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D. H. Scott

Publications and source records attributed to D. H. Scott.

51 records · Page 3Linked to original sources
USGS1980

Lunar remote sensing and measurements

Remote sensing and measurements of the Moon from Apollo orbiting spacecraft and Earth form a basis for extrapolation of Apollo surface data to regions of the Moon where manned and unmanned spacecraft have not been and may be used to discover target regions for future lunar exploration which will produce the highest scientific yields. Orbital remote sensing and measurements discussed include (1) relative ages and inferred absolute ages, (2) gravity, (3) magnetism, (4) chemical composition, and (5) reflection of radar waves (bistatic). Earth-based remote sensing and measurements discussed include (1) reflection of sunlight, (2) reflection and scattering of radar waves, and (3) infrared eclipse temperatures. Photographs from the Apollo missions, Lunar Orbiters, and other sources provide a fundamental source of data on the geology and topography of the Moon and a basis for comparing, correlating, and testing the remote sensing and measurements. Relative ages obtained from crater statistics and then empirically correlated with absolute ages indicate that significant lunar volcanism continued to 2.5 b.y. (billion years) ago-some 600 m.y. (million years) after the youngest volcanic rocks sampled by Apollo-and that intensive bombardment of the Moon occurred in the interval of 3.84 to 3.9 b.y. ago. Estimated fluxes of crater-producing objects during the last 50 m.y. agree fairly well with fluxes measured by the Apollo passive seismic stations. Gravity measurements obtained by observing orbiting spacecraft reveal that mare basins have mass concentrations and that the volume of material ejected from the Orientale basin is near 2 to 5 million km 3 depending on whether there has or has not been isostatic compensation, little or none of which has occurred since 3.84 b.y. ago. Isostatic compensation may have occurred in some of the old large lunar basins, but more data are needed to prove it. Steady fields of remanent magnetism were detected by the Apollo 15 and 16 subsatellites, and the lunar dipole field was revised to no more than 6x 10 19 gauss. High-resolution mapping of fields of weak remanent magnetism (to 0.1 gamma) was made possible by the Apollo plasma and energetic-particle experiment. Although the causes of remanent magnetism are poorly understood, correlations with geologic units suggest the results may ultimately have farreaching significance to lunar history. Maria are much less structured by strong surface magnetic anomalies than the highlands. The strongest anomalies are associated with ejecta of farside basins, plains materials filling pre-Imbrian craters, and other old Imbrian to pre-Imbrian units. The high remanent fields could be due to cooling of ejecta units in an ancient magnetic field, lunar regolith maturity, extensive reworking and disruption of a magnetized layer, or simply surface roughness. Orbital geochemical experiments have shown that lunar high lands have larger Al: Si ratios and smaller Mg: Si ratios than maria. These two ratios are inversely related on a regional basis. With the exception of fresh craters, albedo and Al : Si ratios vary directly, showing that compositional differences as well as exposure of fresh materials are responsible for high albedos. Statistically treated data show that geologic contacts and compositional boundaries are concentric and can be roughly matched. Some craters on mare material have penetrated the mare fill, bringing highland-type materials to the surface. Natural radioactivity from thorium, potassium, and uranium is inversely correlated with elevation. Mare regions are enriched in iron, titanium, and magnesium relative to the highlands. Orbital bistatic-radar results provide estimates of surface roughness at two scale lengths (about 30 m and 250 m), which agree with visual estimates of roughness. The dielectric constant of the lunar surface, where sampled, is uniform to 13-cm radar and near 3. Slope frequency distributions measured by the radar vary and

Professional Paper↗
USGS1978

Mars, highlands-lowlands: Viking contributions to mariner relative age studies

Stratigraphic relations between lowland plains and highlands, two major types of Martian geologic-terrain units, were not directly distinguishable on Mariner-9 images. Morphologic characteristics and crater densities suggested that the lava plains beneath their eolian cover were younger than adjacent highland rocks, which form a plateau bounded in many places by highly dissected escarpments. Alternatively, the lowland plains could be the older unit and represent a broad erosional surface exhumed by southward retreat of the highlands along their frontal scarp. Viking photos across five areas of the highland-lowland boundary, however, tend to confirm the younger age of the plains-forming lava flows. A time interval of several hundred million years probably occurred between the retreat of the highland scarp and its latest embayment by lava extrusions in the lowlands. ?? 1978.

Icarus↗
USGS1978

Geologic map of the Aeolis Quadrangle of Mars

Two principal physiographic provinces of Mars are represented in the Aeolis quadrangle: (1) Elysium Plan itia in the north is part of a broad planet-encircling belt of relatively young lowland plains, and (2) cratered highlands in the south consist of roughly primitive terrain that extends to polar deposits around the southern ice cap (Condit and Soderblom, 1978: Scott and Carr , 1978). These two terrains are separated by an irregular discont inuous northwest-trending scarp that becomes less conspicuous and more segmented toward the east part of the ma p area. Two large channels transect the highlands; they widen northward downslope and have other features cha racteristic of terrestrial river beds . However, now fans or deltaic forms are visible at their mouths and their floors merge with the plains. One large shield volcano, Apollinaris Patera, projects above the plains adjacent to the highlands in the northeast part of the quadrangle. More than 4 km of relief occur across the region from the high plateau in the south and west, downslope northward to plains.

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USGS1977

Moon-Mercury: Relative preservation states of secondary craters

Geologic mapping of the Kuiper quadrangle of Mercury and other geologic studies of the planet indicate that secondary craters are much better preserved than those on the moon around primary craters of similar size and morphology. Among the oldest recognized secondary craters on the moon associated with craters 100 km across or less are those of Posidonius, Atlas and Plato; these craters have been dated as middle to late Imbrian in age. Many craters on Mercury with dimensions, morphologies and superposed crater densities similar to these lunar craters have fields and clusters of fresher appearing secondary craters. The apparent differences between secondary-crater morphology and parent crater may be due in part to: (1) rapid isostatic adjustment of the parent crater; (2) different impact fluxes between the two planets; and (or) (3) to the greater concentration of Mercurian secondaries around impact areas, thereby accentuating crater forms. Another factor which may contribute to the better state of preservation of Mercurian secondaries relative to the moon is the difference in crater ejecta velocities on both bodies. These velocities have been calculated for fields of secondary craters at about equal ranges from lunar and Mercurian parent craters. Results show that ejection velocities of material producing most of the secondary craters are rather low (<1 km/s) but velocities on Mercury are about 50% greater than those on the moon for equivalent ranges. Higher velocities may produce morphologically enhanced secondary craters which may account for their better preservation with time. ?? 1977.

Physics of the Earth and Planetary Interiors↗
USGS1977

Geologic map of the west side of the Moon

The west limb region of the M oon consists of highly cratered terra rising 5 km or more above the mare of Oceanus Procellarum and most of the lunar near side. Crustal material in this area of large basins and craters has been redistributed repeatedly by giant impacts. The early historical record of these events is apparently preserved in a complex of interlayered breccias, which may be partly exposed in the walls of the larger craters. Orientale, the last multiringed basin, was formed early in lunar history during the wanning stages of high impact flux by a large body probably impacting the surface obliquely from the northeast. Ejecta from this impact was widely scattered by over the Moon and appears to form some of the plains materials. Although the major landforms of the Oriental basin were developed instantaneously in geologic terms, isostatic adjustments were more protracted; the accompanying structural dislocations including concentric and radial faults in the floor material may have continued u p to the time of mare basalt flooding after basin formation. Subsequent impacts have produced craters generally less than 60 km diameter.

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USGS1977

The geological investigation of the Taurus-Littrow Valley: Apollo 17 landing site

Astronauts Cernan and Schmitt, of Apollo 17, landed in the Taurus-Littrow valley of the Moon on December 11, 1972. Their major objectives were: (1) to sample very ancient lunar material such as might be found in pre-Imbrian highlands as distant as possible from the Imbrium basin, and (2) to sample pyroclastic materials that had been interpreted as significantly younger than the mare basalts returned from previous Apollo landing sites. The crew worked approximately 22 hours on the lunar surface; they traversed about 30 km, collected nearly 120 kg of samples, took more than 2,200 photographs, and recorded many direct geologic observations. The lunar surface data, sample results, and geologic interpretation of orbital photographs are the bases for this geologic synthesis. The Taurus-Littrow massifs are interpreted as the upper part of thick faulted ejecta deposited on the rim of the transient cavity of the large southern Serenitatis basin, which was formed by a meteor impact about 3.9 to 4.0 b.y. ago. The target rocks, predominantly of the dunite-anorthosite-norite-troctolite suite or its metamorphosed equivalents, were fractured, sheared, crushed, and melted by the impact. The resulting mixture of crushed rock and melt was transported up and out of the transient cavity and deposited on and beyond its rim. Hot fragmental to partly molten ejecta and relatively cool cataclasite and relict target rocks were intermixed in a melange of lenses, pods, and veins. Crystallization of melts and thermal metamorphism of fine-grained fragmental debris produced breccia composed of lithic and mineral fragments in a fine-grained, coherent, crystalline matrix. Such breccia dominates the massif samples. Faults that bound the massifs were activated during formation of the basin, so that structural relief of several kilometers, due to high-angle faulting, was imposed on the ejecta almost as soon as it was deposited. Massive slumping, that produced thick wedges of colluvium on the lower massif slopes, probably occurred nearly contemporaneously with the faulting. Sculptured Hills material, perhaps largely cataclasite excavated from the southern Serenitatis basin by the same impact, was then deposited on and around the faulted ejecta of the massifs. Subfloor basalt, estimated to be about 1,400 m thick in the landing site, flooded the Taurus-Littrow graben prior to approximately 3.7 b. y. ago. The basalt is part of a more extensive unit that was broadly warped and cut by extensional faults before the accumulation in Mare Serenitatis of younger, less deformed basalts that overlap it. A thin volcanic ash unit, probably about 3.5 b. y. old, mantled the subfloor basalt and the nearby highlands. It, too, was subsequently overlapped by the younger basalts of Mare Serenitatis. In the time since deposition of the volcanic ash, continued bombardment by meteors and secondary projectiles has produced regolith, a mechanical mixture of debris derived mainly from the subfloor basalt, the volcanic ash, and the rocks of the nearby massifs and Sculptured Hills. The regolith, in combination with the underlying volcanic ash, forms an unconsolidated surficial deposit with an average thickness of about 14 m, sufficiently thick to permit abnormally rapid degradation of the smaller craters, especially those less than 200 m in diameter, so as to create a surface that seems less cratered than do other mare surfaces. Admixture of volcanic ash gives the surface a distinctive dark color, which, in combination with the less cratered appearance, led to the pre-mission interpretation of a young dark mantling unit. The uppermost part of the regolith in the landing area is basalt rich ejecta from the clustered craters of the valley floor. Most of the craters are interpreted as part of a secondary cluster formed by projectiles of ejecta from Tycho. When they struck the face of the South Massif, the projectiles mobilized fine-grained regolith material that was redeposited on the valley floor as the light mantle. Exposure ages suggest that the swarm of secondary projectiles struck the Taurus-Littrow area about 100 m.y. ago. The Lee-Lincoln fault scarp is part of an extensive system of wrinkle ridges and scarps that transect both mare and highlands rocks. The scarp cuts the crater Lara, but the major part of the displacement occurred before deposition of the light mantle. Minor post-light mantle displacement is shown by small extensional faults that cut its surface west of the Lee-Lincoln scarp.

Open-File Report↗
USGS1973

Geologic map of the Rumker Quadrangle of the Moon

The Rumker quadrangle, in the northwest quadrant of the Moon, is adjacent to the western rim of the multi-ring Imbrium basin and to Sinus Iridum , a large (220 km diameter) mare-filled crater. Both of these great depressions were probably formed by impa c t, as indicated here and elsewhere on the Moon by the characteri stic form, distribution, and texture of surrounding materials and structures. The Imbrium b asin and Iridum crater were filled by mare mat erials during the Imbrain and Eratosthenian Periods. In this quadrangle, the widespread ejecta blanke t of the Imbrium basin, as well as the basin’s concentric ridges and mountain rings, has largely been buried by terra materials of mixed origin and by ejecta from Iridum and numerous smaller impact craters. These materials , together with some terra units of probable volcanic origin, make up the highland terrain. Mare materials of Oceanus Procellarum cover part of t his westward-sloping highland shelf that separate it from the Rumker Hills, an isolated plateau surrounded by the mare. No visible discontinuity distinguishes mare material of Oceanus Procella rum from those in the Imbrium basin, both of which contain several units having similar albedo and color. Parts of the mare are very dark and smooth and appear relatively young, and parts of the terra contain many diverse landforms of Imbrian and younger age that appear to be volcanic . This region may therefore have been more active internally during late stages of lunar history than many others on the near side.

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USGS1973

Preliminary geologic investigation of the Apollo 17 landing site

The Apollo 17 lunar module (LM) landed on the flat floor of a deep valley that embays the mountainous highlands at the eastern rim of the Serenitatis basin. Serenitatis, the site of a pronounced mascon, is one of the major multi-ringed basins on the near side of the Moon. The Taurus-Littrow valley, which is radial to the Serenitatis basis, is interpreted as a deep graben formed by structural adjustment of lunar crustal material to the Serenitatis impact.

Book chapter↗
USGS1972

The geologic setting of the Luna 16 landing site

The Luna 16 landing site is similar in its geologic setting to Apollos 11 and 12. All three sites are located on basaltic mare fill which occurs mostly within multi-ring basins formed by impact earlier in the moon's history. A regolith developed by impact bombardment is present at each of these sites. The regolith is composed mostly of locally derived volcanic material, but also contains exotic fine fragments that have been ballistically transported into the landing sites by large impact events which formed craters such as Langrenus and Copernicus. These exotic fragments probably consist mostly of earlier reworked multi-ring basin debris and, although not directly traceable to individual sources, they do represent a good statistical sample of the composition of most of the premare terrac regions.

Earth and Planetary Science Letters↗
USGS1972

Geologic map of the Maurolycus Quadrangle of the Moon

The Maurolycus quadrangle , located in the southeastern highlands, includes densely to moderately cratered terrain with many craters larger than 45 km in rim crest diameter . Several appea r to be ancient and may be among the most primitive discernable features on the lunar surface. Major stratigraphic units consist of the Janssen Formation, hummocky terra and pitted plains materials, and e xtensive clusters of bowl-shaped craters. Two of these units, hummocky terra and pitted plains , a re probably volcanic whereas the Janssen Formation and bowl-shaped craters appear t o have been formed by ejecta from the multi-ringed Nectaris and Imbrium basins outside the quadrangle.

IMAP↗
USGS1972

Geologic map of the Eudoxus Quadrangle of the Moon

The Eudoxus quadrangle is in the northeastern part of the Moon’s nearside hemisphere . It is bordered on the west by Montes Caucasus, which form part of the main rim of the multi-ring Imbrium basin (Hartmann and Kuiper, 1962), and on the south side by Mare Seren itatis, which occupies another large multi-ringed basin. South and east of the prominent crater Eudoxus ele v ations decrease and the rugged highland terrain becomes more subdued and covered by mare materials in the Serenitatis basin, Lacus Somniorum , and Lacus Mortis.

IMAP↗
USGS1972

Geologic map of the Macrobius Quadrangle of the Moon

The Macrobius quadrangle is in the northeast quadrant of the Moon’s near side. Although predominantly a highland area centered around the Taurus Mountains (Montes Taurus) , it is bounded by three major mare-filled basins: Tranquillitatis , the oldest, to the south; Seren itatis to the west; and Crisium on the east. Most of the geologic units within the quadrangle have been profoundly affected by the forma tion of these basins and by that of the younger Imbrium basin farther to the northwest. Some of the youngest material on the Moon, believed to be of volcanic origin, blanke ts part of the mare and terra along the southwest margin of the map. Sampling this material will be a primary objective of the Apollo 17 mission, whose proposed landing site is approximately at lat. 20 ˚ 10’ N ., long. 30 ˚ 45’ E. near the western edge of the map area.

IMAP↗
USGS1972

Geologic maps of the Taurus-Littrow region of the Moon Apollo 17 pre-mission maps

The Taurus-Littrow region is mainly a highland area at the juncture of Mare Serenitatis and Mare Tranquillitatis (Scott and Pohn , 1972). Highland materials cover most of the area, forming a group or rugged massifs close to the center of the map and more subdued terrain to the east. The highland units ( pItm , IpIh ) are probably mostly breccias formed by the Serenita ti s impact and pre-existing breccias excavated by this event. Younger Crisium and Imbrium ejecta may also be present but cannot be distinguished . To the west and southwest materials typical of lunar maria, almost certainly basalts, encroach upon and embay the highland terrain. Also in the west is a unit of special interest, a relatively young, usually dark material that mantles both terra and mare. It is draped over a wide variety of terrains in much of the western half of the map area and is interpreted as pyroclastic volcanics. The Apollo 17 site lies on this dark mantling material where it covers an embayment of mare materials between upland massifs. At this locality, therefore, relatively young volcanic can be samples as well as the ancient deposits that form the highland massifs.

IMAP↗