Search USGS⌕ Search

SEARCH · Search USGS

Results for “Icarus”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5Linked to original sources
USGS2002

Eros: Shape, topography, and slope processes

Stereogrammetric measurement of the shape of Eros using images obtained by NEAR's Multispectral Imager provides a survey of the major topographic features and slope processes on this asteroid. This curved asteroid has radii ranging from 3.1 to 17.7 km and a volume of 2535±20 km 3 . The center of figure is within 52 m of the center of mass provided by the Navigation team; this minimal difference suggests that there are only modest variations in density or porosity within the asteroid. Three large depressions 10, 8, and 5.3 km across represent different stages of degradation of large impact craters. Slopes on horizontal scales of ∼300 m are nearly all less than 35°, although locally scarps are much steeper. The area distribution of slopes is similar to those on Ida, Phobos, and Deimos. Regions that have slopes greater than 25° have distinct brighter markings and have fewer large ejecta blocks than do flatter areas. The albedo patterns that suggest downslope transport of regolith have sharper boundaries than those on Phobos, Deimos, and Gaspra. The morphology of the albedo patterns, their lack of discrete sources, and their concentration on steeper slopes suggest transport mechanisms different from those on the previously well-observed small bodies, perhaps due to a reduced relative effectiveness of impact gardening on Eros. Regolith is also transported in talus cones and in connected, sinuous paths extending as much as 2 km, with some evident as relatively darker material. Talus material in at least one area is a discrete superposed unit, a feature not resolved on other small bodies. Flat-floored craters that apparently contain ponded material also suggest discrete units that are not well mixed by impacts.

Icarus↗
USGS2002

Topography and geologic characteristics of aeolian grooves in the south polar layered deposits of Mars

The topographic and geologic characteristics of grooves and groove-like features in the south polar layered deposits near the Mars Polar Lander/Deep Space 2 landing sites are evaluated using Mariner 9 images and their derived photoclinometry, normalized using Mars Orbiter Laser Altimeter data. Although both Mariner 9 and Viking images of the south polar layered deposits were available at the time of this study, Mariner 9 images of the grooves were selected because they were generally of higher resolution than Viking images. The dimensions and slopes of the grooves, together with orientations that nearly match the strongest winds predicted in the Martian Global Circulation Model and directions inferred from other wind indicators, suggest that they formed by aeolian scour of an easily erodible surface. Most grooves are symmetric and V-shaped in transverse profile, inconsistent with an origin involving extensional brittle deformation. Although the grooves strike along slopes and terraces of the south polar layered deposits, the variable depths and lack of terracing within the grooves themselves indicate that any stratigraphy in the uppermost 100 m of the polar layered deposits is composed of layers of similar, and relatively low, resistance. The grooves do not represent landing hazards at the scale of the Mariner 9 images (72-86 m/pixel) and therefore probably would not have affected Mars Polar Lander and Deep Space 2, had they successfully reached the surface.

Icarus↗
USGS2002

Low abundance materials at the mars pathfinder landing site: An investigation using spectral mixture analysis and related techniques

Recalibrated and geometrically registered multispectral images from the Imager for Mars Pathfinder (IMP) were analyzed using Spectral Mixture Analysis (SMA) and related techniques. SMA models a multispectral image scene as a linear combination of end-member spectra, and anomalous materials which do not fit the model are detected as model residuals. While most of the IMP data studied here are modeled generally well using "Bright Dust," "Gray Rock," and "Shade" image endmembers, additional anomalous materials were detected through careful analysis of root mean square (RMS) error images resulting from SMA. For example, analysis of SMA fraction and RMS images indicates spectral differences within a previously monolithologic Dark Soil class. A type of Dark Soil that has high fractional abundances in rock fraction images (Gray Rock Soil) was identified. Other anomalous materials identified included a previously noted "Black Rock" lithology, a class of possibly indurated, compacted, or partially cemented soils ("Intermediate Soil"), and a unit referred to as "Anomalous Patches" on at least one rock. The Black Rock lithology has a strong 900-1000-nm absorption, and modeling of the derived image endmembers using a laboratory reference endmember modeling (REM) approach produced best-fit model spectra that are most consistent with the presence of high-Ca pyroxenes and/or olivine, crystalline ferric oxide minerals, or mixtures of these materials as important components of the Black Rock endmember. More unique mineralogic identifications could not be obtained using our initial REM analyses. Both Intermediate Soil and Anomalous Patches units exhibit a relatively narrow 860-950-nm absorption that is consistent with the presence of either low-Ca pyroxenes or a cementing crystalline ferric oxide mineral. ?? 2002 Elsevier Science (USA).

Icarus↗
USGS1967

Distribution of Lunar craters according to morphology from Ranger VIII and IX photographs

A classification of the craters photographed by the Ranger VIII and IX missions into four categories according to relative sharpness shows that at diameters of 100 meters, the predominant craters have broad rims and low depth-diameter ratios and are partly covered with smaller craters which generally have sharper rims and higher depth-diameter ratios but include all classes. If competing processes of crater formation and destruction are responsible for the mix of crater types observed, an abrupt increase in the proportion of sharp craters suggests an intense episode of crater destruction to produce a smoothed surface that was subsequently recratered. Data comparable to those presented can readily be obtained from Lunar Orbiter photographs to determine if an increase in the proportion of sharp craters is present over more extensive areas and to test various cratering histories that may account for it.

Icarus↗
USGS1967

An operational theory of laser-radar selenodesy

A theory of the utilization of laser techniques for ranging from the Earth to the Moon for the purpose of providing control points on the lunar surface at which the figure of the Moon is measured to an accuracy at least an order of magnitude better than that of the present astrometric measurements is presented. This, in turn, increases the accuracy of the horizontal selenocentric coordinates of topographical features measured by present astrometric methods. The improvement in the vertical and horizontal coordinates of control points in the Apollo landing zone will aid in the analysis of Unmanned Lunar Orbiter photographs for the selection of Apollo landing sites. The present discussion proposes the means of obtaining the ground control upon which the Orbiter photogrammetry is to be fastened. In addition, a technique of combining Goldstone tracking data to show where the resulting lunar figure is positioned relative to the Moon's center of mass is presented. If corner reflectors are placed on the lunar surface, as suggested by many members of the scientific community, or on a lunar orbiting vehicle, one or more Earth-based laser ranging systems are essential. These reflectors will give enough enhancement in return signal to allow for an additional increase in range accuracy of one to two orders of magnitude. In addition to the primary data on the figure of the Moon, a number of other measurements of scientific importance are then readily obtainable. As far as the measurement of control points is concerned, however, the use of corner reflectors is not essential for the success of this project. Questions regarding the influence on the present shape of the Moon of the frozen tide, isostasy, and past impacts of large asteroids appear in large part answerable through the data which are indicated to be obtainable under the present theory.

Icarus↗
USGS1967

On the chemistry of Jupiter's upper atmosphere

We conduct a first investigation into the ion-molecule chemistry of the upper Jovian atmosphere. Experimental results show that intense ultraviolet radiation reacts with the constituents of the Jovian atmosphere to produce C 2 H 4 , C 2 H 6 , C 3 H 8 , and higher polymers. The general procedure for calculating both equilibrium and nonequilibrium abundances of these products is formulated and applied to the case of the surface passage of a satellite shadow. A specific example is made of ethylene, for which an analytical approximation gives 10 10 molecules in an atmospheric column of 1 cm 2 cross section after a very rapid rise to equilibrium. Such a concentration of ethylene does not substantially affect the infrared radiation in the shadow.

Icarus↗
USGS1970

Lunar Maria and circular basins-a review

Lunar Orbiter data make it possible to examine the distribution and relations of maria and large circular basins over the entire Moon. The restricted distribution and age of the maria are in marked contrast to the apparently random distribution in time and place of the circular basins, some of which contain mare fillings. The circular basins are believed to be impact scars, and the maria to be volcanic fills which in each case are younger than the structures they fill. Twenty-nine circular basins 300 km wide or wider are recognized. They are placed in an age sequence because successive stages of degradation can be recognized from the fresh Orientale basin to the almost obliterated basin containing Mare Australe. The maria were emplaced during a short span of lunar history, although some light plains of the highlands may be older maria lightened through age. The present maria are topographically low, tend to be associated with large circular basins, and lie in a crude global belt of regional concentrations; 94% are on the hemisphere facing the Earth. Possible explanations offered for these patterns of mare distribution include impact-induced volcanism, volcanic extrusion to a hydrostatic level, isostatic compensation, lateral heterogeneity in the lunar interior, subcrustal convection, and volcanism due to disruption by Earth's gravity.

Icarus↗
USGS1970

Television experiment for Mariner Mars 1971

The Television Experiment objectives are to provide imaging data which will complement previously gathered data and extend our knowledge of Mars. The two types of investigations will be fixed-feature (for mapping) and variable-feature (for surface and atmospheric changes). Two cameras with a factor-of-ten difference in resolution will be used on each spacecraft for medium- and high-resolution imagery. Mapping of 70% of the planet's surface will be provided by medium-resolution imagery. Spot coverage of about 5% of the surface will be possible with the high-resolution imagery. The experiment's 5 Principal Investigators and 21 Co-Investigators are organized into a team. Scientific disciplines and technical task groups have been formed to provide the formulation of experiment requirements for mission planning and instrument development. It is expected that the team concept will continue through the operational and reporting phases of the Mariner Mars 1971 Project.

Icarus↗
USGS1971

Selenography and selenodesy with Apollo whole-disk lunar photographs I. Selenography

The Apollo whole-disk lunar photographs, with spacecraft lunar nadirs about 70° from the center of mean face, have considerable selenodetic potential provided that the requirements of resolution and precision can be met. Uncertainties in the internal camera geometry degrade the precision and make selenodetic applications doubtful, but selenographic work based on the assumption of a rigorously spherical moon makes lesser demands on the data and is still possible with useful accuracy. The selenographic method is fully developed here and applied to photographs 2505 and 2506 of Apollo 8 to produce a catalog of 635 positions. Of these 206 are farside and extend to 130° East Longitude. A new type of 5-character position word, appropriate for the entire lunar sphere, is used to define sequence in the catalog.

Icarus↗
USGS1971

Limited-interval definitions of the photometric functions of lunar crater walls by photography from orbiting Apollo

By the use of only relative photometry (intraframe) it is shown that the photometric functions of material reposed on the inner walls of some of the ypunger lunar craters photographed on the far side of the Moon from the Apollo 11 Command Module are not of a form which can be reduced to a dependence on phase angle and brightness-longitude ( g , α ) alone. Some other dependence on the completely general degrees of freedom described by phase angle, angle of incidence, and angle of emergence ( g , i , ϵ ) seems to be required. In addition, however, it has been found that a dependence of g and α is more closely approached for the crater, in the group observed, which is obviously the oldest by virtue of the roundedness of the rim crest and the mass-wasting which has occured on its inner walls. The possibility thus arises of crater age-dating by making a brightness ratio measurement together with some image geometry measurements. It is at least evident that more than one type of geologic material has been encountered.

Icarus↗
USGS1971

Imaging of Mercury and Venus from a flyby

This paper describes the results of study of an imaging experiment planned for the 1973 Mariner Venus/Mercury flyby mission. Scientific objectives, mission constraints, analysis of alternative systems, and the rationale for final choice are presented. Severe financial constraints ruled out the best technical alternative for flyby imaging, a film/readout system, or even significant re-design of previous Mariner vidicon camera/tape recorder systems. The final selection was a vidicon camera quite similar to that used for Mariner Mars 1971, but with the capability of real time transmission during the Venus and Mercury flybys. Real time data return became possible through dramatic increase in the communications bandwidth at only modest sacrifice in the quality of the returned pictures. Two identical long focal length cameras (1500 mm) were selected and it will be possible to return several thousand pictures from both planets at resolutions ranging from equivalent to Earthbased to tenths of a kilometer at encounter. Systematic high resolution ultraviolet photography of Venus is planned after encounter in an attempt to understand the nature of the mysterious ultraviolet markings and their apparent 4- to 5-day rotation period. Full disk coverage in mosaics will produce pictures of both planets similar in quality to Earthbased telescopic pictures of the Moon. The increase of resolution, more than three orders of magnitude, will yield an exciting first look at two planets whose closeup appearance is unknown.

Icarus↗