SEARCH · Engineering Papers

Results for “Ejecta”

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.

SourceResearch connectionFrom yearThrough year

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

At least 1,333 records · Page 74

All sources NASA NTRS DOE OSTI

NASA NTRS1988

Bilateral symmetry elements of the Zhamanshin impact crater

The internal structure of the Zhamanshin impact structure and the nature of rocks developed within it are studied to establish the impact structure parameters. It is found that the diameter of the visible crater is about 13 km. The small annular structures observed are found to not be secondary craters, and no correlation is found between the asymmetrical distribution of ejecta material and the arrangement of these annular forms.

Masaytis, V. L.↗

NASA NTRS1987

Sub-kilometer rampart craters in the equatorial region of Mars: Possible implications for the state and distribution of regolith H2O

It was long suspected that Martian rampart crater ejecta morphology originates from an impact into a water or ice-rich crust. If the water-impact hypothesis is correct, then the occurrence of rampart craters at all latitudes, elevations, and in all types of terrain, implies that the distribution of regolith H2O on Mars is global. To test this hypothesis, the occurrence of rampart craters was examined at three locations within the latitude band of + or - 30 degrees (specifically, within the ridged plains unit covered by MC-18). The analysis indicates that while few in number, rampart craters with diameters smaller than 3 km are indeed present at several locations withing the equatorial region of Mars. This finding appears to have significant implications for the inferred state and distribution of subsurface H2O. A more comprehensive analysis of the occurrence of sub-kilometer rampart craters is currently underway.

Clifford, Stephen M.↗

NASA NTRS1987

Evolutionary helium and CNO anomalies in the atmospheres and winds of massive hot stars

The ubiquitous evidence for processed materials in the atmospheres, winds, and circumstellar ejecta of massive stars is reviewed. A broad array of normal and peculiar evolutionary stages is considered, up to and including Type II supernova progenitors. The quantitative analysis of these spectra is difficult, and until recently for the most part only qualitative or approximate results have been available. However, several important current programs promise reliable abundance calculations. A significant emerging result is that the morphologically normal majority of both hot and cold supergiants may already display an admixture of CNO-cycle products in their atmospheres. It may become possible in this way to identify blue supergiants returning from the red supergiant region, as appears to have been the case for the SN 1987A progenitor.

Walborn, Nolan R.↗

NASA NTRS1987

Mercurian crater-filling classes constrain the emplacement process of the intercrater plains material

The multivariate method for statistical analysis of crater-filling classes, as presently applied to craters of more than 10-km diameter on Mercury, is noted to be superior to current techniques due to the obviation of any amalgamation of data from regions with different histories in order to arrive at the pertinent counting statistics. In this application to the Mercury intercrater plains, the process responsible for emplacement is constrained to be one that leaves the crater class distribution unaltered from that observed on the densely cratered terrain. The analysis explicitly eliminates the viability of the pulse emplacement of volcanics or basin ejecta.

Woronow, Alex↗

NASA NTRS1987

An analysis of the Mariner 10 color ratio map of Mercury

Errors that emerged in the Hapke et al. (1980) geological analysis reproduction of the Mariner 10 orange/UV color ratio map of Mercury are presently noted, and it is judged that the relationships that emerge between the color and the terrain are nonlunar in that they lack Mercurian analogs of high Fe-Ti lunar maria basalts. The crust is found to be low in Fe(2+) and Ti(4+) in view of three major considerations: (1) rays and ejecta blankets are exceptionally blue; (2) the Fe(2+) band of the reflectance spectrum of Mercury is weak; and (3) Mercury albedo contrasts are less pronounced than the lunar ones. The extrusive origin of the smooth plains is supported by these observations.

Rava, Barry↗

NASA NTRS1984

Glasses formed by hypervelocity impact

This paper presents description, classification, and geological setting of impact glasses, which are formed as a result of meteorite impacts with the planetary surface, and discusses the impact-glass formation process in the context of cratering mechanics. Impact glasses can be classified as belonging to two major groups: (1) mineral glasses, which are identical in composition to a mineral, and (2) rock glasses, which have the composition of a rock or a mixture of various rocks. Rock glasses may be (1) melt ejecta, (2) parts of a coherent melt layer inside the crater cavity, or (3) dikes or veins. The composition of rock glasses at a particular crater can be matched by that of the target. In nonporous rocks, the formation of rock glasses requires peak pressures in excess of 60-80 GPa, while mineral glasses are formed in the pressure range of about 25 to 55 GPa; in porous rocks, interstitial glass forms at pressures as low as 5 GPa.

Stoeffler, D.↗

NASA NTRS1987

Late emission from SN 1987A

Multiwavelength observations of SN 1987A are examined, and the late emission from the mantle gas is modeled under the assumption of energy input by gamma rays from Co-56 decay. An emission line spectrum of low-ionization species has been produced at optical through IR wavelengths. At an age of about 700 days, an IR catastrophe occurs, and most of the radiation is then emitted in IR fine-structure lines. The gamma-ray intensity is found to peak in the 15-solar-mass model at an age of 270 days. Very little production of X-rays below 50 keV is expected if the photon interaction with the hydrogen envelope can be neglected. It is suggested that the radio emission from the pulsar may be absorbed by the ejecta for several years.

Fransson, C.↗

NASA NTRS1987

Talemzane - Algerian impact crater detected on SIR-A orbital imaging radar

In November, 1981, NASA's first Shuttle Imaging Radar mission (SIR-A) began producing maplike photographic strips of Earth scenes from orbital altitude. A Saharan radar image acquired over Algeria clearly delineates two sedimentary basins, Erg Occidental and Erg Oriental, separated by an elongated zone of exposed bedrock, the M'Zab Chebka. At the NE margin of the Chebka, rimrocks, slopes, and ejecta deposits of Talemzane meteorite impact crater appear as a distinct two km wide radar-bright ring. This unique circle of strong radar backscatter distinguishes the solitary impact structure from numerous dayas (similarly appearing karstic depressions) which characterize the region. The crater is prominent on radar, but is obscure on optically obtained satellite and aircraft images, as are partly buried fluvial drainage systems and fault-block traces developed in bedrocks of the Chebka. Radar detection of an annular drainage system indicates possible presence of a ring graben at the crater. Brightest radar signals on the image are cultural features at recently developed gas fields near Hassi er R'Mel.

Mchone, John F.↗

NASA NTRS1988

Outgassing asymmetry of periodic comet Encke. I - Apparitions 1924-1984

A concept of a collimated flow of ejecta from a discrete source (vent) on the surface of a rotating cometary nucleus is applied to P/Encke, based on positional observations of its sunward fanlike coma at 13 apparitions between 1924 and 1984. The major results include a finding that the observations are consistent with an invariable position of the rotation pole during the 60 yr (yielding an obliquity of 70 deg), although this is not to be interpreted as an indication that the nucleus is not precessing. Two vents are identified on the nucleus surface: one on the northern hemisphere at a latitude of +55 deg, of an estimated sublimitation area of 0.4 sq km, which is active along the inbound leg of the comet's orbit until a few days preperihelion and again beginning several weeks postperihelion; the other on the southern hemisphere at -75 deg, of an estimated area of 0.6 sq km, whose activity prevails in the intervening time. There appears to be a significant difference between the two regions in terms of dust content in their emissions.

Sekanina, Z.↗

NASA NTRS1988

X-ray and gamma-ray emissions expected from supernova 1987A

The X-ray and gamma-ray spectra expected from SN 1987A have been calculated. Results for the TWOBF7 model are inconsistent with Ginga observation, but the X-ray flux and its spectral shape strongly depend on the chemical composition and expansion velocity of the ejecta. The distributions of density and chemical compositions for SN 1987A are described. For the TWOBF7 model, the X-ray flux between 10 and 20 keV reaches a peak of 6.7 photons/s/sq m about 1 yr after the explosion. For the 15B5 model, the peak flux is larger by a factor of five. The implications of the Ginga satellite's detection of an excess X-ray flux from the direction of the supernova for the models of SN 1987A are considered. How observations of gamma-ray lines can determine the optical thickness of the expanding shell is discussed.

Ebisuzaki, Toshikazu↗

NASA NTRS1988

Gamma-ray limits on Na-22 production in novae

Data accumulated from 1980 to 1987 by the gamma-ray spectrometer aboard the SMM are analyzed to search for annual increases at 1.275 MeV as evidence of Na-22 decay in the Galactic center region and in the ejecta of recent individual novae. No evidence of any 1.275 MeV emission of celestial origin is found. A limit of 3 x 10 to the -6th solar mass is placed on the accumulated Na-22 from many novae occurring near the Galactic center, and a limit of 7 x 10 to the -7th solar mass is placed on the mass of Na-22 ejected by the closest of the recent neon-rich novae.

Leising, Mark D.↗

NASA NTRS1988

Charged particle depletion surrounding Saturn's F ring - Evidence for a moonlet belt?

An improved model of the Saturn magnetosphere and of the locations of known moons and rings is invoked in the present reconsideration of Pioneer 11 observations of five abrupt depletions in the flux of trapped magnetospheric electrons within a 2000-km-wide band around the F ring. It is inferred that the observed depletions of charged particles are caused by clumps of material with low optical depth; it is further hypothesized that these clumps are composed of regolith ejecta, are generated by collisions occurring within a belt of unseen, moonlet-scale (or smaller) objects occupying the entire radial region between Pandora and Prometheus. Attention is given to a self-consistent scenario in which these debris clouds are created, longitudinally spread, swept up onto belt object surfaces, and then thrown off by a subsequent collision.

Cuzzi, Jeffrey N.↗

NASA NTRS1988

Gamma-ray line emission from SN1987A

The inferred average line flux at about 847 keV in the background-subtracted spectrum of SN1987A from August 1 to October 31, 1987 is about (1.0 + or - 0.25) x 10 to the -3rd photons/sq cm/s at an energy of 843 + or - 5 keV. This feature cannot be explained by any statistical or systematic fluctuations observed in the seven previous years of gamma-ray spectrometer data. There is also evidence for the 1238-keV line from Co-56 decay, with an average flux of about (6 + or - 2) x 10 to the -4th photons/sq cm/s. This observation confirms that Co-56 is present in the supernova ejecta and that nucleosynthesis occurred during the explosion.

Matz, S. M.↗

NASA NTRS1988

The abundances of carbon and nitrogen in I Zw 18

The first measurements of the semiforbidden C III 1909 A and forbidden N II 6583 A emission lines in I Zw 18 are reported. These data are combined with previously published spectrophotometry in order to derive the carbon and nitrogen abundances in I Zw 18 with the aid of a nebular model. The CNO abundances in I Zw 18 are found to exceed those found in the Magellanic Clouds and other well-observed oxygen-poor irregular galaxies and are more similar to those in the sun and nearby Galactic H II regions. It is argued that I Zw 18 may be older and more chemically evolved than previously believed, and that its extremely low O/H results from escape of O-rich supernova ejecta from the Galaxy or from dilution by accretion of primordial gas. Alternatively, I Zw 18 may have formed from a preenriched intergalactic medium. Spectroscopic diagnostics for composite photoionization models to fit the spectrum of I Zw 18 are discussed.

Dufour, Reginald J.↗

NASA NTRS1988

The Progenitor of SN 1987A

Spatially resolved IUE spectra (1150 to 2000 A) taken at the position of SN 1987A in March 1987 show that the 12th mag B3 I star Sk -69 deg 202 disappeared. Only the fainter companion stars (Star 2 and Star 3) are present near the site of the supernova. It is concluded that Sk -69 deg 202 exploded to produce SN 1987A. The known characteristics of Sk -69 deg 202 are consistent with the interpretation that the progenitor was a relatively compact star, having a high-velocity low-density stellar wind prior to the outburst. Recent IUE spectra of SN 1987A (May 1988) show no evidence that Sk -69 deg 202 still exists inside the expanding ejecta.

Sonneborn, G.↗

NASA NTRS1987

Debris-cloud collisions: Accretion studies in the Space Station

The growth of planetesimals in the Solar System reflects the success of collisional aggregation over disruption. It is widely assumed that aggregation must represent relatively low encounter velocities between two particles in order to avoid both disruption and high-ejecta velocities. Such an assumption is supported by impact experiments and theory. Experiments involving particle-particle impacts, however, may be pertinent to only one type of collisional process in the early Solar System. Most models envision a complex protoplanetary nebular setting involving gas and dust. Consequently, collisions between clouds of dust or solids and dust may be a more relistic picture of protoplanetary accretion. Recent experiments performed at the NASA-Ames Vertical Gun Range have produced debris clouds impacting particulate targets with velocities ranging from 100 m/s to 6 km/s. The experiments produced several intriguing results that not only warrant further study but also may encourage experiments with the impact conditions permitted in a microgravity environment. Possible Space Station experiments are briefly discussed.

Schultz, Peter H.↗

NASA NTRS1988

Sampling the ancient volatile-rich areas of Mars

Viking images clearly show areas with a high density of fluidized craters that also display a significant number of wrinkle ridges. Fluidized crater ejecta morphology may indicate that the target material was rich in volatiles at the time of the impact. Therefore, these areas are of the utmost importance in deciphering both the Martian tectonic evolution and the amount of subsurface water, at times when more favorable conditions for life to evolve did exist on Mars. Although a large number of extensional features are associated with Tharsis and Elysium geologic activity, the planet-wide distribution of ridges suggests that Mars' tectonic history is far more complex than the Tharsis-dominated scenario indicates. Like on the Moon and Mercury, ridges on Mars were formed under compressive stresses, probably as a result of thrust-fault mechanism, although surface expressions and direct causes vary. Martian ridges are most easily seen on smooth plains of volcanic origin, but the majority of the 16,000 mapped and classified compressive features are located in the old terrains, far beyond Tharsis influence.

Chicarro, A. F.↗

NASA NTRS1988

Meteorites on Mars

Four types of meteoritic material should be found on Mars: (1) micrometeorites, many of which will survive atmospheric entry unmelted, which should fall relatively uniformly over the planet's surface, (2) ablation products from larger meteorites which ablate, break up and burn up in the Mars atmosphere, (3) debris from large, crater forming objects, which, by analogy to terrestrial and lunar impact events, will be concentrated in the crater ejecta blankets (except for rare, large events, such as the proposed C-T event on earth, which can distribute debris on a planetary scale), and (4) debris from the early, intense bombardment, which, in many areas of the planet, may now be incorporated into rocks by geologic processes subsequent to the intense bombardment era. To estimate the extent of meteoritic addition to indigenous Martian material, the meteoritic flux on Mars must be known. It is estimated that the overall flux is twice that for the Moon and 1.33 that for Earth. For small particles, whose orbital evolution is dominated by Poynting Robertson drag, the flux at Mars can be estimated from the Earth flux. The smaller Martian gravitational enhancement as well as the decrease in the spatial density of interplanetary dust with increasing heliocentric distance should reduce the flux of small particles at Mars to about 0.33 times the flux at Earth. Because of the smaller planetary cross-section the total infalling mass at Mars is then estimated to be 0.09 time the infalling mass in the micrometeorite size range at Earth.

Flynn, G. J.↗