Argon-40 In Moon’s Atmosphere

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Context:

Chandrayaan-2 has made first observations of distribution of Argon-40 in Moon’s atmosphere.

Details:

Origin: Ar-40 originates from the radioactive disintegration of Potassium-40 (K-40) present below the lunar surface.
Diffusion: Once formed, it diffuses through the inter-granular space and makes way up to the lunar exosphere through seepages and faults.
Distribution: The distribution in Ar-40 has significant spatial heterogeneity. There are localized enhancements at places termed as Argon bulge over several regions including the KREEP. KREEP stands for potassium (K), rare-earth elements, and phosphorus (P) and South Pole Aitken terrain.
Variation of Ar-40: Observations provide the diurnal and spatial variation of Ar-40 covering the equatorial and mid latitude regions of the Moon. There is an increase in the number density of Ar-40 during the sunrise, a decrease through the dayside, a secondary peak near sunset and a night-side minima.

What makes Chandrayaan’s findings unique?

Apollo-17 and LADEE missions had detected the presence of Ar-40 in the lunar exosphere. But the measurements were confined to the near-equatorial region of the Moon.
There is a steep latitudinal temperature gradient of the lunar surface. Hence, there was a gap area to study the total dynamics of the lunar exosphere, which is a temperature-driven process.
Observations by Chandrayaan-2 orbiter on Ar-40 up to the mid-latitude regions [−60º to +60º] play a significant role to bridge the gap in the knowledge.

Significance of the observations:

The observations provide insight on the dynamics of the lunar exosphere, as well as on the radiogenic activities in the first few tens of metres below the lunar surface.
It provides the diurnal and spatial variation of Ar-40, an important tracer atom, covering the equatorial and mid latitude regions of the Moon.
The observations of Argon bulge are indicative of Moon quakes or regions with lower Ar-40 activation energies.
This calls for a better understanding of the surface-exosphere interactions and source distributions of Ar-40.

South Pole-Aitken basin is the largest crater on the Moon. It's about 2500 kilometers in diameter.

Chandrayaan:

Chandrayaan-2 featured improved instruments and new technologies.

Chandryaan 2:

About

Chandrayaan-2 is an Indian mission to send an orbiter, lander, and rover to the Moon.
The three vehicles was launched as one combined spacecraft in July 2019 to lunar orbit.
The lander, carrying the rover, attempted but failed to touch down in the Moon's southern hemisphere.
The orbiter continues to study the Moon from above.

Mission objectives

Science goals include

Findings so far:

Water: The presence of water on the Moon had already been confirmed by Chandrayaan-1. But Chandrayaan-2 has now found signatures of water at all latitudes, although its abundance varies from place to place.
Minor Elements: Chandrayaan-2 has detected the minor elements chromium and manganese for the first time through remote sensing. Sodium, also a minor element on the Moon surface, was detected without any ambiguity for the first time.
Mapping: It has mapped nearly 95% of the lunar surface in X-rays for the first time.
Exploration of the permanently shadowed regions: A key outcome from Chandrayaan-2 has been the exploration of the permanently shadowed regions as well as craters and boulders underneath the regolith. Regolith is the loose deposit comprising the top surface extending up to 3-4m in depth. This is expected to help scientists to zero in on future landing and drilling sites, including for human missions.

Chandrayaan 3:

Chandrayaan-3 is a planned third lunar exploration mission by the Indian Space Research Organisation (ISRO).
Chandrayaan-3 is a lander-and rover-specific mission, which will demonstrate India’s capability of soft landing on a celestial body, with the rover.
It will then communicate with Earth via the existing orbiter from Chandrayaan-2 and take images 100 km from Moon’s orbit. The orbiter has an estimated lifespan of seven years.

Objectives:

Studying not just one area of the Moon but all the areas combining the exosphere, the surface as well as the sub-surface in a single mission.
To further the study of the lunar surface, focussing on the South Pole or dark side of the Moon that has not seen sunlight in billions of years, which is believed to have ice and vast mineral reserves.

Why Lunar South Pole of the Moon is targeted for exploration?

The Moon provides the best linkage to Earth’s early history and civilization.
The exploration will offer an undisturbed historical record of the inner Solar system environment.
The Lunar South pole is especially interesting because the lunar surface area that remains in shadow is much larger than that at the North Pole.
Further, there could be a possibility of the presence of water in permanently shadowed areas around it.
In addition, the South Pole region has craters that are cold traps and contain a fossil record of the early Solar System.

Why exploring the Moon is imperative?

The Moon is the closest cosmic body at which space discovery can be attempted and documented.
Further, Moon is a promising testbed to showcase technologies required for deep-space missions.
Exploring the Moon will enhance our understanding of the celestial body clearly, stimulating the advancement of technology, promoting global alliances and inspiring future generations of explorers and scientists.