Mercury’s Weather-Beaten Surface: Understanding Mercury in the Context of Lunar and Asteroidal Space Weathering Studies

Mercury’s regolith, derived from the crustal bedrock, has been altered by a set of space weathering processes. Before we can interpret crustal composition, it is necessary to understand the nature of these surface alterations. The processes that space weather the surface are the same as those that form Mercury’s exosphere (micrometeoroid flux and solar wind interactions) and are moderated by the local space environment and the presence of a global magnetic field. To comprehend how space weathering acts on Mercury’s regolith, an understanding is needed of how contributing processes act as an interactive system. As no direct information (e.g., from returned samples) is available about how the system of space weathering affects Mercury’s regolith, we use as a basis for comparison the current understanding of these same processes on lunar and asteroidal regoliths as well as laboratory simulations. These comparisons suggest that Mercury’s regolith is overturned more frequently (though the characteristic surface time for a grain is unknown even relative to the lunar case), more than an order of magnitude more melt and vapor per unit time and unit area is produced by impact processes than on the Moon (creating a higher glass content via grain coatings and agglutinates), the degree of surface irradiation is comparable to or greater than that on the Moon, and photon irradiation is up to an order of magnitude greater (creating amorphous grain rims, chemically reducing the upper layers of grains to produce nanometer-scale particles of metallic iron, and depleting surface grains in volatile elements and alkali metals). The processes that chemically reduce the surface and produce nanometer-scale particles on Mercury are suggested to be more effective than similar processes on the Moon. Estimated abundances of nanometer-scale particles can account for Mercury’s dark surface relative to that of the Moon without requiring macroscopic grains of opaque minerals. The presence of nanometer-scale particles may also account for Mercury’s relatively featureless visible–near-infrared reflectance spectra. Characteristics of material returned from asteroid 25143 Itokawa demonstrate that this nanometer-scale material need not be pure iron, raising the possibility that the nanometer-scale material on Mercury may have a composition different from iron metal [such as (Fe,Mg)S]. The expected depletion of volatiles and particularly alkali metals from solar-wind interaction processes are inconsistent with the detection of sodium, potassium, and sulfur within the regolith. One plausible explanation invokes a larger fine fraction (grain size <45 μm) and more radiation-damaged grains than in the lunar surface material to create a regolith that is a more efficient reservoir for these volatiles. By this view the volatile elements detected are present not only within the grain structures, but also as adsorbates within the regolith and deposits on the surfaces of the regolith grains. The comparisons with findings from the Moon and asteroids provide a basis for predicting how compositional modifications induced by space weathering have affected Mercury’s surface composition.     

Proton fluxes measured by low-orbit satellites

In this paper we consider the fluxes of protons in the energy range from 30 keV to 140 MeV recorded by instruments onboard the Russian satellites KORONAS-F and UNIVERSITETSKII and on the American satellites GOES-11 and NOAA-17. In order to estimate the reliability of the obtained data, the comparison of measurements of separate energy channels of these instruments between themselves is performed. Experimental fluxes of trapped protons are compared with the fluxes predicted by the AP8 model.     

Turbulent fluctuations of plasma and magnetic field parameters in the magnetosheath and the low-latitude boundary layer formation: Multisatellite observations on March 2, 1996

The results of simultaneous analysis of plasma and magnetic field characteristics measured on the INTERBALL/Tail Probe, WIND and Geotail satellites on March 2, 1996, are presented. During these observations the INTERBALL/Tail Probe crossed the low-latitude boundary layer, and the WIND and Geotail satellites measured the solar wind’s and magnetosheath’s parameters, respectively. The plasma and magnetic field characteristics in these regions have been compared. The data of the Corall, Electron, and MIF instruments on the INTERBALL/Tail Probe satellite are analyzed. Fluctuations of the magnetic field components and plasma velocity in the solar wind and magnetosheath, measured onboard the WIND and Geotail satellites, are compared. The causes resulting in appearance of plasma jet flows in the low-latitude boundary layer are analyzed. The amplitude of magnetic field fluctuations in the magnetosheath for a studied magnetosphere boundary crossing is shown to exceed the magnetic field value below the magnetopause near the cusp. The possibility of local violation of pressure balance on the magnetopause is discussed, as well as penetration of magnetosheath plasma into the magnetosphere, as a result of magnetic field and plasma flux fluctuations in the magnetosheath.     

Metabolic assessments during extra-vehicular activity

Extra-vehicular activity (EVA) has a significant role during extended space flights. It demonstrates that humans can survive and perform useful work outside the Orbital Space Stations (OSS) while wearing protective space suits (SS). When the International Space Station 'Alpha' (ISSA) is fully operational, EVA assembly, installation, maintenance and repair operations will become an everyday repetitive work activity in space. It needs new ergonomic evaluation of the work/rest schedule for an increasing of the labor amount per EVA hour. The metabolism assessment is a helpful method to control the productivity of the EVA astronaut and to optimize the work/rest regime. Three following methods were used in Russia to estimate real-time metabolic rates during EVA: 1. Oxygen consumption, computed from the pressure drop in a high pressure bottle per unit time (with actual thermodynamic oxygen properties under high pressure and oxygen leakage taken into account). 2. Carbon dioxide production, computed from CO2 concentration at the contaminant control cartridge and gas flow rate in the life support subsystem closed loop (nominal mode) or gas leakage in the SS open loop (emergency mode). 3. Heat removal, computed from the difference between the temperatures of coolant water or gas and its flow rate in a unit of time (with assumed humidity and wet oxygen state taken into account). Comparison of heat removal values with metabolic rates enables us to determine the thermal balance during an operative medical control of EVA at "Salyut-6", "Salyut-7" and "Mir" OSS. Complex analysis of metabolism, body temperature and heat rate supports a differential diagnosis between emotional and thermal components of stress during EVA. It gives a prognosis of human homeostasis during EVA. Available information has been acquired into an EVA data base which is an effective tool for ergonomical optimization.     

The development of a Russian communication satellite of small class, operating in the geostationary and high-elliptical orbits

In 1994-1995 Lavochkin Association (Russia) together with the other enterprises in accordance with technical requirements of the Russian Space agency, developed a new Russian communication satellite of a small class that will operate in both the geostationary (GSO) and high-elliptical (HEO) orbits. This satellite may be injected into operational orbits using a SOYUZ-2 launch vehicle (LV) and a FREGAT upper stage (US) from Plesetsk and Baykonur space launch sites (SLS).The main reason for creating such a satellite was to decrease the cost of the support and development of the Russian communication geostationary satellites group.Russian satellites Horizont, Express, Ekran and Gals, which operate in GSO, are the basis of the space segment for communications, radio and TV broadcasting. All of these satellites are injected into GSO by the PROTON LV. PROTON is a launch vehicle of a heavy class. The use of a middle class LV instead of a heavy class will allow to reduce considerably the launch cost. The change of a heavy class LV to a LV of middle class determined one economic reason for this project. Besides, the opportunity to launch S/C into GSO from Russian Plesetsk SLS increases the independence of Russia in the domain of space communications, despite the presence of the contract with Kazachstan about the rent of Baykonur SLS. Finally, use of small satellites with a rather small number of transponders is more effective than the use of big satellites. It will allow also to increase a satellite group (by the launch of additional satellites) precisely in accordance to the development of the ground segment.     

影响星载微波部件微放电阈值的Furman模型研究

星载微波部件的微放电效应是影响航天器微波传输系统独特的瓶颈问题之一。以星载微波部件微放电阈值仿真中广泛使用的Furman模型为研究对象,以平行平板传输线为例,研究并获得了Furman模型中本征二次电子、弹性散射电子、非弹性散射电子3类电子的模型参量对微放电阈值的影响规律,并通过对总二次电子发射系数的影响合理解释了微放电阈值的变化规律,为星载微波部件微放电阈值的精确仿真提供了规律指导。     

Some problems of identifying types of large-scale solar wind and their role in the physics of the magnetosphere

This paper discusses the errors in analyzing solar-terrestrial relationships, which result from either disregarding the types of interplanetary drivers in studying the magnetosphere response on their effect or from the incorrect identification of the type of these drivers. In particular, it has been shown that the absence of selection between the Sheath and ICME (the study of so-called CME-induced storms, i.e., magnetic storms generated by CME) leads to errors in the studies of interplanetary conditions of magnetic storm generation, because the statistical analysis has shown that, in the Sheath + ICME sequences, the largest number of storm onsets fell on the Sheath, and the largest number of storms maxima fell at the end of the Sheath and the beginning of the ICME. That is, the situation is observed most frequently when at least the larger part of the main phase of storm generation falls on the Sheath and, in reality, Sheath-induced storms are observed. In addition, we consider several cases in which magnetic storms were generated by corotating interaction regions, whereas the authors attribute them to CME.     

Precipitation of subrelativistic-energy electrons near the polar boundary of the Earth radiation belt according to the data of measurements on the <Emphasis Type=Italic>Vernov</Emphasis> and <Emphasis Type=Italic>Lomonosov</Emphasis> satellites

The work is devoted to observations of sharp growths of magnetospheric electron fluxes in the vicinity of the polar boundary of the outer radiation belt of the Earth according to the data of measurements on the Vernov and Lomonosov satellites. This precipitation was observed at the high-latitude boundary of the outer radiation belt toward the equator from the isotropization boundary, and can be caused by scattering waves of various physical natures, including electromagnetic and electrostatic waves.     

Spore UV and acceleration resistance of endolithic Bacillus pumilus and Bacillus subtilis isolates obtained from Sonoran desert basalt: implications for lithopanspermia

Bacterial spores have been used as model systems for studying the theory of interplanetary transport of life by natural processes such as asteroidal or cometary impacts (i.e., lithopanspermia). Because current spallation theory predicts that near-surface rocks are ideal candidates for planetary ejection and surface basalts are widely distributed throughout the rocky planets, we isolated spore-forming bacteria from the interior of near-subsurface basalt rocks collected in the Sonoran desert near Tucson, Arizona. Spores were found to inhabit basalt at very low concentrations (相似文献