CHACE (CHandra's Altitudinal Composition Explorer)

The Moon Impact Probe (MIP) experiment on Chandrayaan-1 consisted of three instruments. The CHACE intrument on the MIP was a neutral mass spectrometer from SPL, VSSC. CHACE had the scientific objective to study the latitudinal-altitudinal distribution of neutral composition on the sunlit side of the tenuous lunar atmosphere. CHACE performed well on November 14, 2008, both during the rehearsal phase and during the actual mission when the MIP was released from the mother spacecraft Chandrayaan-1 at 100 km  from the Lunar surface, and had a free-fall along the 140 degree East loungituted landing  close to  the Lunar South Pole at 89 degree. Observations were obtained with an altitude resolution of 250 m and a latitudinal resolution of 0.1 degree from 45N to 89 degree South latitude. The CHACE was the first successful experiment to measure the composition of the Lunar atmosphere in its sunlit side. The major scientific outcomes from CHACE data analysis are listed below:

  • Direct evidence for water (H2O) in the sunlit lunar exosphere.
  • CO2 dominance in the sunlit lunar exosphere.
  • Indication of lunar North - South asymmetry (spatial heterogeneity) in radiogenic activity through 40Ar to 36Ar ratio in the lunar exosphere.
  • Presence of significant amount of heavier (mass number>60 amu) constituents in the lunar exosphere.
  • Spatial distribution of molecular Hydrogen and Neon in lunar dayside exopshere.

Publications from CHACE experiment

  • Sridharan, R., S. M. Ahmed, T. P. Das, P. Sreelatha, P. Pradeepkumar, N. Naik, and G. Supriya, " 'Direct evidence of water (H2O) in the sunlit lunar ambience from CHACE on MIP of Chandrayaan-I", Planetary and Space Science, 58, 947-950, 2010. (
  • Sridharan, R., S. M. Ahmed, T. P. Das, P. Sreelatha, P. Pradeepkumar, N. Naik, and G. Supriya, "The sunlit lunar atmosphere: a comprehensive study by CHACE on the Moon Impact Probe of Chandrayaan-1", Planetary and Space Science, 58, 1567-1577, 2010. (
  • Sridharan, R., T. P. Das, S. M. Ahmed, and A. Bhardwaj, "Indicators for localized regions of heavier species in the lunar surface from CHACE on Chandrayaan-1", Current Science, 105 (11), 1470-1472, 2013.
  • Sridharan, R., T. P. Das, S.M. Ahmed, G. Supriya, A. Bhardwaj, and J.A. Kamalakar, "Spatial heterogeneity in the radiogenic activity of the lunar interior: Inferences from CHACE and LLRI on Chandrayaan-1", Advances in Space Research, 51, 168-178, 2013. (
  • Thampi, S. V., R. Sridharan, T. P. Das, S. M. Ahmed, J. A. Kamalakar, and A. Bhardwaj (2015), "The spatial distribution of molecular hydrogen in the lunar atmosphere - new results", Planetary and Space Science, 106, 142-147 (
  • Das, T. P., S. Thampi, A. Bhardwaj, S. M. Ahmed, and R Sridharan (2016), "Observation of Neon at mid and high latitudes in the sunlit Lunar Exosphere: Results from CHACE aboard MIP/Chandrayaan-1", Icarus, doi: 10.1016/j.icarus.2016.02.030.

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