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Abstracts of reports from Principal Investigators of NASA's Planetary Geology and Geophysics Program are compiled. The research conducted under this program during 1989 is summarized. Each report includes significant accomplishments in the area of the author's funded grant or contract.
This paper reports the Ir content of a variety of geological samples determined by the high-purity Ge-coincidence/NaI(Tl)-anticoincidence gamma-ray spectrometry (henceforth referred to as coincidence/anticoincidence technique) and by the conventional INAA. The advantages of this technique are: (1) the Ir content of the samples is obtained (ppm to a fraction of ppb ranges) not only by the 468.1 keV peak as in the conventional INAA but also by the 784.6 keV and 920.9 keV sum peaks, which gives more confidence in the values obtained; and (2) it is well suited for the samples with high Compton background for which it is difficult to measure the Ir content by the conventional INAA technique. The practical sensitivity of this technique depends on the sample matrix. Under present experimental conditions, it varied from 0.1 ng for Mn nodules and 0.004 ng for Libyan Desert Glass. Iridium values obtained on small (about 1 microg) olivine grains demonstrate the potential application of this new technique to microsamples. The principle and methodology of this new technique as well as its advantages and disadvantages over the conventional INAA are discussed.
Electromagnetic echo-scattering models, empirical and theoretical considerations on regolith formation, and ice physics, are presently invoked in a geologic treatment of the anomalous radar properties of the icy Galilean satellites. These are held to arise because of the electrical differences between ice and silicates, and the absence of icy regoliths' ice-density structures in silicate regoliths. Icy regoliths may uniquely smooth out discontinuities between solid ejecta fragments and more porous surroundings, forming refraction-scattering 'lenses'; high-order multiple scatterings will thereby become more likely responsible for the echoes than low-order scattering.
The directional emission properties of geologic surfaces were investigated using a ground-based, hand-held infrared radiometer and thermistor probe. Field sites involved surfaces ranging from smooth playa and sand surfaces to a very rough aa lava flow. Large directional variations in thermal emission were found; they result from the presence of surface roughness at large scales producing spatial variations in kinetic temperature and at small scales producing emissivity variations. These variations are important in remotely determining surface structure and understanding surface energy balance and emission spectra.
A number of distinctive types of geologic features have been identified on Venus that are interpreted to be related to thermal plumes including domal rises, coronae, and major composite shield volcanoes. The basic characteristics of these features as well as their distribution are documented. The three types of features have related morphologies and are interpreted to represent a continuum of features formed by mantle plumes at scales from 100s to over 1000 km. The Artemis structure, located in Aphrodite Terra, is proposed to be a large corona. If crustal spreading processes are operating on Venus, hotspot features should form chains on the surface as seen in terrestrial ocean basins. On the basis of current data on hotspot-related feature distribution on Venus, no clear evidence exists for hotspot chains. The complete distribution of hotspot features in Magellan data will be used to understand better the relationship between interior processes and surface features, as well as to provide a test for the crustal spreading hypothesis.
This is a compilation of selected bibliographic data specifically relating to recent publications submitted by principle investigators and their associates, supported through the NASA Office of Space Science and Applications, Solar System Exploration Division, Planetary Geology and Geophysics Program.
Observations from approximately one-half of the Magellan nominal eight-month mission to map Venus are summarized. Preliminary compilation of initial geologic observations of the planet reveals a surface dominated by plains that are characterized by extensive and intensive volcanism and tectonic deformation. Four broad categories of units have been identified: plains units, linear belts, surficial units, and terrain units.
A bibliography of scientific papers, articles, and books based on research supported by the NASA Geology Program is given. The citations cover the period 1980 to 1990. An author index is included.
Photogeologic mapping of the Ophir Planum quadrangle was undertaken to solve two main problems: (1) what controlled the location, orientation, and growth of Ophir Planum grabens; and (2) how are the grabens and trough faulting related. The rich geological history of the Ophir Planum quadrangle underscores the fundamental importance of faulting in the early growth of Valles Marineris.
Available data on Martian multi-ring basins were compiled and evaluated using the new 1:15 million scale geologic maps of Mars and global topography was revised as base maps. Published center coordinates and ring diameters of Martian basins were plotted by computer and superimposed onto the base maps. In many cases basin centers or ring diameters or both had to be adjusted to achieve a better fit to the revised maps. It was also found that additional basins can explain subcircular topographic lows as well as map patterns of old Noachian materials, volcanic plains units, and channels in the Tharsis region.
Information is provided about currently funded scientific research within the Planetary Geology and Geophysics Program. The directory consists of the proposal summary sheet from each proposal funded by the program during fiscal year 1991. Information is provided on the research topic, principal investigator, institution, summary of research objectives, past accomplishments, and proposed investigators.
The data collected by Pioneer Venus have been used to map the broad radar characteristics of the equatorial region on the basis of radar brightness and texture. Seven units are defined and are used to assess the geologic character of the equatorial region. The correspondence between features in the 15 deg region of overlap between Pioneer Venus ans Venera 15/16 images is examined and used to extend units mapped in the northern high latitudes into the equatorial region. Using the properties of rms slope, reflectivity, the scattering behavior of the surface, and topographic signature, seven physiographic units are mapped on the basis of the distribution of the radar units in the equatorial region and are identified by increasing complexity as plains, dark halo plains, upland rises, upland plateaus, interhighland tectonic zones, tectonically segmented linear highlands, and tectonic junctions. The distribution of larger circular structures interpreted as coronae is also examined.
The surface of the Uranian satellite Oberon is characterized on the basis of ground-based and Voyager photometric observations. Disk-integrated phase-curve and disk-resolved data are presented in extensive tables, graphs, maps, and black-and-white and false-color images and discussed in terms of fits to the Hapke (1986) parameters, local variations in albedo and color, and their possible geological significance. It is found that most of the leading hemisphere is covered with dark materials like those in the crater floors, while the trailing hemisphere has patches of the dark material on a surface with a higher proportion of icy materials which are spectrally neutral.
The fundamental principles of the global positioning system (GPS) are reviewed, with consideration given to geological and geophysical applications and related accuracy requirements. Recent improvements are emphasized which relate to areas such as equipment cost, limitations in the GPS satellite constellation, data analysis, uncertainties in satellite orbits and propagation delays, and problems in resolving carrier phase cycle ambiguities. Earthquake processes and near-fault crustal deformation monitoring have been facilitated by advances in GPS data acquisition and analysis. Horizontal positioning capability has been improved by new satellite constellation, better models, and global tracking networks. New classes of tectonic problems may now be studied through GPS, such as kinematic descriptions of crustal deformation and the measurement of relative plate motion at convergent boundaries. Continued improvements in the GPS are foreseen.
Abstracts of reports from NASA's Planetary Geology and Geophysics Program are presented. Research is documented in summary form of the work conducted. Each report reflects significant accomplishments within the area of the author's funded grant or contract.
Field measurements for the Geologic Remote Sensing Field Experiment (GRSFE) were concentrated in the Lunar Lake area of Nevada. The GRSFE data are meant to be used in a variety of investigations, including tests of multispectral radiative transfer models for scattering and emission from planetary surfaces in support of the Earth Observing System (EOS), Mars Observer, and Magellan Missions. Studies will also be pursued to establish the neotectonic and paleoclimatic history of the arid southwestern United States. The data will also be used to support Mars Rover Sample Return (MRSR) simulation studies.
Lunae Planum is an elevated region east of the Tharsis rise, and ridged plains containing numerous Sacra Dorsa wrinkle ridges, cross-cutting Sacra Fossae grabens, and lobate scarps compose this Martian Plateau. Geologic mapping of the northern Lunae Planum region was undertaken to better understand to emplacement history of the ridge plains, the structural history of deformation, and the periods of fluvial processes that have modified the region. These investigations are important for several reasons: (1) the history of plains emplacement yields information valuable for understanding the evolution of Tharsis volcanism; (2) interpretation of structural deformation has implications on the lithology of the Martian crust; and (3) determining the history and fate of Martian volatiles is dependent upon knowing the periods of outflow activity. A discussion of the findings is presented.
The Claritas Fossae system is a complex, linear fracture zone that extends from its northern intersection with Noctis Labyrinthus 1800 km south-southeast to its southern intersection with Thaumasia Fossae. The width of the fracture zone varies from 150 km in the north to 550 km in the south; topographic relief, based on radar data from Earth, is 1.0 to 1.5 km. Claritas Fossae and its coincident ridge or rise have been interpreted to be a horst with more than 8 km of vertical uplift, the greatest such uplift on Mars. Viking orbital images of sufficiently high resolution exist to provide the basis only for two 1:500,000 scale photomosaic base maps of Claritas Fossae. They extend en in echelon east and west, i.e., the southeast corner of the northern and western quadrangle (MTM-30102) is coincident with the northwest corner of the eastern and southern quadrangle (MTM-25107). Preliminary geologic maps of the two quadrangles were prepared. Materials in the quadrangles are Noachian and Hesperian age, and the quadrangles are characterized by the widespread occurrence of fractured and cratered plateau material, the oldest material in the map areas. Other information about the quadrangles is presented.