Islands in the Dark

Image of illuminated peaks near the rim of Shackleton crater
Darkness surrounds illuminated peaks between Shackleton crater (rim crest at right) and de Gerlache crater (out of scene left). As lunar days and seasons progress, darkness creeps along this elevated ridge near the south pole. Image width 15 kilometers, NAC M1195011983LR [NASA/GSFC/Arizona State University].

Close to the south pole, the Sun never rises far from the horizon, but as the Moon spins on its axis, the direction to the Sun changes. Local ridges cast ragged shadows that shift dramatically over the landscape as the Sun circles the horizon. Many high points are illuminated for extended periods of time. Conversely, low areas near the poles remain in darkness all year. Areas that never receive direct sunlight are called Permanently Shadowed Regions (PSRs); the interior of Shackleton crater is one such area.

Rim and interior of Shackleton crater at the lunar south pole
The rim crest and upper part of the rim of Shackleton crater; the south pole is located on the rim near the upper right corner of the image. The upper slopes of the crater's interior are very steep, often exceeding 30 degrees. The shadowed interior never receives direct sunlight; image width approximately 11 kilometers M1195011983LR [NASA/GSFC/Arizona State University].

 Shackleton crater is 21 kilometers in diameter and over 4 kilometers deep. An elevated ridge runs roughly between Shackleton and de Gerlache craters, and the relatively high elevation of this landscape means that some portions are illuminated up to 90% of the time, but nowhere is permanently illuminated. Future explorers could take advantage of this persistent illumination by setting up solar panels in several closely spaced locations providing nearly constant solar generated electricity. The proximity to Permanently Shadowed Regions in and around Shackleton crater adds scientific value to this destination, as PSRs are often home to compounds such as water ice that are not found elsewhere on the Moon, but which contain clues to the history of of inner Solar System water and other volatile elements. A nearby, ready source of water-ice would also be of benefit to human surface activities, either as a consumable (air or water) or as spacecraft fuel.

Shaded relief model of the south pole, arrows showing illuminated portions
Shaded-relief model from Lunar Orbiter Laser Altimeter (LOLA) elevation data with 5-meter sampling. For visibility of the terrain, the shaded relief model portrays illumination as if the sun were 45 degrees above the horizon (which it never is at this latitude). Green dot indicates location of the south pole; green arrows indicate illuminated terrain shown in the opening image above [NASA/GSFC/Arizona State University].
Shaded relief model of the south pole showing locations of PSRs
Same image as above, but with areas of permanent shadow indicated in blue  [NASA/GSFC/Arizona State University].

Explore the full NAC oblique image of Shackleton crater.

Read More about PSRs

Casting Light on Permanently Shadowed Regions

Searching for Ice at the Moon's Poles

Did you know that LROC's first image of the Moon was of Shackleton crater? 1000 Day Anniversary of LROC Imaging

More about Shackleton crater

On the Rim of Shackleton

Lunar South Pole - Out of the Shadows

 Mosaics of the south pole

WAC mosaic

WAC illumination percent map

Published by J. Stopar on 20 May 2019

Oblique Permanently Shadowed Regions Polar Regions