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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.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Molecules and Dust in the Humunculus: Ejecta of Eta Carinae

In the 18401s, Eta Carinae ejected massive amounts of nitrogen-rich, carbon- and oxygen-poor material which we see as the hourglass-shaped Homunculus. With the Hubble Space Telescope Imaging Spectrograph, we detected multiple shells in line of sight, the most massive and intriguing being at -513 km/s. Numerous lines of Fe I, Fe II, Ni II, Cr II, Sc II, Sr II, Ti II, V II, etc are identified as well as nearly a thousand H2 lines. The metals have energy level populations consistent with 760K and excited by photons < 8.5eV. We have now identified CH, CH+, OH, and NH at the same velocity, but at 60K, suggesting stratification in the outer ejecta. Analysis of the interior, photoionized emission hourglass structure, known as the Little Homunculus, indicates He, N overabundances and C, 0 underabundances (approximately 1/80 solar). A skirt of neutral and partially ionized gas lies between the lobes of the hourglasses. A portion is seen as the Strontium Filament, a metal- ionized, neutral hydrogen structure. Relative abundances of TiNi are 1/80 solar, CrNi are 1/20 solar. This complex of ejecta appears to have been ejected by a massive star(s) at the end of the hydrogen-burning phase when convection led to overproduction of nitrogen at the expense of carbon and oxygen. Given the underabundances of carbon and oxygen, the chemistry of this system is quite different to the normal ISM, leading to a nitrogen- dominated chemistry. What little C and 0 that is formed is immediately taken up by SiO and Al0 molecules leading to a very different gas/dust ratio than the normal ISM. Dust in this ejecta is abundance, but known to be very grey in character. Observations with HST/STIS and VLT/UVES will be presented along with simple physical models and CLOUD modeling. Insight by the participants will be solicited.

Gull, T.↗
NASA NTRS2008

X-Ray Emitting Ejecta in Puppis A Observed with Suzaku

We report the detection and localization of X-ray emitting ejecta in the middle-aged Galactic supernova remnant Puppis A using five observations with the Suzaku X-ray Imaging Spectrometer to survey the eastern and middle portions of the remnant. A roughly 3' x 5', double-peaked region in the north center is found to be highly enriched in Si and other elements relative to the rest of the remnant. The X-ray fitted abundances are otherwise well below the solar values. While the ejecta-enhanced regions show some variation of relative element abundances, there is little evidence for a very strong enhancement of one element over the others in the imaged portion of the remnant, except possibly for a region of 0 and Ne enhancement in the remnant's south center. There is no spatial correlation between the compact [0 1111 emitting ejecta knots seen optically and the abundance enhancements seen in X-rays, although they are located in the same vicinity. The map of fitted column density shows strong variations across the remnant that echo earlier X-ray spectral hardness maps. The ionization age (as fitted for single temperature models) is sharply higher in a ridge behind the northeast-east boundary of the remnant, and is probably related to the strong molecular cloud interaction along that boundary. The temperature map, by comparison, shows relatively weak variations.

Hwang, U.↗
NASA NTRS2008

Magnetohydrodynamic Effects in Propagating Relativistic Ejecta: Reverse Shock and Magnetic Acceleration

We solve the Riemann problem for the deceleration of arbitrarily magnetized relativistic ejecta injected into a static unmagnetized medium. We find that for the same initial Lorentz factor, the reverse shock becomes progressively weaker with increasing magnetization s (the Poynting-to-kinetic energy flux ratio), and the shock becomes a rarefaction wave when s exceeds a critical value, sc, defined by the balance between the magnetic pressure in the ejecta and the thermal pressure in the forward shock. In the rarefaction wave regime, we find that the rarefied region is accelerated to a Lorentz factor that is significantly larger than the initial value. This acceleration mechanism is due to the strong magnetic pressure in the ejecta.

Mizuno, Y.↗
NASA NTRS2009

The Circumstellar Medium of Cassiopeia A Inferred from the Outer Ejecta Knot Properties

We investigate the effect of the circumstellar medium density profile on the X-ray emission from outer ejecta knots in the Cassiopeia A supernova remnant using the 1 Ms Chandra observation. The spectra of a number of radial series of ejecta knots at various positions around the remnant are analyzed using techniques similar to those devised in previous papers. We can obtain a reasonable match to our data for a circumstellar density profile proportional to r(sup -2) as would arise from the steady dense wind of a red supergiant, but the agreement is improved if we introduce a central cavity around the progenitor into our models. Such a profile might arise if the progenitor emitted a, fast tenuous stellar wind for a short period immediately prior to explosion. We review other lines of evidence supporting this conclusion. The spectra also indicate the widespread presence of Fe-enriched plasma that was presumably formed by complete Si burning during the explosion, possibly via alpha-rich freezeout. This component is typically associated with hotter and more highly ionized gas than the bulk of the O- and Si-rich ejecta.

Hwang, Una↗
NASA NTRS2011

X-Ray Illumination of the Ejecta of Supernova 1987A

When a massive star explodes as a supernova, substantial amounts of radioactive elements-primarily Ni-56, Ni-57 and Ti-44 are produced. After the initial from shock heating, the light emitted by the supernova is due to the decay of these elements. However, after decades, the energy powering a supernova remnant comes from the shock interaction between the ejecta and the surrounding medium. The transition to this phase has hitherto not been observed: supernovae occur too infrequently in the Milky Way to provide a young example, and extragalactic supernovae are generally too faint and too small. Here we report observations that show this transition in the supernova SN 1987A in the Large Magellan Cloud. From 1994 to 200l, the ejecta faded owing to radioactive decay of Ti-44 as predicted. Then the flux started to increase, more than doubling by the end of 2009. We show that this increase is the result of heat deposited by X-rays produced as the ejecta interacts with the surrounding material. In time, the X-rays will penetrate farther into the ejects, enabling us to analyse the structure and chemistry of the vanished star.

Larsson, J.↗
NASA NTRS2012

Craters Without Ejecta

A significant portion of the Solar System's population of minor bodies may be quite porous. A unique aspect of crater formation in porous bodies is that large craters may form without the ejecta deposits that are associated with craters on less porous bodies. In this paper. laboratory experiments and scaling theories are used to identify the conditions under which ejecta deposits are suppressed. The results are consistent with the interpretation that large craters on asteroid Mathilde (porosity approx. 50%) and Saturn's moon Hyperion (porosity >40%) apparently formed without producing Significant ejecta deposits. while smaller bodies do have notable regoliths.

Housen, Kevin R.↗
NASA NTRS2013

The Importance of Physical Models for Deriving Dust Masses and Grain Size Distributions in Supernova Ejecta. I. Radiatively Heated Dust in the Crab Nebula

Recent far-infrared (IR) observations of supernova remnants (SNRs) have revealed significantly large amounts of newly condensed dust in their ejecta, comparable to the total mass of available refractory elements. The dust masses derived from these observations assume that all the grains of a given species radiate at the same temperature, regardless of the dust heating mechanism or grain radius. In this paper, we derive the dust mass in the ejecta of the Crab Nebula, using a physical model for the heating and radiation from the dust. We adopt a power-law distribution of grain sizes and two different dust compositions (silicates and amorphous carbon), and calculate the heating rate of each dust grain by the radiation from the pulsar wind nebula. We find that the grains attain a continuous range of temperatures, depending on their size and composition. The total mass derived from the best-fit models to the observed IR spectrum is 0.019-0.13 Solar Mass, depending on the assumed grain composition. We find that the power-law size distribution of dust grains is characterized by a power-law index of 3.5-4.0 and a maximum grain size larger than 0.1 micron. The grain sizes and composition are consistent with what is expected for dust grains formed in a Type IIP supernova (SN). Our derived dust mass is at least a factor of two less than the mass reported in previous studies of the Crab Nebula that assumed more simplified two-temperature models. These models also require a larger mass of refractory elements to be locked up in dust than was likely available in the ejecta. The results of this study show that a physical model resulting in a realistic distribution of dust temperatures can constrain the dust properties and affect the derived dust masses. Our study may also have important implications for deriving grain properties and mass estimates in other SNRs and for the ultimate question of whether SNe are major sources of dust in the Galactic interstellar medium and in external galaxies.

Importance↗
NASA NTRS2014

Geologic Mapping of Ejecta Deposits in Oppia Quadrangle, Asteroid (4) Vesta

Oppia Quadrangle Av-10 (288-360 deg E, +/- 22 deg) is a junction of key geologic features that preserve a rough history of Asteroid (4) Vesta and serves as a case study of using geologic mapping to define a relative geologic timescale. Clear filter images, stereo-derived topography, slope maps, and multispectral color-ratio images from the Framing Camera on NASA's Dawn spacecraft served as basemaps to create a geologic map and investigate the spatial and temporal relationships of the local stratigraphy. Geologic mapping reveals the oldest map unit within Av-10 is the cratered highlands terrain which possibly represents original crustal material on Vesta that was then excavated by one or more impacts to form the basin Feralia Planitia. Saturnalia Fossae and Divalia Fossae ridge and trough terrains intersect the wall of Feralia Planitia indicating that this impact basin is older than both the Veneneia and Rheasilvia impact structures, representing Pre-Veneneian crustal material. Two of the youngest geologic features in Av-10 are Lepida (approximately 45 km diameter) and Oppia (approximately 40 km diameter) impact craters that formed on the northern and southern wall of Feralia Planitia and each cross-cuts a trough terrain. The ejecta blanket of Oppia is mapped as 'dark mantle' material because it appears dark orange in the Framing Camera 'Clementine-type' colorratio image and has a diffuse, gradational contact distributed to the south across the rim of Rheasilvia. Mapping of surface material that appears light orange in color in the Framing Camera 'Clementine-type' color-ratio image as 'light mantle material' supports previous interpretations of an impact ejecta origin. Some light mantle deposits are easily traced to nearby source craters, but other deposits may represent distal ejecta deposits (emplaced greater than 5 crater radii away) in a microgravity environment.

Asteroids↗
NASA NTRS2020

Spatial Variation in Erosion Rates in Mars Equatorial Regions Inferred from Ejecta Retention of 1-3 Km Diameter Craters

The modification of impact craters has long been used to infer the geomorphic forcing on Mars [1], as well as estimate the spatial and temporal variability of this erosion and gradation [e.g., 2]. Here, we studied the population of small primary craters (1-3 km) to understand differences in ejecta retention across equatorial Mars. Specifically, we evaluated whether craters in our study population had observable ejecta deposits (defined on the basis of distinct tone or texture with respect to their surroundings).This is a proxy for the resurfacing rate because only relatively fresh craters retain their ejecta deposits. More broadly, this is part of a larger project we are undertaking [3] to examine crater morphometry and other characteristics from CTX-derived digital terrain models (DTMs), augmented by qualitative observations.

Fassett, C. I.↗
NASA NTRSDate not supplied

Experimental Impacts into Strength-Layered Targets: Ejecta Kinematics and Crater Morphometry

Impact craters can serve as probes of the subsurface structure of a planetary body and provide hints about a target's properties. Crater morphology, for example, can be used to estimate the thickness of a regolith layer above a more competent unit. Small lunar craters in the maria show a morphological progression from a simple bowl shape to flat-floored and concentric as crater diameter increases for a given regolith thickness. The final shape is a result of the subsurface flow-field initiated as the projectile transfers its energy and momentum to the target surface. In strength-layered targets, such as the lunar maria, the substrate modifies the flow field and thereby the excavation of the crater. Here we report on a series of experimental impacts into targets composed of a layer of loose sand above a stronger substrate. As we varied the sand's thickness, we imaged individual ejecta trajectories as the craters grew, from which we derived ejection-speed scaling relationships. In addition, we used a 3D scanner to construct topographic maps of the substrate, pre-impact target, and post-impact surface. This permitted us to examine the final craters' morphologies and morphometries with respect to the original stratigraphy of the target. As expected, craters became shallower and smaller as the sand's thickness decreased, transitioning from bowl-shaped to concentric as observed on the Moon. Subtle and important details show that the stronger substrate affected the subsurface flow-field by redirecting material upward and outward even when the interface was still well below the final crater's floor. Compared to the control target (loose sand only), the stronger substrate below the sand layer resulted in a much more complex pattern of ejecta. While most of the ejected material was still contained within a typical outward-moving curtain, a number of ejected particles moved along low-speed, high-angle (near 90°) trajectories. The number of these high-angle trajectories increased as the sand layer thinned, perhaps implying that self-secondary cratering would require the presence of a strong subsurface layer below the impact site. Such results refine our understanding of crater excavation in layered targets with implications for ejecta deposits and final crater shapes observed on the Moon.

Jennifer L B Anderson↗
NASA NTRSDate not supplied

Scaling Laws of Ejecta Streaks in Lunar Landings

From the crewed Apollo missions of the 1960s to the recent Chang’e uncrewed lunar missions, the interaction between the supersonic exhaust and the lunar surface generates a striking ray system of ejecta particles that travel radially outward at high speeds. While this intriguing pattern has been observed in experiments and simulations, the underlying mechanism remains unclear. These radial ejecta streaks were also observed during an experimental campaign using a Mach 5.3 jet impinging on a granular bed within a large-scale vacuum chamber. Our findings reveal that the radial ejecta streaks are caused by the Gortler instability, which, due to the curvature of the extremely underexpanded jet, induces counter-rotating streamwise vortices within the jet shear layer. These vortices impact the ground and entrain particles in their upwash regions. Experimental measurements from both ground tests and the literature show that the number of streaks strongly depends on the jet diameter at impact and the shear layer thickness, further revealing a power-law scaling with the jet pressure ratio. These insights highlight the pivotal role of fluid dynamics in extraterrestrial landings and provide a foundation for mitigating risks in future planetary missions.

Lunar Landing↗
NASA NTRS2020

Exploratory Experiments to Probe the Effect of Bulk Density and Porosity on The Morphology and Ejecta Kinematics of Impact Craters

The morphometry of relatively small impact craters are influenced by the physical properties of the target. To investigate the control of bulk density and porosity on the crater-formation processing the gravity regime, we conducted a series of impact experiments, varying each these target parameters while holding the other constant. Three different sands were used to construct cohesionless targets: quartz (0.4-0.8 mm), garnet (0.425-1.0 mm), and alumina (0.297-0.71mm), representing a range of intrinsic grain densities from 2.65 to 4.02 g cm-3. High-porosity targets were constructed by carefully pouring the sand into the center of a cylindrical PVC target bucket (inner diameter 26.2 cm, height 12 cm) and allowing it to fill the bucket at the angle of repose before being leveled flat at the top of the bucket. Low-porosity targets were obtained by pluviation of the granular material through a 1 mm sieve that was set directly above the target bucket. With the disparate intrinsic densities of the sand in combination with the variations of the packing technique, we attained differences in the bulk-target density of up to 32%while keeping porosity constant. The impact experiments were conducted with the vertical gun in the Experimental Impact Laboratory at NASA Johnson Space Center; using 3/16” (4.76 mm) diameter aluminum projectiles launched at1.55 ± 0.03 km s-1. The ejecta were observed using the laser-based Ejection Velocity Measurement System, providing data on launch positions and velocities of ejected particles. Submillimeter topographic data of the resulting craters were collected after each experiment with a NextEngine 3D scanner. Regardless of target material or density, all craters exhibited a simple bowl shape, but a trend of increasing depth-diameter ratio with increasing target porosity is observed across the entire experimental suite. Despite these morphometric differences, ejecta launch angles and speeds remain remarkably similar amongst all of the target configurations.

impact cratering↗
NASA NTRS1973

Lunar ejecta and meteorites experiment

The test equipment installed during the Apollo 17 flight to conduct the lunar ejecta and meteorites (LEAM) investigation is described. The LEAM experiment intercepts ejecta particles created by meteoroid impact on the lunar surface and records information useful in establishing the history of the moon. The deployment of the system in the Taurus-Littrow area and the method for controlling the equipment are explained. The effects of lunar surface temperatures on the operation of the sensors are reported.

Berg, O. E.↗
NASA NTRS1973

Radial thickness variation in impact crater ejecta - Implications for lunar basin deposits

An expression is proposed for radial thickness variations in lunar impact crater ejecta. The expression was inferred from available cratering data and semi-empirical calculations for approximate modeling of variations in ejecta thickness with the increasing range of lunar craters. A table of predicted stratigraphic sections for the Apollo Landing sites is included. The predictions were made by using this expression. The results suggest that the pre-Nubium crustal material at upland Apollo sites lies at depths of above 280 up to 1940 m.

Mcgetchin, T. R.↗
NASA NTRS1976

Impact ejecta on the moon

The response of a lunar-sized object to the impact of meteoroids no more than about 100 km in radius is studied by means of a numerical model. The partitioning of impact energy into the kinetic and internal energy of the ejecta is obtained by using the conservation of mass, momentum, and energy conservation equations in finite-difference form within an Eulerian framework with approximate equations of state. The calculations are performed for a 15 km/sec impact of an iron object 5 cm in radius on a gabbroic anorthosite surface. Ejecta ballistic analysis is then performed. Most of the material lost escaping the moon is lunar crust material. Only 0.2% of the meteoroid escapes, all in the vapor phase.

Okeefe, J. D.↗
NASA NTRS1978

An analytic study of impact ejecta trajectories in the atmospheres of Venus, Mars, and earth

Calculations have been made to determine the effects of atmospheric drag and gravity on impact ejecta trajectories on Venus, Mars, and earth. The equations of motion were numerically integrated for a broad range of body sizes, initial velocities, and initial elevation angles. A dimensionless parameter was found from approximate analytic solutions which correlated the ejecta range, final impact angle, and final impact velocity for all three planets.

Tauber, M. E.↗
NASA NTRS1977

Energies of formation for ejecta blankets of giant impacts

Ejection energy-diameter scaling relations for impact craters are studied by assuming the energy is equal to a constant times the diameter raised to a (different) constant power. These scaling relations are derived from least-squares fits to calculated ejection energies over a range of crater diameters and vary according to ejection angle, ejecta blanket distribution, planetary radius, and the depth-diameter ratio. Extremely broad changes in ejection angle and ejecta blanket distribution result in relatively small changes in the total energy. The way in which the exponent in the scaling relation is dependent on the planetary radius of curvature as well as on the exponent of the power-law depth-diameter scaling relation is described. Two ejection energy-diameter scaling relations, one for simple craters with depth-diameter ratios of approximately 0.2 and the other for large complex craters, are presented. The scaling relations explicitly include target density, surface gravity, and planetary radius.

Croft, S. K.↗
NASA NTRS1978

Orbital infrared observations of lunar craters and possible implications for impact ejecta emplacement

The Apollo 17 Scanning Infrared Radiometer experiment showed that the ejecta deposits of large lunar craters (D greater than 3 km) typically exhibit uniform nighttime temperatures comparable to or less than those of the surrounding mare plains. This thermal signature implies that the surface of ejecta deposits displays block sizes typically smaller than 30 cm and that the nonblocky surface extends out to three crater radii from the crater rim. Four mechanisms are proposed to account for the observed thermal signatures.

Schultz, P. H.↗