness of remote sensing from space increased worldwide.The paper presents in an overview former remote sensing missions with their applications and the system elements required for gathering Earth observation information. Main elements are the sensors (optical, microwave, and other instruments), the platforms (satellites, space stations, aircraft and Earth based stations) and their orbits.It is shown how these elements are interrelated and which constraints must be considered for planning an Earth observation mission. The feasibility, the amount of hard- and software, the costs, and the performance of a system are decisive for the realization of a satellite concept.Examples for different concepts investigated to date at Dornier System are given; included is the first ESA Remote Sensing Satellite ERS-1, which is now under definition at Dornier System, the main contractor of ESA.     

The near-Earth plasma sheet: An AMPTE/IRM perspective

During the last five years, statistical studies using plasma measurements made by the AMPTE/IRM satellite have lead to a better understanding of the structure and dynamics of the near-Earth plasma sheet between about 10 and 20R _E. The most notable new findings are: (1) the adiabatic non-isentropic behavior of the tail plasma during quiet times; (2) the strong non-adiabatic heating of ions and electrons during substorms and the strong coupling of the ion and electron temperature withT _i/T_i7; and (3) the high-speed flow bursts which carry most of the tail plasma transport. Moreover, it became clear that it is the central plasma sheet, and not the plasma sheet boundary layer, which is most affected by substorm activity.     

Pulsar radio emission

25 years after their discovery, pulsars still pose fundamental problems, in particular when the whole range of their periodsP is considered: 1.56 ms P0.09 s. This communication reviews my understanding of the pulsar magnetosphere, windzone, and (coherent) radio emission. New are details of the preferred magnetic structure, wind generation, and amplification of the emitted (pseudo) curvature radiation, the inferred brightness of which exceeds that of all other terrestrial and astrophysical sources by many orders of magnitude.     

Overview of Differential VLBI Observations of Lunar Orbiters in SELENE (Kaguya) for Precise Orbit Determination and Lunar Gravity Field Study

The Japanese lunar explorer SELENE (Kaguya), which was launched on September 14th, 2007, was the target of VLBI observations over the period November 2007 to June 2009. These observations were made in order to improve the lunar gravity field model, in particular the lower degree coefficients and the model near the limb. Differential VLBI Radio sources, called VRAD instruments, were on-board the subsatellites, Rstar (Okina) and Vstar (Ouna), and the radio signals were observed by the Japanese VERA (VLBI Exploration of Radio Astrometry) network, and an international VLBI network. Multi-frequency and same-beam VLBI techniques were utilized and were essential aspects of the successful observing program. Multi-frequency VLBI was employed in order to improve the accuracy of the orbit determination obtained from the phase delay from the narrow-band satellite signals, while the same-beam VLBI method was used to resolve the cycle ambiguity which is inherent in the multi-frequency VLBI method. The observations were made at three S-band frequencies (2212, 2218 and 2287 MHz), and one X-band frequency (8456 MHz). We have succeeded in correlating the recorded signals from Okina/Ouna, and we obtained phase delays with an accuracy of several pico-seconds at S-band.     

Particle Scattering by Magnetic Fields

The need for a correct quantitative treatment of the interactions between cosmic rays and turbulent magnetic fields continues to be one of the fundamental problems of modern astrophysics. It is the aim of this paper to review new developments in the understanding of mechanisms involved in the scattering of charged particles by magnetic field fluctuations. Special emphasis is given to a comparison of transport parameters determined from the modeling of spacecraft and neutron monitor observation of solar particle events, with theoretical predictions derived from a spectral analysis of simultaneously measured fluctuation spectra. It appears that the traditional quasi-linear theory of particle scattering requires only a slight modification, and the major problem still is our lack of knowledge of the three-dimensional structure of the magnetic turbulence. Possibilities to better reconcile the theory with observations by properly taking into account the microphysics of wave and turbulence aspects of the fluctuations, and to use energetic particles as probes to study certain properties of the magnetic turbulence, are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Simulation study for the determination of the lunar gravity field from PRARE-L tracking onboard the German LEO mission

A simulation study has been performed at GFZ Potsdam, which shows the anticipated improvement of the lunar gravity field model with respect to current (LP150Q model) or near-future (SELENE) knowledge in the framework of the planned German Lunar Explorations Orbiter (LEO) mission, based on PRARE-L (Precise Range And Range-rate Equipment – Lunar version) Satellite-to-Satellite (SST) and Satellite-Earth-Satellite (SEST) tracking observations. It is shown that the global mean error of the lunar gravity field can be reduced to less than 0.1 mGal at a spatial resolution of 50 km. In the spectral domain, this means a factor of 10 (long wavelengths) and some 100 (mid to short wavelengths) improvement as compared to predictions for SELENE or a factor of 1000 with respect to LP150Q. Furthermore, a higher spatial resolution of up to 28 km seems feasible and would correspond to a factor of 2–3 improvement of SELENE results. Moreover, PRARE-L is expected to derive the low-degree coefficients of the lunar gravity field with unprecedented accuracy. Considering long mission duration (at least 1 year is planned) this would allow for the first time a precise direct determination of the low-degree tidal Love numbers of the Moon and, in combination with high precision SEST, would provide an experimental basis to study relativistic effects such as the periselenium advance in the Earth–Moon system.     

Rock surfaces as life indicators: new ways to demonstrate life and traces of former life

Life and its former traces can only be detected from space when they are abundant and exposed to the planetary atmosphere at the moment of investigation by orbiters. Exposed rock surfaces present a multifractal labyrinth of niches for microbial life. Based upon our studies of highly stress-resistant microcolonial fungi of stone monument and desert rock surfaces, we propose that microbial biofilms that develop and become preserved on rock surfaces can be identified remotely by the following characteristics: (1) the existence of spectroscopically identifiable compounds that display unique adsorption, diffraction, and reflection patterns characteristic of biogenerated organic compounds (e.g., chlorophylls, carotenes, melanins, and possibly mycosporines), (2) demonstrably biogenic geomorphological features (e.g., biopitting, biochipping, and bioexfoliation), and (3) biominerals produced in association with biofilms that occupy rock surfaces (e.g., oxalates, forsterite, and special types of carbonates, sulfides, and silicates). Such traces or biosignatures of former life could provide macroscopically visible morphotypes and chemically identifiable products uniquely indicative of life.