Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Impact cratering”

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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Origin of bright ring-shaped craters in radar images of Venus

Radar images of the Venusian surface taken at the Arecibo Observatory are examined in the context of recent study of the radar appearance of lunar craters to provide insight into the formation and evolution of Venusian features and to propose the thesis that bright ring-shaped features contain information about the rate at which Venus is being modified by depositional or erosional processes. Radar crater signatures are analyzed by crater floor and interior properties and by properties of ejecta deposits. Morphological comparisons with radar images of lunar craters are made, as well as morphometric comparisons with lunar radar crater haloes. The populations of radar bright craters on the moon and Venus is analyzed using a Monte Carlo simulation. It is concluded that the bright ring crater population does not resemble an impact crater production population.

Cutts, J. A.↗
NASA NTRS1992

Asteroid collisional evolution - An integrated model for the evolution of asteroid rotation rates

A comprehensive model for the changes in asteroid spin rates due to large collisions was developed by combining the theoretical results of Cellino et al. (1990) with previously published work on spin rate changes for cratering impacts (Harris, 1979; Dobrovolskis and Burns, 1984). The spin change algorithm, when incorporated into an existing simulation of collisional effects on asteroid sizes, produced an integrated model for studying the simultaneous evolution of asteroid sizes and spin rates over the solar system history. As a result of an analysis of 32 collisional scenarios with regard to the change in the spin rate as a function of asteroid size, it is concluded that the spin rates of all asteroids, except possibly the largest ones, have been significantly altered by collisions over the solar system history and that, in general, shattering impacts are much more important than cratering events in changing the spin of asteroids.

Farinella, P.↗
NASA NTRS1993

Resolving topographic detail on Venus by modeling complex Magellan altimetry echoes

Magellan's altimeter is providing some of the finest resolution topography of Venus achieved to date. Nevertheless, efforts continue to improve the topographic resolution whenever possible. One effort to this end is stereoscopic imaging, which provides topography at scales similar to that of the synthetic aperture radar (SAR). However, this technique requires two SAR images of the same site to be obtained and limits the utility of this method. In this paper, we present another method to resolve topographic features at scales smaller than that of an altimeter footprint, which is more globally applicable than the stereoscopic approach. Each pulse which is transmitted by Magellan's altimeter scatters from the planet and echoes to the receiver, delayed based on the distance between the spacecraft and each surface element. As resolved in time, each element of an altimetry echo represents the sum of all points on the surface which are equidistant from the spacecraft. Thus, individual returns, as a function of time, create an echo profile which may be used to derive properties of the surface, such as the scattering law or, in this case, the topography within the footprint. The Magellan project has derived some of this information by fitting model templates to radar echo profiles. The templates are calculated based on Hagfor's Law, which assumes a smooth, gently undulating surface. In most regions these templates provide a reasonable fit to the observed echo profile; however, in some cases the surface departs from these simple assumptions and more complex profiles are observed. Specifically, we note that sub-footprint topographic relief apparently has a strong effect on the shape of the echo profile. To demonstrate the effects of sub-resolution relief on echo profiles, we have calculated the echo shapes from a wide range of simple topographic models. At this point, our topographic models have emphasized surfaces where only two dominant elevations are contained within a footprint, such as graben, ridges, crater rims, and central features in impact craters.

Lovell, Amy J.↗
NASA NTRS2005

Age of Lunar Meteorite LAP02205 and Implications for Impact-Sampling of Planetary Surfaces

We have measured the age of lunar meteorite LAP02205 by the Rb-Sr and Ar-Ar methods. Sm-Nd analyses are in progress. The Rb-Sr and Ar-Ar ages indicate a crystallization age of approx. 3 Ga. Comparing the ages of LAP02205 and other lunar mare basaltic meteorites to mare surface ages based on the density of impact craters shows no significant bias in impact- sampling of lunar mare surfaces. Comparing the isotopic and geochemical data for LAP02205 to those for other lunar mare basalts suggests that it is a younger variant of the type of volcanism that produced the Apollo 12 basalts. Representative impact-sampling of the lunar surface

Nyquist, L. E.↗
NASA NTRS2005

A Novel Porosity Model for Use in Hydrocode Simulations

Introduction: Numerical modeling of impact cratering has reached a high degree of sophistication; however, the treatment of porous materials still poses a large problem in hydrocode calculations. Porosity plays only a minor role in the formation of large craters on most planetary objects, but impacts on comets are believed to be highly affected by the presence of porosity, which may be as much as 80%. The upcoming Deep Impact Mission (launched January 2005) will provide more detailed data about the composition of a comet (Tempel 1) by shooting a approx.370 kg projectile onto the surface of its nucleus. The numerical simulations of such impact events requires an appropriate model for how pore space in the comet is crushed out during the violent initial stage of the impact event. Most hydro-codes compute the pressure explicitly using an "equation of state" (EOS) for each material, which relates changes in density and internal energy to changes in pressure. The added complication introduced by porosity is that changes in a material s density are due to both the closing of pore space (compaction) and compression of the matrix. The amount of resistance to volume change and the amount of irreversible work done during these two processes is very different; it is far easier to compact a porous material sample than to compress a non-porous sample of the same material. As an alternative to existing porosity models, like the Pdot(alpha) model [1], we present a novel approach for dealing with the compaction of porosity in hydrocode calculations.

Wuennemann, K.↗
NASA NTRS2015

McLaughlin Crater as a Candidate Landing Site for Humans on Mars

McLaughlin Crater is an ancient (Noachian) Martian impact crater located at 337.6 East, 21.9 North, just south of the dichotomy boundary. This site should be considered for future landed exploration because: a) it is located at the boundary of three types of scientifically important terrain that will yield key results about the geological evolution and habitability of Mars; b) it contains surfaces where radiometric dating can be related to age dates estimated from crater counting, c) it contains volatile-rich rocks that will not only yield interesting results regarding ancient atmospheric chemistry, but will also be high quality, accessible targets for in-situ resource utilization (ISRU), and d) the site within the crater provides a flat, low-risk and low-elevation landing zone, which will facilitate landing large payloads on Mars.

Michalski, J. R.↗
NASA NTRS2016

Geology of McLaughlin Crater, Mars: A Unique Lacustrine Setting with Implications for Astrobiology

McLaughlin crater is a 92-kmdiameter Martian impact crater that contained an ancient carbonate- and clay mineral-bearing lake in the Late Noachian. Detailed analysis of the geology within this crater reveals a complex history with important implications for astrobiology [1]. The basin contains evidence for, among other deposits, hydrothermally altered rocks, delta deposits, deep water (>400 m) sediments, and potentially turbidites. The geology of this basin stands in stark contrast to that of some ancient basins that contain evidence for transient aqueous processes and airfall sediments (e.g. Gale Crater [2-3]).

Michalski, J. R.↗
NASA NTRS2023

New Insights Into Aristarchus Crater With LRO LAMP Far-Ultraviolet Observations

Aristarchus crater is a Copernican-age impact crater well known for its high-albedo ejecta blanket and nearby flow features rich in pyroclastic materials. The Lyman Alpha Mapping Project (LAMP) is a far-ultraviolet (FUV) spectrograph (57–197 nm) on board the Lunar Reconnaissance Orbiter (LRO). LAMP data identified Aristarchus crater as having a high Off-band (155–184 nm) to On-band (130–155 nm) albedo (Off/On) ratio, providing new insight into the mineral composition of the area. Previous LAMP observations of bright crater rays and lunar swirls show that regions of high Off/On-band ratios may indicate highly feldspathic compositions. In this study we use LAMP data to understand FUV compositional signatures at Aristarchus. We investigate four well-characterized regions of interest around Aristarchus crater, and we compare Off/On-band ratios at Aristarchus crater to laboratory-derived ratios of several endmembers such as anorthite and olivine. We further analyze LAMP FUV spectra alongside near-infrared spectra from the Moon Mineral Mapper (M3) on board Chandrayaan-1 to characterize the mineralogy in several regions of interest. We find that LAMP Off/On-band ratios are able to distinguish between plagioclase feldspars and minerals such as quartz and mafic-dominated compositions. The LAMP Off/On-band ratios at Aristarchus are higher than previously reported ratios for plagioclase-rich regions, suggesting that the composition is unique to Aristarchus. Spectra from LAMP and M 3 both show that the central peak and high-albedo ejecta around Aristarchus contain shocked, possibly alkalic, plagioclase feldspar.

Elizabeth Czajka↗
NASA NTRS2004

Lunar and Planetary Science XXXV: Impact Experiments

This document covers the following topics: The Shock Compression Laboratory at Harvard: A New Facility for Planetary Impact Processes; What Controls the Intensity of Impact-induced Luminescence?; Isolating the Ricochet-induced Vaporization Process; An Experimental Study of Excavation Flow in Impact Cratering; Migration of the Cratering Flow-Field Center with Implications for Scaling Oblique Impacts; Raman Spectroscopy of Olivine in Dunite Experimentally Shocked to Pressures Between 5 and 59 GPa; and An Experimental Tomography Study of Impact-induced Damage Beneath Craters.

Source record↗
NASA NTRS1993

Geology of Galileo Regio quadrangle, Ganymede

Galileo Regio quadrangle, including most of Galileo Regio, contains two basic geologic units: older dark, furrowed, and heavily cratered material and younger light, grooved, relatively less-cratered material. Dark material dominates, the light material occurring to the W and SW in about five percent of the quadrangle. Dominant structural features, of uncertain origin, are the NW-trending arcuate furrows and associated orthogonal and oblique furrows in the dark material; grooves in the light material are not as well-ordered nor as intensely developed as elsewhere on Ganymede. Fifteen palimpsests, located partly or totally in the quadrangle and representing the period when the crust became sufficiently strong to record impact events, are subdivided into three relative-age classes, as are the numerous impact craters, some of which are dome, moat, and rampart-like. Galileo Regio is believed to have formed when, because of cooling, differentiation, and expansion, the thin, weak, icy lithosphere broke into blocks and light material filled the space between, or overspread those blocks that subsided, or both. Grooves formed in most of the light material and both light and dark material were cratered by impact, the most recent of which created bright-ray craters, the youngest features visible in the quadrangle.

Underwood, James R., Jr.↗
NASA NTRS1981

The modification stage of basin formation - Conditions of ring formation

The impact cratering process may be divided into three stages, including a short high pressure phase of initial contact between the projectile and target, a longer cratering flow phase during which material is both ejected and displaced to form the transient crater, and a still longer modification phase during which the transient crater is modified into the final observed form. The present investigation is concerned with the nature of the modification stage as constrained by the initial boundary condition which comprises the transient crater and its surroundings, and the final boundary condition which comprises the structure of observed craters and basins. A brief description is provided of an interpretation of basin ring structure based on geophysical, geological, and dimensional analysis of craters and basins on the moon, Mercury, and Mars, on structural observations of terrestrial impact and explosion craters, and on an empirical crater restoration model. A scenario of basin formation is constructed, and relations of this scenario to observed morphology are discussed.

Croft, S. K.↗
NASA NTRSDate not supplied

Evidence of High-Angle Ejecta from Impacts Iinto Various Granular Materials

The dominant mechanism for resurfacing airless bodies is the excavation and ejection of material during the formation of impact craters. Ejecta that is deposited proximal to the rim of craters formed in the gravity-regime (where gravitational forces are greater than material strength) form a relatively smooth and continuous deposit. Aside from far-field secondary craters, craters observed on continuous ejecta deposits are mostly assumed to be representative of the primary impactor flux after the time of deposition. Sustained primary bombardment should produce a homogeneous crater population across this surface, thus providing an opportunity to determine crater size-frequency distributions and surface chronologies. Deviations from this ideal have been observed as different crater-size distributions appearing between the continuous deposits and their superimposed melt ponds. Numerous explanations for this discrepancy have been proposed, one of which is the occurrence of self-secondary craters, which would be created by ejecta launched at sufficiently high-angles to re-impact the fresh continuous ejecta deposits. Here, we present results from cratering experiments to explore the influence of density, porosity, and friction on ejecta kinematics and report on the observation of such high-angle ejecta in cohesionless granular targets.

Impact crater↗
NASA NTRS1993

Hypervelocity impact study: The effect of impact angle on crater morphology

The Space Power Institute (SPI) of Auburn University has conducted preliminary tests on the effects of impact angle on crater morphology for hypervelocity impacts. Copper target plates were set at angles of 30 deg and 60 deg from the particle flight path. For the 30 deg impact, the craters looked almost identical to earlier normal incidence impacts. The only difference found was in the apparent distribution of particle residue within the crater, and further research is needed to verify this. The 60 deg impacts showed marked differences in crater symmetry, crater lip shape, and particle residue distribution. Further research on angle effects is planned, because the particle velocities for these shots were relatively slow (7 km/s or less).

Crawford, Gary↗
NASA NTRS1974

Smooth plains and continuous deposits of craters and basins

Apollo 16 photographic data are analyzed which suggest that smooth plains are related in origin to large primary cratering events, and that the plains material is mainly the ejecta of local and regional primary impact craters with only minor contributions from distant craters and basins. This material, then, has been emplaced in its present location by secondaries of distant craters and directly by primary craters near the site. Calculations indicate that the material excavated from large primary craters typically excavates much larger amounts of material from local terrain when it impacts in the secondary crater field. There is a correlation between the extent of development of smooth plains inside large high-land craters and the erosional state of the crater rims and walls. It is incorrect to consider the continuous deposits to be solely basin ejecta.

Oberbeck, V. R.↗
NASA NTRS1983

The Manicouagan impact structure - An analysis of its original dimensions and form

A reanalysis of the preerosional geology of the Canadian impact crater, Manicouagan, is presented. Although most of the current features of the annular moat are primarily a result of erosional processes, the original dimensions of the cavity have been determined to include a transient cavity 60 km in diam. The final floor of the crater was studied and found to be an impact melt-covered inner plateau 55 km in diam. Comparisons with similar crater bottoms on the moon are used to estimate a final crater rim diameter of 85-95 km. The inner plateau and relatively smooth deposits on the crater floor are noted to be most similar to the lunar crater Copernicus.

Grieve, R. A. F.↗
NASA NTRS2017

The Geographic Distribution of Boulder Halo Craters at Mid-to-High Latitudes on Mars

Extensive evidence exists for ground ice at mid-to-high latitudes on Mars, including results from neutron spectroscopy [1-3], thermal properties [4-5], geomorphology [e.g., 6-9], and the in situ observations of Mars Phoenix [10]. This ground ice has been hypothesized to be emplaced diffusively and fill pores [11], or to have accumulated by ice and dust deposition that draped or mantled the terrain [7, 12]. These two processes are not mutually exclusive; both potentially have occurred on Mars [5]. One of the landforms found in areas where ground ice is common on Mars are boulder halo craters [e.g., 13-15] (Figure 1), which are topographically muted impact craters that are filled by ice-rich regolith. They are outlined by boulders that trace a circular outline of the original crater rim. Boulder halos generally have distinctly higher boulder densities than the surrounding background plains and have few boulders in their interiors. The mechanism of boulder halo crater formation is somewhat uncertain. Our working model is that an impact event occurs with sufficient size to excavate to a depth greater than the boulder-poor, ice-rich soils. Excavated boulders are deposited around the crater's rim and in its proximal ejecta. Quite rapidly [14], the crater becomes infilled by icy soil. Rather than being buried, boulders in the halo remain at the surface, perhaps be-cause they 'float' relative to finer-grained materials [14, 16]. Regardless of the details of this process, the life-time of boulders at the surface is much greater than the timescale needed to remove most of the craters' topography. Physical weathering of rocks must be greatly out-paced by crater infilling (the opposite of what is typical, e.g., on the Moon [17]). The rapidity of this infilling is easiest to understand if icy mantling material is deposited and accumulates, rather than simply being added by pore filling of soils. If this model is correct, boulder halos only form when they excavate rock-producing materials from beneath the upper surface. Thus, the distribution and size of craters that result in boulders halos may provide in-sight into the thickness of the ice-rich surface layer in different locations. Note that this thickness is necessarily that of the ice-rich layer at the time of impact, not at present. This study is an initial survey of boulder halo crater locations in the 50deg to 80degN and 50deg to 80degS latitude bands on Mars.

Ice↗
NASA NTRS1970

Lunar dimple craters

Lunar dimple craters formation by meteoritic erosion of concentric impact craters

Oberbeck, V. R.↗