Locations of Atmospheric Photoelectron Energy Peaks Within the Mars Environment

By identifying peaks in the photoelectron spectrum produced by photoionization of CO₂ in the Martian atmosphere, we have conducted a pilot study to determine the locations of these photoelectrons in the space around Mars. The significant result of this study is that these photoelectrons populate a region around Mars bounded externally by the magnetic pileup boundary, and internally by the lowest altitude of our measurements (∼250 km) on the dayside and by a cylinder of approximately the planetary radius on the nightside. It is particularly noteworthy that the photoelectrons on the nightside are observed from the terminator plane tailward to a distance of ∼3 R _M, the Mars Express apoapsis. The presence of the atmospherically generated photoelectrons on the nightside of Mars may be explained by direct magnetic field line connection between the nightside observation locations and the Martian dayside ionosphere. Thus the characteristic photoelectron peaks may be used as tracers of magnetic field lines for the study of the magnetic field configuration and particle transport in the Martian environment.     

The Geophysics of Mercury: Current Status and Anticipated Insights from the MESSENGER Mission

Current geophysical knowledge of the planet Mercury is based upon observations from ground-based astronomy and flybys of the Mariner 10 spacecraft, along with theoretical and computational studies. Mercury has the highest uncompressed density of the terrestrial planets and by implication has a metallic core with a radius approximately 75% of the planetary radius. Mercury’s spin rate is stably locked at 1.5 times the orbital mean motion. Capture into this state is the natural result of tidal evolution if this is the only dissipative process affecting the spin, but the capture probability is enhanced if Mercury’s core were molten at the time of capture. The discovery of Mercury’s magnetic field by Mariner 10 suggests the possibility that the core is partially molten to the present, a result that is surprising given the planet’s size and a surface crater density indicative of early cessation of significant volcanic activity. A present-day liquid outer core within Mercury would require either a core sulfur content of at least several weight percent or an unusual history of heat loss from the planet’s core and silicate fraction. A crustal remanent contribution to Mercury’s observed magnetic field cannot be ruled out on the basis of current knowledge. Measurements from the MESSENGER orbiter, in combination with continued ground-based observations, hold the promise of setting on a firmer basis our understanding of the structure and evolution of Mercury’s interior and the relationship of that evolution to the planet’s geological history.     

超音尾喷流流场的自动测试系统

提出一套用于对超音速尾喷流场进行全自动测试与控制的系统。在系统中采用软件模拟硬件的独特方法，自行设计的由步进电机驱动的三维坐标架，能平滑无停滞地在流场中作三维往复移动，精确定位并实现数据自动采集。实验结果表明，系统工作性能稳定可靠，数据传送率达500Kbit/s，较常用的A／D板相比，其精度大大提高，并可有效地节省试验费用。     

Various methods of calibration of the STEREO/WAVES antennas

On October 25th, 2006, NASA’s two STEREO spacecraft were launched which are designed to increase our knowledge of the physics of the solar system. On board they carry a sophisticated radio experiment, called S/WAVES. The key technology, used by S/WAVES is the direction finding capability in addition to the use of two spacecraft which makes it possible to triangulate radio sources. Direction finding requires the reception properties of the antennas to be known very accurately. We applied several different methods to calibrate the S/WAVES antennas. In this paper the methods are described and compared and the results are presented and discussed with respect to advantages and disadvantages of the different methods.     

Simulation of cometary jets in interaction with the solar wind

The influence of cometary jets on the solar wind interaction is studied with a 3D hybrid simulation. Anisotropic outgassing patterns were until recently not considered in cometary simulations, despite strong anisotropies found at observations. Comet 67P Churyumov–Gerasimenko, the target of the ROSETTA mission, was chosen as a case study for a simulation series. The cometary outgassing at 2.7 AU is modeled to originate from a single sun-facing jet with different levels of collimation, from isotropy to extremely thin jets. As no bow shock is present at this distance, solar wind patterns resulting from the anisotropic outgassing become more apparent. We find narrower jets to increase the standoff distance of the plasma interaction structures. Also, the Mach cone is wider and stronger for certain jet profiles. The magnetic field remains unable to propagate through the coma, resulting in strong draping patterns for narrow jets due to the increased standoff distance.     

Coronal Hole Properties Observed with Sumer

We analyze SUMER spectra of 14 lines belonging to 12 ions, obtained on both sides of the boundary of polar coronal holes as well as at other locations along the limb. We compare line intensities, shifts and widths in coronal holes with values obtained in the quiet Sun. We find that with increasing formation temperature, spectral lines show an increasingly stronger blueshift in coronal holes relative to the quiet Sun at an equal heliospheric angle. The width of the lines is generally larger (by a few km/s) inside the coronal hole. Intensity measurements show the presence of the coronal hole in Ne VIII lines as well as in Fe XII, with evidence for a slightly enhanced emission in polar coronal holes for lines formed below 10⁵ K. This revised version was published online in June 2006 with corrections to the Cover Date.     

THE ELECTRON DRIFT INSTRUMENT FOR CLUSTER

The Electron Drift Instrument (EDI) measures the drift of a weak beam of test electrons that, when emitted in certain directions, return to the spacecraft after one or more gyrations. This drift is related to the electric field and the gradient in the magnetic field, and these quantities can, by use of different electron energies, be determined separately. As a by-product, the magnetic field strength is also measured. The present paper describes the scientific objectives, the experimental method, and the technical realization of the various elements of the instrument.     

The visible imaging system (VIS) for the polar spacecraft

The Visible Imaging System (VIS) is a set of three low-light-level cameras to be flown on the POLAR spacecraft of the Global Geospace Science (GGS) program which is an element of the International Solar-Terrestrial Physics (ISTP) campaign. Two of these cameras share primary and some secondary optics and are designed to provide images of the nighttime auroral oval at visible wavelengths. A third camera is used to monitor the directions of the fields-of-view of these sensitive auroral cameras with respect to sunlit Earth. The auroral emissions of interest include those from N ₂ ⁺ at 391.4 nm, Oi at 557.7 and 630.0 nm, Hi at 656.3 nm, and Oii at 732.0 nm. The two auroral cameras have different spatial resolutions. These resolutions are about 10 and 20 km from a spacecraft altitude of 8R _e . The time to acquire and telemeter a 256×256-pixel image is about 12 s. The primary scientific objectives of this imaging instrumentation, together with thein-situ observations from the ensemble of ISTP spacecraft, are (1) quantitative assessment of the dissipation of magnetospheric energy into the auroral ionosphere, (2) an instantaneous reference system for thein-situ measurements, (3) development of a substantial model for energy flow within the magnetosphere, (4) investigation of the topology of the magnetosphere, and (5) delineation of the responses of the magnetosphere to substorms and variable solar wind conditions.     

Crystalline Silicates

One of the big surprises of the Infrared Space Observatory (ISO) has been discovery of crystalline silicates outside our own Solar system. It was generally assumed before that all cosmic silicates in space were of amorphous structure. Thanks to ISO we know now that crystalline silicates are ubiquitous in the Galaxy (except for the diffuse ISM) and sometimes even in very large quantities (> 50% of the small dust particles). The evolution of the crystalline silicates is still not completely clarified, but the combination of theoretical modeling and observations have already shed light on their life-cycle. The absence of crystalline silicates in the diffuse ISM provides us with information about the dust amorphization rate in the ISM.