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

Recently, the Chandra's Atmospheric Composition Explorer-2 (CHACE-2), a quadrupole mass spectrometer on board Chandrayaan-2 mission, has made the first-of-its-kind observations of the global distribution of Argon-40 in the tenuous lunar exosphere.

About observations:

• These observations provide insight on the dynamics of the lunar exospheric species, as well as on the radiogenic activities in the first few tens of metres below the lunar surface.
• The CHACE-2 observations provide the diurnal and spatial variation of Ar-40 covering the equatorial and mid latitude regions of the Moon.
• CHACE-2 observations reveal an increase in the number density of Ar-40 near the sunrise terminator, a decrease through the dayside, a secondary peak near sunset terminator and a night-side minima. This is the typical behaviour of a condensable gas, it was stated.
• For the mid latitude regions, CHACE-2 observations showed for the first time that the variation in the number density of Ar-40 with respect to solar longitudes are similar to that of low latitude regions, despite the differences in temperature and topography.
• Further, the CHACE-2 observations reveal that the distribution in Ar-40 has significant spatial heterogeneity. There are localised enhancements (termed as Argon bulge) over several regions including the KREEP [potassium (K), rare-earth elements, and phosphorus (P)] and South Pole Aitken terrain.
• The observations of Argon bulge by CHACE-2 are indicative of unknown or additional loss processes, Moon quakes or regions with lower activation energies, which call for a better understanding of the surface-exosphere interactions and source distributions of Ar-40.