Ground Report | New Delhi: Chandrayaan-2 orbiting the Moon has made yet another discovery as it prepares for the arrival of its successor Chandrayaan-3. The spacecraft peered into the surface of the Moon and picked up a new activity that was initially believed to be limited to just one region of the Moon.
The Chandra’s Atmospheric Composition Explorer-2 (CHACE-2) instrument on Chandrayaan-2 found Argon-40 in the tenuous lunar exosphere. Isro in a statement said that the new observations provide insight on the dynamics of the lunar exospheric species and activities in the first few tens of meters below the lunar surface.
Published in the journal Geophysical Research Letters, the observations provide the diurnal and spatial variation of Ar-40 covering the equatorial and mid-latitude regions of the Moon. Initially, Argon-40 was believed to present only in the near-equatorial region of the Moon as seen by the Apollo-17 mission.
“As there is a steep latitudinal temperature gradient of the lunar surface, it was, so far, a gap area to study the global dynamics of the lunar exospheric species, which is a temperature-driven process,” Isro said in a statement
Argon-40 is an inert, colorless, and odorless element of the Argon family, which 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.
In this context, the observations by CHACE-2 onboard 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.
An inert, colorless and odorless element, Argon is a noble gas. A vast majority of argon on Earth is the isotope argon-40 that originates from the radioactive disintegration of Potassium-40 (K-40) present below the lunar surface. According to Isro, once formed, it diffuses through the inter-granular space and makes way up to the lunar exosphere through seepages and faults.
Meanwhile, the lunar exosphere is the outermost region of the upper atmosphere of the Moon where the constituent atoms and molecules rarely collide with each other and can escape into space. “Earth’s Moon features a surface-boundary-exosphere. For Moon, different constituents in the exosphere are fed from the surface by a variety of processes, such as thermal desorption, solar wind sputtering, photo-stimulated desorption, and micrometeorite impact vaporization. The exospheric atoms may be lost to space by the thermal escape,” Isro said.
“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,” Isro said.
The CHACE-2 was a sequel to the CHACE experiment on the Moon Impact Probe (MIP) of Chandrayaan-1 mission and also draws heritage from the Mars Exospheric Neutral Composition Analyser (MENCA) experiment aboard the Indian Mars Orbiter Mission.
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