Mass loading of planetary atmospheres by rocky satellites—II: Transport and enhanced lifetimes of satellite ejecta in planetary magnetospheres

Extensive studies have been conducted concerning individual mass, temporal and positional distribution of submicron rocky ejecta existing in the satellite-planetary gravitational sphere of influence. The transit time of the major portion of the ejecta that is transported from the satellite's gravitational sphere of influence to the planetary magnetopause is about one week and represents a mass loading pulse occurring each satellite orbit. The mass-flux distributions of lunar ejecta at the surface of the magnetopause for a complete lunar orbit are presented. Spatial mass densities of lunar ejecta in specific zones of the magnetosphere provide a means to compare sporadic interplanetary dust spatial mass densities in the same zones.     

Meteoroid bombardment as a source of the lunar exosphere

The column densities of impact-produced metal atoms in the exosphere during the peaks of activity of the main meteor showers – Geminids, Quadrantids and Perseids – and during quiet periods are estimated. The Na supply rate is estimated to be 2 × 10⁴, 3 × 10³, 10⁴, and 2 × 10⁴ atoms cm⁻² s⁻¹ for sporadic meteoroids, Perseid, Geminid, and Quadrantid meteor showers, respectively. A low upper limit on Ca in the lunar exosphere is explained by the condensation of Ca into dust grains during expansion of the cooling impact-produced vapor cloud. The chemical composition of gas-phase species released to the lunar exosphere during meteoroid impacts has been estimated. Most impact-produced molecules that contain metals are destroyed by solar photons while on ballistic trajectories. Energies of Na, K, Ca, and Mg atoms produced via photolysis of the respective monoxides are estimated to be 0.4, 0.35, 0.6, and 0.45 eV, respectively. The relative content of impact-produced Na and K atoms is maximal at altitudes of about 1000–2000 km and during the main meteor showers, lunar eclipses, and passages of the Moon through the Earth’s magnetosphere.     

Creating an artificial Geminid meteor shower: Correlation between ejecta velocity and observability

One of the interesting arguments for a space impact mission to asteroid 3200 Phaethon is to create an artificial Geminid meteor shower. In this work we investigate the artificial shower’s dates of observability and dependence on ejecta velocity using dust trail theory. We find that when the dust ejecta velocities are 200 m/s the artificial meteor showers start to be visible in 2204 and continue for about 30 years. If the dust ejecta velocity is 20 m/s they only last 10 years from 2215 to 2225. Thus, the onset of artificial shower activity begins sooner and lasts longer with higher ejecta velocities. To produce an artificial meteor shower with 3200 Phaethon as the parent will require higher impact energy than the Deep Impact spacecraft delivered to 9P/Tempel 1.     

Orbital dynamics of magnetospherically trapped lunar ejecta

$\text{In situ}$ measurements by dust experiments on HEOS II showed significant enhancement of fluxes for submicron particles. Recent studies have shown that lunar ejecta in this size range can, in a highly simplified model, be trapped in the earth's magnetosphere. The present work is a more detailed study of the dynamics of lunar ejecta in the magnetosphere. The particle size ranges for which the guiding center approximation is valid, for which corotation is negligible, and for which electromagnetic forces dominate gravitational forces have been calculated. Temporal details of charge acquisition by ejecta in the plasmasphere are considered.     

Flux rope passage at the Moon while in the terrestrial magnetotail

The Moon spends 20% of its orbit within the terrestrial magnetosphere. During this time it experiences a dynamic plasma environment, including high-speed streams, flux ropes and a flux of heavy ions from ionospheric outflows. 3D multi-fluid simulations of the Moon within the magnetosphere during a substorm shows that a highly variable plasma flow can develop in the vicinity of the Moon due to the passage of a flux rope. The transit of a flux rope past the Moon potentially leads to a plasma wake that is mis-aligned from the optical wake by nearly 30°$30°$. This will have implications when determining the range of space weathering and surface charging the lunar surface experiences.     

Asteroid and comet hazard: Identification problem of observed space objects with the parental bodies

This article focuses on the genetic identification of observed small cosmic bodies with alleged parental bodies; namely, comets, asteroids and meteoroid swarms. There is a problem of the upper D-value limit as a measure of proximity between the orbits of the bodies in the five-dimensional phase space (Southworth and Hawkins, 1963). In the study of genetic relationships of the comet and meteor complexes, the D value is usually taken as equal to 0.2 for all meteor showers. However, the upper D limit should be investigated for each meteoroid complex. For example, such investigation was performed for the Taurid meteor complex (Porub?an et al., 2006). In this paper, the upper D-criterion limit value was investigated for the Perseid meteor shower. The 1862 III Swift–Tuttle comet is its parental comet.     

Analysis of the brightness temperature features of the lunar surface using 37 GHz channel data from the Chang'E-2 microwave radiometer

Compared with other remote observations, brightness temperatures (T_B) derived from microwave emission measurements provide a unique means to characterize the physical properties of the lunar surface. Using Chang’E-2 microwave radiometer data, we produced 12 global T_B images of the lunar surface during a diurnal cycle with different local times separated by approximately 2?h. There are two types of remarkable T_B units on the lunar surface, the “hot regions” occurring during the lunar day in the lunar Maria regions and the “microwave cold spots” occurring during the nighttime typically related to young craters. Compared with their surroundings, the hot regions are much warmer during the lunar day and slightly colder at night, while the microwave cold spots are much colder during the lunar night and slightly warmer in the daytime. Moreover, the T_B heating and cooling rates of these two units are larger than others at the same average latitude where they are located during the lunar day, especially after sunrise and before sunset. The hot regions have a good agreement with the mare regions with high TiO₂ abundance. Besides, brightness temperatures in the lunar Maria correlate closely with their TiO₂ abundance. For most microwave cold spots, they agree with the young craters, and their brightness temperature distributions have a significant negative correlation with the lunar surface nighttime temperature and rock abundance.     

Antarctic meteor observations using the Davis MST and meteor radars

This paper presents the meteor observations obtained using two radars installed at Davis (68.6°S, 78.0°E), Antarctica. The Davis MST radar was installed primarily for observation of polar mesosphere summer echoes, with additional transmit and receive antennas installed to allow all-sky interferometric meteor radar observations. The Davis meteor radar performs dedicated all-sky interferometric meteor radar observations. The annual count rate variation for both radars peaks in mid-summer and minimizes in early Spring. The height distribution shows significant annual variation, with minimum (maximum) peak heights and maximum (minimum) height widths in early Spring (mid-summer). Although the meteor radar count rate and height distribution variations are consistent with a similar frequency meteor radar operating at Andenes (69.3°N), the peak heights show a much larger variation than at Andenes, while the count rate maximum-to-minimum ratios show a much smaller variation. Investigation of the effects of the temporal sampling parameters suggests that these differences are consistent with the different temporal sampling strategies used by the Davis and Andenes meteor radars. The new radiant mapping procedure of [Jones, J., Jones, W., Meteor radiant activity mapping using single-station radar observations, Mon. Not. R. Astron. Soc., 367(3), 1050–1056, doi: 10.1111/j.1365-2966.2006.10025.x, 2006] is investigated. The technique is used to detect the Southern delta-Aquarid meteor shower, and a previously unknown weak shower. Meteoroid speeds obtained using the Fresnel transform are presented. The diurnal, annual, and height variation of meteoroid speeds are presented, with the results found to be consistent with those obtained using specular meteor radars. Meteoroid speed estimates for echoes identified as Southern delta-Aquarid and Sextantid meteor candidates show good agreement with the theoretical pre-atmospheric speeds of these showers (41 km s⁻¹ and 32 km s⁻¹, respectively). The meteoroid speeds estimated for these showers show decreasing speed with decreasing height, consistent with the effects of meteoroid deceleration. Finally, we illustrate how the new radiant mapping and meteoroid speed techniques can be combined for unambiguous meteor shower detection, and use these techniques to detect a previously unknown weak shower.     

流星参数的数值分析和流星高度分布模型

流星余迹能够被后向散射雷达观测到, 利用观测结果, 可以分析和研究流星的空间分布和时间变化规律. 同时, 利用流星空间分布还可以进行空间碎片的研究. 基于标准理论, 对影响雷达回波功率的主要因素, 例如如双极扩散、余迹的初始半径、流星的有限速度, 以及雷达的脉冲重复频率在不同频率和速度下进行了数值分析和计算, 得到的流星衰减时间及双极扩散系数的观测结果与理论结果一致. 通过对昆明流星雷 达观测到的571632个流星进行统计分析, 得到了流星高度分布统计模型, 并利用该模型的分析结果与不同月份流星的观测数据进行对比, 结果比较一致.      

Modelling of the new formation structures in the near space.

Complex numerical model of young meteor stream formation taking into account reactive deceleration of cometary nucleus and its form change in the process of stream formation is discussed. The model made it possible to predict the existence of fine and superfine structures for young meteor streams, the characteristics of which agree with the observational data on the Draconid and Leonid meteor showers.     

Monitoring the moon's transient atmosphere with an all-sky imager

An indispensable tool in terrestrial aeronomy, all-sky imaging has recently been shown to be useful in studies of the Moon's exosphere. Two days after the peak of the 1998 Leonid meteor shower, an extended region of neutral sodium emission was detected in the night sky using a bare-CCD imaging system. The feature was found to be a train of sodium gas originating from the Moon. Subsequent observations indicate the feature is normally visible (max. brightness ∼15–90 Rayleighs (R)) during nights near the time of new Moon. Monthly monitoring of the feature using an all-sky system can provide useful information about the time-variability of the lunar atmosphere. Several processes are believed to be responsible for the production of lunar Na and evidence is presented indicating that two of these processes were each responsible for the observed brightness enhancements of the sodium feature on two separate new Moon periods in January and March 2000.     

全天空流星雷达相位差监测分析方法研究

介绍了一种直接利用流星观测数据, 根据流星的时空分布特性和天线的空间布阵关系建立数学模型, 对全天空流星雷达各天线通道的相位差进行监测分析和估算的新方法. 通过分析全天空流星雷达的流星观测数据, 获得了流星时空分布特性, 天线阵相位差变化对流星空间分布的影响, 特别是流星高度分布的标准差特性与各天线相位差的关系. 在此基础上, 模拟研究了利用流星高度分布的标准差来估算天线相位差的偏差, 并应用于中国三亚地区全天空流星雷达进行相位差监测分析和校正. 结果表明, 新方法无需任何附加硬件, 通过日常观测数据就能对某一通道的相位差变化或多个通道的相位差变化进行估算和分析,相位差监测精度优于2°. 对这些相位差变化进行校正, 可有效提高全天空流星雷达对流星的定位测量精度.      

X-ray fluorescence spectrometrywith the SELENE orbiter

X-ray fluorescence spectrometry of the Moon using a CCD-based instrument “XRS” is planned with the SELENE (Selenological and Engineering Explorer) orbiter, which will be launched in 2003. In the Apollo 15 and 16 missions, elemental mapping of Mg, Al and Si has been performed at the lunar equatorial regions for only 9% of the total surface. Much improved datasets will be obtained by using the XRS to map most of major elements, for 90% coverage of the total surface, and within 20 km spatial resolution. Key scientific objectives are (a) to measure the global average of lunar surface composition for investigation of the overall properties of lunar crust, (b) to map the rock-type distribution to study the formation and evolution of the crust and the maria, and to speculate the origin of the dichotomy, (c) to survey the chemical pattern of lava flows, or bottoms of craters or basins, for surveying the vertical structure and composition of the lunar crust and mantle. We describe the XRS instrument.     

Plasma and electromagnetic wave simulations of meteors

Every day billions of meteoroids impact and disintegrate in the Earth’s atmosphere. Current estimates for this global meteor flux vary from 2000 to 200,000 tons per year, and estimates for the average velocity range between 10 km/s and 70 km/s. The basic properties of this global meteor flux, such as the average mass, velocity, and chemical composition remain poorly constrained. We believe much of the mystery surrounding the basic parameters of the interplanetary meteor flux exists for the following reason, the unknown sampling characteristics of different radar meteor observation techniques, which are used to derive or constrain most models. We believe this arises due to poorly understood radio scattering characteristics of the meteor plasma, especially in light of recent work showing that plasma turbulence and instability greatly influences meteor trail properties at every stage of evolution. We present our results on meteor plasmas simulations of head echoes using particle in cell (PIC) ions, which show that electric fields strongly influence early stage meteor plasma evolution, by accelerating ions away from the meteoroid body. We also present the results of finite difference time domain electromagnetic simulations (FDTD), which can calculate the radar cross section of the simulated meteor plasmas. These simulations have shown that the radar cross section depends in a complex manner on a number of parameters. These include the angle between radar and meteor entry, a large dependence on radar frequency, which shows that for a given meteor plasma size and density, the reflectivity as a function of probing radar frequency varies, but typically peaks below 100 MHz.     

Solar particle dynamics during magnetic storms of July 23–27, 2004

It is a case study of a chain of three magnetic storms with a special attention to the particle dynamics based on CORONAS-F and SERVIS-1 low altitude satellite measurements. Solar proton penetration inside the polar cap and inner magnetosphere and dynamics at different phases of the magnetic storms was studied. We found, that solar protons were captured to the inner radiation belt at the recovery phase of the first and the second magnetic storms and additionally accelerated during the last one. No evidence of sudden commencement (SC) particle injection was found. Enhanced solar proton belt intensity with small pitch angles decreased slowly during satellite orbits for 30 days until the next magnetic storm. Then in 20–30 h we registered strong precipitation of these protons followed by the trapped proton flux dropout. Intensity decrease was more pronounced at lower altitudes and higher particle energies.     

Magnetic cloud and magnetosphere — Ionosphere response to the 6 November 1997 CME

In the present work we analyse the magnetic cloud (MC) at 1 AU on 9 November 1997. The appearance of a hotter and dense part (dense filament), with radial extent 10⁶ km, immediately behind the frontal part of the MC, is a distinctive feature of the event. The INTERBALL - Aurora] Probe had a chance to observe field-aligned currents in the mid - altitude magnetosphere during the substorm expansion phase intensification related to the dense filament. We emphasise the appearance of unusual “N”- shape magnetic structure, duration 3 min, amplitude 50 nT between field-aligned current region 1 and the magnetosphere lobe in the late evening hours. To explain some of the MC features we refer to a model scenario of the 6 November 1997 coronal mass ejection.     

On the measurements of the moon’s infrared temperature and its relation to the phase angle

Radiometric measurements of the thermal radiation originating from the moon’s surface were obtained using an infrared detector operating at wavelengths between 8 and 14 μm. The measurements cover a full moon cycle. The variation of the moon’s temperature with the lunar phase angle was established. The lunar temperatures were 391 ± 2.0 K for the full moon, 240 ± 3.5 K for the first quarter, and 236 ± 3 K for the last quarter. For the rest of the phase angles, the lunar temperature varied between 170 and 380 K. Our results are comparable with those obtained previously at these phase angles. For the new moon phase, the obtained temperature was between 120 and 133 K. With the exception of the new moon phase, our measurements at all the phase angles were consistent with those obtained using Earth-based data and those obtained by the Diviner experiment and the Clementine spacecraft. At the new phase, our measurements were comparable with those obtained from the ground but were significantly higher than those obtained by the Diviner and Clementine data. We attribute this inconsistency to either the calibration curve of our detector, which does not perform well at very low temperatures, or to infrared emission from the atmosphere. A simple linear model to predict the lunar temperature as a function of the phase angle was proposed. The experimental errors that affect the measured temperatures are discussed.     

Planetary rings

The individual ring systems are described with dust/magnetosphere interactions high-lighted somewhat. Jupiter's main ring is tenuous and enveloped by the magnetosphere; it principally contains micron-sized silicate grains. A vertically-extended, radially-localized “halo” of submicron particles lies inward of the main ring while a newly-discovered very faint ring lies outside it. The classical Saturnian system is composed of water ice chunks with sizes principally between cm and meters. Satellite resonances determine some ring structure but most is not understood. The faint exterior rings (E, G, F and one just identified between the A and F rings) are intimately associated with magnetospheric particles and contain mainly small grains, which are also prominent in the “spokes” located in the dense, middle portion of the B ring. Most of the nine narrow Uranian rings are slightly inclined and eccentric, and presumably lie within the putative Uranian magnetosphere. Particles are likely carbonaceous; sizes are thought to be larger than microns.     

廊坊中频雷达流星观测及初步结果

中频雷达用来开展夜间100km高度以上的流星观测,获得流星随时间、高度、方位的分布情况及流星体速度、流星辐射点、流星余迹径向速度等参数,其探测数据可用于流星天文学、中层大气动力学等领域的研究.利用2017年11月16日12:00UT-22:00UT期间廊坊观测站（39.4°N,116.7°E）的中频雷达数据,首次开展了中国中纬度地区夜间流星观测实验,共检测到94个流星回波信号,集中分布在97～115km高度范围内,平均高度为106.5km,计算得到了流星回波的双极扩散系数、方位分布等相关参数,并与国外中频雷达流星探测结果进行了初步比较.      

The flux of Earth-crossing and moon-cratering interplanetary bodies

Methods of determining the present flux and total number of kilometer-sized Earth-crossing objects are discussed, including (1) probability considerations based on the frequency of chance rediscoveries of the lost objects, (2) evaluation of large-scale photographic surveys for the detection of fast moving objects, and (3) evaluation of close encounters of interplanetary bodies with the Earth. The results are interfaced with the lunar and terrestrial cratering history. It is shown that the discrepancies between these two independent lines of evidence are still within the margin of uncertainty set by observational biases, cratering efficiencies, and surface reflectivities of the objects, in particular as regards extinct cometary nuclei. Impacts of active comets can only be held responsible for a very small fraction of the craters, and impacts of high-albedo Apollo asteroids are consistent with a steady state. There is no definite enhancement of the present-day flux as compared with the average level of cratering during the last 3 Gyr which would require significant variations in the stellar environment of the solar system, affecting the rate of delivery of new comets from the Oort cloud. There is also no evidence of a recent major collisional event in the asteroid belt. Deviations from an equilibrium between source and sink only become effective in the size range of meteor particles, where no long-term cratering record is available. They are apparently due to a very limited number of parent objects, and appear on a time scale which is very short compared with the age of the solar system.