Strange Illuminations at the PSRs: A Study of the Dark Regions of the South
Over the last two decades, the lunar South Pole has emerged as a focal point for great scientific inquiry, driven by its potential to support future human missions and the possibility of establishing a permanent base on the Moon. This forward-thinking approach aims to lay the groundwork for more ambitious explorations such as Artemis.
Exploring the Moon isn't just about understanding its history; it's also crucial for planning our future in space. Many have expressed their desire for NASA to continue leading this effort. Frankly – it's evident that other spacefaring nations are rapidly advancing, narrowing the gap in exploration capabilities. I believe that future endeavors will necessitate a collective and collaborative approach, fostering a synergy that will benefit the advancement of space exploration.
Permanently Shadowed Regions
The term "Permanently Shadowed Regions" (PSRs) refers to areas on the Moon that never receive direct sunlight due to the low obliquity of the Moon (1.54°). The PSRs at the South Pole are particularly intriguing because they are theorized to contain water ice and are shaded more than those at the North Pole, making them a key focus for research and exploration [8].
Water, a volatile substance on the lunar surface, is especially known to be present and is identified as the most stable compared to other naturally occurring volatiles that might have been released at any point. The quantity of water potentially lost since the lunar surface conditions evolved to the current state is very small.
As a result, the current levels of lunar ice are believed to closely reflect the total amount of water historically present on the lunar surface [7]. Naturally, these regions are of significant interest in planetary science and exploration. The believed water is thought to be trapped in the lunar soil, possibly deposited by impacts from space millions of years ago. This makes them not just important for scientific study but also potential sources of water for future lunar missions. The potential for extracting this ice signifies the importance of studying and exploring PSRs.
Cold Trapping
Cold-trapping is a process where certain regions can trap and freeze volatile substances like water vapor due to their extremely low temperature. Because of the lack of direct sunlight, these PSRs remain cold and have extremely low temperatures. Water sublimation (water to gas) is highly non-linear and slow at low temperatures. Hence, the probability of frozen water.
| Temperature (C / K) | Area (km²) |
|---|---|
| -163 / 110 | 3.73 × 10^4 |
| -162 / 111 | 3.79 × 10^4 |
| -161 / 112 | 3.86 × 10^4 |
| -160 / 113 | 3.92 × 10^4 |
| -159 / 114 | 3.98 × 10^4 |
| -158 / 115 | 4.04 × 10^4 |
Seasonal Winter Cold‐Trapping Area in South Polar Region for Threshold Temperatures [11]
Temperature Variations at PSR
The temperature at Permanently Shadowed Regions (PSRs) and the corresponding cold trapping depend on several factors, including topographical facets and the thermal conductivity of the regolith. One such factor is the phenomenon known as Secondary Illumination [1], I'll talk about it in the next sections.
