| Popis: |
2023-July Notes: I wrote this during the summer after my senior year in high school. Some minor fixes and added some Wikipedia links. This report was prepared for William J. (Bill) Borucki. The goal was to try to be able to simulate martian soil and to understand the risks to space suits on Mars. Topics / Notes Martian Soil Smectite Palagonite SNC meteorites - Doesn't look promising Triboluminescence / Thermoluminescence Charges in Martian & Terrestrial Dust Storms Charging of dust in space UV Light Ring particle collision. Kurt Schwehr 7-90 Dust Storms,Volcanic Dust, and Electricity in Volcanic Clouds Investigations show that lightning can result from charge-separation processes in a volcanic cloud and dust storms. Kamra (1972) presents the data from his field observations of two months. The data taken was potential gradient, space charge, wind speed, and dust particle size. He quotes several sources ( Rudge 1914, Demon 1953, Uchikawa 1951, and Harris 1967 & 1969) for potential gradients in dust storms of -10 kV/m, +15 kV/m, -600 V/m, and -5 kV/m respectively. At a farm near Lubbock, Texas some small puffs or whirls of dust could be seen around the measuring site. Whenever such puffs passed close, potential gradient and space charge generally experienced a negative excursion. On May 2, 1971 near Lubbock, Texas, with wind speeds about 10(+/-5) m/sec , Kamra recorded a potential gradient peak at -90 V/m and with a space charge of +9*10^-3 el/cm^3. The relative humidity was 25% with a temp. of 31.1 deg. C. On May 4, he recorded a period with a potential gradient around -5 kV/m for 8 minutes and a space charge peak of about -45*10^-3 el/cm^3 (wind speed unknown). The wind was blowing 12-17 m/s with a rel. humidity of close to 16%, a temp. of about 33 deg. C., and large amounts of dust were blowing. Measurements were at 1.25 meters above the earth's surface. The area's soil consisted of quartz, feldspar, and clay minerals. In collecting a sample of wind blown dust, the 3 to 200 micron diameter particles were counted. 52% of the particles were 3 microns in diameter. 23% were 5 microns. 10% were 10 microns. 5% were 12 microns. 4% were 20 microns. 3% were 28 microns. 2% were 38 microns. 70 through 200 microns consist of about 3/4%. Kamra (1989) describes the amount of point discharge from and charge in dust clouds in India. Charge densities and charge transferred below storms(comparison of dust versus thunderstorms) are given by month for the time period of one year. The point discharge from dust storms is always negative. In one dust storm Kamra recorded a potential gradient of about 1 kV/m and point discharge of about 1.5 to 2 micro amps over a period of one hour. The highest point discharge over a one month period was -32.5 mC. Anderson (1965) presents observations made off Iceland of the formation of the volcanic island of Surtsey. Potential gradient was measured with an electrometer and a radioactive probe. Measurements were also taken by plane during several flights along the dust cloud. The observations go from November 28 1963 through to about July 1964. The magnitude of the charge created was estimated. At an altitude of 3800 m while flying over the volcano cloud, the vertical component of the electrical field was measured at >110, 15, and 2 V/cm. During the largest eruption they measured point discharge up to about -10 micro amps and potential gradient up to 50 times the undisturbed gradient. In estimating that 0.1 to 0.5 C was neutralized per discharge in the cloud, they inferred a charging current of 30 milliamperes. Heonig (1975) investigated the electrostatic charging associated with the generation of dust particles. His data indicates that the smallest(one micron) particles are negatively charged. This was observed with EVERY material tested with the exception of magnetite. He suggested that the one micron particles in the Earth's atmosphere are levitated by the electrostatic field of the Earth. He suggests that low velocity Martian winds move the surface material about and induce electrostatic charging. The laboratory study by H. F. Eden(1973) has indicated that significant charging occurs when a sand/dust mixture is agitated under simulated Martian conditions. With a 1-liter flask containing 50 g of dried sand in an atm of CO2 at 10 mm-Hg, Eden recorded potentials of up to 500 V over 10 cm, which is 5 kV/m. Wind Tunnel Simulation of Martian Storms Electrification is proposed to occur within Martian dust clouds, generating silt-clay aggregates which would settle to the surface where they may be deposited in the form of sand like structures (Greeley 1979, JGR). In these structures the binding forces would later be destroyed, and the particles resume the physical properties of silt and clay. Viking observations suggest similar processes occur on Mars. The fine grain material seen by Viking is estimated to be considerably less than 100 microns(Moore 1977), which is consistent with particles in the atmosphere (Pollack 1977). In wind tunnel erosion experiments, fine particles apparently aggregated due to electrostatic forces. During these experiments an electrometer gave electrical currents of 2.4 * 10^-9 and 2.5 * 10^-8 A in the impact area. A comparable charge was also observed in wind tunnel simulations for saltating sand grains under simulated Martian conditions. The conclusion is drawn that electrostatic charges occur with both wind blown particles on Earth and simulated Martian conditions and that such charges can hold silt and clay-sized particles together as sand sized aggregates. Windblown particles may be charged by Contact electrification - different materials coming into contact Fictional electrification - rubbing one surface over another piezoelectric charges - from pressure cleavage electrification - from the breakup of minerals electrification from freezing and thawing of water photoelectric charging Electrification may be even more pronounced in the low-density Martian atm. Laboratory experiments were conducted on three areas that may affect charge effect of reduced atm pressure effect of high particle velocities effect of particle size. Greeley showed that current from the impact of quartz sand varies with pressure. The current increased from 1.2 A*10^-9 to 3*10^-9 as the pressure dropped from 400 mbar to 80 mbar. The current then followed a general decrease to 2.4 A*10^-9 as the pressure dropped to near 0. In the range from about 10 to 2 mbar there were three large peaks in the range of 5.5 to 6.5 A*10^-9. Particles were approximately 250 micron quartz grains. Greeley also showed that there is an exponential increase in current as the impact velocity is increased. At 10 m/s he recorded a +10^-10 A current compared to a -1.8 * 10^-9 A at 40 m/s. There was also a change from positive to negative current as the velocity increased above about 20 m/s. The particles were approximately 120 micron quartz grains. Greeley(1980) describes experiments done to try to determine the wind speed on Mars required to cause saltation. He predicts a wind speed of 25 to 30 m/s for saltation to start. This means that saltation should occur only in the Martian winter. Greeley(1978) says the estimated particle size for dust storms is a few microns or less (Pollack 1977). References ANDERSON, R.(1965). Electricity in Volcanic Clouds, Science 148, 1179-1189. EDEN, F. H.(1973). Electrical Breakdown Caused by Dust Motion in Low-Pressure Atmospheres: Considerations for Mars, Science 180, 962-963. GREELEY, R.(1978). "Steam" Injection of Dust on Mars: Laboratory Simulation, NASA-CR-163262, See: NASA MicroFiche. GREELEY, R.(1979). Silt-Clay Aggregates On Mars, JGR 84 , 6248-54. GREELEY, R.(1980). Threshold Wind Speeds for Sand on Mars: Wind Tunnel Simulations, Geophys. Res. Letters 7, 121-4. HARRIS, D. J.(1967). Electrical Effects of the Harmattan Dust Storms, Nature 214, 585. HOENIG, S.A.(1975). Detection Techniques for Tenuous Planetary Atmospheres, NASA-CR-143098, Field Emission and Space Systems Laboratory, Electrical Engineering Department, University of Arizona, Tucson Arizona 85721 (See:NASA MicroFiche). KAMRA, A. K.(1972). Measurements of the Electrical Properties of Dust Storms, JGR 77, 5856-5869. KAMRA, K. A.(1989). Charge Transfer By Point Discharges Below Dust Storms, GeoPhys. Res. Letters 16, 127-129. MARSWIT - Martian Surface Wind Tunnel at NASA Ames Research Center Kurt Schwehr 7-90 Palagonite Allen(1981) uses the term "palagonite" to mean the vitreous, yellow-brown to orange-brown material that is found in association with sideromelane in certain volcanic tuffs. In conclusion: Mineralogically, palagonite apparently consists of poorly crystallized phyllosilicates ( smectite- or serpentine-group or mixed layer clays). Zeolites are common in palagonite tuffs. They suggest palagonite is a good analog to the soil of Mars in composition, particle size, spectral signature, and magnetic properties. The bulk of surface fines in landing areas are between 10 and 100 microns (Hargraves et al. 1976). Pollack et al. (1979) suggest 2.5 microns for rep. particle size for dust in large storms. References ALLEN,C.C.(1981). Altered Basaltic Glass: A terrestrial Analog to the Soil of Mars, Icarus 45, 347-69. Smectites(saponite) can form in the process of weathering palagonites(????). GRAMBOW, B.(1985). Weathered Basalt Glass: A Natural Analogue for the Effects of Reaction Progress On Nuclear Waste Alteration, Mat. Res. Soc. Symp. Proc. 5, 263-72. Kurt Schwehr 7-90 SNC Meteorites The shergottites, nakhlites and Chassigny, collectively termed the SNC meteorites, are also closely related achondrites. Their bulk composition, trapped noble gasses and relatively young formation ages (around 1.25 Gyr) suggest that they came from Mars. ( p. 12 ) Silicate-Rich Differentiated Meteorites SNC Group. Among silicate-rich meteorites the SNC group do not appear relevant to this discussion because their young ages, noble-gas composition, oxidized state, and presence of water suggest an origin on Mars. This cannot be confirmed, however, until the return of known Mars samples. ( p. 78 ) classified as an igneous meteorite group. (p.911) Comparison with Viking measurements of the Martian atmosphere provide strong evidence supporting the suggestion that SNCs are impact ejecta from the surface of Mars. (p.286) + more on p.572 GLOSSARY chassignite - a very rare type of achondrite(only one known, Chassigny) consisting of olivine with minor amounts of pyroxene, plagioclase, chromite and sulfide. nakhlite - a rare type of achondritic meteorite consisting of calcic pyroxene(augite) and olivine. shergottite - a rare type of meteorite, consisting of pyroxene(pigeonite) and maskelynite. KERRIDGE, J. F., MATTHEWS, M.S.(eds.)(1988). Meteorites and the Early Solar System, 1269 pp. Kurt Schwehr 7-90 Triboluminescence (TL) Glow Discharge Mills(1977) proposed that glow discharge cleaning could be the explanation for the absence of organic matter observed by the Viking landers. He explains how he performed an experiment to show the triboelectric phenomenon that occurs in sandstorms and volcanic eruptions. This would occur on Mars from charge separation in dust clouds. According to Blaustein(1969), glow discharge is most prominent in the pressure range of 0.1 to 10 torr. The Martian surface fits this range at 5 to 6 torr. Mills goes on to explain his lab setup to show triboluminescence on a small scale and the factors that make glow discharge seem likely to occur on Mars. Note: (2) Under other conditions (with water) glow discharge promotes synthesis of organic molecules. Kaska(1980) deals with triboluminescence from mobile fractures in crystals. The authors created the fractures by impact of a piston. In crystal fractures the movement of cracks and sudden creation of new surfaces causes TL. The article focuses on organic molecules. It looks at force and compression verses TL. Lahav(1982) shows the results of experiments on the amount tribo- luminescence and its decay rate in several clays. It was noted that,"a surprisingly high photon flux continues, although at a diminishing rate, for several days." The experiment induced TL by mortar/pestle or hammer, or by freezing by either -10 degree C salt-ice or liquid nitrogen. Montmorillonite was shown to produce luminescence under all of the listed methods. Previously Coyne(1981) say that the freezing and drying of montmorillonite showed luminescence. According to Zink(1978), there are eight ways for TL to occur(in roughly decreasing order): crystal fluorescence, crystal phosphorescence, luminescence from nitrogen or other gasses, metal-centered luminescence, luminescence from charge-transfer complexes, and single examples of luminescence from free radicals and possibly blackbody radiation and conduction-band to surface-band transitions. The mechanical energy can come from anisotropic pressure by grinding or crushing crystals, motion of a fluid over the surface of a solid, thermal shock, and rapid crystallization. Two hard objects struck together or frictionally heated and electrical arcing from static electrification by rubbing dissimilar objects are referred to as trivial forms of TL. In the section on mechanical aspects of TL, there are three mechanisms of triboexcitation discussed: electrical, thermal, and chemical. The proposed electrical mechanisms include: piezoelectric effects, frictional electrification from dissimilar materials, and electrification within crystals from shear, cleavage, or rupture of crystal. The results were that piezoelectric and frictional electrification were not of primary or general importance. In crystal fracture intensity seemed to depend on new surfaces created by fracture. It is noted that some worker believed that TL can be excited by plastic deformation. BLAUSTEIN, B. D. (ed.)(1969). Chemical Reactions in Electrical Discharges Adv. Chem Series No. 80, American Chemical Society. COYNE, L. M. (1981). Dehydration-induced luminescence in clay minerals, Nature 292, 819-821 (abstract only). KASKA, William C.(1980). Triboluminescence, Final Report, RPT# AD-A093805, University of California, Los Angeles, CA 90024 , 28 Pages (See NASA Micro Fiche). LAHAV, N.(1982). Prolonged Triboluminescence In Clays and Other Minerals, Clays and Clay Minerals 30, 73-75. MILLS, A. A.(1977). Dust clouds and frictional generation on Mars Nature 268, 614. ZINK, J. I.(1978). Triboluminescence, Account of Chem. Res. 11, 289-95. Kurt Schwehr 7-90 Martian Surface Soil and Dust Through the research done towards the knowledge of the composition of the surface fines of Mars two major opinions have come forward. One group presents a combination of smectite clays, nontronite and montmorillonite, as the major constituents of a good Martian soil analog. The other major opinion is that the soil is composed of a weathering product of basaltic glass known as palagonite. Two other opinions exist. The SNC meteorites (Clark 1987) are believed to originate from Mars but probably represent the minerals found in the crust, not the surface soil. Walsh(1987) presented the idea that the soil is a matrix of palagonite possibly containing smectite clays. Toulmin's (1977) normative calculations, comparisons with reference libraries have led to a qualitative mineralogical model in which the fines consist largely of iron-rich smectites (or their degradation products), carbonates, iron oxides, and sulfate minerals. From lander samples - TABLE 1 Material aprox ave Est abs err (% by wt) -------- --------- ----------- SiO 44.0 5.3 2 Al O 5.6 1.7 2 3 Fe O 18.8 2.9 2 3 MgO 8.5 4.1 CaO 5.4 1.1 K O 2 TiO 0.9 0.3 2 SO 8.3 1.2 3 Cl 0.8 0.3 Possible but not in the equipment's detection range H O,CO ,Na(NaO ),and NO . (the first two are most likely) 2 2 2 x (Reference: Toulmin, 1977, Fig. 1, p. 4628) "Note should be taken of the work of Hunt et al. [1973] and Loga |
