In the day of the Summer Solstice – the longest day of the year – I thought appropriate talking about the famous peaks of eternal light, which recently became popular (again).
The expression “peak of eternal light” (that is, a point on a body within the Solar System that is always in sunlight) is by no mean recent. Their existence was first proposed by Beer and Mädler in 1837 when talking about mountains on the Lunar Poles : “…many of these peaks have (with the exception of eclipses caused by the Earth) eternal sunshine.” and then again by Camille Flammarion in 1879.
To enjoy constant sunlight, PELs must have high altitude, and be on a body with small axial tilt. Do they exist? Yes, and no – depending how you apply the definition. NASA and ESA have actually found a small number (namely six) of illuminated ridges within 17 km of the Lunar Southern Pole, each of them much like an island of no more than a few hundred mt across in an ocean of (eternal) darkness, where a lander could receive near-permanent lighting (about 70–90% of the lunar winter, and likely all of the lunar summer).
These places would be extremely important for space exploration and to set up colonies in outer space, both in terms of energy availability and environmental condition stability.
“If you didn’t want to rely on complex power systems, you could install solar power stations at the peaks and use the energy to run small rovers and landers. Such systems are easier to design than electrical and mechanical systems that must withstand the extreme variation of temperature between lunar day and night. Branching out from there, you could build a spider web of facilities and habitats, with the core feeding energy to surrounding areas. A peak of eternal light would be a good place to retreat to in winter, where we could maintain low-level operations. […] The peaks provide some temperature stability. On the moon’s equator, the temperature can vary from minus 170 degrees C to plus 110 degrees C. The peaks have less variation, and an average temperature of minus 30 degrees C. A solar collector placed on a peak could provide enough energy to maintain a habitat with a very comfortable temperature of 20 degrees C.
With such a stable environment, you could do life science experiments to test how life adapts in another world. We could see how bacteria withstand the radiation environment. We could develop plant growth experiments in preparation for human bases.” (For the whole article, see this). On the other hand, the permanently-shadowed regions at the bottom of craters could be used to safely deposit of water ice for water, oxygen and rocket fuel.
Want to have a feeling of what such a place would look like? ESA created a hi-res video using images taken by ESA’s SMART-1 lunar orbiter. It shows the Shackleton Crater and, nearby, a location 17 km from the Moon’s South Pole – possibly the base of our future manned outpost on the satellite (for a discussion about who owns them or can exploit them, see this article.) I’ll write about lunar law in a future post, but yes, it’s going to be complicated. In the meantime, happy PEL, everybody!