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21.
Extraterrestrial organic matter may have been chemically altered into forms more ameanable for prebiotic chemistry in the wake of a meteor after ablation. We measured the rate of cooling of the plasma in the meteor wake from the intensity decay just behind a meteoroid by freezing its motion in high frame-rate 1000 frames/s video images, with an intensified camera that has a short phosphor decay time. Though the resulting cooling rate was found to be lower than theoretically predicted, our calculations indicated that there would have been insufficient collisions to break apart large organic compounds before most reactive radicals and electrons were lost from the air plasma. Organic molecules delivered from space to the early Earth via meteors might therefore have survived in a chemically altered form. In addition, we discovered that relatively small meteoroids generated far-ultraviolet emission that is absorbed in the immediate environment of the meteoroid, which may chemically alter the atmosphere over a much larger region than previously recognized. 相似文献
22.
Werner R. Balogh Hans J. Haubold 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009,43(12):1847-1853
The United Nations Programme on Space Applications, implemented by the United Nations Office for Outer Space Affairs, promotes the benefits of space-based solutions for sustainable economic and social development. The Programme assists Member States of the United Nations to establish indigenous capacities for the use of space technology and its applications. In the past the Programme has primarily been focusing on the use of space applications and on basic space science activities. However, in recent years there has been a strong interest in a growing number of space-using countries to build space technology capacities, for example, the ability to develop and operate small satellites. In reaction to this development, the United Nations in cooperation with the International Academy of Astronautics has been organizing annual workshops on small satellites in the service of developing countries. Space technology related issues have also been addressed as part of various other activities of the Programme on Space Applications. Building on these experiences, the Office for Outer Space Affairs is now considering the launch of a new initiative, preliminarily titled the United Nations Basic Space Technology Initiative (UNBSTI), to promote basic space technology development. The initiative would be implemented in the framework of the Programme on Space Applications and its aim would be to help building sustainable capacities for basic space technology education and development, thereby advancing the operational use of space technology and its applications. 相似文献
23.
Dilip Kumar Hans J. Haubold 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
The major problem in the cosmological nucleosynthesis is the evaluation of the reaction rate. The present scenario is that the standard thermonuclear function in the Maxwell–Boltzmann form is evaluated by using various techniques. The Maxwell–Boltzmannian approach to nuclear reaction rate theory is extended to cover Tsallis statistics (Tsallis, 1988) and more general cases of distribution functions. The main purpose of this paper is to investigate in some more detail the extended reaction probability integral in the equilibrium thermodynamic argument and in the cut-off case. The extended reaction probability integrals will be evaluated in closed form for all convenient values of the parameter by means of residue calculus. A comparison of the standard reaction probability integrals with the extended reaction probability integrals is also done. 相似文献
24.
The two-stream instability as a fundamental process in a current-carrying plasma is reconsidered. Its well-established linear
version, based on kinetic Landau theory, predicts a threshold for the drift velocity between both species below which the
plasma should be stable. We report on simulations which, however, show that a plasma as a non-linearly responding medium can
be destabilized well below this threshold. Responsible for this unexpected behaviour are coherent, electrostatic, trapped
particle structures such as phase space vortices or holes which can grow non-linearly out of thermal noise receiving their
energy from the net imbalance of loss of electron kinetic energy and gain of ion kinetic energy. The birth of predominantly
zero-energy holes is shown numerically being associated with initial, non-topological fluctuations. The latter are not subject
to Landau damping, as they lie outside the realm of linear wave theory. For a pair plasma a typical scenario is presented,
which encompasses several regimes such as non-linear growth of multiple holes, saturation and fully developed structural turbulence
as well as an asymptotic approach to a new collisionless equilibrium. During the transient, structural state the plasma transport
appears to be highly anomalous. 相似文献
25.
In previous publications (Keppens et al.: 2002, Astrophys. J. 569, L121; Goedbloed et al.: 2004a, Phys. Plasmas
11, 28), we have demonstrated that stationary rotation of magnetized plasma about a compact central object permits an enormous
number of different MHD instabilities, with the well-known magneto-rotational instability (Velikhov, E. P.: 1959, Soviet Phys.–JETP Lett. 36, 995; Chandrasekhar, S.: 1960, Proc. Natl. Acad. Sci. U.S.A. 46, 253; Balbus, S. A. and Hawley, J. F.: 1991, Astrophys. J. 376, 214) as just one of them. We here concentrate on the new instabilities found that are driven by transonic transitions of
the poloidal flow. A particularly promising class of instabilities, from the point of view of MHD turbulence in accretion
disks, is the class of trans-slow Alfv’en continuum modes, that occur when the poloidal flow exceeds a critical value of the slow magnetosonic speed. When this happens, virtually
every magnetic/flow surface of the disk becomes unstable with respect to highly localized modes of the continuous spectrum.
The mode structures rotate, in turn, about the rotating disk. These structures lock and become explosively unstable when the
mass of the central object is increased beyond a certain critical value. Their growth rates then become huge, of the order
of the Alfv’en transit time. These instabilities appear to have all requisite properties to facilitate accretion flows across
magnetic surfaces and jet formation. 相似文献
26.
27.
28.
We explore the sensitivity of the fluxes of heliospheric energetic neutral atoms (ENA) at 1 AU to the ionization state of
the local interstellar cloud (LIC). The solar wind plasma is compressed and heated in the termination shock transition. The
shocked solar plasma is convected toward the heliospheric tail in the heliosheath, the region between the termination shock
and the heliopause. The ENAs are produced in charge exchange of the plasma protons and background neutral gas and can be readily
detected at 1 AU. The expected ENA fluxes depend on the shocked plasma density, temperature, and velocity in the heliosheath.
The size and structure of the heliospheric interface region depend on the parameters of the interstellar medium. ENA fluxes
would thus reveal the LIC parameters. We demonstrate the sensitivity of the heliospheric ENA fluxes to the ionization state
of the LIC. The axi-symmetric model of the solar wind/LIC interaction includes the self-consistent treatment of the plasma-gas
coupling and Monte Carlo simulations of the neutral gas distribution.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
29.
Martin Pätzold Bernd Häusler Kaare Aksnes John D. Anderson Sami W. Asmar Jean-Pierre Barriot Michael K. Bird Hermann Boehnhardt Werner Eidel Eberhardt Grün Wing H. Ip Essam Marouf Trevor Morley Fritz M. Neubauer Hans Rickman Nicolas Thomas Bruce T. Tsurutani Max K. Wallis N. C. Wickramasinghe Eirik Mysen Oystein Olson Stefan Remus Silvia Tellmann Thomas Andert Ludmila Carone Markus Fels Christina Stanzel Iris Audenrieth-Kersten Alexander Gahr Anna-Liane Müller Dusan Stupar Christina Walter 《Space Science Reviews》2007,128(1-4):599-627
The Rosetta spacecraft has been successfully launched on 2nd March 2004 to its new target comet 67 P/Churyumov-Gerasimenko. The science objectives of the Rosetta Radio Science Investigations (RSI) experiment address fundamental aspects of cometary physics such as the mass and bulk density of the nucleus, its gravity field, its interplanetary orbit perturbed by nongravitational forces, its size and shape, its internal structure, the composition and roughness of the nucleus surface, the abundance of large dust grains, the plasma content in the coma and the combined dust and gas mass flux. The masses of two asteroids, Steins and Lutetia, shall be determined during flybys in 2008 and 2010, respectively. Secondary objectives are the radio sounding of the solar corona during the superior conjunctions of the spacecraft with the Sun during the cruise phase. The radio carrier links of the spacecraft Telemetry, Tracking and Command (TT&C) subsystem between the orbiter and the Earth will be used for these investigations. An Ultrastable oscillator (USO) connected to both transponders of the radio subsystem serves as a stable frequency reference source for both radio downlinks at X-band (8.4 GHz) and S-band (2.3 GHz) in the one-way mode. The simultaneous and coherent dual-frequency downlinks via the High Gain Antenna (HGA) permit separation of contributions from the classical Doppler shift and the dispersive media effects caused by the motion of the spacecraft with respect to the Earth and the propagation of the signals through the dispersive media, respectively. The investigation relies on the observation of the phase, amplitude, polarization and propagation times of radio signals transmitted from the spacecraft and received with ground station antennas on Earth. The radio signals are affected by the medium through which the signals propagate (atmospheres, ionospheres, interplanetary medium, solar corona), by the gravitational influence of the planet on the spacecraft and finally by the performance of the various systems involved both on the spacecraft and on ground. 相似文献
30.
Larry W. Esposito Charles A. Barth Joshua E. Colwell George M. Lawrence William E. McClintock A. Ian F. Stewart H. Uwe Keller Axel Korth Hans Lauche Michel C. Festou Arthur L. Lane Candice J. Hansen Justin N. Maki Robert A. West Herbert Jahn Ralf Reulke Kerstin Warlich Donald E. Shemansky Yuk L. Yung 《Space Science Reviews》2004,115(1-4):299-361
The Cassini Ultraviolet Imaging Spectrograph (UVIS) is part of the remote sensing payload of the Cassini orbiter spacecraft. UVIS has two spectrographic channels that provide images and spectra covering the ranges from 56 to 118 nm and 110 to 190 nm. A third optical path with a solar blind CsI photocathode is used for high signal-to-noise-ratio stellar occultations by rings and atmospheres. A separate Hydrogen Deuterium Absorption Cell measures the relative abundance of deuterium and hydrogen from their Lyman-α emission. The UVIS science objectives include investigation of the chemistry, aerosols, clouds, and energy balance of the Titan and Saturn atmospheres; neutrals in the Saturn magnetosphere; the deuterium-to-hydrogen (D/H) ratio for Titan and Saturn; icy satellite surface properties; and the structure and evolution of Saturn’s rings.This revised version was published online in July 2005 with a corrected cover date. 相似文献