Pre-Nectarian Period

Brianchon, N?, 134km Hermite, 104 km Hippocrates, 60km Rozhdestvensky, 177 km Seares, 1 1 0km Thiesssen, 66 km

Nectarian Period

Froelich, 58 km Nansen, PN?, 104 km Merrill, 57km Mezentsev, El?, 89km Milankovic, 1 01 km Niepce, 57km Roberts, 89 km Schwarzschild, 212 km Shi Shen, 43 km

Early Imbrian Period

Heymans, 50km Karpinsky, 9km

Late Imbrian Period

Lovelace, 54 km Plaskett, 109 km

Eratosthenian Period

Ricco, 65 km

This north polar cap base image is an orthographic projection from the pole to 70° The far side is in the lower half of this image; the near side is on the upper half. The north latitude. It is derived from Clementine visual data from the NRL. This image, craters listed by period in the key above are all on the far side, processed by USGS, is from the 1PL web page.

Near Side

180 E/W

Far Side

North Polar Cap

The North Pole is within the cavity of the Near Side Megabasin and that of the South Pole-Aitken Basin. The Birkhoff ejecta blanket is in the eastern far side, below 80° north latitude. Ejecta from the Humboldtianum Basin softened the limb near 90° east longitude. The area from 135° to 180° east longitude is relatively free of basin ejecta later than that of the South Pole-Aitken Basin and therefore displays Nectarian craters Milankovic and Seares clearly.

The topography within 5° of the North Pole is dramatically lighted by the low sun angle, making it appear more rugged. It also is actually less smoothed by ejecta because the pole is near the edge of the ejecta blankets described above.

The crater walls that were shadowed during the Clementine mission are illuminated at other times of the year, because of the 1.5° tilt of the lunar axis relative to the plane of the Earth's orbit around the sun. There are no large areas of permanent shadow near the North Pole.

Far Side Region


Bel'kovich K



Northwest Far Side: Western Sector


Schwarzschild, 212 km Vol terra, PN?, 52 km

Early Imbrian

Compton, 162 km


Bel'kovich K, 47 km

Schwartzschild arrived in the Nectarian Period, somewhat later than the formation of the Humboldtianum Basin. Schwartzschild rests on the rim and ejecta blanket of that basin and has obscured its rim. The sharp, young crater in the northern floor of Belkovich, designated as Belkovich K, is the only crater assigned to the Copernican

Period on the far side within 30° of either the North or South Poles. Compton is a feature of the Early Imbrian Period. Note that few craters have impacted either its floor or extensive ejecta blanket.

Northwest Far Side: Western Sector, 55° north to 75° north, 90° east to 135° east The North Polar ^^ Far Side Region

ichjellerup ■

Avogadro singer



> Stormer

Northwest Far Side: Central Sector

Pre-Nectarian Period

Avogadro, 139 km Gamow, 129 km Olivier, 69 km Sea res, 1 10km Stormer, 69 km Tikhov, 83 km Tsinger, 44 km Yamamoto, 76 km

Nectarian Period

Oberth, 60 km

Early Imbrian Period

Karpinsky, 92 km

Late Imbrian Period

Schjellerup, 62 km

Eratosthenian Period

Ricco, 65 km

The depression of the Near Side Megabasin is north of the rim line shown here. The rim of the Near Side Megabasin bends away from the basin's center (on the near side) because the basin covers more than half of the Moon's globe. Relative to other sectors, this one is free of basin ejecta younger than that of the South Pole-Aitken Basin, and so it shows greater detail of older craters.

The youngest crater here is Ricco, assigned to the Eratosthenian Period. Schjellerup is older, assigned to the Late Imbrian Period. Karpinsky is even older, of the Early Imbrian Period.

Northwest Far Side: Central Sector, 55° north to 75° north, 135° east to 180° east/west The North Polar ^^ Far Side Region

Heymans i^a





Birkhoff Z



Northeast Far Side: Central Sector

Pre-Nectarian Period

Birkhoff, 345km Emden, 1 1 1 km Hippocrates, 60km Stebbins, 131 km Thiesssen, 66km


Roberts, 89 km Rowland, 1 71 km Sommerfeld, 169 km

Early Imbrian

Heymans, 50 km

Eratosthenian Period


Copernican Period

Birkhoff Z, 30 km

The northern edge of the Near Side Megabasin continues here. Because of scalloping, the actual rim may be as much as 5° of latitude away from the dotted line, the elliptic edge predicted by the model based on the Clementine elevation data.

Stebbins is clearly younger than Birkhoff, although both are of the pre-Nectarian Period. Birkhoff Z, the sharp crater on the floor of Birkhoff near Stebbins, is assigned to the Copernican Period. An even younger small crater on its floor causes the brightness that could be mistaken for a peak.

Northeast Far Side: Central Sector, 55°north to 75°north, 135°west to 180°east/west The North Polar ^^ Far Side Region

Lindblad F

Cremona i Paneth


Northeast Far Side: Eastern Sector

Pre-Nectarian Period

Brianchon, 134 km Omar Khayyam, 70 km Poczobutt, 195 km Van't Hoff, 92 km

Nectrian Period

Coulomb, 89 km Cremona, 85 km Dyson, 63 km Merrill, 57km Mezentsev, El?, 89km Niepce, 57km Paneth, 85 km Smoluchowski, 83 km Zsigmondy, 65 km

Early Imbrian Period

Ellison, 36 km Noether, 67 km

Late Imbrian Period

Lindblad F, 42 km

The ejecta blanket of the Imbrium Basin has covered nearly all of this sector, except for a few degrees on the western (left) edge and the lower left corner, roughly the area beyond the rim of the Near Side Megabasin (by concidence). Imbrium ejecta softened the shapes of many of the craters that are older than Imbrium, obscuring evidence for exact ages. Striations from Van't Hoff, a Nectarian crater, can be seen exposed where the Imbrium ejecta blanket has not covered them. Further, Lindbad F has impacted the Imbrium ejecta blanket after it was deposited.

Northeast Far Side: Eastern Sector, 55° north to 75° north, 90° west to 135° west The North Polar ^^ Far Side Region

Chapter 12

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