Engineering Papers⌕ Search

Engineering topics

Wilhelms, D. E.

Publications and source records attributed to Wilhelms, D. E..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Geologic-magnetic correlations on the moon - Apollo subsatellite results

Comparison of the magnetic-field measurements of the Apollo subsatellite magnetometers with USGS geologic maps suggests that the ancient lunar field may have been greater during the Imbrian Period than the earlier Pre-Nectarian and Nectarian periods. Further, the field seems to have varied in direction. These data are consistent with a model in which the ancient lunar magnetizing field arises from a core dynamo which does not form until the Imbrian Period. Impacts during this period then result in magnetized crater melt and ejecta blankets. It is emphasized, however, that the area sampled by the subsatellite magnetometers is but a small fraction of the lunar surface. These results must be confirmed with studies of independent regions of the lunar surface before they can be considered conclusive.

Russell, C. T.↗
NASA NTRS1977

Nested-crater model of lunar ringed basins

We propose a model for the origin of impact-basin rings whereby the main topographic rim of a basin approximates the limit of excavation and inner rings approximate the rims of craters formed inside the transient crater by some perturbation in the cratering process. The cause of this complexity in transient cavities may be the presence of discontinuities in the target material. The second inward ring may have formed at the seismic discontinuity about 20 km deep in the lunar crust, and the third, innermost ring of a few large basins at the crust-mantle interface about 60 km deep. Slumping increased the original diameters of many rings and split some initially coherent rings into subsidiary or partial rings. Deformation outside the transient crater produced external arcs. This model differs from prevalent hypotheses of ring formation whereby an inner ring approximates the transient crater rim and major faulting of the flank produced the outer ring structures.

Wilhelms, D. E.↗
NASA NTRS1976

Mercurian volcanism questioned

It is noted that reports of the Mariner 10 television team favor a volcanic origin for the plains materials on Mercury. The present paper advances the argument that the Mercurian plains more closely resemble the lunar light plains (which are not of volcanic origin) in terms of stratigraphic relations, surface morphology, and albedo contrast. It is suggested that the plains on Mercury may have been formed from impact materials, possibly impact melts or other basin ejecta which behaved more like a fluid than did the lunar ejecta. It is concluded that if the old intercrater plains and younger smooth plains of Mercury were formed from impact materials, then Mercury underwent neither the volcanic interlude between early cratering episodes nor the late mare-type volcanic phase deduced by the Mariner 10 investigators.

Wilhelms, D. E.↗
NASA NTRS1976

Stratigraphy and structural geology

The immediate goal of stratigraphy and structural geology is to reduce the enormous complexity of a planetary surface to comprehensible proportions by dividing the near-surface rocks into units and mapping their distribution and attitude.

Carr, M. H.↗
NASA NTRS1976

Secondary impact craters of lunar basins

Numerous lunar features are examined and identified as being secondary to basins, that is, as having been formed by secondary impact of ejecta from basins. Most of the terra features previously attributed to volcanism and tectonism and many attributed previously to primary impact must be attributed to basin-secondary impact. Secondary craters of the Imbrium Basin cover a large part of the south-central near side. Imbrium secondaries are more numerous than primaries in the size ranges 3 or 4 to 10 km on the near side, and may be more numerous at diameters of 10-25 km. Preliminary stratigraphic dating results based on superposition relations among basin secondaries suggest that the Crisium and south Serenitatis basins are younger than Nectaris and Humboldtianum.

Wilhelms, D. E.↗
NASA NTRS1975

Photogeological, geophysical, and geochemical data on the east side of the moon

Correlations between Apollo orbital data and geologic data for eight map provinces are reported for a region centered on the east limb of the moon (50 deg N to 50 deg S and 50 deg E to 140 deg E). The appearance of the provinces is described, and the basins in or near the region are assigned relative ages. The western (nearside) part of the region averages about 3 km lower in elevation than the eastern (farside) part, according to laser altimeter measurements which are used to make geologic cross sections. Gravity data correlate with most geologic provinces and the surface profiles made by the laser altimeter and lunar sounder. The distribution of concentration ratios of Al/Si and Mg/Si as well as the distribution of relatively low natural radioactivity are considered.

El-Baz, F.↗
NASA NTRS1974

Comparison of Martian and lunar geologic provinces

Mars and the moon have superficially similar dichotomies between old elevated terrain and young low-lying terrain. On Mars the older terrain contains much less basin and crater material and much more plains material than the older terrain on the moon. These elevated Martian plains, constituting the plateau plains province, are believed to be depositional, perhaps volcanic, in origin. Some of the plateau plains are equivalent in crater density to a province of old lunar mare material in Mare Australe but are much more extensive. Like their lunar equivalents, these plateau plains are believed to have formed while the impact flux was declining from an early torrential rate to a later much slower rate. Other, younger Martian plains generally are also considerably more extensive relative to planet size than their lunar equivalents.

Wilhelms, D. E.↗
NASA NTRS1974

Lunar basin formation and highland stratigraphy

Multiring impact basins, formed after solidification of the lunar crust, account for most or all premare regional deposits and structures expressed in the lunar landscape and for major topographic and gravity variations. A fresh basin has two or more concentric mountain rings, a lineated ejecta blanket, and secondary impact craters. Crackled material on the floor may be impact melt. The ejecta blanket was emplaced at least partly as a ground-hugging flow and was probably hot. A suggested model of basin formation is that the center lifts up and the rings form by inward collapse during evisceration. The resulting basin is shallow and has a central uplift of the mantle. This results in a central gravity high and a ring low. Later flooding by mare basalt has since modified most near side basins. Highland deposits of plains, furrowed and pitted terrain, and various hills, domes, and craters that were interpreted before the Apollo missions as being volcanic can now be interpreted as being basin related.

Howard, K. A.↗
NASA NTRS1973

Comparison of Martian and lunar multi-ringed circular basins

Many similarities between Martian and lunar multi-ringed basins are outlined. There is a similar relation between basin size and number of rings; the second ring seems to appear in the crater-basin continuum in roughly the same diameter range. The similarities are tentatively considered great enough to indicate that Martian and lunar basins were formed by the same process. Morphological and statistical studies of lunar basins have strongly indicated this process to be impact.

Wilhelms, D. E.↗
NASA NTRS1973

Geologic map of the northern Crisium region

Apollo 17 metric photographs provide the best available coverage for geologic interpretation of northern Mare Crisium and the northern Crisium basin. One region in particular, between Alhazen Crater and longitude 66 E, had previously been covered very poorly. The Apollo 17 photographs provide excellent monoscopic as well as stereoscopic viewing because of the favorably low sun illuminations (15 deg to 49 deg). These new photographic data allow the geology of the basin, the mare, and other nearby terrains to be reevaluated. This reexamination, together with data from continuing moon-wide photogeologic studies and analyses of returned rocks from Apollo landing sites, has produced a simple evolutionary picture of the region, expressed by fewer map units and explained by fewer basic processes than previously thought necessary.

Wilhelms, D. E.↗
NASA NTRS1972

Preliminary Mariner 9 report on the geology of Mars.

Mariner 9 results indicate that Mars is geologically far more heterogeneous than previously suspected from earlier flyby missions; the surface has been shaped by volcanic, tectonic, erosional, and depositional activity. The equatorial region between 30 deg N and 30 deg S latitude is depicted in four geologic sketch maps, and seventeen geologic units are defined on the basis of their textural characteristics. The maps and the brief descriptions of geological units portrayed are followed by a series of more interpretive discussions dealing with topical problems and a summary geologic history. Topics covered include cratering, circular basins, volcanism, canyons, chaotic terrain, channels, and eolian activity.

Mccauley, J. F.↗
NASA NTRS1972

Mariner 9 television reconnaissance of Mars and its satellites - Preliminary results.

At orbit insertion, the Martian surface was largely obscured by a dust haze with an extinction optical depth that ranged from near unity in the south polar region to probably greater than two over most of the planet. The only features clearly visible were the south polar cap, one dark spot in Nix Olympica, and three dark spots in the Tharsis region. During the third week, the atmosphere began to clear and surface visibility improved, but contrasts remained a fraction of their normal value. Each of the dark spots that apparently protrude through most of the dust-filled atmosphere has a crater or crater complex in its center. The craters apparently were formed by subsidence and resemble terrestrial calderas.

Masursky, H.↗
NASA NTRS1972

Preliminary geologic map of the region around the candidate Proclus Apollo landing site, part J

The Proclus Crater region was mapped to test the value, for photogeologic mapping purposes, of Apollo 15 metric photographs and to estimate the scientific value of the area as a potential landing site. Adjacent frames of the metric photography were overlapped with the base frame to provide stereographic images. Because of the high quality of the photographs, it was found that the geologic units could be more definitely interpreted and dated than those of earlier maps. The photographs tend to confirm the earlier interpretation of the rugged area as composed of bedrock uplifted when the Crisium basin formed. They also suggest that an earlier predominantly volcanic interpretation of the terra in this area might be replaced by an interpretation in which mass wasting and fracturing play the major roles in producing different terrain types. It was concluded that because of apparent lithologic homogeneity, the terra of the Proclus region is an undesirable objective for an extensive manned lunar landing mission.

Wilhelms, D. E.↗
NASA NTRS1972

Reinterpretations of the northern Nectaris Basin, part F

Photogeologic analysis was attempted on a strip of Apollo 16 metric photographs; the superior quality and stereographic properties of the photography permitted this reevaluation. Geologic contacts, as redrawn closely resemble those of earlier maps, but some differences resulted because of improved photographic quality and a conscious attempt to test fully the impact hypothesis. All or most of the nonmare material of the region of the northern Nectaris Basin rim can be explained by the formation of impact basins. This interpretation seems strained only for some irregular and clustered craters north of Mare Nectaris and for the southern facies of the Descartes material. If the latter material is shown to have been sampled and to be of impact origin, then extensive hill and crater-forming volcanic material of Imbrian or younger age probably does not exist on the lunar terra.

Wilhelms, D. E.↗