India, the US, and China have turned their attention to the Moon’s South Pole for upcoming missions, driven by the region’s plentiful water ice reserves. The South Pole’s appeal as a landing site stems from its historical significance, with missions in the 1990s concentrating their efforts on this specific area. This emphasis has solidified the South Pole’s position as the favoured destination for future lunar explorations.  Led by Jeff Bezos, Blue Origin – a private American aerospace company collaborating closely with NASA – plans to mine water ice from the Shackleton Crater near the Moon’s South Pole.

When assessing the two lunar poles, the South Pole does not possess a significant advantage in terms of material resources, solar energy availability, or spacecraft landing feasibility when compared to the North Pole. Both poles share similar traits, including highland terrain, rugged landscapes characterised by both large, degraded craters and smaller, fresher ones, and an anorthositic composition.

Sunlit Regions and Solar Visibility

While certain regions on the lunar poles receive continuous sunlight, known as “peaks of eternal light,” it’s important to note that this name can be misleading. These sunlit areas are only illuminated for approximately 90% of the Moon’s 18.6-year nutation cycle. Interestingly, seven out of the top 20 Sun-illuminated sites on the Moon are situated near the North Pole, as it experiences a longer period of sunlight compared to the South Pole. Nevertheless, the overall disparity in solar visibility between the best and worst sites on the Moon is relatively small, with a mere 5% difference. This slight variance has minimal practical implications for power generation and storage at lunar bases.

In terms of solar energy, the South Pole holds a slight advantage over the North Pole, albeit not significantly remarkable. Nevertheless, the North Pole also offers areas with favourable solar visibility, making it a viable option for energy production.

Ice Resources: North vs. South Pole

Ice resources play a crucial role in guiding future lunar missions. While it was previously presumed that there would be a substantial disparity in ice resources between the north and south poles, recent data reveals a less pronounced difference. The true ratio of Permanently Shadowed Regions (PSRs) between the two poles is approximately 1.25:1, indicating a smaller variance than initially believed.

Abundance of Water Ice on the Moon

The Moon boasts a substantial quantity of water ice, estimated to be up to 100 billion metric tonnes. While the variance in water ice between the north and south poles is not significant, it becomes a relevant factor only when a substantial portion of the ice is mined. Current mining plans focus on extracting relatively small amounts, in the range of tens to hundreds of tonnes per year. Consequently, both poles offer ample supplies of water ice that can sustain lunar missions for decades to come, making the disparity between the poles negligible in practical terms.

The Myth of the Leibniz Mountains

In the 1800s, astronomers erroneously believed that the south pole of the Moon boasted sunlit mountains known as the ‘Leibniz Mountains.’ This misconception led to the South Pole gaining popularity as a preferred destination for lunar exploration, despite its origins being tied to the South Pole-Aitken (SPA) basin, unknown to astronomers at the time.

Mapping Efforts

During the 1970s and 1980s, John Westfall and a group of amateur astronomers undertook extensive mapping efforts around the lunar South Pole. These regions, previously referred to as ‘Luna incognita’ (unknown moon), had received inadequate mapping during the Apollo missions of 1960s. Westfall’s work played a pivotal role in enhancing our understanding of the South Pole and increased its appeal for future exploration endeavours.

Findings of Lunar Missions

Launched on January 25, 1994, the Clementine spacecraft, funded by the Ballistic Missile Defense Organisation and NASA, orbited the Moon for 71 days, capturing images and creating maps of its entire surface. While exploring both poles, the first month’s orbit focused primarily on the South Pole, providing a comprehensive view and valuable data.

In December 1994, Gene Shoemaker and his team published a seminal paper in the journal Science, titled ‘The South Pole Region of the Moon as Seen by Clementine.’ The publication highlighted the previously limited knowledge of the lunar South Pole and the wealth of new information gleaned from the Clementine mission. The presence of heavier shadows in the South Pole’s shadowed regions suggested the potential existence of ice.

In May 1999, Ben Bussey and his team published a paper titled ‘Illumination Conditions at the Lunar South Pole,’ further utilising Clementine mission data. The study underscored the extended periods of shadow at the South Pole, making it an ideal location to search for ice, given its preference for cold and dark environments. The research contributed to an improved understanding of illumination conditions in the lunar South Pole.

The South Pole’s location within the expansive South Pole-Aitken basin has amplified its significance for lunar missions. Geologically, the basin presents an alluring prospect for excavating materials from the upper mantle and deep crust, potentially obtainable on or near the surface. The paper includes a compelling colour plate showcasing the Shackleton Crater and adjacent ridge, reinforcing the South Pole’s potential as a prime site for ice exploration compared to the North Pole.

Between 2006 and 2009, the Lunar Reconnaissance Orbiter (LRO) mission had additional space, leading to the launch of a companion mission called the Lunar Crater Observation and Sensing Satellite (LCROSS). The primary objective was to search for ice on the Moon. While both poles were considered as potential landing sites, multiple launch delays resulted in the selection of the Cabeus Crater on the lunar South Pole. The landing at this specific site further established the undeniable preference for conducting ice search missions in the southern region. The availability of more space for detailed observations and the opportunity to explore uncharted territories played a significant role in this decision.

Enhanced Observations

On May 4, 2015, the LRO transitioned from a circular to a polar orbit. This orbital shift allowed for more comprehensive and detailed observations of the lunar South Pole compared to the North Pole. As a result, data coverage and characterisation of the north polar sites became more challenging in comparison to the well-documented and extensively studied southern counterpart.

Ongoing Focus

NASA and other space agencies maintain their focus on the Shackleton Crater and accompanying ridge, as depicted in the Bussey image, representing merely a fraction of the lunar South Pole’s potential. These areas continue to captivate researchers due to their perceived value in ongoing efforts to uncover the Moon’s resources and advance exploration endeavours.

Summing Up

The lunar South Pole gained prominence as the preferred destination for exploration and ice search in the late 1990s for two primary reasons. Firstly, it had received less photographic and mapping coverage compared to the North Pole. Secondly, the timing of the Clementine mission during the lunar southern winter provided better data coverage for the South Pole. The extensive exploration efforts, availability of uncharted territories, and potential for valuable discoveries have solidified the South Pole’s standing in the scientific and space exploration community.

-The writer is a Defence, Aerospace & Political analyst. The views expressed are personal and do not necessarily reflect the views of Raksha Anirveda