In-Situ Observations of Reconnection in Space

This paper gives an overview of the insights into the magnetic reconnection process obtained by in-situ measurements across current sheets found in planetary magnetospheres and the solar wind. Emphasis is placed on results that might be of interest to the study of reconnection in regions where no in-situ observations are available. These results include the role of symmetric versus asymmetric boundary conditions, the identification of the onset conditions, the reconnection rates, and the spatial and temporal scales. Special attention is paid to observations in the so-called diffusion region surrounding the reconnection sites, where ions and eventually also electrons become demagnetized and reconnection is initiated.     

NaK release model for MASTER-2009

Sodium–potassium droplets from the primary coolant loop of Russian orbital reactors have been released into space. These droplets are called NaK droplets. Sixteen nuclear powered satellites of the type RORSAT launched between 1980 and 1988 activated a reactor core ejection system, mostly between 900 and 950 km altitude. The core ejection causes an opening of the primary coolant loop. The liquid coolant consists of eutectic sodium–potassium alloy and has been released into space during these core ejections. The NaK coolant has been forming droplets up to a diameter of 5.5 cm. NaK droplets have been modeled before in ESA's MASTER Debris and Meteoroid Environment Model. The approach is currently revised for the MASTER-2009 upgrade. A mathematical improvement is introduced by substituting the current size distribution function by the modified Rosin–Rammler equation. A bimodal size distribution is derived which is based on the modified mass based Rosin–Rammler equation. The equation is modified by truncating the size range and normalizing over the finite range between the size limits of the smallest and the biggest droplet. The parameters of the model are introduced and discussed. For the validation of the NaK release model, sixteen release events are simulated. The resulting size distribution is compared with radar measurement data. The size distribution model fits well with revised published measurement data of radar observations. Results of orbit propagation simulation runs are presented in terms of spatial density.     

The first SETI observations with the Allen telescope array

The Search for ExtraTerrestrial Intelligence (SETI) finally has its own full-time telescope. The Allen telescope array (ATA) in Northern California was dedicated on October 11, 2007. This array, which will eventually be composed of 350 small radio antennas, each 6.1 m in diameter, is being built as a partnership between the SETI Institute and the University of California Radio Astronomy Laboratory. Last October, Paul G. Allen (who provided the funds for the technology development and the first phase of array construction) pushed a silver button and all 42 antennas of the current ATA-42 slewed to point in the direction of the distant galaxy M81. Specialized electronic backend detectors attached to the ATA began making a radio map of that galaxy and simultaneously began SETI observations of HIP48573, a G5V star near M81 on the sky and a distance of 264 light years from Earth. The Allen telescope array will greatly improve the speed of conducting SETI searches over the next few decades, and it will allow a suite of different search strategies to be undertaken. This paper summarizes some of the earliest SETI observations from the array, and describes the search strategies currently being planned.     

Hemodynamic and neurohormonal responses to extreme orthostatic stress in physically fit young adults

Blood pressure stability may be jeopardized in astronauts experiencing orthostatic stress. There is disagreement about cardiovascular and endocrine stress responses that emerge when a critical (presyncopal) state is reached. We studied hemodynamic and neurohormonal changes as induced by an orthostatic stress paradigm (head-up tilt combined with lower body negative pressure) that leads to a syncopal endpoint. From supine control to presyncope, heart rate increased by 78% and thoracic impedance by 12%. There was a 49% fall in stroke volume index, 19% in mean arterial blood pressure, 14% in total peripheral resistance index and 11% in plasma volume. Plasma norepinephrine rose by 107, epinephrine by 491, plasma renin activity by 167, and cortisol by 25%. Hemodynamic and hormonal changes of clearly different magnitude emerge in presyncope as compared to supine rest. Additional studies are warranted to reveal the exact time course of orthostatic changes up to syncopal levels.     

Scaling Relations from Stellar to Supermassive Black Holes

Accretion is a ubiquitous phenomenon—it is seen in sources ranging from young stars to accreting supermassive black holes in the centres of galaxies. Here, we present the known empirical connections between stellar mass X-ray binaries and active galactic nuclei. We argue that this implies that both the accretion disc and the jet are scale invariant with respect to the black hole mass. Finally, we show that also accretion discs and jets in sources with a different accretor can be connected empirically to accreting black holes, hinting towards a common mechanism of accretion in all sources.     

Recent Evidence for Convection in Sunspot Penumbrae

Whereas penumbral models during the last 15 years have been successful in explaining Evershed flows and magnetic field inclination variations in terms of flux tubes, the lack of contact between these models and a convective process needed to explain the penumbral radiative heat flux has been disturbing. We report on recent observational and theoretical evidence that challenge flux tube interpretations and conclude that the origin of penumbral filamentary structure is overturning convection.     

Energisation of O+ and O+ 2 Ions at Mars: An Analysis of a 3-D Quasi-Neutral Hybrid Model Simulation

We have studied the loss of O⁺ and O⁺ ₂ ions at Mars with a numerical model. In our quasi-neutral hybrid model ions (H⁺, He⁺⁺, O⁺, O⁺ ₂) are treated as particles while electrons form a massless charge-neutralising fluid. The employed model version does not include the Martian magnetic field resulting from the crustal magnetic anomalies. In this study we focus the Martian nightside where the ASPERA instrument on the Phobos-2 spacecraft and recently the ASPERA-3 instruments on the Mars Express spacecraft have measured the proprieties of escaping atomic and molecular ions, in particular O⁺ and O⁺ ₂ ions. We study the ion velocity distribution and how the escaping planetary ions are distributed in the tail. We also create similar types of energy-spectrograms from the simulation as were obtained from ASPERA-3 ion measurements. We found that the properties of the simulated escaping planetary ions have many qualitative and quantitative similarities with the observations made by ASPERA instruments. The general agreement with the observations suggest that acceleration of the planetary ions by the convective electric field associated with the flowing plasma is the key acceleration mechanism for the escaping ions observed at Mars.     

On uncertainties in carbon flux modelling and remotely sensed data assimilation: The Brasschaat pixel case

Uncertainty on carbon fluxes is determined by the uncertainties of ecosystem model structure, data and model parameter uncertainties and the temporal and spatial inaccuracy of the input data retrieval. The objective of this paper is to understand the error propagation and uncertainty of evaporative fraction (EF), soil moisture content (SMC) and water limited net ecosystem productivity (NEP). In this respect, C-Fix and spaceborne remote sensing are used for the ‘Brasschaat’ pixel. A simple model based on error theory and a Monte-Carlo approach are used. Different error scenarios are implemented to assess input uncertainty on EF, SMC and NEP as estimated with C-Fix.     

Compressive and Rarefactive Electron-Acoustic Solitons and Double Layers in Space Plasmas

Space observations in several near-Earth environments have revealed the presence of positive-potential, large-amplitude electrostatic structures, associated with high-frequency disturbances, and indicative of electron dynamics. Earlier models proposed in terms of electron-acoustic solitary waves in a two-electron-temperature plasma were inadequate, because only negative potential structures could thus be obtained, whereas the observations point to positive potential structures. In this paper, it is shown that the theoretical restriction to negative potential solitons is due to the neglect of the inertia of the hot electrons, implicitly or explicitly assumed in previous papers. If hot electron inertia is retained, however, there exists a parameter range where positive potential solitary waves are formed, which can have important consequences for the re-interpretation of several astrophysical phenomena involving two-electron-temperature plasmas. PACS: 52.35.Mw, 52.35.Sb, 96.50.Ry