Craters of Eternal Darkness
— Victor Hugo
One of the oldest tropes pertains to the interplay between lightness and darkness. Without one, does the other exist? Certain ruminations liken light and dark to being two sides of the same coin. This comparison makes sense on a cosmic scale, as we have numerous examples that display that physical function. Night and day interchange as our home coin – Earth – revolves.
We recently explored points in the universe that might receive constant starlight, called peaks of eternal light. The same geographic ingredients that allow for these conditions also create the opposite phenomenon. If the obverse of a coin is a peak of eternal light, the reverse is a crater of eternal darkness (or permanently shadowed regions/craters).
The general recipe for peaks of eternal light includes a small axial tilt for the host body, a location near the pole of the body, and a high elevation. Put all the pieces together and a location might receive constant starlight. For a peak to reach 100% sunlight, all these attributes need to be perfect. If just one small blip arises, the spots turns from eternally sunny to just mostly sunny.
Craters of eternal darkness have a secret weapon, allowing these locations to be much more plentiful than their opposites. As we learned with the spots on the Moon, the peaks that come closest to eternal light lie on the rims of craters. Our satellite is riddled with the scars of asteroid hits. The far side of the Moon is even more riddled than the side we see:
If a crater is in the right place on the Moon, or on other celestial orbs that demonstrate the needed recipe, the indentations can easily be deep enough to drown the surface in eternal darkness.
As we learned in the article about PELs, the lunar locations that approach constant light are very close to the poles. The cavity-form of CEDs is such an advantage that neverending night can exist as “low” as 58 degrees latitude on an orb (poles sit at 90-degree latitudes).
We currently know of the existence of at least 324 regions on the Moon that qualify as craters of eternal darkness. Around 50 of those reside in a band between 58 and 65 degrees latitude. While the PELs are closer to small points, the craters add up to some serious acreage. Approximately 12,000 square miles of the lunar surface never see sunlight. That’s an area larger than Lake Erie.
The following video from NASA helps to visualize how these spots avoid sunlight:
As you might imagine, CEDs are frosty.
NASA orbiters report approximate temperatures of 25 degrees Kelvin. That’s -415 degrees Fahrenheit! To put that into perspective, the freezing temperature on the Fahrenheit scale – 32 degrees – is 273 degrees Kelvin. Absolute zero, theoretically the lowest universal temperature and the point at which fundamental particles reach a minimum of motion, is defined as 0 degrees Kelvin. The craters of the Moon clock in just 25 ticks above that measurement.
To date, the craters of eternal darkness on the Moon are the coldest known locations in the solar system.
Like their brighter counterparts, CEDs present certain opportunities in relation to wayfaring through space. Maneuvering in darkness will be a problem for both humans and robots alike, while the extreme coldness will pose additional engineering roadblocks. However, this frigid attribute can be a positive.
We know that water in icy form exists in the craters of the Moon. This resource could be translated into drinking water, rocket propellant, or even breathable oxygen. Further, there’s no need to worry about maintenance; a natural refrigeration system will keep the ice locked up for eons. We could additionally employ these locations as refrigerators. Certain substances that need to remain at extremely low temperatures might find refuge in the many lunar craters.
Cold temps are fantastic for infrared telescopes, as well. The James Webb Space Telescope sits in semi-deep space, partially to take advantage of the temperatures. That engineering marvel needs to shield itself from the sun to function properly. Chilly spots on the moon that don’t receive sunlight? Could be the perfect location for a new telescope.
On today’s noisily bright Earth, we often yearn for the dark skies of our ancestors. Think about the field of stars one might see from a crater of eternal darkness. The lack of light and the temperatures might sound foreboding, but to visit such a place in a safe manner would provide an unrivaled view of the cosmos. Victor Hugo would rejoice.
We ruined the party for peaks of eternal light by realizing that, even should a location on the Moon fit the requirements perfectly, eclipses would occasionally mar their titles. Craters of eternal darkness don’t get to escape the wet-blanket treatment. Though many craters do receive zero light from the sun, one could take umbrage with the nomenclature: if we can see a brilliant star field from these holes, we’re seeing faint light from other suns.
Absolute zeroes are hard to find.
Further Reading and Exploration
Permanently Shadowed Regions Atlas – Lunar Reconnaissance Orbiter Camera
Secrets of the Moon’s Permanent Shadows Are Coming to Light – Quanta Magazine
Taking the Moon’s Temperature – NASA
White Christmas: The Coldest Places in the Solar System – Space.com
Eternal Darkness Near the North Pole – LROC