Space Science Reviews

The Lunar Mineralogical Spectrometer (LMS) is one of the main payloads on the Chang’E-5 (CE-5) lunar probe, belonging to the China Lunar Exploration Program. The scientific objective of the LMS is to explore the mineralogical composition and search for evidence of -OH/H2O in the sampling area. The LMS consists of an optomechanism unit, a dustproof calibration unit (DPCU) and an electronic unit. The LMS is installed on the lander about 1.4-m above the lunar surface, the field of view (FOV) is $4.17\times 4.17^{\circ }$ , the instant FOV of the visible imaging channel is 0.28 mrad, and the typical spatial resolution is 0.56 mm/pixel @ 2 m distance. The rotation range of the 2D scanner is $\pm 22.5^{\circ}$ along the azimuth axis and $0\sim 30^{\circ }$ along the elevation axis, making it possible to observe the sampling area or to select important observing targets. The dispersing beam uses acousto-optic tunable filters, and target detection is performed with a 2D scanner. The LMS acquires spectral imaging information covering 480–950 nm, and reflectance spectra of 900–3,200-nm, both at a 5-nm/band sampling interval. The spectral resolution is $2.4\sim 9.4\text{ nm}$ in the visible and near-infrared channels and $7.6\sim 24.9\text{ nm}$ in the short–medium-wave infrared channel. The LMS has a 588-band detection capability designed for fine spectral observation of sampling points and wields a 20-band full-view multi-spectral mode to observe candidate areas prior to sampling. The DPCU of the LMS is integrated with a calibration diffuser that is used for in-flight calibration on the lunar surface using solar irradiation, thus improving the quantitative level of scientific data.

The main results of radio noise measurements taken in Poland for 220 and 400 kV power lines are presented. The influence of various line parameters, such as conductor diameter and number, phase spacing, and height of conductor above ground on the radio noise level for power lines is discussed. The basic philosophy of choosing the line parameters and route at the design stage in Poland is described taking into account radio noise levels, electrical field gradients, and corona losses.

We investigate numerically the dynamical evolution of a boundary driven, topologically complex low β plasma. The initial state is a simple, but topologically nontrivial 3D magnetic field, and the evolution is driven by forced motions on two opposite boundaries of the computational domain. A large X-type reconnection event with a supersonic one-sided jet occurs as part of a process that brakes down the large scale topology of the initial field. An energetically steady state is reached, with a double arcade overall topology, in which the driving causes continuous creation of small scale thin current sheets at various locations in the arcade structures.

This paper is a review of current theoretical topics concerning the solar wind. Broadly speaking the questions outstanding at the present time concern the loss of angular momentum to the sun, the origin of the fluctuations observed in the wind at the orbit of earth, conditions in the wind in regions yet unvisited by spacecraft (inside the orbit of Venus, beyond the orbit of Mars, and out of the plane of the ecliptic), conditions at the terminus of the wind, etc. The question of angular momentum loss is important in understanding the evolution of the sun to its present form with a slowly rotating surface. Evidence from both comet and spacecraft observations of the wind indicate that the rate at which angular momentum is being carried away by the solar wind is very large, of the order of 1031 dyne/cm in the gas flow and half as much by the interplanetary magnetic field. But theory cannot account for more than about 1030 dynes/cm in the gas without special assumptions. The fluctuations presently observed in the wind at the orbit of earth have scales ranging upward from 102 km. Their presence is puzzling because fluctuations with scales less than about 106 km are not expected to survive from the sun. Presumably, therefore, the fluctuations are generated by the velocity differences of more than 100 km/sec in the wind from different regions in the solar corona and by instabilities produced by the anisotropy of the electrons of the wind plasma. Conditions in the wind at places far removed from the orbit of earth can be inferred from the behavior of cosmic rays. The evidence is that the wind becomes relatively placid beyond about 5 AU, extending from there out to 30–300 AU without much small-scale turbulence. There are also some suggestions that the wind may perhaps be less turbulent toward the sun from 1 AU, and that the wind may be faster and more turbulent at higher solar latitudes. But the ambiguity of the situation does not permit a firm conclusion on this yet.

The NASA Ionospheric Connection Explorer Far-Ultraviolet spectrometer, ICON FUV, will measure altitude profiles of the daytime far-ultraviolet (FUV) OI 135.6 nm and N2 Lyman-Birge-Hopfield (LBH) band emissions that are used to determine thermospheric density profiles and state parameters related to thermospheric composition; specifically the thermospheric column O/N2 ratio (symbolized as $\Sigma$ O/N2). This paper describes the algorithm concept that has been adapted and updated from one previously applied with success to limb data from the Global Ultraviolet Imager (GUVI) on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission. We also describe the requirements that are imposed on the ICON FUV to measure $\Sigma$ O/N2 over any 500-km sample in daytime with a precision of better than 8.7%. We present results from orbit-simulation testing that demonstrates that the ICON FUV and our thermospheric composition retrieval algorithm can meet these requirements and provide the measurements necessary to address ICON science objectives.

Recent observations of high energy (>20 keV) X-ray emission in a few clusters of galaxies broaden our knowledge of physical phenomena in the intracluster space. This emission is likely to be nonthermal, probably resulting from Compton scattering of relativistic electrons by the cosmic microwave background (CMB) radiation. Direct evidence for the presence of relativistic electrons in some 50 clusters comes from measurements of extended radio emission in their central regions. We briefly review the main results from observations of extended regions of radio emission, and Faraday rotation measurements of background and cluster radio sources. The main focus of the review are searches for nonthermal X-ray emission conducted with past and currently operating satellites, which yielded appreciable evidence for nonthermal emission components in the spectra of a few clusters. This evidence is clearly not unequivocal, due to substantial observational and systematic uncertainties, in addition to virtually complete lack of spatial information. If indeed the emission has its origin in Compton scattering of relativistic electrons by the CMB, then the mean magnetic field strength and density of relativistic electrons in the cluster can be directly determined. Knowledge of these basic nonthermal quantities is valuable for the detailed description of processes in intracluster gas and for the origin of magnetic fields.

The Earth’s diffuse auroral precipitation provides the major source of energy input into the nightside upper atmosphere and acts as an essential linkage of the magnetosphere-ionosphere coupling. Resonant wave-particle interactions play a dominant role in the scattering of injected plasma sheet electrons, leading to the diffuse auroral precipitation. We review the recent advances in understanding the origin of the diffuse aurora and in quantifying the exact roles of various magnetospheric waves in producing the global distribution of diffuse auroral precipitation and its variability with the geomagnetic activity. Combined scattering by upper-and lower-band chorus accounts for the most intense inner magnetospheric electron diffuse auroral precipitation on the nightside. Dayside chorus can be responsible for the weaker dayside electron diffuse auroral precipitation. Pulsating auroras, the dynamic auroral structures embedded in the diffuse aurora, can be mainly caused by modulation of the excitation of lower band chorus due to macroscopic density variations in the magnetosphere. Electrostatic electron cyclotron harmonic waves are an important or even dominant cause for the nightside electron diffuse auroral precipitation beyond ${\sim}8R_{e}$ and can also contribute to the occurrence of the pulsating aurora at high $L$ -shells. Scattering by electromagnetic ion cyclotron waves could quite possibly be the leading candidate responsible for the ion precipitation (especially the reversed-type events of the energy-latitude dispersion) in the regions of the central plasma sheet and ring current. We conclude the review with a summary of current understanding, outstanding questions, and a number of suggestions for future research.

Many of the significant theoretical advances in understanding the origin and behaviour of low frequency hydromagnetic waves originating in the magnetosphere in the last decade are reviewed. Topics covered include wave generation mechanisms, wave damping, effects of inhomogeneity, signal behaviour in the ionosphere and atmosphere.