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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Ganymede and Callisto - Surface textural dichotomies and photometric analysis

Complete solar phase curves of the Ganymede and Callisto leading and trailing hemispheres, which have been obtained by reducing Voyager imaging observations and combining them with ground-based telescopic data, are presently fit to scattering models in order to derive hemispherical values of the single scattering albedo, the single particle phase function (SPPF), the compaction state (CS) of the optically active portion of the regolith, and the mean slope angle of macroscopic features. While Callisto's leading side is composed of particles that are more strongly backscattering than the trailing side, no hemispheric differences are found in the CS, surface roughness, or SPPF.

Buratti, Bonnie J.↗
NASA NTRS1991

Ganymede and Callisto - Complex crater formation and planetary crusts

Results are presented on measurements of crater depths and other morphological parameters (such as central peak and terrace frequency) of fresh craters on Ganymede and Callisto, two geophysically very similar but geologically divergent large icy satellites of Jupiter. These data were used to investigate the crater mechanics on icy satellites and the intersatellite crater scaling and crustal properties. The morphological transition diameters of and complex crater depths on Ganymede and Callisto were found to be similar, indicating that the crusts of both satellites are dominated by water ice with only a minor rocky component.

Schenk, Paul M.↗
NASA NTRS1992

Impact-generated atmospheres over Titan, Ganymede, and Callisto

The current distribution of atmospheres among Ganymede, Titan, and Callisto are presently accounted for by a process of competition between impact erosion and impact-furnished supply of atmosphile-laden late veneers. Titan's lower impact velocities have allowed it to accommodate an atmosphere, while Callisto and Ganymede remain barren. The model applied entails that the threshold impact velocity for atmospheric cratering by icy impactors be in the 10-14 km/sec range, consistent with the implications of the Schmidt and Housen (1987) crater-energy scaling for nonporous targets.

Zahnle, Kevin↗
NASA NTRS1993

Central pit and dome craters - Exposing the interiors of Ganymede and Callisto

Central pit craters on Ganymede and Callisto are an unusual crater class, perhaps related to the unusual properties of water ice. The domes and pits form rapidly, on the time scale of the impact itself, rather than by long-term, post-impact intrusion or extrusion. The bright domes in pit craters are most simply explained as the uplift and exposure of relatively ice-rich material from depths of approximately 3.5 to 5 km during impact. The unusual pit morphology on icy satellites may be the result of impact into crust that is mechanically much weaker at shallow depth than on rocky bodies such as the moon. Because crater morphology is strongly dependent on ice-rock composition, the similarity of pit and dome dimensions on Ganymede and Callisto indicates that the structure and rheology of the crusts of these bodies are very similar, and have been for several billion years. Pit crater morphology indicates that the crusts of both satellites are probably ice-rich and differentiated.

Schenk, Paul M.↗
NASA NTRS1994

Radar ranging to Ganymede and Callisto

Arecibo observations from 1992 February to March have yielded the first successful radar range measurements to the Galilean satellites. Round-up time delays were measured for Ganymede and Callisto with accuracies of 20 to 50 micrometer (3 to 7 km) and 90 micrometer (14 km), respectively. Both satellites showed round-trip delay residuals (relative to the E-3 ephemeris) of about a millisecond, most of which can be attributed to errors in the predicted along-track positions (orbital phases). Using a simple model that assumed that all of the ephemeris error was due to constant orbital phase and Jupiter range errors we estimate that Ganymede was leading its ephemeris by 122 +/- 4 km, Callisto was lagging its ephemeris by 307 +/- 14 km, and Jupiter was 11 +/- 4 km more distant than predicted by the PEP740 planetary ephemeris.

Harmon, J. K.↗
NASA NTRS1996

Cometary Nuclei and Tidal Disruption: The Geologic Record of Crater Chains on Callisto and Ganymede

Prominent crater chains on Ganymede and Callisto are most likely the impact scars of comets tidally disrupted by Jupiter and are not secondary crater chains. We have examined the morphology of these chains in detail in order to place constraints on the properties of the comets that formed them and the disruption process. In these chains, intercrater spacing varies by no more than a factor of 2 and the craters within a given chain show almost no deviation from linearity (although the chains themselves are on gently curved small circles). All of these crater chains occur on or very near the Jupiter-facing hemisphere. For a given chain, the estimated masses of the fragments that formed each crater vary by no more than an order of magnitude. The mean fragment masses for all the chains vary by over four orders of magnitude (W. B. McKinnon and P. M. Schenk 1995, Geophys. Res. Lett. 13, 1829-1832), however. The mass of the parent comet for each crater chain is not correlated with the number of fragments produced during disruption but is correlated with the mean mass of the fragments produced in a given disruption event. Also, the larger fragments are located near the center of each chain. All of these characteristics are consistent with those predicted by disruption simulations based on the rubble pile cometary nucleus model (in which nuclei are composed on numerous small fragments weakly bound by self-gravity), and with those observed in Comet D/Shoemaker-Levy 9. Similar crater chains have not been found on the other icy satellites, but the impact record of disrupted comets on Callisto and Ganymede indicates that disruption events occur within the Jupiter system roughly once every 200 to 400 years.

Schenk, Paul M.↗
NASA NTRS1997

IUE's View of Callisto: Detection of an SO2 Absorption Correlated to Possible Torus Neutral Wind Alterations

Observations taken with the International Ultraviolet Explorer (IUE) detected a 0.28 micron absorption feature on Callisto's leading and Jupiter-facing hemispheres. This feature is similar to Europa's 0.28 micron feature, however it shows no correlation with magnetospheric ion bombardment. The strongest 0.28 micron signature is seen in the region containing the Valhalla impact. This absorption feature also shows some spatial correlation to possible neutral wind interactions, suggestive of S implantation (rather than S(sub x)) into Callisto's water ice surface, Indications of possible temporal variations (on the 10% level) are seen at other wavelengths between the 1984-1986 and the 1996 observations.

Lane, Arthur L.↗
NASA NTRS2000

Subsurface Oceans on Europa and Callisto: Constraints from Galileo Magnetometer Observations

Galileo measured the magnetic field perturbations of Europa and Callisto, which are consistent with dipole fields created by temporal variations of the surrounding jovian magnetospheric field. These fields almost match those expected for perfectly conducting moons. Using a simple shell model, we analyze the implications of these observations for the electrical structure for the interiors of the moons. It is discovered that Europa and Callisto must possess areas where the conductivity exceeds 0.06 and 0.02 S/m at a depth of no more than 200 and 300 km below the surface, respectively. This conductivity is not attainable in ice or silicates, unless large temperature gradients can be maintained below the ice or the ice layer is at least partially molten. A cloud of pick-up ions or an ionosphere are probably insufficiently conductive. Global Earth-like oceans under the surface of both moons could explain the observations if they are at least a few kilometers thick.

Zimmer, Christophe↗
NASA NTRS2003

Crewed Mission to Callisto Using Advanced Plasma Propulsion Systems

This paper describes the engineering of several vehicles designed for a crewed mission to the Jovian satellite Callisto. Each subsystem is discussed in detail. Mission and trajectory analysis for each mission concept is described. Crew support components are also described. Vehicles were developed using both fission powered magneto plasma dynamic (MPD) thrusters and magnetized target fusion (MTF) propulsion systems. Conclusions were drawn regarding the usefulness of these propulsion systems for crewed exploration of the outer solar system.

Callisto↗
NASA NTRS1995

NIMS - Callisto Science Objectives and Observational Plans

The Galileo Near Infrared Spectrometer (NIMS) provides a combination of spectroscopic and imaging capabilities. For geological studies of Callisto, this instrument can perform regional mapping while simultaneously determining composition and mineralogy. This data can help determine the surface evolution. NIMS will search for hydroxilated silicates, opaque minerals, and organic material.

Galileo Callisto near infrared spectrometer planet↗
NASA NTRS1998

Distribution of Silicates and Ices in Callisto

Using radio Doppler data from a single encounter (C3) of the Galileo spacecraft with Callisto, we have reported previously that this outermost Galilean moon might be undifferentiated.

Callisto Silicates Ice Galileo↗
NASA NTRS1982

Radar properties of Europa, Ganymede, and Callisto

The radar properties of Europa, Ganymede, and Callisto are summarized and present understanding of these properties is documented. The radar techniques are described, observational results reviewed, and salient aspects of the radar data set discussed. Theoretical interpretation of the satellites' anomalous radar properties is addressed, including aspects such as external scattering and double reflection from hemispherical craters, the random-facet model, total internal reflection, multiple total internal reflection, the high radar geometric albedos, the tenous upper layer, the two-component regolith, and compositional effects. It is concluded that multiple total internal reflection from randomly oriented subsurface facets can explain the anomalous circular polarization inversion in the radar echoes from the three satellites. Several refinements of the Goldstein-Green (1980) scattering model are suggested.

Ostro, S. J.↗
NASA NTRS1982

Interpreting the cratering record - Mercury to Ganymede and Callisto

A first analysis is presented of what the Galilean satellites' crater production function is, along with some interpretations of the conclusion. The basic premise is that the larger crater population of the lunar highlands is not at saturation density. The saturation issue is addressed, showing why the concept of saturation of lunar highlands can no longer be regarded as the best hypothesis, at least for large craters. The cratering records of Mars, Mercury, and the moon are reviewed and synthesized, and crater characteristics and statistics for Callisto and Ganymede are discussed and interpreted. It is shown that even the very densely cratered lunar highlands still retain considerable information about their production function; that remarkable similarities exist among the cratering histories of all of the terrestrial planets, both in terms of their production functions and of their total crater densities; and that the Gallilean satellites seem to have experienced quite a different impact history from that of the terrestrial planets.

Woronow, A.↗
NASA NTRS1985

Tectonics of the Valhalla Structure on Callisto

The surficial morphology of Callisto is dominated by large concentric patterns of ridges, scarps, and furrows. The largest one, Valhalla, shows a smooth central area 350 km in radius, surrounded by concentric sinuous ridges which extend as far as 600km from the center. Beyond the ridged area, scarps and furrows are observed as far as 2000 km. The global azimuthal distribution of the scarps and furrows of the outer ring (beyond 700 km from the center) was analyzed. It is proposed that the local geometry and the global distribution of scarps and furrows around Valhalla are the results of the reactivation of an old pattern by the Valhalla event. The coincidence of these local directions of a preexisting pattern (NW-SE and NE-SW) with the directions of the grids observed on most bodies observed so far in the solar system would indicate that this local pattern is a part of a global calistean grid.

Thomas, P. G.↗
NASA NTRS1985

Ganymede and Callisto: Beauty is only skin deep

Ganymede and Callisto, the two giant icy satellites of Jupiter, have very nearly the same size, composition, and location in the solar system, yet their surfaces are profoundly different. A new scenario of their geologic histories indicates that the differences may be only skin deep.

Croft, S. K.↗
NASA NTRS1984

Mobility of water ice on Callisto - Evidence and implications

Voyager images of Callisto reveal evidence for the accumulation of a bright volatile, presumably water ice, on north-facing slopes in the north polar region. The geometry of these accumulations suggests that ice migration in Callistoan high latitudes is dominated by thermal sublimation, controlled by insolation-dependent surface temperature contrasts. Such sublimation-dominated migration may result in the cold-trapping of most of the surface ice in discrete high-albedo regions.

Spencer, J. R.↗