Eternal darkness on the Moon’s poles and future colonies

There are regions on the Moon which have not seen sunlight for 2+ billion years. Seen here is a yearly illumination map of the Moon’s south pole.

Yearly aggregated illumination map of the Moon’s south pole, as observed by NASA’s Lunar Reconnaissance Orbiter (LRO). Pitch black regions are the ones in eternal darkness. Source: LROC blog

The illumination map has been created using NASA’s Lunar Reconnaissance Orbiter (LRO) by collating observations of the lunar poles over multiple six-month periods. The brightest pixels are near-permanently lit areas, whereas the pitch black ones are the permanently shadowed regions (PSRs).

The Moon’s axis with respect to the Sun’s equator is tilted only by 1.54°. The Moon is not an ideal sphere, it has elevated and depressed regions (mountains and craters). At the poles, the Sun is always close to the horizon and thus the shadows cast by objects are long. Even a small elevated feature can block light from reaching the areas behind. Heck, even raised walls of crater rims can block light from entering the crater interior. A full 360° blocking of sunlight can take place. Such regions are thus in eternal darkness. A corollary to that are the sufficiently elevated areas which by the same logic are near-continuously lit. Future Moon colonies can be powered at locations of near constant sunlight.

The PSRs however, having not received any sunlight for billions of years and being exceptionally cold (can go as low as -250° Celsius!), are an excellent trap for volatiles. Volatiles are elements which would vaporize in space if exposed to sunlight; these include water, carbon dioxide, methane, ammonia, etc. It is estimated that there could be 100 billion kg of water ice in these dark regions. NASA’s LCROSS spacecraft detached a part of it to deliberately impact one of these regions on the lunar south pole. The impact plume was estimated to have 100 kg of water ice, among other volatiles.

Artist’s rendering of LCROSS (bottom left) observing its Centaur upper stage en route to impact the lunar surface in 2009. Source: NASA
LCROSS camera showing the ejected plume post-impact, which included water. Source: NASA

The water ice in the PSRs can be harnessed to supply water to the Moon colonies built in the nearby lit regions. The water can also be split into hydrogen and oxygen to use as rocket fuel, using solar power generated by the colonies.

Before planning and building lunar habitats at the poles, we must learn more about regions of permanent darkness. This is why NASA is sending the ShadowCam instrument on Korea Pathfinder Lunar Orbiter (KPLO). It will map the PSR regions at 200x the resolution that LRO did. A landing mission exploring the PSR regions, like the cancelled Resource Prospector rover, is the next logical step that drives sustainable habitats on the Moon.

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