Chandrayaan-2 orbiter makes First Observations about distribution of gas in lunar atmosphere
Chandra’s Atmospheric Composition Explorer-2 (CHACE-2) instrument onboard India’s 2017 Chandrayaan-2 orbiter has made new exciting observations related to the distribution of an important gas (Argon-40) in the tenuous lunar exosphere.
The observations:
According to the latest findings published in the journal Geophysical Research Letters, Argon-40 (Ar-40) exists in the lunar exosphere but the knowledge of its distribution at higher latitudes was lacking. It is stated that for the first time, the CHACE experiment onboard Chandrayaan-2 orbiter has continuously observed Ar-40 in the latitude range of -60 to +60 degrees.
The study also mentioned that the observed global distribution indicated that the interaction of Ar-40 with the surface is similar in low and mid-latitude regions. The new observations from CHACE-2 hint at a requirement for improvement in our understanding of the surface exosphere interactions and source distributions of Ar-40.
A deeper understanding
This new observation is responsible for providing insights into the dynamics of the lunar exosphere in the first few tens of meters below the lunar surface. This further will enhance our understanding of the composition of the lunar surface. This is not the first time that Argon-40 has been detected on the lunar surface, the detections earlier were limited to near-equatorial regions as seen by the Apollo-17 mission.
Know about Argon-40
Argon-40 is one of the isotopes of the noble gas Argon, which is an important constituent of the lunar exosphere. The lunar exosphere is the outermost region of the upper atmosphere of a celestial body where the constituents atoms and molecules rarely collide with each other and can escape into the deep dark space.
Argon is an inert, colourless and odourless element found on the Earth that originated from the radioactive disintegration of Potassium-40 (K-40) present below the lunar surface.
According to ISRO, once the disintegration is formed, it diffuses through the inter-granular space and makes its way up to the lunar exosphere through faults.
Revelations by CHACE-2
According to the official release of ISRO, the CHACE-2 observations reveal an increase in the number density of Argon-40 near the sunrise terminator, a decrease along the dayside, a secondary peak near the sunset terminator and a night-side minimum. However, the biggest revelation was that the density of Argon-40 with respect to solar longitudes is similar to that of low latitude regions, despite the differences in temperature and topography.
ISRO further stated that “The observations of the 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.”
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.
