The Crater Hausen

Hausen (Figure 12.2, Eratosthenian, 167 km) is the third largest impact feature to have ever followed Oriental, the last of the basins. Of craters that were formed after the Orientale event, only Humboldt (189 km) and Tsiolkovskiy (185 km), both Late Imbrian, are larger than Hausen.

The sudden shift in the size of impact features between the 950 km Orientale and the 189 km Humboldt suggests an abrupt end of the time of large impactors.

Lunar Orbiter High-Resolution Subframes

There are three high-resolution subframes for each of the medium-resolution principal ground points that are labeled in Figure 12.4. In addition, there are four subframes, LO4-196H3, LO4-195H1, LO4-195H2, and LO4-195H3, whose medium-resolution frames are unusable. In general, subframes overlap in the east-west direction, and are presented as mosaics. However, the subframes of LO4-189H, H2, and H3 and LO4-188 H1 and H2 are shown on separate pages.

Figure 12.1. The 950 km Orientale Basin is centered on the far side (20° south, 95° west). This young basin is the archetype for all ringed basins of the Moon. Part of LO4-187M and LO4-181M.

D.OO

-4000.00

-6000.00

D.OO

-4000.00

rim (Mc

ntesCordi

era),-—-v.

ejecla (Helvetius

Formation)

/ ir r^ {•-

termediate juter Monte

ring s Rook)

/

inner ring (inner Mon

tes Rook)

Mars (Ma

e Orientale

Radius (hin)

400 600

Radius (hin)

1000

Figure 12.2. The 167 km Hausen crater (65° south, 88.1° west) is shown at the same scale as the Orientale Basin (Figure 12.1). It is only 15% smaller than Humboldt, the largest crater formed after the Orientale event. Part of LO4-186M.

Figure 12.1. The 950 km Orientale Basin is centered on the far side (20° south, 95° west). This young basin is the archetype for all ringed basins of the Moon. Part of LO4-187M and LO4-181M.

2000.00

North Polar

4-189Mi

Q)

4-196H3

• 4-188M

% CO

,<B Uj

4-195H •

4-187M 4-181M • *

t-ta i

4-194M 4-186M

4-180 M

South Polar

100 w

Figure 12.3. Radial profile of the Orientale Basin, showing the mare, inner ring, intermediate ring, the main ring (rim), and the ejecta blanket. The slope and estimated curvature of the preimpact surface have been removed in this graph. This profile was derived from the Clementine elevation map (Topogrd2, 0.25° resolution; Zuber, 2004). The elevations were averaged over azimuth as a function of radius.

Longitude

70 W

Figure 12.4. This figure labels the principal ground points of the medium-resolution Lunar Orbiter photos included in this chapter. The principal ground points are also shown for LO4-196H3 and LO4-195H, which are combined in a high-resolution mosaic.

For the Lunar Orbiter 4 photos of this chapter, the highresolution subframe H2 is centered on the principal ground point, H3 is to the north of H2, and H1 is to the south of H2.

When the notes accompanying the high-resolution subframes mention specific features, they specify code letters that appear in the images.

in Braun

.avoisier

Russell

Einstéiii

Grimaldi

Montes Cordillara

North Pole

L04-189M

Sun Elevation: 18.36°

Distance: 2882.19 km

The striated ejecta blanket of the Orientale Basin extends from Montes Cordillara to about Röntgen, near 30° north latitude. North of there, the ejecta blanket of Imbrium is exposed where it has not been flooded with mare.

Key for far side features above 40°

Pre-Nectectarian Paneth, 65 km Avicenna, 74km Poczobutt, 195 km

Chapman, 71 km McLaughlin, N?, 79km Onar Khayyam, 70km

Nectarian

Cremona, 85 km Smoluchowski, 21 km

^^Q- Von Braun O Lavoisier H LllughV Beigh \ ' ontgen \

J Balbpa I Balten

;a Valerius

Montes Cordillera

L04-188M

Sun Elevation: 14.52°

Distance: 2677.28 km

Orientale's ejecta blanket has erased or grossly modified nearly all sizable craters in this area, evidence for the decline in the rate of large impact events after the Orientale event.

Key to far side features from 0° north/south to 40° north

Pre-Nectarian

Helberg, 62 km Laue, 87 km Lorentz Basin, 312km Röntgen, 126 km Sundman, N?, 40km

Nectarian

Bell, El?, 86 km Elvey, El?, 74 km Nernst, 1 1 6km Nobel, El?, 48 km

Einstein

Vasco __ ida Gama

MeesQ

tSIushko

■rimatdi

Inner ring

Mare Orientale

O Cruger

Montes Rook

Çolitsyn

Intermediarte ring

Montes— Cordillera

¡Lagrange Piazzi

¡rami Schickard

L04-187M (left) and L04-181M (right)

Distance: -2724 km

This image shows the complex pattern of the Orientale Basin, the internal and external concentric rings and the striations that start at the main ring (Montes Cordillera) and extend to the edge of the ejecta blanket. The rim of the Near Side Megabasin (dashed line) passes through the region dominated by the Orientale Basin, raising the western part of that basin above its eastern part. Because the Near Side Megabasin covers more than half of the Moon, its rim curves away from its center.

Key to far side features from 40° south to 0° north/south

Pre-Nectarian Early Imbrian Eratosthenian

Kopf, N?, 41 km Orientale Basin, 930km Maunder, 55 km

Late Imbrian

Golitsyn, 36 km

Mare ' Orientale

Grim aidi

Montes Cordillera

Lagrange

Mendel-Rydberg

R/dberg ç 1 Guthnick

Inghirami

Mare Humorum

[Yakovkin

ArrheniusQ

Wargentin

Schickard j)-Nasmyth Phocylides

Hausen

The apparent deep valley crossing this image is simply an artifact of the mosaic. The Mendel-Rydberg Basin is more than half as big as the Orientale Basin, but is much more degraded. The best photographic view of the rim of the Near Side Megabasin anywhere is in this image, between Inghirami and the western Montes Cordellaris.

Key to far side features below 40° south

Pre-Nectarian Late Imbrian

Pingre-Hausen Basin, 300km Graff, 36km

Nectarian

Mendel-Rydberg Basin, 630 km

L04-194M (left), L04-186M (upper left), and L04-180M Sun Elevation: -15°

Distance: -3036 km

Montes Cordillera

Orientale B.

Mendel-Rydberg B.

Pingre

L04-193M

Sun Elevation: 10.31°

Distance: 3557.30 km

The area between the Orientale Basin and Bailly is rich in impact features younger than the Orientale Basin; their ejecta patterns lie on top of that from Orientale, and could be easily sampled. The rim of the proposed Near Side Megabasin would provide relatively pristine crust as the target material for these features.

Nectarian

Bailly, 287km Pingre, 88 km

Early Imbrian

Fenyi, 38 km Orientale Basin, 930km

Late Imbrian

Baade, 55 km Chant, 33 km Steklov, 36 km

Erastosthenian

Hausen, 167km Rydberg, 49 km

Copernican

Guthnik, 36 km

The features in this image are all on the near side, but it introduces the boundary between Oceanus Procellarum and the rising crust within the Near Side Megabasin. The interplay between the mare flood and the earlier cratered features is clearly illustrated by the stress cracks in Repsold (R, 109 km). These cracks were probably opened by contraction of the basaltic mare as it cooled. Further spreading of fractures may be due to upward pressure by intrusion of magma beneath Repsold.

ii w

01 "O

LO4-189H2

Sun Elevation: 18.36°

Distance: 2882.19 km

LO4-189H2

Sun Elevation: 18.36°

Distance: 2882.19 km

The area around and to the northwest of Gerard (G, 90 km) is somewhat puzzling. Gerard itself may be two or three separate craters that have left an overlapping pattern. Further, there may be a very old pre-Nectarian basin whose center is just beyond the upper left corner of this subframe. The entire area appears to have been flooded with mare, but at an older time than the fresh mare surface of Oceanus Procel-larum to the east. Von Braun (VB, 22 km) is named after the engineer who led the Saturn 5 project, which brought men to the Moon.

LO4-189H1

Sun Elevation: 18.36°

Distance: 2882.19 km c

LO4-189H1

Sun Elevation: 18.36°

Distance: 2882.19 km

The dark area between Aston (A, 43 km) and Voskresen-sky (V, 49 km) is mapped as Imbrium ejecta, but seems to have the characteristics of a dark plains deposit, sometimes seen on the margins of maria on the near side. Voskresensky shows some flooding by mare mate rial, which may be just beneath the surface here. There are signs that the upward pressure of lava has lifted a melt sheet on the floor of Voskresensky. The ray passing south of Voskresensky has come from Ohm, far to the southwest.

This is a mosaic of adjacent subframes, spanning from 98° west longitude to 85° west longitude. The uniform sizes of the small craters indicate they are secondaries from the Orientale Basin. The field of secondaries surrounding Orientale is called the Outer Hevelius Formation. The secondary impactors must have been coherent bodies whose diameters were of the order of 1 km in order to form these craters, whose typical diameter is about 10 km. The scale of this image can be determined from the size of Bell (B, 86 km). Bell has received some of these Orientale secondaries, but also has older craters that show more erosion. It is assigned to the Nectarian Period, but could be either pre-Nectarian or Early Imbrian.

LO4-188H2

Sun Elevation: 14.52°

Distance: 2677.28 km c

LO4-188H2

Sun Elevation: 14.52°

Distance: 2677.28 km

The large crater in the top of this subframe has been named to honor Albert Einstein (E, 198 km). Bohr (Bo, 71 km) is younger, of the Nectarian Period. Einstein A (EA, 51 km) appears free of Orientale ejecta, but a few substantial craters have impacted it, indicating it was formed in the Late Imbrian Period. The edge of the Near Side Megabasin runs through this image (dashed line). To the right is the interior of that basin and to the left is the fragmented, porous rim. Although there are no identifiable features of the rim here, the upward slope of the rim causes the greater average brightness west of the dashed line.

This entire subframe shows a sector of the ejecta blanket of the Orientale Basin, called the Inner Hevelius Formation. The northern arc of Montes Cordillera runs just below the bottom edge of this image. The chaotic radial pattern of the ridges and troughs is clearly illuminated by the low sun angle. Faint outlines of craters that have been buried by the ejecta have survived. Maunder A (MA, 15 km) is the only feature available for scale here.

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