Search NASA⌕ Search

SEARCH · Search NASA

Results for “Cometary Dust”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Sulfur in Cometary Dust

The computer-intensive project consisted of the analysis and synthesis of existing data on composition of comet Halley dust particles. The main objective was to obtain a complete inventory of sulfur containing compounds in the comet Halley dust by building upon the existing classification of organic and inorganic compounds and applying a variety of statistical techniques for cluster and cross-correlational analyses. A student hired for this project wrote and tested the software to perform cluster analysis. The following tasks were carried out: (1) selecting the data from existing database for the proposed project; (2) finding access to a standard library of statistical routines for cluster analysis; (3) reformatting the data as necessary for input into the library routines; (4) performing cluster analysis and constructing hierarchical cluster trees using three methods to define the proximity of clusters; (5) presenting the output results in different formats to facilitate the interpretation of the obtained cluster trees; (6) selecting groups of data points common for all three trees as stable clusters. We have also considered the chemistry of sulfur in inorganic compounds.

Fomenkova, M. N.↗
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 NTRS1999

Cometary Dust in the Debris Disks of HD 31648 and HD 163296: Two "Baby" (BETA) Pictoris Stars

The debris disks surrounding the pre-main-sequence stars HD 31648 and HD 163296 were observed spectroscopically between 3 and 14 microns. Both stars possess a silicate emission feature at 10 microns that resembles that of the star beta Pictoris and those observed in solar system comets. The structure of the band is consistent with a mixture of olivine and pyroxene material, plus an underlying continuum of unspecified origin. The similarity in both size and structure of the silicate band suggests that the material in these systems had a processing history similar to that in our own solar system prior to the time that the grains were incorporated into comets.

Sitko, Michael L.↗
NASA NTRS1999

Cometary Dust in the Debris of HD 31648 and HD163296: Two "Baby" Beta pictoris Stars

The debris disks surrounding the pre-main-sequence stars HD 31648 and HD 163296 were observed spectroscopically between 3 and 14 microns. Both stars possess a silicate emission feature at 10 Am that resembles that of the star P Pictoris and those observed in solar system comets. The structure of the band is consistent with a mixture of olivine and pyroxene material, plus an underlying continuum of unspecified origin. The similarity in both size and structure of the silicate band suggests that the material in these systems had a processing history similar to that in our own solar system prior to the time that the grains were incorporated into comets.

Sitko, Michael L.↗
NASA NTRS2005

Supernova olivine from cometary dust

An interplanetary dust particle contains a submicrometer crystalline silicate aggregate of probable supernova origin. The grain has a pronounced enrichment in 18O/16O (13 times the solar value) and depletions in 17O/16O (one-third solar) and 29Si/28Si (<0.8 times solar), indicative of formation from a type II supernova. The aggregate contains olivine (forsterite 83) grains <100 nanometers in size, with microstructures that are consistent with minimal thermal alteration. This unusually iron-rich olivine grain could have formed by equilibrium condensation from cooling supernova ejecta if several different nucleosynthetic zones mixed in the proper proportions. The supernova grain is also partially encased in nitrogen-15-rich organic matter that likely formed in a presolar cold molecular cloud.

Iron Compounds/analysis↗
NASA NTRS1995

Dynamics of cometary dust

This paper summarizes recent progress in our understanding of the morphological diversity of dust comets. This diversity is a product of dust emission from discrete active areas on the nucleus surface and provides information on the comet's rotation state and source function. Advances in computer simulations of dust coma morphology are described and the diagnostic properties of various dusty features are emphasized. Also addressed are some of the issues of dust tail morphology and particle fragmentation. Finally, lessons learnt from investigations of the dust population of comet Shoemaker-Levy 9 are discussed and implications for physical studies of the comet's collision with Jupiter are identified.

comets↗
NASA NTRS2007

Analysis of Cometary Dust Impact Residues in the Aluminum Foil Craters of Stardust

In January 2006, the sample return capsule from NASA s Stardust spacecraft successfully returned to Earth after its seven year mission to comet Wild-2. While the principal capture medium for comet dust was low-density graded silica aerogel, the 1100 series aluminum foil (approximately 100 m thick) which wrapped around the T6064 aluminum frame of the sample tray assembly (STA) contains micro-craters that constitute an additional repository for Wild-2 dust. Previous studies of similar craters on spacecraft surfaces, e.g. the Long Duration Exposure Facility (LDEF), have shown that impactor material can be preserved for elemental and mineralogical characterization, although the quantity of impact residue in Stardust craters far exceeds previous missions. The degree of shock-induced alteration experienced by the Wild-2 particles impacting on foil will generally be greater than for those captured in the low-density aerogel. However, even some of the residues found in LDEF craters showed not only survival of crystalline silicates but even their solar flare tracks, which are extremely fragile structures and anneal at around 600 C. Laboratory hypervelocity experiments, using analogues of Wild-2 particles accelerated into flight-grade foils under conditions close to those of the actual encounter, showed retention of abundant projectile residues at the Stardust encounter velocity of 6.1 km/s. During the preliminary examination (PE) of the returned foils, using optical and electron microscopy studies, a diverse range in size and morphologies of micro-craters was identified. In this abstract we consider the state of residue preservation in a diverse range of craters with respect to their elemental composition and inferred mineralogy of the original projectiles.

Graham, G. A.↗
NASA NTRS2007

Cometary Dust Characteristics: Comparison of Stardust Craters with Laboratory Impacts

Aluminium foils exposed to impact during the passage of the Stardust spacecraft through the coma of comet Wild 2 have preserved a record of a wide range of dust particle sizes. The encounter velocity and dust incidence direction are well constrained and can be simulated by laboratory shots. A crater size calibration programme based upon buckshot firings of tightly constrained sizes (monodispersive) of glass, polymer and metal beads has yielded a suite of scaling factors for interpretation of the original impacting grain dimensions. We have now extended our study to include recognition of particle density for better matching of crater to impactor diameter. A novel application of stereometric crater shape measurement, using paired scanning electron microscope (SEM) images has shown that impactors of differing density yield different crater depth/diameter ratios. Comparison of the three-dimensional gross morphology of our experimental craters with those from Stardust reveals that most of the larger Stardust impacts were produced by grains of low internal porosity.

Kearsley, A. T.↗
NASA NTRS2014

Shock Effects on Cometary-Dust Simulants

While comets are perhaps best known for their ability to put on spectacular celestial light shows, they are much more than that. Composed of an assortment of frozen gases mixed with a collection of dust and minerals, comets are considered to be very primitive bodies and, as such, they are thought to hold key information about the earliest chapters in the history of the solar system. (The dust and mineral grains are usually called the "refractory" component, indicating that they can survive much higher temperatures than the ices.) It has long been thought, and spacecraft photography has confirmed, that comets suffer the effects of impacts along with every other solar system body. Comets spend most of their lifetimes in the Kuiper Belt, a region of the solar system between 30 and 50 times the average distance of the Earth from the Sun, or the Oort Cloud, which extends to approximately 1 light year from the Sun. Those distances are so far from the Sun that water ice is the equivalent of rock, melting or vaporizing only through the action of strong, impact-generated shock waves.

Lederer, Susan M.↗
NASA NTRS1984

Interplanetary dust experiment (A0201)

The objective of this experiment is to study interplanetary dust, variously referred to as cosmic dust, cometary dust, zodiacial dust, or meteoric dust particles. Specific objectives are to obtain information regarding particle mass and velocity, and to undertake correlative analyses with other experiments, both on LDEF or near the time of the LDEF flight.

Singer, S. F.↗
NASA NTRS2007

Dust in Cometary Comae: Present Understanding of the Structure and Composition of Dust Particles

In situ probing of a very few cometary comae has shown that dust particles present a low albedo and a low density, and that they consist of both rocky material and refractory organics. Remote observations of solar light scattered by cometary dust provide information on the properties of dust particles in the coma of a larger set of comets. The observations of the linear polarization in the coma indicate that the dust particles are irregular, with a size greater (on the average) than about one micron. Besides, they suggest, through numerical and experimental simulations, that both compact grains and fluffy aggregates (with a power law of the size distribution in the -2.6 to -3 range), and both rather transparent silicates and absorbing organics are present in the coma. Recent analysis of the cometary dust samples collected by the Stardust mission provide a unique ground truth and confirm, for comet 81P/Wild 2, the results from remote sensing observations. Future space missions to comets should, in the next decade, lead to a more precise characterization of the structure and composition of cometary dust particles.

Levasseur-Regourd, A. C.↗
NASA NTRS1994

Carbonaceous Components in the Comet Halley Dust

Cometary grains containing large amounts of carbon and/or organic matter (CHON) were discovered by in situ measurements of comet Halley dust composition during VEGA and GIOTTO flyby missions. In this paper, we report the classification of these cometary, grains by means of cluster analysis, discuss the resulting compositional groups, and compare them with substances observed or hypothesized in meteorites, interplanetary dust particles, and the interstellar medium. Grains dominated by carbon and/or organic matter (CHON grains) represent approx. 22% of the total population of measured cometary dust particles. They, usually contain a minor abundance of rock-forming elements as well. Grains having organic material are relatively more abundant in the vicinity of the nucleus than in the outer regions of the coma, which suggests decomposition of the organics in the coma environment. The majority of comet Halley organic particles are multicomponent mixtures of carbon phases and organic compounds. Possibly, the cometary CHON grains may be related to kerogen material of an interstellar origin in carbonaceous meteorites. Pure carbon grains, hydrocarbons and polymers of cyanopolyynes, and multi-carbon monoxides are present in cometary dust as compositionally simple and distinctive components among a variety of others. There is no clear evidence of significant presence of pure formaldehyde or HCN polymers in Halley dust particles. The diversity of types of cometary organic compounds is consistent with the inter-stellar dust model of comets and probably reflects differences in composition of precursor dust. Preservation of this heterogeneity among submicron particles suggest the gentle formation of cometary, nucleus by aggregation of interstellar dust in the protosolar nebula without complete mixing or chemical homogenization at the submicron level.

Fomenkova, M. N.↗
NASA NTRS1997

STARDUST: Discovery's InterStellar Dust and Cometary Sample Return Mission

The STARDUST Discovery mission will collect samples of cometary and interstellar dust and return them to Earth. The Jet Propulsion Laboratory provides project management with Lockheed Martin Astronautics as the spacecraft industrial partner. STARDUST management is aggressively pursuing cost control through the use of Total Quality Management principles, specifically operating in a Project Engineering and Integration Team that

STARDUST↗
NASA NTRS1995

Chemical Evolution of Interstellar Dust into Planetary Materials

Comets are believed to retain some interstellar materials, stored in fairly pristine conditions since-their formation. The composition and properties of cometary dust grains should reflect those of grains in the outer part of the protosolar nebula which, at least in part, were inherited from the presolar molecular cloud. However, infrared emission features in comets differ from their interstellar counterparts. These differences imply processing of interstellar material on its way to incorporation in comets, but C and N appear to be retained. Overall dust evolution from the interstellar medium (ISM) to planetary materials is accompanied by an increase in proportion of complex organics and a decrease in pure carbon phases. The composition of cometary dust grains was measured in situ during fly-by missions to comet Halley in 1986. The mass spectra of about 5000 cometary dust grains with masses of 5 x 10(exp -17) - 5 x 10(exp -12) g provide data about the presence and relative abundances of the major elements H, C, N, O,Na, Mg, Al, Si, S, Cl, K, Ca, Ti, Cr, Fe, Ni. The bulk abundances of major rock-forming elements integrated over all spectra were found to be solar within a factor of 2, while the volatile elements H, C, N, O in dust are depleted in respect to their total cosmic abundances. The abundances of C and N in comet dust are much closer to interstellar than to meteoritic and are higher than those of dust in the diffuse ISM. In dense molecular clouds dust grains are covered by icy mantles, the average composition of which is estimated to be H:C:N:O = 96:14:1:34. Up to 40% of elemental C and O may be sequestered in mantles. If we use this upper limit to add H, C, N and O as icy mantle material to the abundances residing in dust in the diffuse ISM, then the resulting values for H. C, and N match cometary abundances. Thus, ice mantles undergoing chemical evolution on grains in the dense ISM appear to have been transformed into less volatile and more complex organic residues wherein the H, C and N are largely retained and ultimately accreted in cometary dust. The abundance of O is about the same for cometary dust, meteorites and interstellar dust. In all these samples, most of O in a solid phase is bonded to silicates. In dense molecular clouds, the abundance of O in dust+mantles is significantly higher then in cometary dust. This difference may reflect the greater lability of oxygenated species toward astrophysical processing. Laboratory studies show that O-bearing functional groups in organic compounds tend to be relatively easily removed by heating and/or UV and particle irradiation . In Halley's coma, O-containing organic grains, being unstable, were located closest to the nucleus. The decomposition of the organic grain component in the coma provided a significant extended source contribution to O-containing gaseous species such as CO and H2CO.

Fomenkova, M. N.↗
NASA NTRS1991

The electrodynamics of charged dust in the cometary environment

Dust in the plasma and radiative environment of a comet is necessarily electrically charged. This charging has both physical and dynamical effects on the dust, being particularly important on the smallest particles observed in the dust size spectrum. In this paper, these dynamical effects are reviewed and the pertinent observations are discussed.

Horanyi, M.↗
NASA NTRS1991

Dust-plasma interactions in the cometary environment

Cometary dust, by virtue of being immersed in a plasma and UV radiative environment are necessarily electrically charged. This charging can lead to both physical and dynamical effects on the dust. On the other hand, the dust could have certain effects on the plasma as well as on the interplanetary magnetic field. These processes are discussed and the observations, both remote and in situ, which pertain to them are critically reviewed.

Mendis, D. A.↗