Magnetic Fields, Relativistic Particles, and Shock Waves in Cluster Outskirts

It is only now, with low-frequency radio telescopes, long exposures with high-resolution X-ray satellites and γ-ray telescopes, that we are beginning to learn about the physics in the periphery of galaxy clusters. In the coming years, Sunyaev-Zel’dovich telescopes are going to deliver further great insights into the plasma physics of these special regions in the Universe. The last years have already shown tremendous progress with detections of shocks, estimates of magnetic field strengths and constraints on the particle acceleration efficiency. X-ray observations have revealed shock fronts in cluster outskirts which have allowed inferences about the microphysical structure of shocks fronts in such extreme environments. The best indications for magnetic fields and relativistic particles in cluster outskirts come from observations of so-called radio relics, which are megaparsec-sized regions of radio emission from the edges of galaxy clusters. As these are difficult to detect due to their low surface brightness, only few of these objects are known. But they have provided unprecedented evidence for the acceleration of relativistic particles at shock fronts and the existence of μG strength fields as far out as the virial radius of clusters. In this review we summarise the observational and theoretical state of our knowledge of magnetic fields, relativistic particles and shocks in cluster outskirts.     

Direct observation of charge state abundances of energetic He,C, O,and Fe emitted in solar flares

The ionic charge states of helium, carbon, oxygen, and iron have been determined for three solar particle enhancements by an electrostatic deflection analyzer, which is combined with a thin window proportional counter dE/dX vs. E system. The observations are obtained during the periods September 23 to 29, 1978, June 6 to 8, 1979, and September 15 to 26, 1979, with an instrument onboard the ISEE-3 spacecraft. The mean ionic charge states for He, C, and oxygen exhibit a high degree of ionization with values of Q = 2, 6, and 7.2, respectively. The charge state of iron is near 13 charge units. Variations from flare to flare and within the September 23, 1978 flare are small. The most surprising feature of the charge state measurement is the observation of a small (～10%) but finite contribution of singly ionized helium.     

Coronal mass ejection (CME) activity of low mass M stars as an important factor for the habitability of terrestrial exoplanets. II. CME-induced ion pick up of Earth-like exoplanets in close-in habitable zones

Atmospheric erosion of CO2-rich Earth-size exoplanets due to coronal mass ejection (CME)-induced ion pick up within close-in habitable zones of active M-type dwarf stars is investigated. Since M stars are active at the X-ray and extreme ultraviolet radiation (XUV) wave-lengths over long periods of time, we have applied a thermal balance model at various XUV flux input values for simulating the thermospheric heating by photodissociation and ionization processes due to exothermic chemical reactions and cooling by the CO2 infrared radiation in the 15 microm band. Our study shows that intense XUV radiation of active M stars results in atmospheric expansion and extended exospheres. Using thermospheric neutral and ion densities calculated for various XUV fluxes, we applied a numerical test particle model for simulation of atmospheric ion pick up loss from an extended exosphere arising from its interaction with expected minimum and maximum CME plasma flows. Our results indicate that the Earth-like exoplanets that have no, or weak, magnetic moments may lose tens to hundreds of bars of atmospheric pressure, or even their whole atmospheres due to the CME-induced O ion pick up at orbital distances 相似文献   

Calculation of the Initial Magnetic Field for Mercury’s Magnetosphere Hybrid Model

Several types of numerical models are used to analyze the interactions of the solar wind flow with Mercury’s magnetosphere, including kinetic models that determine magnetic and electric fields based on the spatial distribution of charges and currents, magnetohydrodynamic models that describe plasma as a conductive liquid, and hybrid models that describe ions kinetically in collisionless mode and represent electrons as a massless neutralizing liquid. The structure of resulting solutions is determined not only by the chosen set of equations that govern the behavior of plasma, but also by the initial and boundary conditions; i.e., their effects are not limited to the amount of computational work required to achieve a quasi-stationary solution. In this work, we have proposed using the magnetic field computed by the paraboloid model of Mercury’s magnetosphere as the initial condition for subsequent hybrid modeling. The results of the model have been compared to measurements performed by the Messenger spacecraft during a single crossing of the magnetosheath and the magnetosphere. The selected orbit lies in the terminator plane, which allows us to observe two crossings of the bow shock and the magnetopause. In our calculations, we have defined the initial parameters of the global magnetospheric current systems in a way that allows us to minimize paraboloid magnetic field deviation along the trajectory of the Messenger from the experimental data. We have shown that the optimal initial field parameters include setting the penetration of a partial interplanetary magnetic field into the magnetosphere with a penetration coefficient of 0.2.     

ARTEMIS Science Objectives

NASA??s two spacecraft ARTEMIS mission will address both heliospheric and planetary research questions, first while in orbit about the Earth with the Moon and subsequently while in orbit about the Moon. Heliospheric topics include the structure of the Earth??s magnetotail; reconnection, particle acceleration, and turbulence in the Earth??s magnetosphere, at the bow shock, and in the solar wind; and the formation and structure of the lunar wake. Planetary topics include the lunar exosphere and its relationship to the composition of the lunar surface, the effects of electric fields on dust in the exosphere, internal structure of the Moon, and the lunar crustal magnetic field. This paper describes the expected contributions of ARTEMIS to these baseline scientific objectives.     

Turbulence, Magnetic Reconnection in Turbulent Fluids and Energetic Particle Acceleration

Turbulence is ubiquitous in astrophysics. It radically changes many astrophysical phenomena, in particular, the propagation and acceleration of cosmic rays. We present the modern understanding of compressible magnetohydrodynamic (MHD) turbulence, in particular its decomposition into Alfvén, slow and fast modes, discuss the density structure of turbulent subsonic and supersonic media, as well as other relevant regimes of astrophysical turbulence. All this information is essential for understanding the energetic particle acceleration that we discuss further in the review. For instance, we show how fast and slow modes accelerate energetic particles through the second order Fermi acceleration, while density fluctuations generate magnetic fields in pre-shock regions enabling the first order Fermi acceleration of high energy cosmic rays. Very importantly, however, the first order Fermi cosmic ray acceleration is also possible in sites of magnetic reconnection. In the presence of turbulence this reconnection gets fast and we present numerical evidence supporting the predictions of the Lazarian and Vishniac (Astrophys. J. 517:700–718, 1999) model of fast reconnection. The efficiency of this process suggests that magnetic reconnection can release substantial amounts of energy in short periods of time. As the particle tracing numerical simulations show that the particles can be efficiently accelerated during the reconnection, we argue that the process of magnetic reconnection may be much more important for particle acceleration than it is currently accepted. In particular, we discuss the acceleration arising from reconnection as a possible origin of the anomalous cosmic rays measured by Voyagers as well as the origin cosmic ray excess in the direction of Heliotail.     

A Review of Low Frequency Electromagnetic Wave Phenomena Related to Tropospheric-Ionospheric Coupling Mechanisms

Investigation of coupling mechanisms between the troposphere and the ionosphere requires a multidisciplinary approach involving several branches of atmospheric sciences, from meteorology, atmospheric chemistry, and fulminology to aeronomy, plasma physics, and space weather. In this work, we review low frequency electromagnetic wave observations in the Earth-ionosphere cavity from a troposphere-ionosphere coupling perspective. We discuss electromagnetic wave generation, propagation, and resonance phenomena, considering atmospheric, ionospheric and magnetospheric sources, from lightning and transient luminous events at low altitude to Alfvén waves and particle precipitation related to solar and magnetospheric processes. We review ionospheric processes as well as surface and space weather phenomena that drive the coupling between the troposphere and the ionosphere. Effects of aerosols, water vapor distribution, thermodynamic parameters, and cloud charge separation and electrification processes on atmospheric electricity and electromagnetic waves are reviewed. Regarding the role of the lower boundary of the cavity, we review transient surface phenomena, including seismic activity, earthquakes, volcanic processes and dust electrification. The role of surface perturbations and atmospheric gravity waves in ionospheric dynamics is also briefly addressed. We summarize analytical and numerical tools and techniques to model low frequency electromagnetic wave propagation and to solve inverse problems and outline in a final section a few challenging subjects that are important to advance our understanding of tropospheric-ionospheric coupling.     

Optimization of the trajectory of the spacecraft insertion into the system of heliocentric orbits

The possibility of the spacecraft insertion into the system of operational heliocentric orbits has been analyzed. It has been proposed to use a system of several operational heliocentric orbits. On each orbit, the spacecraft makes one or more revolutions around the Sun. These orbits are characterized by a relatively small perihelion radius and relatively high inclination, which allows one to investigate the polar regions of the Sun. The transition of the spacecraft from one orbit to another has been performed using an unpowered gravity assist maneuver near Venus and does not require the cruise propulsion operation. Each maneuver transfers the spacecraft into the sequence of operational heliocentric orbits. We have analyzed several systems of operational heliocentric orbits into which the spacecraft can be inserted by means of the considered transportation system with electric propulsion (EP). The mass of the spacecraft delivered to these systems of operational orbits has been estimated.     

Microcomputer-based monitoring of cardiovascular functions in simulated microgravity.

A microcomputer-based system for non-invasive monitoring of cardiovascular system in simulated microgravity is described. The system evaluates automatically, accurately and interactively heart beat intervals, beat-to-beat non-invasive finger arterial blood pressure (systolic, diastolic, mean and pulse pressure) using a Finapres device and beat-to-beat changes of thoracic blood volume using impedance changes. In addition, beat-to-beat evaluation of cardiac mechanical function including left ventricular ejection time, diastolic time, systolic time intervals, left ventricular ejection fraction estimate and several other contractility parameters, left ventricular volume, stroke volume and cardiac output estimates are performed with high degree of automaticity.     

Lunar Reconnaissance Orbiter Overview: The Instrument Suite and Mission

NASA’s Lunar Precursor Robotic Program (LPRP), formulated in response to the President’s Vision for Space Exploration, will execute a series of robotic missions that will pave the way for eventual permanent human presence on the Moon. The Lunar Reconnaissance Orbiter (LRO) is first in this series of LPRP missions, and plans to launch in October of 2008 for at least one year of operation. LRO will employ six individual instruments to produce accurate maps and high-resolution images of future landing sites, to assess potential lunar resources, and to characterize the radiation environment. LRO will also test the feasibility of one advanced technology demonstration package. The LRO payload includes: Lunar Orbiter Laser Altimeter (LOLA) which will determine the global topography of the lunar surface at high resolution, measure landing site slopes, surface roughness, and search for possible polar surface ice in shadowed regions, Lunar Reconnaissance Orbiter Camera (LROC) which will acquire targeted narrow angle images of the lunar surface capable of resolving meter-scale features to support landing site selection, as well as wide-angle images to characterize polar illumination conditions and to identify potential resources, Lunar Exploration Neutron Detector (LEND) which will map the flux of neutrons from the lunar surface to search for evidence of water ice, and will provide space radiation environment measurements that may be useful for future human exploration, Diviner Lunar Radiometer Experiment (DLRE) which will chart the temperature of the entire lunar surface at approximately 300 meter horizontal resolution to identify cold-traps and potential ice deposits, Lyman-Alpha Mapping Project (LAMP) which will map the entire lunar surface in the far ultraviolet. LAMP will search for surface ice and frost in the polar regions and provide images of permanently shadowed regions illuminated only by starlight. Cosmic Ray Telescope for the Effects of Radiation (CRaTER), which will investigate the effect of galactic cosmic rays on tissue-equivalent plastics as a constraint on models of biological response to background space radiation. The technology demonstration is an advanced radar (mini-RF) that will demonstrate X- and S-band radar imaging and interferometry using light weight synthetic aperture radar. This paper will give an introduction to each of these instruments and an overview of their objectives.