Chandrayaan-2 makes first observations of distribution of Argon-40 in Moon’s atmosphere

What is the News?

Chandra’s Atmospheric Composition Explorer-2(CHACE-2), a payload onboard Chandrayaan-2, has made the first-of-its-kind discovery on the distribution of one of the noble gasses, Argon-40.

What is Chandrayaan-2?

Chandrayaan-2 is the second lunar exploration mission launched by ISRO in 2019.

Objective: To demonstrate ISRO’s capability to make a soft landing on the moon.

The mission had a lander and a rover component that was supposed to carry out a number of experiments on the lunar surface. 

However, due to technical glitches in the final moments ahead of the touchdown, the lander was unable to make a soft landing. Instead, it crash-landed and got destroyed.

But the Orbiter is continuing to carry out its scientific experiments. It is carrying eight instruments, including CHACE-2, for different kinds of measurements. 

Read more about Chandrayaan-2

What is the discovery made by the CHACE-2 payload?

Argon-40 (Ar-40) is known to exist in the lunar exosphere. But the knowledge on its distribution at higher latitudes is lacking. 

Now, the CHACE-2 payload has shown that the distribution of Argon-40 gas in the lunar ‘exosphere’ exists beyond the areas that were known. It has detected the presence of Argon in the equatorial and mid-latitude regions of the Moon.

The payload has also revealed that the distribution of Ar-40 has significant spatial heterogeneity. 

For example, there are localised enhancements (termed as Argon bulge) over several regions including the KREEP [potassium (K), Rare-Earth Elements, and Phosphorus (P)] on South Pole Aitken terrain (impact crater on the far side of the Moon).

Note: ‘Exosphere’ is the outermost region of the upper atmosphere of a celestial body where the constituent atoms and molecules rarely collide with each other and can escape into space.

What is the significance of this discovery?

Noble gases serve as important tracers to understand the processes of surface-exosphere interaction, and Argon-40 (Ar-40) is such an important tracer atom to study the dynamics of the lunar exospheric species.

Ar-40 originates from the radioactive disintegration of Potassium-40 (K-40) present below the lunar surface. Once formed, it diffuses through the inter-granular space and makes its way up to the lunar exosphere through seepages and faults.

The CHACE-2 observations provide the diurnal and spatial variation of Ar-40 covering the equatorial and mid-latitude regions of the Moon.

The uniqueness of this discovery lies in the fact that although Apollo-17(1972) and Lunar Atmosphere and Dust Environment Explorer (LADEE Mission 2014) have detected the presence of Ar-40 in the lunar exosphere, the measurements were confined to the near-equatorial region of the Moon.

Moreover, the observations of Argon bulge by CHACE-2 are indicative of unknown or additional loss processes.

Source: This post is based on the article “Chandrayaan-2 makes first observations of distribution of Argon-40 in Moon’s atmosphere” published in The Hindu on 10th Mar 2022