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At least 343 records · Page 19
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NASA NTRS1987

The Martian dust cycle: A proposed model

Despite more than a decade of study of martian dust storms, many of their characteristics and associated processes remain enigmatic, including the mechanisms for dust raising, modes of settling, and the nature of dust deposits. However, observations of Mars dust, considerations of terrestrial analogs, theoretical models, and laboratory simulations permit the formulation of a Martian Dust Cycle Model, which consists of three main processes: (1) suspension threshold, (2) transportation, and (3) deposition; two associated processes are also included: (4) dust removal and (5) the addition of new dust to the cycle. Although definitions vary, dust includes particles less than 4 to approx. 60 microns in diameter, which by terrestrial usage includes silt, loess, clay, and aerosolic dust particles. The dust cycle model is explained.

Greeley, Ronald↗
NASA NTRS1989

What if chondritic porous interplanetary dust particles are not the real McCoy

To select a target comet for a Comet Nucleus Sample Return Mission (CNSRM) it is necessary to have an experimental data base to evaluate the extent of diversity and similarity of comets. For example, the physical properties (e.g., low density) of chondritic porous (CP) interplanetary dust particles (IDPs) are believed to resemble these properties of cometary dust although it is yet to be demonstrated that the porous structure of CP IDPs is inherent to presolar dust particles stored in comet nuclei. Porous structures of IDPs could conceivably form during sublimation at the surface of active comet nuclei. Porous structures are also obtained during annealing of amorphous Mg-SiO smokes which initially forms porous aggregates of olivine + platey tridymite and which, upon continued annealing, react to fluffy enstatite aggregates. It is therefore uncertain that CP IDPs are entirely composed of unmetamorphosed presolar dust. Conceivably, new minerals and textures may form in situ in nuclei of active comets as a function of their individual thermal history. Unmetamorphosed comet dust is probably structurally amorphous. Thermal annealing of this dust can produce ultra fine-grained minerals and this ultrafine grain size of CP IDPs should be considered in assessments of aqueous alterations that could affect presolar dust in comet nuclei between 200 and 400 K. Devitrification and hydration may occur in situ in ice-dust mixtures and the mantle of active comet nuclei. Devitrification, or uncontrolled crystallization, of amorphous precursor dust can produce a range of chemical compositions of ultrafine-grained minerals and (non-equilibrium) mineral assemblages and textures in dust contained in comet nuclei as a function of period and trajectory of orbit and number of perihelion passages (not considering internal heating). Thus, experimental data on relevant processes and reaction rates between 200 and 400 K are needed in order to evaluate comet selection, penetration depth for sampling device and curation of samples for CNSRM.

Rietmeijer, Frans J. M.↗
NASA NTRS1991

Lunar dust transport and potential interactions with power system components

The lunar surface is covered by a thick blanket of fine dust. This dust may be readily suspended from the surface and transported by a variety of mechanisms. As a consequence, lunar dust can accumulate on sensitive power components, such as photovoltaic arrays and radiator surfaces, reducing their performance. In addition to natural mechanisms, human activities on the Moon will disturb significant amounts of lunar dust. Of all the mechanisms identified, the most serious is rocket launch and landing. The return of components from the Surveyor 3 provided a rare opportunity to observe the effects of the nearby landing of the Apollo 12 Lunar Module. The evidence proved that significant dust accumulation occurred on the Surveyor at a distance of 155 m. From available information on particle suspension and transport mechanisms, a series of models was developed to predict dust accumulation as a function of distance from the lunar module. The accumulation distribution was extrapolated to a future Lunar Lander scenario. These models indicate that accumulation is expected to be substantial even as far as 2 km from the landing site. Estimates of the performance penalties associated with lunar dust coverage and photovoltaic arrays are presented. Because of the lunar dust adhesive and cohesive properties, the most practical dust defensive strategy appears to be the protection of sensitive components from the arrival of lunar dust by location, orientation, or barriers.

Katzan, Cynthia M.↗
NASA NTRS1991

Design of equipment for lunar dust removal

NASA has a long range goal of constructing a fully equipped, manned lunar base on the near side of the moon by the year 2015. During the Apollo Missions, lunar dust coated and fouled equipment surfaces and mechanisms exposed to the lunar environment. In addition, the atmosphere and internal surfaces of the lunar excursion module were contaminated by lunar dust which was brought in on articles passed through the airlock. Consequently, the need exists for device or appliance to remove lunar dust from surfaces of material objects used outside of the proposed lunar habitat. Additionally, several concepts were investigated for preventing the accumulation of lunar dust on mechanisms and finished surfaces. The character of the dust and the lunar environment present unique challenges for the removal of contamination from exposed surfaces. In addition to a study of lunar dust adhesion properties, the project examines the use of various energy domains for removing the dust from exposed surfaces. Also, prevention alternatives are examined for systems exposed to lunar dust. A concept utilizing a pressurized gas is presented for dust removal outside of an atmospherically controlled environment. The concept consists of a small astronaut/robotic compatible device which removes dust from contaminated surfaces by a small burst of gas.

Belden, Lacy↗
NASA NTRS1992

Dust protection for environmental control and life support systems in the lunar environment

Lunar dust is pervasive, and requirements for dust protection will affect both hardware design and operations planning for lunar surface systems. On Earth, mechanical problems caused by particulates include erosive and abrasive effects, clogging of mechanical equipment, and impairment of seals and bonds. In addition, dust tends to degrade the heat rejection properties of contaminated surfaces. All these effects have been observed on the lunar surface as well. This paper discusses the potential applicability of current dust protection methods to the problem of dust protection for the environmental control and life support (ECLS) systems of a lunar base, and highlights areas where development may be necessary. A review of dust problems experienced during the Apollo missions and of additional, ground-based experience with lunar dust provides a baseline for identifying operations and areas where dust may be expected to affect the ECLS systems. Current Earth-based methods of dust protection are identified and the impact of differences between the Earth and lunar environments on these methods is evaluated. Finally, integration of dust protection equipment with ECLS systems equipment is discussed.

Fuhs, Susan↗
NASA NTRS1993

Mars dust-driven tides and their impact on the thermosphere

It has been known since the early Mariner 6, 7, and 9 missions that dust loading of the lower atmosphere and the subsequent aerosol heating during dusty periods impacts the martian middle and upper atmospheres. A quantitative measure of this lower atmosphere forcing was obtained by the Viking 1 and 2 landers, from which observed amplitudes of semidiurnal surface-pressure oscillations were correlated with normal-incidence dust optical depths. It appears that the dominant semidiurnal mode is a good indicator of global dust content or mean dust optical depth, especially during dust storm events. A classical tidal model that reproduces the surface pressure oscillations measured by these Viking landers in 1977 was used to calculate tidal amplitudes and phases up to approximately 43 km. These tidal characteristics were calculated for various dust optical depth conditions ranging from typical dusty periods to global dust storm times. Reasonable extrapolations can be made to higher altitudes if one assumes that the vertically propagating tidal modes continue to grow without dissipation or breaking. It is very likely that gravity waves also play an important role in the structure and dynamics of the middle atmosphere of Mars, since the large topographical relief should produce vigorous gravity wave fluxes. Semidiurnal tidal modes, significantly enhanced by lower atmosphere dust-induced heating, may indeed propagate to the Mars thermosphere (approximately less than 100 km) before breaking and generating turbulence. The preferential enhancement of the semidiurnal tides during dust storm onset is primarily due to the elevation of the tidal heating source in a very dusty atmosphere. The (2,2) semidiurnal tidal tidal mode was shown to have the largest variation with dust optical depth, as measured by Viking lander instruments. Also, the (2,2) mode has the largest vertical wavelength of all the semidiurnal tidal modes, and thus is most likely to penetrate into the thermosphere before breaking and to modify the largely in situ solar-driven behavior otherwise expected. The tides may also be partially responsible for determining the height of the martian homopause (approximately 125 km).

Bougher, Stephen W.↗
NASA NTRS1993

Particle sizes and composition of Mars atmospheric dust based upon Viking and Mariner 9 observations

Mars atmospheric dust can play an important role in the thermal structure of the Mars atmosphere during periods of high dust loading. However, the radiative properties of Mars atmospheric dust remain uncertain due to uncertain definitions of the dust composition and size distribution. The analysis by Toon et al., of Mariner 9 IRIS spectra during the 1971-1972 global dust storm indicated a reasonable match between the modeled 9-micron absorption of montmorillinite and the observed 9-micron absorption. Toon et al. also determined that an effective (cross-section weighted) mean radius of 2.5 microns (R(sub mode) = 0.4 microns) provided a consistent fit of montmorillinite to the IRIS dust spectra at 9 microns. Pollack et al. analyzed Viking lander observations of atmospheric extinction and scattering at visible-near IR wavelengths (0.5-1.0 microns), and obtained consistency with the Toon et al. dust size distribution when the effects of nonspherical particle shapes were included. An additional, minor (1 percent) component of visible-ultraviolet absorbing material was required to model the derived visible (0.86) and ultraviolet (0.4-0.6) single-scattering albedos of the dust, since montmorillinite does not absorb sufficiently in this wavelength region. A combined analysis of the Viking IRTM and Mariner 9 observations was conducted to reassess the model of Mars atmospheric ultraviolet-to-infrared measurements of dust absorption and scattering. The optical constants for palagonite are incorporated in a doubling-adding radiative transfer model of the Mars atmosphere to simulate Mariner 9 IRIS spectra as well as the Viking IRTM IR band observations. Visible and ultraviolet single-scattering albedos based on the Hansen and Travis Mie scattering code were also derived. A tentative conclusion is that smaller dust particles (R(sub mode) = 0.15 microns, cross-section weighted mean R = 1.2 microns) composed of palagonite provide a much improved fit to the Mariner 9 IRIS spectra; agreement with the observed ratio of visible-to-infrared extinction opacities; and ultraviolet and visible single-scattering albedos comparable to their observed values.

Clancy, R. T.↗
NASA NTRS1994

Large-scale characteristics of interstellar dust from COBE DIRBE observations

Observations from the COBE Diffuse Infrared Background Experiment of the 140 and 240 micrometer emissions from the Galatic plane region (absolute value of b less than 10 deg) are combined with radio surveys that trace the molecular (H2), neutral atomic (H I), and extended low-density (n(sub e) approximately 10 to 100/cm(exp 3)) ionized (H II) gas phases of the interstellar medium to derive physical conditions such as the dust temperature, dust-to-gas mass ratio, and far-infrared emissivity (1) averaged over these gas phases along each line of sight and (2) within each of these three gas phases. This analysis shows large-scale longitudinal and latitudinal gradients in the dust temperature and a decrease in dust temperature with increasing Galactocentric distance. The derived dust temperatures are significantly different from those derived in similar analyses using the Infrared Astronomical Satellite (IRAS) 60 and 100 micrometer data, suggesting that small (5 A approximately less than radius approximately less than 200 A) transiently heated dust particles contribute significantly o the Galactic 60 micrometer emission. It is found that 60% to 75% of the far-infrared luminosity arises from cold (approximately 17 to 22 K) dust associated with diffuse H I clouds, 15% to 30% from cold (approximately 19 K) dust associated with molecular gas, and less than 10% from warm (approximately 29 K) dust in extended low-density H II regions, consistent with the results of the IRAS analyses of the Galactic 60 and 100 micrometer emission. Within 2 deg of longitude of the Galactic center, the derived gas-to-dust mass ratio along the line of sight, G(sub d), reverses its general trend of decreasing G(sub d) toward the inner Galaxy and increases by a factor of approximately 2 to 3 toward the Galactic center. One possible explanation for this result is that the ratio of H2 column density to (12)CO intensity is lower in the Galactic center region than in the Galactic disk.

Sodroski, T. J.↗
NASA NTRS1994

Day 640 infrared line and continuum measurements: Dust formation in SN 1987A

We have measured day 640-645 line and continuum spectra of (Ni II) 6.6 micrometer (Ne II) 12.8 micrometer (line emission was not detected), and (Fe II) 17.9 and 26.0 micrometer from SN 1987A. The high velocity feature at v(sub HVF) approximately 3900 km/sec found in both of our day 410 (Fe II) spectra is again detected in the day 640 (Ni II) spectrum, although the signal-to-noise of the day 640 (Fe II) spectra is insufficient to show this feature. The continuum fluxes provide clear evidence for the formation of dust between day 410 and day 640 and are best fitted by a graybody spectrum with a temperature of 342 +/- 17 K at day 640 and a surface area corresponding to a minimum dust velocity v(sub dust) = 1910 +/- 170 km/sec. Optically thin dust emissivity laws proportional to lambda(exp -1) or lambda(exp -2) are inconsistent with the data. Either the dust grains are large (radius a much greater than 4 micrometer and radiate like individual blackbodies, or else they are located in clumps optically thick in the 6-26 micrometer range. The (Ni II) 6.6 micrometer line flux yields a minimum Ni(+) mass of 5.8 +/- 1.6 x 10(exp -4) solar mass and a Ni/Fe abundance ratio of 0.06 +/- 0.02, equal to the solar value. The ratio of the two (Fe II) line profiles implies a gas temperature 2600 +/- 700 K, a drop of 1800 +/- 800 K from our day 410 measurement. The (Fe II) 26.0 micrometer line flux has decreased by a factor of 2 and the day 640 (Ni II) profile is blueshifted by -440 +/- 270 km/sec, relative to observations before day 500. We show that the decrease in the (Fe II) flux and the blueshift are not produced by a decrease in electron scattering optical depth, electron density, or temperature, but rather are probably due to obscuration by the same dust which produces the infrared continuum. This supports the interpretation that the dust spectrum is produced by optically thick clumps. We discuss possible explanations for the discrepancy between the mass of Fe(+) detected and the total iron mass required to power the light curve. The decrease in the (Fe II) fluxes relative to the decrease required to account for the blueshifts of optical lines from non-iron-group elements and the similarity between v(sub dust) and the Ni(+) expansion velocity imply a spatial association between the dust clumps and the iron-group elements. In addition, the larger blueshift observed for the near and far-infrared, heavy metal transitions relative to non-iron-group lines suggests that the iron-group elements are somewhat segregated from lighter elements such as the Mg(sup 0) and O(sup 0) responsible for shorter wavelength lines. We speculate that FeS may be an important constituent of the dust. A comparison of our line profiles with radiative transfer models shows that while power law and exponential density distributions yield reasonable fits to the data, polytrope distributions provided significantly worse agreement. The best fits require a substantial fraction of the iron to be undetectable, and are consistent with maximum expansion velocities of v(sub max) approximately 3000 km/sec.

Colgan, Sean W. J.↗
NASA NTRS1997

Interstellar and Cometary Dust

'Interstellar dust' forms a continuum of materials with differing properties which I divide into three classes on the basis of observations: (a) diffuse dust, in the low-density interstellar medium; (b) outer-cloud dust, observed in stars close enough to the outer edges of molecular clouds to be observed in the optical and ultraviolet regions of the spectrum, and (c) inner-cloud dust, deep within the cores of molecular clouds, and observed only in the infrared by means of absorption bands of C-H, C=O, 0-H, C(triple bond)N, etc. There is a surprising regularity of the extinction laws between diffuse- and outer-cloud dust. The entire mean extinction law from infrared through the observable ultraviolet spectrum can be characterized by a single parameter. There are real deviations from this mean law, larger than observational uncertainties, but they are much smaller than differences of the mean laws in diffuse- and outer-cloud dust. This fact shows that there are processes which operate over the entire distribution of grain sizes, and which change size distributions extremely efficiently. There is no evidence for mantles on grains in local diffuse and outer-cloud dust. The only published spectra of the star VI Cyg 12, the best candidate for showing mantles, does not show the 3.4 micro-m band which appreciable mantles would produce. Grains are larger in outer-cloud dust than diffuse dust because of coagulation, not accretion of extensive mantles. Core-mantle grains favored by J. M. Greenberg and collaborators, and composite grains of Mathis and Whiffen (1989), are discussed more extensively (naturally, I prefer the latter). The composite grains are fluffy and consist of silicates, amorphous carbon, and some graphite in the same grain. Grains deep within molecular clouds but before any processing within the solar system are presumably formed from the accretion of icy mantles on and within the coagulated outer-cloud grains. They should contain a mineral/carbonaceous matrix, without organic refractory mantles, in between the ices. Unfortunately, they may be significantly processed by chemical processes accompanying the warming (over the 10 K of the dark cloud cores) which occurs in the outer solar system. Evidence of this processing is the chemical anomalies present in interplanetary dust particles collected in the stratosphere, which may be the most primitive materials we have obtained to date. The comet return mission would greatly clarify the situation, and probably provide samples of genuine interstellar grains.

Mathis, John S.↗
NASA NTRS2001

Burning Velocity Measurements in Aluminum-Air Suspensions using Bunsen Type Dust Flames

Laminar burning velocity (sometimes also referred in literature as fundamental or normal flame propagation speed) is probably the most important combustion characteristic of the premixed combustible mixture. The majority of experimental data on burning velocities in gaseous mixtures was obtained with the help of the Bunsen conical flame. The Bunsen cone method was found to be sufficiently accurate for gaseous mixtures with burning velocities higher than 10-15 cm/s at normal pressure. Hans Cassel was the first to demonstrate that suspensions of micron-size solid fuel particles in a gaseous oxidizer can also form self-sustained Bunsen flames. He was able to stabilize Bunsen flames in a number of suspensions of different nonvolatile solid fuels (aluminum, carbon, and boron). Using the Bunsen cone method he estimated burning velocities in the premixed aluminum-air mixtures (particle size less than 10 microns) to be in the range of 30-40 cm/s. Cassel also found, that the burning velocity in dust clouds is a function of the burner diameter. In our recent work, we have used the Bunsen cone method to investigate dependence of burning velocity on dust concentration in fuel-rich aluminum dust clouds. Burning velocities in stoichiometric and fuel-rich aluminum dust suspensions with average particle sizes of about 5 microns were found to be in the range of 20-25 cm/s and largely independent on dust concentration. These results raise the question to what degree burning velocities derived from Bunsen flame specifically and other dust flame configurations in general, are indeed fundamental characteristics of the mixture and to what degree are they apparatus dependent. Dust flames in comparison to gas combustion, are thicker, may be influenced by radiation heat transfer in the flame front, respond differently to heat losses, and are fundamentally influenced by the particular flow configuration due to the particles inertia. Since characteristic spatial scales of dust flames are larger, one can expect that they will also be more sensitive than homogeneous combustion to a particular experimental geometric configuration of the flame and the flow. With such sensitivity the introduction of the very concept of the fundamental flame speed may be problematic for dust combustion. With this in mind, the objective of the present work is to further investigate Bunsen dust flames and evaluate to what degree burning velocities derived from Bunsen cone depend on experimental conditions (i.e. flow rate and nozzle diameter).

Lee, John↗
NASA NTRS2003

Dust Transport, Deposition and Radiative Effects Observed from MODIS

Carlson (1977) used satellite (AVHRR) observation of dust episodes 3 estimate that 90 tg of dust are emitted from Africa (0-30 N) to the Atlantic Ocean between June and August. MODIS systematic measurements of aerosol optical thickness (AOT) and the fraction of the AOT (f) due to the fine mode (see Remer et al abstract), are used to derive the column concentration, flux and deposition of African dust over the Atlantic Ocean. The main data set is for 2001 but the results are consistent with MODIS measurements from 2002. The analysis first determines the properties of maritime baseline aerosol (AOT=0.06, f=0.5); followed by linear scaling of the dust AOT and the anthropogenic AOT, based on MODIS measured values of the fraction "f" being 0.9 for anthropogenic aerosol and 0.5 for dust. NCEP winds are used in the analysis and are evaluated against observed dust movements between the Terra and Aqua passes (see Koren et al. abstract). Monthly values of dust transport and deposition are calculated. Preliminary results show that 280 tg of dust are emitted annually from Africa to the Atlantic Ocean between 20s and 30N, with 40 tg returning to Africa and Europe between 30N and 50N. 85 tg reach the Americas, with 130-150 tg are deposited in the Atlantic Ocean. The results are compared with dust transport models that indicate 110-230 tg of dust being deposited in the Ocean. It is interesting to note that the early estimates of Carlson (1977) and Carlson & Prosper0 (1972) are very close to our estimate from MODIS of 100 tg for the same latitude range and monthly period.

Kaufman, Y. J.↗
NASA NTRS2003

Dust, Climate, and Human Health

Air pollution from both natural and anthropogenic causes is considered to be one of the most serious world-wide environment-related health problems, and is expected to become worse with changes in the global climate. Dust storms from the atmospheric transport of desert soil dust that has been lifted and carried by the winds - often over significant distances - have become an increasingly important emerging air quality issue for many populations. Recent studies have shown that the dust storms can cause significant health impacts from the dust itself as well as the accompanying pollutants, pesticides, metals, salt, plant debris, and other inorganic and organic materials, including viable microorganisms (bacteria, viruses and fungi). For example, thousands of tons of Asian desert sediments, some containing pesticides and herbicides from farming regions, are commonly transported into the Arctic during dust storm events. These chemicals have been identified in animal and human tissues among Arctic indigenous populations. Millions of tons of airborne desert dust are being tracked by satellite imagery, which clearly shows the magnitude as well as the temporal and spatial variability of dust storms across the "dust belt" regions of North Africa, the Middle East, and China. Th~s paper summarizes the most recent findings on the effects of airborne desert dust on human health as well as potential climate influences on dust and health.

Maynard, Nancy G.↗
NASA NTRS2003

Dust, Climate, and Human Health

Air pollution from both natural and anthropogenic causes is considered to be one of the most serious world-wide environment-related health problems, and is expected to become worse with changes in the global climate. Dust storms from the atmospheric transport of desert soil dust that has been lifted and carried by the winds - often over significant distances - have become an increasingly important emerging air quality issue for many populations. Recent studies have shown that the dust storms can cause significant health impacts from the dust itself as well as the accompanying pollutants, pesticides, metals, salt, plant debris, and other inorganic and organic materials, including viable microorganisms (bacteria, viruses and fungi). For example, thousands of tons of Asian desert sediments, some containing pesticides and herbicides from farming regions, are commonly transported into the Arctic during dust storm events. These chemicals have been identified in animal and human tissues among Arctic indigenous populations. Millions of tons of airborne desert dust are being tracked by satellite imagery, which clearly shows the magnitude as well as the temporal and spatial variability of dust storms across the "dust belt" regions of North Africa, the Middle East, and China. This paper summarizes the most recent findings on the effects of airborne desert dust on human health as well as potential climate influences on dust and health.

Maynard, Nancy G.↗
NASA NTRS2004

Formation and Destruction Processes of Interstellar Dust: From Organic Molecules to carbonaceous Grains

The study of the formation and destruction processes of cosmic dust is essential to understand and to quantify the budget of extraterrestrial organic molecules. interstellar dust presents a continuous size distribution from large molecules, radicals and ions to nanometer-sized particles to micron-sized grains. The lower end of the dust size distribution is thought to be responsible for the ubiquitous spectral features that are seen in emission in the IR (UIBs) and in absorption in the visible (DIBs). The higher end of the dust-size distribution is thought to be responsible for the continuum emission plateau that is seen in the IR and for the strong absorption seen in the interstellar UV extinction curve. All these spectral signatures are characteristic of cosmic organic materials that are ubiquitous and present in various forms from gas-phase molecules to solid-state grains. Although dust with all its components plays an important role in the evolution of interstellar chemistry and in the formation of organic molecules, little is known on the formation and destruction processes of dust. Recent space observations in the UV (HST) and in the IR (ISO) help place size constraints on the molecular component of carbonaceous IS dust and indicate that small (ie., subnanometer) PAHs cannot contribute significantly to the IS features in the UV and in the IR. Studies of large molecular and nano-sized IS dust analogs formed from PAH precursors have been performed in our laboratory under conditions that simulate diffuse ISM environments (the particles are cold -100 K vibrational energy, isolated in the gas phase and exposed to a high-energy discharge environment in a cold plasma). The species (molecules, molecular fragments, ions, nanoparticles, etc) formed in the pulsed discharge nozzle (PDN) plasma source are detected with a high-sensitivity cavity ring-down spectrometer (CRDS). We will present new experimental results that indicate that nanoparticles are generated in the plasma. From these unique measurements, we derive information on the nature, the size and the structure of interstellar dust particles, the growth and the destruction processes of IS dust and the resulting budget of extraterrestrial organic molecules.

Salama, F.↗
NASA NTRS2003

Uptake of Nitrate and Sulfate on Dust Aerosols during TRACE-P

Aerosol data collected near Asia on the DC-8 aircraft platform during TRACE-P has been examined for evidence of uptake of NO3(-) and SO4(-) on dust surfaces. Data is compared between a sector where dust was predominant and a sector where dust was less of an influence. Coincident with dust were higher mixing ratios of anthropogenic pollutants. HNO3, SO2, and CO were higher in the dust sector than the nondust sector by factors of 2.7, 6.2, and 1.5, respectively. The colocation of dust and pollution sources allowed for the uptake of NO3(-) and nss-SO4(-) on the coarse dust aerosols, increasing the mixing ratios of these particulates by factors of 5.7 and 2.6 on average. There was sufficient nss-SO4(-) to take up all of the NH4(+) present, with enough excess nss-SO4(-) to also react with dust CaCO3. This suggests that the enhanced NO3(-) was not in fine mode NH4NO3. Particulate NO3(-) (p-NO3(-)) constituted 54% of the total NO3(-), (t-NO3(-)) on average, reaching a maximum of 72% in the dust sector. In the nondust sector, p-NO3(-) contributed 37% to t-NO3(-), likely due to the abundance of sea salts there. In two other sectors where the influence of dust and sea salt were minimal, p-NO3(-), accounted for < 15% of t-NO3(-).

Jordan, C. E.↗
NASA NTRS2005

Comparison of Morphologies of Apollo 17 Dust Particles with Lunar Simulant, JSC-1

Lunar dust (< 20 microns) makes up approx.20 wt.% of the lunar soil. Because of the abrasive and adhering nature of lunar soil, a detailed knowledge of the morphology (size, shape and abundance) of lunar dust is important for dust mitigation on the Moon. This represents a critical step towards the establishment of long-term human presence on the Moon (Taylor et al. 2005). Machinery design for in-situ resource utilization (ISRU) on the Moon also requires detailed information on dust morphology and general physical/chemical characteristics. Here, we report a morphological study of Apollo 17 dust sample 70051 and compare it to lunar soil stimulant, JSC-1. W e have obtained SEM images of dust grains from sample 70051 soil (Fig. 1). The dust grains imaged are composed of fragments of minerals, rocks, agglutinates and glass. Most particles consist largely of agglutinitic impact glass with their typical vesicular textures (fine bubbles). All grains show sub-angular to angular shapes, commonly with sharp edges, common for crushed glass fragments. There are mainly four textures: (1) ropey-textured pieces (typical for agglutinates), (2) angular shards, (3) blocky bits, and (4) Swiss-cheese grains. This last type with its high concentration of submicron bubbles, occurs on all scales. Submicron cracks are also present in most grains. Dust-sized grains of lunar soil simulant, JSC-1, were also studied. JSC-1 is a basaltic tuff with relatively high glass content (approx.50%; McKay et al. 1994). It was initially chosen in the early 90s to approximate the geotechnical properties of the average lunar soil (Klosky et al. 1996). JSC-1 dust grains also show angular blocky and shard textures (Fig. 2), similar to those of lunar dust. However, the JSC-1 grains lack the Swiss-cheese textured particles, as well as submicron cracks and bubbles in most grains.

Liu, Yang↗
NASA NTRS2006

The Evolution of Dust in Extreme Astrophysical Environments

The recent discovery of QSOs located at redshift z greater than 6, with high infrared luminosities (typically 1.E13 solar luminosities), challenges our understanding of dust evolution. Indeed, these high infrared luminosities imply more than 1.E8 solar masses of dust and nearly solar gas-to-dust mass ratios. An interesting question is how do we make so much dust within approx. 400 Myr, which is roughly the age of the galaxy assuming it formed at z-10. During this epoch, AGB stars could not have enriched the ISM, so that all the dust must have formed by supernovae (SN). However, SN blast waves also play an important role in destroying the dust in the ISM. Understanding the formation and evolution of the dust in such objects requires therefore the construction of a detailed model for the chemical evolution of the gas and dust phases of the ISM. We focus on the well-studied quasar SDSS J1148+5251, at z=6.42. Using the IR luminosities as tracers of of the star formation rate (SFR) in these objects implies a rates of 3E3 Msun/yr, and SN rates of about 200/yr. However, this quasar contains an embedded AGN, so that the IR luminosity may not be a good tracer of the SFR in this object. Using the estimated mass of gas as a tracer of the SFR we construct a self-consistent model for the evolution of interstellar dust, which also follows the formation and destruction of the dust by SN. Finally, we discuss the contribution of the AGN to the total infrared luminosity, and its implications for the mass of the black hole that is required to power the observed IR emission.

Dwek, Eli↗