The ‘Exosphere’ happens to be the outermost region of the upper atmosphere of the celestial body wherein the constituent molecules and atoms rarely collide with each other and are able to escape into space.
According to the Indian Space Research Organisation, Chandra’s Atmospheric Composition Explorer-2 (CHACE-2) that is a quadrupole mass spectrometer onboard Chandrayaan-2 mission, has made the first-of-its-kind observations in the tenuous lunar exosphere of the global distribution of Argon-40. The Bengaluru-headquartered space agency said in a statement on Tuesday that these observations helped in providing insight into the dynamics of the lunar exospheric species along with the radiogenic activities in the first few tens of metres below the lunar surface.
The ‘Exosphere’ happens to be the outermost region of the upper atmosphere of the celestial body wherein the constituent molecules and atoms rarely collide with each other and are able to escape into space.
The Moon which the Earth has features a surface-boundary exposure. For Earth’s Moon, there are different constituents in the exosphere that are fed from the surface by many processes like solar wind sputtering, thermal desorption, micrometeorite impact vaporisation and photo-stimulated desorption.
The exospheric atoms may be lost to space by the thermal escape and get ionised by photo-ionisation that charge exchange with the solar wind ions.
They can be whisked away by the solar wind’s convective electric field, but some of these atoms/ions can be deposited back on the lunar surface. Hence the lunar exosphere exists as a result of a dynamic equilibrium between sink processes and several sources.
According to ISRO, the CHACE-2 observations provide the diurnal and spatial variation of Ar-40 covering the equatorial and mid-latitude regions of the Moon.
Despite the differences in topography and temperature for the mid-latitude regions, the CHACE-2 observations for the first time showed that the variation in the number density of Ar-40 with respect to solar longitudes are similar to that of low latitude regions.