Search NASA⌕ Search

SEARCH · Search NASA

Results for “resurfacing”

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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

The evolution of tectonic features on Ganymede

The bands of bright resurfaced terrain on Ganymede are probably broad grabens formed by global expansion and filled with deposits of ice. Grooves within the bands are thought to be extensional features formed during the same episode of expansion. The crust of Ganymede is modeled as a viscoelastic material subjected to extensional strain. With sufficiently high strain rates and stresses, deep normal faulting will occur, creating broad grabens that may then be filled. Continuing deformation at high strain rates and stresses will cause propagation of deep faults up into the flood deposits and normal faulting at the surface, while lower strain rates and stresses will cause formation of open extension fractures or, if the crustal strength is very low, grabens at the surface. The spacing between adjacent fractures may reflect the geothermal gradient at the time of deformation. Surface topography resulting from fracturing and normal faulting will decay with time as a result of viscous relaxation and mass-wasting.

Squyres, S. W.↗
NASA NTRS1983

Anomalous bulk viscosity of two-phase fluids and implications for planetary interiors

The irreversible entropy production is calculated for the imposition of a pressure perturbation on a two-phase medium composed of a dilute suspension of droplets (or snowflakes) and a liquid phase of other materials. An absence of metastability is assumed, allowing the relaxation to be dominated by the solute finite diffusivity. The fluid medium was found to display a behavior suggestive of a bulk viscosity near 10 trillion P, a finding that is significant for studies of dissipation in planetary cores for tidal or seismic disturbances. A minimum quality factor for acoustic or tidal pressure oscillations and the accompanying frequency are calculated. An example is provided in terms of helium rain clouds in the deep interiors of giant planets. Additionally, a tidal quality factor of 10 to the 15th is found necessary to account for Io volcanism and resurfacing on Enceladus.

Stevenson, D. J.↗
NASA NTRS1984

Short time-scale surface changes on Io

Imaging data from the Voyager 1 and 2 encounters with the Jupiter system provide a data set for the examination of short time-scale variations of surface features on Io. Clear evidence exists for variations near the known eruption sites and for other areas which appeared to have erupted between the encounters. Regions outside the known active eruption sites were examined in order to look for variations in the surface scattering properties which is due to undetected small-scale volcanic activity. The phase functions of many areas are intercompared in order to look for regions with phase functions outside the normal range for satellite surface properties. Areas with unusual scattering properties are related to small-scale eruptions of gas or particles. Determination of the distribution of these areas has strong implications for the resurfacing rates for Io.

Terrile, R. J.↗
NASA NTRS1984

Planetary geomorphology field studies: Washington and Alaska

Field studies of terrestrial landforms and the processes that shape them provide new directions to the study of planetary features. Investigations discussed address principally mudflow phenomena and drainage development. At the Valley of 10,000 Smokes (Katmai, AK) and Mount St. Helens, WA, studies of the development of erosional landforms (in particular, drainage) on fresh, new surfaces permitted analysis of the result of competition between geomorphic processes. Of specific interest is the development of stream pattern as a function of the competition between perennial seepage overland flow (from glacial or groundwater sources), ephemeral overland flow (from pluvial or seasonal melt sources), and ephemeral/perennial groundwater sapping, as a function of time since initial resurfacing, material properties, and seasonal/annual environmental conditions.

Malin, M. C.↗
NASA NTRS1984

Geologic investigations of outer planets satellites

Four tests are examined: (1) investigation of volcanism on Io; Interim results of thermal and structural modeling of volcanism on Io are presented, (2) a study of the ancient heavily cratered regions on Ganymede, (3) a geologic comparison of the cratering record on Ganymede and Callisto, and (4) a geological and chemical investigation of internal resurfacing processes on the Saturnian satellites. Tasks 2, 3, and 4 utilize Voyager imaging data.

Strom, R. G.↗
NASA NTRS1984

Ring torque on Janus and the melting of Enceladus

The absence of craters noted on Voyager 2 images of Encedalus indicates geologically recent resurfacing, probably due to internal melting; heating mechanism calculations, however, yield heating rates too small to cause melting. If Janus, whose orbital mean motion is currently decreasing as Janus' orbit evolves outward due to resonant torques from Saturn's rings, were ever to become locked into a stable 2:1 orbital commensurability with Encedalus, the resulting angular momentum transfer could have sufficiently enhanced the eccentricity of Encedalus' orbit for the ensuing tidal heating to have melted Encedalus' interior. However, the predicted rapid time scale for ring evolution due to resonant torques from Saturn's inner moons remains a major problem.

Lissauer, J. J.↗
NASA NTRS1985

Dark Halo Craters and the Thickness of Grooved Terrain on Ganymede

Dark halo craters on grooved terrain on Ganymede represent potential probes of the subsurface geology. These craters are surrounded by a broad, diffuse low albedo annulus, or halo and have apparently lost the bright rim and ray deposits associated with very young craters. The recognition of dark halo craters, almost all greater than 12 km in diameter, indicates that material darker and redder than grooved terrain material forms a stratigraphy horizon at about 1 km depth the present surface of grooved terrain in Uruk Sulcus. This material is most likely downdropped cratered terrain material, which only larger craters have excavated into. This is most consistent with extensional tectonic models for grooved terrain formation whereby the lithosphere is stretched and blocks of ancient cratered terrain are downdropped along bounding faults, and subsequently resurfaced by a shallow layer of relatively clean icy material. Evidence for the preservation of cratered terrain material at shallow depth beneath grooved terrain material poses great difficulties for alternative grooved and smoothed terrain formation mechanisms.

Schenk, P. M.↗
NASA NTRS1985

Giant Planets and Their Satellites: Cosmochemistry, Evolution and Structure

The following topics were discussed: surface state of Titan; statistical mechanical treatment of clathrate hydrates; planetary dynamos; formation of the giant planets; the e-ring; Uranian satellites and atmosphere; 10 sulfur lakes; episodic tidal evolution; resurfacing of Ganymede; and the origin of the Moon.

Stevenson, D. J.↗
NASA NTRS1985

Mars: Stratigraphy of Western Highlands and Polar Regions

Geologic mapping and stratigraphic studies of Mars based on Viking images improved knowledge of the relative age and occurrence of geologic units on a global scale. Densities of geologic units or features during the Noarchian, Hesperian, and Amazonian periods are indicated for the North and South polar regions as well as the equatorial region of Mars. Cumulative counts of crater size frequencies for craters larger than 2 km in diameter on plateau units mapped in the western region of Mars counts indicate that the plateau terrain as a whole was thinly resurfaced during the Hesperian Period, and a large proportion of pre-existing craters less than 10 to 15 km in diameter was buried. The formation of northern plains, subpolar highlands, and both polar regions is also described.

Tanaka, K. L.↗
NASA NTRS1984

Sulfur flows of Ra Patera, Io

Voyager 1 imaging data have been used to investigate the color and morphology of several radial flow-like features at Ra Patera, a broad volcanic structure at approximately 8 deg latitude and 325 deg longitude on the Galilean satellite Io. It was found that downstream progressions of flow color and morphology are consistent with lava of a predominately sulfur composition cooling radiatively and erupting in the range of 470 to 520 K at effusion rates at 10 to the 10th to 10 to the 11th cubic cm/sec. This implies global resurfacing rates by volcanic flows on Io of the order of 1 cm/year. Calculated energy content and effusion rates for flows at Ra Patera, using the physical parameters of sulfur, are of the order of the largest known terrestrial basaltic eruptions and are consistent with calculations of globally available energy.

Pieri, D. C.↗
NASA NTRS1985

Impact cratering history of the Saturnian satellites

The impact flux history of the Saturn system has been modelled, and absolute ages estimated. The model assumes that the general history of impact flux was similar to that of the inner solar system and that the dominant source of material in the postaccretionary phases was external to the Saturn system. Population I and II craters represent the synheavy and postheavy bombardment periods, respectively. Observed crater densities are representative of the actual ages and do not appear to be saturation-equilibrium surfaces. It is concluded that some of the satellites have geologic histories which extend to about 3.5 b.y. Significant endogenic resurfacing has occurred on several satellite surfaces, which indicates that thermal conditions and material compositions are more complicated than might have been anticipated prior to Voyager encounters.

Plescia, J. B.↗
NASA NTRS1985

The geomorphology of Rhea - Implications for geologic history and surface processes

Morphological analyses of landforms on Rhea are used to define three physiographic provinces: cratered terrain 1 undifferentiated; cratered terrain 1 lineated; and cratered terrain 2. The important statigraphic relationships between the different provinces are examined with respect to major impact basins and tectonic features. It is shown that the formation of multiringed basins may have caused, or at least controlled the locations of major resurfacing and mantling events. The diameters of the central peaks relative to the impact crater diameters are found to be significantly larger than those within the craters of the moon or Mercury. Both cratered and noncrater lineaments have regional orientations which do not fit current global or regional stress models. On the basis of the morphological analysis, a chronological order is established for the origin of the three provinces: the cratered terrain 1 province was formed first; and cratered terrain 1 lineated and cratered terrain 2 were formed second, and last, respectively. It is shown that the chronological order is generally consistent with current theoretical models of the evolution of Rhea.

Moore, J. M.↗
NASA NTRS1984

Satellites of Saturn - Geological perspective

The Voyager encounters have added the satellites of Saturn to those planetary bodies for which geological studies are possible. These satellites are surprisingly heterogeneous, in spite of their apparently common composition of more than half water ice. All are more or less heavily cratered, but most also show clear evidence of substantial endogenic modification and resurfacing during the first few hundred million years of their existence. In the case of Enceladus, this internal activity has been most dramatic and may have persisted into the past billion years of solar-system history. Iapetus also remains a major mystery with its still unexplained hemispheric dichotomy, for which both external and internal causes have been suggested. The current knowledge of the satellites is reviewed from a geologic perspective, using primarily Voyager imaging data. Emphasis is placed on the six larger bodies (except Titan): Rhea, Iapetus, Dione, Tethys, Enceladus, and Mimas.

Morrison, D.↗
NASA NTRS1985

Evaluation of thermal control surface on-orbit servicing methods for long term missions

Future activities of NASA will include the long-term (10 - 30 years) operation of space vehicles. For this reason, there will be an urgent need to provide the basic technology for space vehicle thermal control surfaces and their functional maintenance for future long-term missions. One of the problems arising in connection with such missions is related to contamination which can degrade operational design parameters of critical and thermal control surfaces. All Space Based Payloads will arrive on orbit with a certain level of contamination from ground handling, and, on orbit, will be subjected to some level of contamination over their mission life. For the extension of mission life, it appears practical to institute surface refurbishment procedures for contaminated and degraded surfaces. Potential resurfacing methods are evaluated, taking into account three potential processes. The most promising of these is a cleaning procedure based on the utilization of atomic oxygen.

Saylor, W.↗
NASA NTRS1985

Hot-spot tectonics on Io

The thesis is that extensional tectonics and low-angle detachment faults probably occur on Io in association with the hot spots. These processes may occur on a much shorter timescale on Ion than on Earth, so that Io could be a natural laboratory for the study of thermotectonics. Furthermore, studies of heat and detachment in crustal extension on Earth and the other terresrial planets (especially Venus and Mars) may provide analogs to processes on Io. The geology of Io is dominated by volcanism and hot spots, most likely the result of tidal heating. Hot spots cover 1 to 2% of Io's surface, radiating at temperatures typically from 200 to 400 K, and occasionally up to 700K. Heat loss from the largest hot spots on Io, such as Loki Patera, is about 300 times the heat loss from Yellowstone, so a tremendous quantity of energy is available for volcanic and tectonic work. Active volcanism on Io results in a resurfacing rate as high as 10 cm per year, yet many structural features are apparent on the surface. Therefore, the tectonics must be highly active.

Mcewen, A. S.↗
NASA NTRS1987

Cratering history of Miranda

The surface of the southern hemisphere of Miranda imaged by Voyager 2 is divisible into two general types of terrain: cratered terrain, characterized by numerous craters and undulating intercrater plains; and basins, circular to rectangular areas of complex morphology having large-scale albedo markings. To determine the relative ages of the terrains and the length of geological activity, crater-frequency data were compiled for various parts of the cratered terrain and basins. Crater-frequency data indicate that the cratered terrain is the oldest terrain on Miranda and that it was locally resurfaced.

Plescia, J. B.↗
NASA NTRS1987

Geology and cratering history of Ariel

The surface of Ariel imaged by Voyager 2 can be divided into several types of terrain on the basis of morphology: cratered terrain, subdued terrain, ridged terrain, and plains. Crater statistics were compiled for each of the terrain types. Despite differing morphology, the various terrains on Ariel do not exhibit large variations in crater frequency. None of the observed surfaces on Ariel record the period of accretion. It seems that conditions appropriate for resurfacing could have occurred during the early history of Ariel.

Plescia, J. B.↗
NASA NTRS1987

Accretional heating of the satellites of Saturn and Uranus

Voyager images of the satellites of Saturn and Uranus have shown that these bodies are characterized by remarkable diversity and surprisingly complex geologic histories. Despite their small sizes, a number of the satellites show unambiguous evidence for resurfacing. The goal was to develop a detailed model for heating of these small satellites, and then to explore the consequences of variations in the free parameters in the model. Specifically an attempt was made to determine for what range of conditions melting will occur in these satellites. Along with varying a number of model parameters, the important effects of inclusion of small amounts of ammonia and methane in the system were considered.

Squyres, Steven W.↗