LIBS and the Moon Mineralogy

Moon Mineralogy

The moon, which is our nearest astronomical neighbor, has been portrayed in several ancient writings and works of art. However, there is still a lot of disagreement among experts regarding the moon's origin. And many theories have been put up to explain it. According to the capture theory, the Moon was once a roving body (similar to an asteroid) that formed somewhere in the solar system and was drawn in by the gravity of Earth as it went by. Based on the lunar accretion hypothesis, the Moon and Earth both formed at the same time. In accordance to the fission theory, the Earth's rapid spin caused some of its constituent parts to fragment. According to the giant-impact theory, the Moon was created when the Earth collided with a smaller planet that was roughly the size of Mars. This impact's material accumulated in an orbit around Earth to create the Moon [1].

Remains of Moon-forming impact may lie deep in Earth | Science

Fig 1: Depiction of giant impact theory[14]

With the beginning of the Apollo Missions, it played a significant part in uncovering the mineralogy and composition of the moon through its numerous sample returns. The gaint impact theory is currently the most widely accepted since numerous elements comparable to earth have been discovered [2]. A molten lunar magma ocean (LMO), which first erupted during the early phases of lunar formation, gradually cooled to produce characteristic rock-forming minerals. Denser olivine and pyroxene sank, and plagioclase ascended to produce the lunar crust. The KREEP layer, which is abundant in incompatible elements like potassium (K), rare earth elements (REE), and phosphorus (P), persisted until the end of LMO cooling and formed solid rocks, is what distinguishes lunar chemistry from other planets. Magmatic activity reshaped the Moon, mixing KREEP into other rocks. By bringing back samples from the Moon's surface, such as KREEP-bearing rocks, the Apollo and Soviet missions played a crucial part in advancing our understanding of lunar geology [3]. The Apollo Missions returned 382kg of 2,200 distinct samples from six different landing sites between 1969 and 1972, and three Soviet Automated Spacecraft returned an additional 300grams [4].

The most prevalent five elements on the moon are oxygen (42%) followed by magnesium (6%), silicon (21%), calcium (8%), and iron (15%) [5]. In order to add to the evidence, the Laser-Induced Breakdown Spectroscopy (LIBS) [6] instrument on India's Chandrayaan-3 lunar rover verified the presence of aluminum (Al), sulphur (S), calcium (Ca), iron (Fe), chromium (Cr), and titanium (Ti) on the lunar surface. While the examination into the finding of hydrogen (H) is ongoing, other measurements have also shown the presence of manganese (Mn), silicon (Si), and oxygen (O) from the vicinity of the lunar south pole [7].

Fig 2: LIBS results showing emission of spectrum on Lunar South Polar Region [13].

Why moon mineralogy is important?

Since the minerals and elements found on the moon are comparable to those found on Earth, this fact aids in understanding the composition and development of the primordial crust in the Earth-Moon system [8]. Mineral detection will make it easier to examine the relationships between these geological, physical, and chemical mechanisms on the lunar surface [9].

The number of current and upcoming missions to the Moon is continuously growing, demonstrating the growing interest in the Moon from a scientific perspective as well as the desire to return humans there through the Artemis program and even use the Moon as a base for additional manned Solar System exploration [10]. Before starting the considerably longer journey to Mars, the Artemis mission will build the groundwork for a long-term, permanent presence on the lunar surface and use the Moon to test deep space procedures and technologies [11]. As humans exploit and develop technology from the Moon's available resources, like its water and metal deposits, our presence will grow over the coming decades and centuries[12]. To properly complete the missions, comprehensive knowledge of the moon's resources and mineralogy must be available by that point.

Conclusion

Scientists who were eager to confirm different minerals on the moon finally had their wish thanks to technology, which is improving daily. And future interplanetary flights and technical demonstrations of emerging space technologies both heavily rely on the lunar mineralogy. Intriguing findings are always in line with grand ambitions for the future.

References

[1] https://www.nhm.ac.uk/discover/how-did-the-moon-form.html

[2] https://www.space.com/19275-moon-formation.html

[3] https://www.lpi.usra.edu/education/IYPT/Moon.pdf

[4] https://www.nasa.gov

[5] Warren and Taylor(2014), Treatise on the geochemistry(2nd ed; Vol.2) Boston, MA: Elsevier)

[6] https://www.currentscience.ac.in/Volumes/118/04/0573.pdf

[7] https://www.isro.gov.in/LIBSResults.html

[8] https://www.sciencedirect.com/science/article/pii/S1674987116300238#:~:text=Mineralogy%20of%20the%20Lunar%20surface,Magma%20Ocean%20(LMO)%20hypothesis

[9] https://www.niser.ac.in/~smishra/teach/cs460/2021/project/21cs460_group05/

[10] https://www.sciencedirect.com/topics/earth-and-planetary-sciences/lunar-resource

[11] https://spaceref.com/status-report/report-nasas-plan-for-sustained-lunar-exploration-and-development/