Why is the South Pole of the moon preferred for moon missions such as Chandrayaan 3 and why are countries such as the US, China and India infatuated for Moon’s South Pole and not the North Pole? There are mixed views as few space experts are of the view that the South Pole has more water ice, which is a valuable resource but few say that the lunar South Pole is not necessarily better than the north pole in terms of solar energy, material resources, or ease of landing. However, the south pole has been favored for exploration due to historical reasons.
In the 1990s, a number of missions to the Moon focused on the South Pole, and this helped to solidify the South Pole as the preferred landing site for future missions.
Space experts say that the lunar poles are very similar. They both have highland terrain and a rugged landscape with large, degraded craters and smaller fresher ones. The differences between the poles are very small. They are not significant enough to make one pole a better landing site than the other, experts point out.
The lunar poles have spots that are always sunny. These spots are called “peaks of eternal light” but the light is not eternal and the name is quite misleading. The areas are only lit for about 90 percent of the Moon’s 18.6-year nutation cycle. Of the top 20 sites on the Moon that are illuminated by the sun, seven of them are located near the North Pole. This is because the North Pole has a longer period of sunlight than the South Pole.
“The South Pole of the moon gets a slight advantage over the North Pole in terms of solar energy. However, this advantage is not significant enough to make a practical difference. There are plenty of places on the North Pole that have good solar visibility,” Girish Linganna, space and aerospace expert told THE WEEK.
“An additional motivating factor for focusing on the south is that the South Pole is located in the South Pole-Aitken basin, which is a huge crater. This makes the South Pole a geologically interesting place because it is possible that there is material from the deep crust and upper mantle of the Moon on or near the surface. The South Pole is also a more promising place to look for ice than the North Pole,” he said.
Linganna points out that ice resources are an important consideration for future missions to the Moon. However, the differences in ice resources between the north and south poles are not as great as they once seemed. This is because we now have more complete data about the ice resources at both poles.
“Water ice has been detected at both poles of the Moon. The South Pole has more area in permanent shadow and colder temperatures, so it is thought to have more water ice. However, the difference in permanently shadowed area between the two poles is not as great as originally thought. The true ratio of permanently shadowed area between the south and the north poles is about 1.25:1,” added Linganna.
Experts point out that the reason why the South Pole is favoured for exploration is because of a historical misconception about the existence of mountains that are always lit by the sun. This misconception helped to popularize the idea of the South Pole as a place of eternal light, and this has led to more missions being planned to the South Pole than the North Pole.
In the 1970s and 1980s, a group of amateur astronomers led by John Westfall worked to map the region around the south pole of the Moon. The region was poorly mapped during the Apollo missions in the 1960s, and it was nicknamed “Luna incognita” (Latin for “unknown moon”). The work of Westfall and his team helped to fill in the gaps in our knowledge of the South Pole, and it made the region more attractive for future exploration.
In December 1994, Gene Shoemaker and his team published a paper in the journal Science called “The South Pole Region of the Moon as Seen by Clementine.” The paper talked about how the South Pole was the least well-known region of the Moon before the Clementine mission, and how the mission had revealed a lot of new information about it.
The decision to title the paper “The South Pole Region” instead of “The Polar Regions” was important, because even though Clementine had collected data from both poles, the south pole was much more heavily shadowed during the mission, which made it more likely to contain ice. The paper described the shadowed regions as potential hosts of ice.
“From 2006-2009 NASA had extra room on the Lunar Reconnaissance Orbiter (LRO) mission, so they decided to launch a second mission called Lunar Crater Observation and Sensing Satellite (LCROSS) to look for ice on the Moon. They considered landing sites at both poles, but the LRO launch was delayed multiple times, so they ended up landing at Cabeus crater on the South Pole. This cemented the south pole as the leading candidate for future missions to search for ice on the Moon,” said Linganna.
“The South Pole became the preferred destination for lunar exploration in the late 1990s due to a combination of factors, including the fact that it was less well-mapped and imaged than the North Pole. The decision to focus on the South Pole has been largely unchallenged since then, even though there is no clear evidence that it is a better destination than the North Pole,” he added.