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Argon-40 in Moon’s Atmosphere

Posted on March 10, 2022 by admin1  50

In News

  • Recently, Chandrayaan-2 made the first observations of distribution of Argon-40 in the Moon’s atmosphere.

Key Findings

  • Lunar exospheric species: 
    • 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.
  • Number density: 
    • 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.
  • Mid latitudes: 
    • 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.
  • Spatial heterogeneity: 
    • It also reveals that the distribution in Ar-40 has significant spatial heterogeneity. 
  • Argon Bulge:
    • 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, Moonquakes or regions with lower activation energies, which call for a better understanding of the surface-exosphere interactions and source distributions of Ar-40.

Exosphere

  • Definition: 
    • ‘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.
  • Earth’s moon: 
    • It 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 vaporisation.
  • Exospheric atoms: 
    • The exospheric atoms may be lost to space by the thermal escape (also known as the Jean’s escape). 
    • Also, the atoms get ionised by photo-ionisation and charge exchange with the solar wind ions. 
    • Subsequently, they can be swept away by the convective electric field of the solar wind. 
    • Some of these atoms/ions can also be deposited back on the lunar surface. 
    • Thus, the lunar exosphere exists as a result of a dynamic equilibrium between several source and sink processes.

CHACE 2

  • The Chandra’s Atmospheric Composition Explorer-2 (CHACE-2), a quadrupole mass spectrometer onboard Chandrayaan-2 mission, has made the first-of-its-kind observations of the global distribution of Argon-40 in the tenuous lunar exosphere
  • CHACE-2 was a sequel to the CHACE experiment on the Moon Impact Probe (MIP) of Chandrayaan-1 mission.
  • It draws heritage from the Mars Exospheric Neutral Composition Analyser (MENCA) experiment aboard the Indian Mars Orbiter Mission.

Chandrayaan-2

  • It was launched in July 2019 and was scheduled to be an effort aimed at landing a rover on the Lunar South Pole.
  • It was sent abroad by a geosynchronous launch vehicle, the GSLV-Mk 3.
  • Its lander Vikram carshed and prevented rover Pragyaan from successful travel on the surface of the moon.
  • Had the mission been successful, it would have been the first time a country landed its rover on the moon on its maiden attempt.

Argon-40

  • About:
    • 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
  • Origin: 
    • 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.
  • Observations by CHACE 2:
    • It provides the diurnal and spatial variation of Ar-40 covering the equatorial and mid latitude regions of the Moon.
  • Uniqueness of this finding: 
    • Although Apollo-17 and LADEE missions have detected the presence of Ar-40 in the lunar exosphere, the measurements were confined to the near-equatorial region of the Moon

Upcoming Missions of ISRO

  • Venus Mission:
    • The Shukrayaan-1 could launch in December 2024 as an orbiter headed towards the neighbouring planet Venus.
    • This will be the Indian space agency’s first mission to Venus and is expected to have a mission life of 4 years. 
      • The Venus orbiter will be launched on the rockets made by ISRO.
  • DISHA (Disturbed and quiet-type System at High Altitude):
    • It is a twin-satellite system that will study Earth’s aeronomy, the uppermost layer of Earth’s atmosphere.
    • It will involve twin satellites orbiting Earth at an altitude of 450km. 
  • TRISHNA (Thermal infraRed Imaging Satellite for High-resolution Natural resource Assessment):
    • ISRO and CNES have completed the feasibility study to realise the earth observation satellite mission with a thermal infrared imager, TRISHNA.
    • It is meant for accurate mapping of land surface temperatures.
    • It will acquire imagery of Earth’s surface in the thermal infrared with a resolution and revisit frequency never seen before.
    • Expected launch: In 2024
    • India and France are working on their third joint satellite mission. 
  • ISRO and French space agency CNES (Centre National dEtudes Spatiales) have undertaken two joint missions ‘Megha-Tropiques’, which was launched in 2011, and ‘Saral-Altika’ in 2013.
  • Chandrayaan-3: 
    • It could be set for a launch date by the middle of 2023 with huge progress in incorporating design and testing. 
    • It is the third Moon mission of the ISRO and the successor of the Chandrayaan-2 mission.
    • It involves various processes, including finalisation of configuration, subsystems realisation, integration, spacecraft level detailed testing and several special tests to evaluate the system performance on earth. 
    • Progress was hampered due to the Covid-19 pandemic.
  • Gaganyaan:
    • India’s first human spaceflight mission.
    • It is expected in 2023. 
    • The spacecraft is jointly made by ISRO and HAL.
    • It will carry three Indian astronauts to low earth orbit (of 2000 km or less) for a period of five to seven days.
  • Other Missions: XpoSat, IRNSS

Source: TH


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