Imaging the solar corona in the EUV

The SOHO (SOlar and Heliospheric Observatory) satellite was launched on December 2nd 1995. After arriving at the Earth-Sun (L1) Lagrangian point on February 14th 1996, it began to continuously observe the Sun. As one of the instruments onboard SOHO, the EIT (Extreme ultraviolet Imaging Telescope) images the Sun's corona in 4 EUV wavelengths. The He II filter at 304 Å images the chromosphere and the base of the transition region at a temperature of 5 − 8 × 10⁴ K; the Fe IX–X filter at 171 Å images the corona at a temperature of 1.3 × 10⁶ K; the Fe XII filter at 195 Å images the quiet corona outside coronal holes at a temperature of 1.6 × 10⁶ K; and the Fe XV filter at 284 Å images active regions with a temperature of 2.0 × 10⁶ K. About 5000 images have been obtained up to the present. In this paper, we describe also some aspects of the telescope and the detector performance for application in the observations. Images and movies of all the wavelengths allow a look at different phenomena present in the Sun's corona, and in particular, magnetic field reconnection.     

Studies of Comets in the Ultraviolet: The Past and the Future

The remote sensing of comets in the ultraviolet bandpass has been a valuable tool for studying the structure, composition, variability, and physical processes at work in cometary comae. By extension, these studies of comae have revealed key insights into the composition of cometary nuclei. Here we briefly review the ultraviolet studies of comets, and then take a look toward the future of such work as anticipated by the advent of several key new instruments. This revised version was published online in June 2006 with corrections to the Cover Date.     

Energetics of the magnetosphere

Energy flow in various large-scale processes of the Earth's magnetosphere is examined. This energy comes from the solar wind, via the dawn-to-dusk convection electric field, a field established primarily by magnetic merging but with viscous-like boundary interaction as a possible contributor. The convection field passes about 5 × 10¹¹ W to the near-Earth part of the plasma sheet, and also moves the plasma earthward. In addition, 1–3 × 10¹¹ W are given to the complex system of the Birkeland currents: about 4 × 10¹⁰ of this, on the average, goes to parallel acceleration, chiefly of auroral electrons, about 2–3 times that amount to joule heating of the ionosphere, and the rest heats the ring current. The ring current stores energy (mainly as kinetic energy of particles) of the order of 2 × 10¹⁵ J, and this value rises and decays during magnetic storms, on time scales ranging from a fraction of a day to several days. The tail can store comparable amounts as magnetic energy, and appreciable fractions of its energy may be released in substorms, on time scales of tens of minutes. The sporadic power level of such events reaches the order of 3 × 10¹² W. The role of magnetic merging in such releases of magnetic energy is briefly discussed, as is the correlation between properties of the solar wind and magnetospheric power levels.     

Corotating interplanetary streams and associated ionospheric disturbances at Venus and Earth

During the summer of 1979, solar coronal structure was such that a sequence of recurrent regions produced a corresponding sequence of corotating solar wind streams, with pronounced downstream signatures. One of these stream events passed Earth on July 3, and was observed later at Venus late on July 11th, with similar characteristics. Corresponding in-situ measurements at Earth from the Atmospheric Explorer-E satellite and at Venus from the Pioneer Venus Orbiter are examined for evidence of comparable perturbations of the planetary ionospheres. The passage of the stream shock front is found to be associated with pronounced fluctuations in n(0⁺) which appear as pronounced local depletion of ion concentrations in both ionospheres. The ionosphere disturbances appear to be closely associated with large variations in the solar wind momentum flux. The implied local ionospheric depletions observed at each planet are interpreted to be the consequence of plasma redistribution, rather than actual depletions of plasma.     

Electric currents and voltage drops along auroral field lines

The current state of knowledge concerning Birkeland currents (j _∥) and parallel electric field (E _∥) is briefly reviewed. Four types of j _∥ are discussed-the primary ‘region 1’ sheets, the ‘region 2’ sheets which parallel them and which seem to close in the partial ring current, the cusp currents which appear to correlate with interplanetary B _y, and the ‘Harang filament’. The energy required by E _∥ and by the associated particle acceleration processes seems to be derived from j _∥. Much of the evidence for e _∥ comes from particles, from ‘inverted V’ spectra, rising ion beams and expanded loss cones, while ‘conies’ may signify acceleration by Electrostatic Ion Cyclotron (EIC) waves, associated with beams accelerated by E _∥. Different theoretical studies predict for E _∥ a smooth, disordered or abrupt structure, and evidence for all 3 types can be deduced from S3-3 electric field probe observations.

     

Landsat data for population estimates — Approaches to inter-censal counts in the rural Sudan

The accuracy of traditional censuses and the need for other census methods are discussed, and remote sensing methods for rough population estimates are described.     

New Horizons: Anticipated Scientific Investigations at the Pluto System

The New Horizons spacecraft will achieve a wide range of measurement objectives at the Pluto system, including color and panchromatic maps, 1.25–2.50 micron spectral images for studying surface compositions, and measurements of Pluto’s atmosphere (temperatures, composition, hazes, and the escape rate). Additional measurement objectives include topography, surface temperatures, and the solar wind interaction. The fulfillment of these measurement objectives will broaden our understanding of the Pluto system, such as the origin of the Pluto system, the processes operating on the surface, the volatile transport cycle, and the energetics and chemistry of the atmosphere. The mission, payload, and strawman observing sequences have been designed to achieve the NASA-specified measurement objectives and maximize the science return. The planned observations at the Pluto system will extend our knowledge of other objects formed by giant impact (such as the Earth–moon), other objects formed in the outer solar system (such as comets and other icy dwarf planets), other bodies with surfaces in vapor-pressure equilibrium (such as Triton and Mars), and other bodies with N₂:CH₄ atmospheres (such as Titan, Triton, and the early Earth).     

无人机航迹规划技术研究及发展趋势

通过对无人机航迹规划的研究,构建了无人机航迹规划的结构框架;分析了无人机系统约束及威胁场约束,探讨了无人机航迹几何建模方法及规划算法的国内外研究概况;并着重分析了规划算法。最后,阐述了无人机航迹规划面临的关键问题及发展趋势。     

Delayed gratification habitable zones: when deep outer solar system regions become balmy during post-main sequence stellar evolution

Like all low- and moderate-mass stars, the Sun will burn as a red giant during its later evolution, generating of solar luminosities for some tens of millions of years. During this post-main sequence phase, the habitable (i.e., liquid water) thermal zone of our Solar System will lie in the region where Triton, Pluto-Charon, and Kuiper Belt objects orbit. Compared with the 1 AU habitable zone where Earth resides, this "delayed gratification habitable zone" (DGHZ) will enjoy a far less biologically hazardous environment - with lower harmful radiation levels from the Sun, and a far less destructive collisional environment. Objects like Triton, Pluto-Charon, and Kuiper Belt objects, which are known to be rich in both water and organics, will then become possible sites for biochemical and perhaps even biological evolution. The Kuiper Belt, with >10(5) objects > or =50 km in radius and more than three times the combined surface area of the four terrestrial planets, provides numerous sites for possible evolution once the Sun's DGHZ reaches it. The Sun's DGHZ might be thought to only be of academic interest owing to its great separation from us in time. However, approximately 10(9) Milky Way stars burn as luminous red giants today. Thus, if icy-organic objects are common in the 20-50 AU zones of these stars, as they are in our Solar System (and as inferred in numerous main sequence stellar disk systems), then DGHZs may form a niche type of habitable zone that is likely to be numerically common in the Galaxy.     

对接综合试验台轨迹规划算法研究

为实现模拟空间两飞行器对接动力学过程的对接综合试验台的平稳对接，提出了一种基于加速度控制的轨迹规划算法。给出了不同初始条件下的规划方法，以及时转动自由度的特殊处理。物理试验结果表明，规划模型能精确控制平台从初始零位运动到主被动对接机构初次接触位置，且最后时刻平台姿态与对接试验的初始条件完全吻合。该算法可直接用于对接综合试验台的控制。