The Aster project: Flight to a near-Earth asteroid

The information on the project being developed in Brazil for a flight to binary or triple near-Earth asteroid is presented. The project plans to launch a spacecraft into an orbit around the asteroid and to study the asteroid and its satellite within six months. Main attention is concentrated on the analysis of trajectories of flight to asteroids with both impulsive and low thrust in the period 2013-2020. For comparison, the characteristics of flights to the (45) Eugenia triple asteroid of the Main Belt are also given.     

Long-Term Evolution of the Martian Crust-Mantle System

Lacking plate tectonics and crustal recycling, the long-term evolution of the crust-mantle system of Mars is driven by mantle convection, partial melting, and silicate differentiation. Volcanic landforms such as lava flows, shield volcanoes, volcanic cones, pyroclastic deposits, and dikes are observed on the martian surface, and while activity was widespread during the late Noachian and Hesperian, volcanism became more and more restricted to the Tharsis and Elysium provinces in the Amazonian period. Martian igneous rocks are predominantly basaltic in composition, and remote sensing data, in-situ data, and analysis of the SNC meteorites indicate that magma source regions were located at depths between 80 and 150 km, with degrees of partial melting ranging from 5 to 15 %. Furthermore, magma storage at depth appears to be of limited importance, and secular cooling rates of 30 to 40 K?Gyr^?1 were derived from surface chemistry for the Hesperian and Amazonian periods. These estimates are in general agreement with numerical models of the thermo-chemical evolution of Mars, which predict source region depths of 100 to 200 km, degrees of partial melting between 5 and 20 %, and secular cooling rates of 40 to 50 K?Gyr^?1. In addition, these model predictions largely agree with elastic lithosphere thickness estimates derived from gravity and topography data. Major unknowns related to the evolution of the crust-mantle system are the age of the shergottites, the planet’s initial bulk mantle water content, and its average crustal thickness. Analysis of the SNC meteorites, estimates of the elastic lithosphere thickness, as well as the fact that tidal dissipation takes place in the martian mantle indicate that rheologically significant amounts of water of a few tens of ppm are still present in the interior. However, the exact amount is controversial and estimates range from only a few to more than 200 ppm. Owing to the uncertain formation age of the shergottites it is unclear whether these water contents correspond to the ancient or present mantle. It therefore remains to be investigated whether petrologically significant amounts of water of more than 100 ppm are or have been present in the deep interior. Although models suggest that about 50 % of the incompatible species (H₂O, K, Th, U) have been removed from the mantle, the amount of mantle differentiation remains uncertain because the average crustal thickness is merely constrained to within a factor of two.     

Microphysics of Cosmic Plasmas: Background, Motivation and Objectives

With the maturing of space plasma research in the solar system, a more general approach to plasma physics in general, applied to cosmic plasmas, has become appropriate. There are both similarities and important differences in describing the phenomenology of space plasmas on scales from the Earth’s magnetosphere to galactic and inter-galactic scales. However, there are important aspects in common, related to the microphysics of plasma processes. This introduction to a coordinated collection of papers that address the several aspects of the microphysics of cosmic plasmas that have unifying themes sets out the scope and ambition of the broad sweep of topics covered in the volume, together with an enumeration of the detailed objectives of the coverage.     

X-ray and extreme ultraviolet emissions from comets

There is significant progress in the observations, theory, and understanding of the x-ray and EUV emissions from comets since their discovery in 1996. That discovery was so puzzling because comets appear to be more efficient emitters of x-rays than the Moon by a factor of 80 000. The detected emissions are general properties of comets and have been currently detected and analyzed in thirteen comets from five orbiting observatories. The observational studies before 2000 were based on x-ray cameras and low resolution (E/δE ≈ 1.5-3) instruments and focused on the morphology of xrays, their correlations with gas and dust productions in comets and with the solar x-rays and the solar wind. Even those observations made it possible to choose uniquely charge exchange between the solar wind heavy ions and cometary neutrals as the main excitation process. The recently published spectra are of much better quality and result in the identification of the emissions of the multiply charged ions of O, C, Ne, Mg, and Si which are brought to comets by the solar wind. The observed spectra have been used to study the solar wind composition and its variations. Theoretical analyses of x-ray and EUV photon excitation in comets by charge exchange, scattering of the solar photons by attogram dust particles, energetic electron impact and bremsstrahlung, collisions between cometary and interplanetary dust, and solar x-ray scattering and fluorescence in comets have been made. These analyses confirm charge exchange as the main excitation mechanism, which is responsible for more than 90% of the observed emission, while each of the other processes is limited to a few percent or less. The theory of charge exchange and different methods of calculation for charge exchange are considered. Laboratory studies of charge exchange relevant to the conditions in comets are reviewed. Total and state-selective cross sections of charge exchange measured in the laboratory are tabulated. Simulations of synthetic spectra of charge exchange in comets are discussed. X-ray and EUV emissions from comets are related to different disciplines and fields such as cometary physics, fundamental physics, x-rays spectroscopy, and space physics.This revised version was published online in July 2005 with a corrected cover date.     

Low-Cost Operation of the ORBCOMM Satellite Constellation

Financial pressures are forcing organizations to minimize operations costs. Although the easiest way to achieve this goal is simply to reduce operational requirements, often this is not possible. Therefore, automation must be employed. This paper discusses the system trade-offs that must be performed to maximize the impact of automation efforts. The discussion begins with the development of generic automation guidelines. Since many automation issues are program-specific, the paper addresses the application of these principles to operation of the ORBCOMM satellite constellation. This example demonstrates how automation can be used to produce a highly efficient satellite operations system.     

Mars Global MHD Predictions of Magnetic Connectivity Between the Dayside Ionosphere and the Magnetospheric Flanks

Atmospheric photoelectrons have been observed well above the ionosphere of Mars by the ASPERA-3 ELS instrument on Mars Express. To systematically interpret these observations, field lines from two global MHD simulations were analyzed for connectivity to the dayside ionosphere (allowing photoelectron escape). It is found that there is a hollow cylinder behind the planet from 1–2 R _M away from the Mars-Sun line that has a high probability of containing magnetic field lines with connectivity to the dayside ionosphere. These results are in complete agreement with the ELS statistics. It is concluded that the high-altitude photoelectrons are the result of direct magnetic connectivity to the dayside at the moment of the measurement, and no extra trapping or bouncing mechanisms are needed to explain the data.     

Degradation of cyanobacterial biosignatures by ionizing radiation

Primitive photosynthetic microorganisms, either dormant or dead, may remain today on the martian surface, akin to terrestrial cyanobacteria surviving endolithically in martian analog sites on Earth such as the Antarctic Dry Valleys and the Atacama Desert. Potential markers of martian photoautotrophs include the red edge of chlorophyll reflectance spectra or fluorescence emission from systems of light-harvesting pigments. Such biosignatures, however, would be modified and degraded by long-term exposure to ionizing radiation from the unshielded cosmic ray flux onto the martian surface. In this initial study into this issue, three analytical techniques--absorbance, reflectance, and fluorescence spectroscopy--were employed to determine the progression of the radiolytic destruction of cyanobacteria. The pattern of signal loss for chlorophyll reflection and fluorescence from several biomolecules is characterized and quantified after increasing exposures to ionizing gamma radiation. This allows estimation of the degradation rates of cyanobacterial biosignatures on the martian surface and the identification of promising detectable fluorescent break-down products.     

使用液态化学循环的高热效率动力研究(英文)

要使碳氢燃油在常规燃烧循环中高效燃烧,需要非常高的温度,化学循环燃烧可以为大型动力装置提供一个可行的方法。在化学循环燃烧中,使用含氧介质分子来传输两个氧化还原反应之间的氧气,含氧介质在一个反应中被氧化,在另一个与燃油的反应中被减少。从燃烧残余物中分离出含氧介质可以借助于不同的物态,如果介质用钠、钾或锌,这是液态化学循环燃烧的显著优点。液态化学循环燃烧的原理是能量和熵的循环,在考虑用于分离氮和二氧化碳零部件效率、结合水燃气交换、以及用空气作为氧气源的情况下,高的热效率(35Pa下约75%)在理论上可以达到。     

Interplanetary Origin of Intense,Superintense and Extreme Geomagnetic Storms

We present a review on the interplanetary causes of intense geomagnetic storms (Dst≤−100 nT), that occurred during solar cycle 23 (1997–2005). It was reported that the most common interplanetary structures leading to the development of intense storms were: magnetic clouds, sheath fields, sheath fields followed by a magnetic cloud and corotating interaction regions at the leading fronts of high speed streams. However, the relative importance of each of those driving structures has been shown to vary with the solar cycle phase. Superintense storms (Dst≤−250 nT) have been also studied in more detail for solar cycle 23, confirming initial studies done about their main interplanetary causes. The storms are associated with magnetic clouds and sheath fields following interplanetary shocks, although they frequently involve consecutive and complex ICME structures. Concerning extreme storms (Dst≤−400 nT), due to the poor statistics of their occurrence during the space era, only some indications about their main interplanetary causes are known. For the most extreme events, we review the Carrington event and also discuss the distribution of historical and space era extreme events in the context of the sunspot and Gleissberg solar activity cycles, highlighting a discussion about the eventual occurrence of more Carrington-type storms.     

The Surface Composition of Ceres

Our understanding of the composition of Ceres is driven by remote sensing of its surface. We review spectral observations of Ceres over wavelengths from the ultraviolet to the radio, as well as non-spectral data such as thermal inertia, photometric properties, radar experiments, and surface variability. We also discuss the closest likely meteorite analogs to Ceres and consider the likelihood that material from Ceres could be delivered to Earth.