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Geology: Regional setting
ICARUS 12, 161-166
(1370)
Geology:
Regional
Setting1
E. C. MORRIS U.S. Geological Survey, Flagstaff, Arizona 86001 The first four successful Surveyor spacecraft landed on broad mare plains. Surveyor I landed on a gently undulating mare surface partly enclosed by the rim of a large, nearly buried crater about 100 km in diameter (Fig. 1) in the southern part of Oceanus Procellarum. The mare material in the eastern half of this crater is considerably darker than the more typical mare material of Oceanus Procellarum, and the Surveyor I site is on the dark mare material. No large rays are found in fullmoon photographs of this area. 1 References for the first three Geology papers are collected at the end of the fourth paper, Physics of Fragmental Debris. Figures for the four Geology papers are numbered consecutively.
Surveyor III landed about halfway up the inner, northwest-facing slope of a 200-m-wide, subdued crater (Fig. 2) located in the eastern part of Oceanus Procellarum, about 120 km southeast of the crater Lansberg (Fig. 3a). The Surveyor III site is crossed by faint rays from the large crater Copernicus (Fig. 3b), 400 km to the north. About 20 km west of the site, the mare surface is broken by rough, hummocky terrain and numerous isolated hills of the Frau Mauro formation of Imbrian age (Eggleton, 1965). Low mare ridges and hummocky terrain form the eastern boundary of the smooth patch of mare material upon which Surveyor III rests. Surveyor V landed in the southwestern
FIG. 1. Lunar Orbiter IV photograph k-143 of the Surveyor I landing site. Hills north of the landing site, which are part of the rim of the buried crater 100 km in diameter, can be seen in Surveyor panoramas. 161
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F ‘IG. 2. Small part of Lunar Orbiter III photograph H-154 showing location of Surveyor III in a 200 -meter-diameter crater. The small triangle represents the true size and orientation of the spacecraft.
part of Mare Tranquillitatis in the eastern part of the Moon (Fig. 4), about 70 km north of the southern boundary of the mare. The region is crossed by faint rays associated with the large crater Theophilus, 350 km to the south. The highlands to the west of Mare Tranquillitatis are characterized by prominent northwest-trending ridges and valleys, which are part of a system of ridges and valleys known as the Imbrian sculpture. High-resolution Lunar Orbiter photographs of an area near the Surveyor V site reveal many craters about 10 meters across which are also aligned in a northwest direction. Some individual craters are markedly elongate in this same direction. These craters may be drainage or collapse craters that are structurally controlled by subsurface fissures and
fractures that are related to the Imbrian sculpture. Surveyor V came to rest in one of these small, elongate, rimless craters. The Surveyor V crater is about 9 meters wide, 12 meters long, and about 1 meter deep. Surveyor VI landed in Sinus Medii, an isolated patch of mare material near the center of the sub-Earth side of the Moon (Fig. 5). The surface of Sinus Medii has a higher average albedo than most of the maria. The detailed shapes and trends of mare ridges, crater chains, and small shallow trenches on Sinus Medii reflect the dominant structural patterns that occur in the highlands that surround the maria. The most conspicuous structural pattern in the highlands is the northwest-trending Imbrian sculpture. The second most prom-
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: REGIONAL
SETTING
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EhG. 3. The Surveyor III landing site. (a) The crater Lansberg and region to the southwest shlowing the Stnveyor III location (small circle). The low evening illumination emphasizes the low mare rid&:e 5segments northeast of the landing site and the rough, hummocky topography northv rest of the la1xding site (photograph taken with the 82-inch reflector at McDonald Observatory). (b) Same r egion as Fig. 3(a) with full-moon illumination showing relationship between Surve, or III lo cation (smtall circle) and Copernicus rays (photograph taken with a 40-inch refractor at Yerkes Observe ttory).
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FIG. 4. Earth-based, telescopic photograph of Mare Tranquillitatis and the highlands to the west. Prominent northwest-trending ridges and valleys in the highlands are part of Imbrian sculpture (photograph taken through the 36-inch refractor at Lick Observatory).
inent set oflinear structures is a northeasttrending system of scarps and ridges. The most prominent topographic feature in the vicinity of the landed Surveyor VI is a mare ridge about 40 km long that follows a zig-zag pattern and trends generally east-west (Fig. 6). Individual elements of the ridge trend northwest and northeast. The ridge is somewhat smaller than ridges that have been studied through Earth-based telescopes, but it is the first such feature to be studied from a landed spacecraft. Surveyor VII, the only spacecraft sent to a highland area, landed on the outer flank of the rim of the crater Tycho, one of the most prominent and well known features in the lunar highlands (Fig. 7). The crater is surrounded by the most conspicuous and extensive system of bright rays on the sub-Earth side of the Moon.
From the crest, extending outward a distance of 10 to 15 km, the rim of Tycho is composed of irregular hills and intervening depressions. From 15 km to a radial distance of about 35 to 40 km, the surface is marked by numerous subradial ridges and valleys, typically 2 to 5 km in length and 3 to 1 km in width, superimposed on a broadly undulating surface. Surveyor VII landed about 30 km north of the rim crest of Tycho on the part of the rim flank marked by these linear ridges. The rim of Tycho is composed of debris, probably ejected from the crater during its formation, and a sequence of flows that form mappable geologic units. The ilows range in form from hummo,cky, steepfronted flows to smooth-surfaced flows without marginal scarps. The differences in form are attributed to differences in viscosity of the flows at the time they
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FIG. 5. Earth-based telescopic photograph of the central region of the Moon. The white circle indicates the location of Surveyor VI (photograph taken through the 100-inch telescope at Mt. Wilson Observatory).
FILG. 6. Lunar Orbiter II photograph M-113 of Sinus Medii. The Surveyor VI landing site is indic:ated by the white circle. A mare ridge, which passes just south of the Surveyor VI landing site, can be seen extending across the center of the picture.
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FIG. 7. Lunar Orbiter V rJhotoaraph M-127 of the crater Tycho and its northern flank. The arrow points to the Surveyor VII-land& site.
came to rest. Surveyor VII landing site is on one of the flows whose surface is composed of irregular, low hills and depressions ranging from 100 m to several hundred meters across with scattered blocks, small craters, and swarms of north-trending
fissures that occur on the flow’s crest. The Surveyor VII landing site is geologically more complex and contains a greater variety of rock fragments than any of the Surveyor landing sites on the maria.
(1370)
Geology:
Regional
Setting1
E. C. MORRIS U.S. Geological Survey, Flagstaff, Arizona 86001 The first four successful Surveyor spacecraft landed on broad mare plains. Surveyor I landed on a gently undulating mare surface partly enclosed by the rim of a large, nearly buried crater about 100 km in diameter (Fig. 1) in the southern part of Oceanus Procellarum. The mare material in the eastern half of this crater is considerably darker than the more typical mare material of Oceanus Procellarum, and the Surveyor I site is on the dark mare material. No large rays are found in fullmoon photographs of this area. 1 References for the first three Geology papers are collected at the end of the fourth paper, Physics of Fragmental Debris. Figures for the four Geology papers are numbered consecutively.
Surveyor III landed about halfway up the inner, northwest-facing slope of a 200-m-wide, subdued crater (Fig. 2) located in the eastern part of Oceanus Procellarum, about 120 km southeast of the crater Lansberg (Fig. 3a). The Surveyor III site is crossed by faint rays from the large crater Copernicus (Fig. 3b), 400 km to the north. About 20 km west of the site, the mare surface is broken by rough, hummocky terrain and numerous isolated hills of the Frau Mauro formation of Imbrian age (Eggleton, 1965). Low mare ridges and hummocky terrain form the eastern boundary of the smooth patch of mare material upon which Surveyor III rests. Surveyor V landed in the southwestern
FIG. 1. Lunar Orbiter IV photograph k-143 of the Surveyor I landing site. Hills north of the landing site, which are part of the rim of the buried crater 100 km in diameter, can be seen in Surveyor panoramas. 161
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REPORTS
F ‘IG. 2. Small part of Lunar Orbiter III photograph H-154 showing location of Surveyor III in a 200 -meter-diameter crater. The small triangle represents the true size and orientation of the spacecraft.
part of Mare Tranquillitatis in the eastern part of the Moon (Fig. 4), about 70 km north of the southern boundary of the mare. The region is crossed by faint rays associated with the large crater Theophilus, 350 km to the south. The highlands to the west of Mare Tranquillitatis are characterized by prominent northwest-trending ridges and valleys, which are part of a system of ridges and valleys known as the Imbrian sculpture. High-resolution Lunar Orbiter photographs of an area near the Surveyor V site reveal many craters about 10 meters across which are also aligned in a northwest direction. Some individual craters are markedly elongate in this same direction. These craters may be drainage or collapse craters that are structurally controlled by subsurface fissures and
fractures that are related to the Imbrian sculpture. Surveyor V came to rest in one of these small, elongate, rimless craters. The Surveyor V crater is about 9 meters wide, 12 meters long, and about 1 meter deep. Surveyor VI landed in Sinus Medii, an isolated patch of mare material near the center of the sub-Earth side of the Moon (Fig. 5). The surface of Sinus Medii has a higher average albedo than most of the maria. The detailed shapes and trends of mare ridges, crater chains, and small shallow trenches on Sinus Medii reflect the dominant structural patterns that occur in the highlands that surround the maria. The most conspicuous structural pattern in the highlands is the northwest-trending Imbrian sculpture. The second most prom-
GEOLOGY
: REGIONAL
SETTING
163
EhG. 3. The Surveyor III landing site. (a) The crater Lansberg and region to the southwest shlowing the Stnveyor III location (small circle). The low evening illumination emphasizes the low mare rid&:e 5segments northeast of the landing site and the rough, hummocky topography northv rest of the la1xding site (photograph taken with the 82-inch reflector at McDonald Observatory). (b) Same r egion as Fig. 3(a) with full-moon illumination showing relationship between Surve, or III lo cation (smtall circle) and Copernicus rays (photograph taken with a 40-inch refractor at Yerkes Observe ttory).
164
SURVEYOR
FINAL
REPORTS
FIG. 4. Earth-based, telescopic photograph of Mare Tranquillitatis and the highlands to the west. Prominent northwest-trending ridges and valleys in the highlands are part of Imbrian sculpture (photograph taken through the 36-inch refractor at Lick Observatory).
inent set oflinear structures is a northeasttrending system of scarps and ridges. The most prominent topographic feature in the vicinity of the landed Surveyor VI is a mare ridge about 40 km long that follows a zig-zag pattern and trends generally east-west (Fig. 6). Individual elements of the ridge trend northwest and northeast. The ridge is somewhat smaller than ridges that have been studied through Earth-based telescopes, but it is the first such feature to be studied from a landed spacecraft. Surveyor VII, the only spacecraft sent to a highland area, landed on the outer flank of the rim of the crater Tycho, one of the most prominent and well known features in the lunar highlands (Fig. 7). The crater is surrounded by the most conspicuous and extensive system of bright rays on the sub-Earth side of the Moon.
From the crest, extending outward a distance of 10 to 15 km, the rim of Tycho is composed of irregular hills and intervening depressions. From 15 km to a radial distance of about 35 to 40 km, the surface is marked by numerous subradial ridges and valleys, typically 2 to 5 km in length and 3 to 1 km in width, superimposed on a broadly undulating surface. Surveyor VII landed about 30 km north of the rim crest of Tycho on the part of the rim flank marked by these linear ridges. The rim of Tycho is composed of debris, probably ejected from the crater during its formation, and a sequence of flows that form mappable geologic units. The ilows range in form from hummo,cky, steepfronted flows to smooth-surfaced flows without marginal scarps. The differences in form are attributed to differences in viscosity of the flows at the time they
GEOLOGY
: REGIONAL
SETTING
165
FIG. 5. Earth-based telescopic photograph of the central region of the Moon. The white circle indicates the location of Surveyor VI (photograph taken through the 100-inch telescope at Mt. Wilson Observatory).
FILG. 6. Lunar Orbiter II photograph M-113 of Sinus Medii. The Surveyor VI landing site is indic:ated by the white circle. A mare ridge, which passes just south of the Surveyor VI landing site, can be seen extending across the center of the picture.
166
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FINAL REPORTS
FIG. 7. Lunar Orbiter V rJhotoaraph M-127 of the crater Tycho and its northern flank. The arrow points to the Surveyor VII-land& site.
came to rest. Surveyor VII landing site is on one of the flows whose surface is composed of irregular, low hills and depressions ranging from 100 m to several hundred meters across with scattered blocks, small craters, and swarms of north-trending
fissures that occur on the flow’s crest. The Surveyor VII landing site is geologically more complex and contains a greater variety of rock fragments than any of the Surveyor landing sites on the maria.