Chandrayaan-2 Makes First-Ever Observation of Sun’s Coronal Mass Ejection Effects on Moon With CHACE-2 Instrument

New Delhi, October 19: India's Chandrayaan-2 lunar orbiter on Saturday made the first-ever observation of the effects of the Sun's Coronal Mass Ejection (CME) on the Moon, with one of its scientific instruments, Chandra's Atmospheric Composition Explorer-2 (CHACE-2), onboard.

Observations from CHACE-2 showed an increase in the total pressure of the dayside lunar exosphere (fragile atmosphere) when the CME impacted the Moon. The total number density (number of neutral atoms or molecules present in an environment per unit volume) derived from these observations showed an increase by more than an order of magnitude. This increase is consistent with earlier theoretical models, which predicted such an effect, but CHACE-2 onboard Chandrayaan-2 has observed such an effect for the first time, an official statement said. ISRO’s Lunar Orbiter Chandrayaan-2 Detects Solar Impact on Moon’s Atmosphere.

ISRO’s Chandrayaan-2 Detects Solar Impact on Moon’s Atmosphere

The Earth's Moon has a fragile atmosphere, which falls under the category of 'exosphere', implying that the gas atoms and molecules in the lunar environment rarely interact despite their coexistence. The boundary of the exosphere is the surface of the Moon, and hence the Moon's exosphere falls under the category of 'surface boundary exosphere'. The exosphere on the Moon is produced by a number of processes, which involve the interaction of solar radiation, solar wind (ions of Hydrogen, Helium and a small quantity of heavier ions emanated from the Sun) and the impact of the meteorites with the surface of the Moon.

These processes liberate atoms/molecules from the surface of the Moon, which become a part of the exosphere. In general, the exosphere of the Moon is highly sensitive to even small variations of the factors that are responsible for its creation, and such a factor is the emission of the coronal mass of the Sun, known as CME (short form of Coronal Mass Ejection). CMEs are events when the Sun ejects significant quantities of its building material, mainly comprising Helium and Hydrogen ions. ISRO Chairman V Narayanan Lists 9 Areas Where India Is Number 1 in Space Technology, Check List Here.

These effects are substantial on the Moon, as the Moon is an airless body, which is also deprived of any global magnetic field, the presence of which would have shielded (even partially) the solar effects on its surface. This opportunity to directly observe the effects of the CME impacting the Moon came in a rare occurrence, on May 10, 2024, when a series of coronal mass ejections (CMEs) were hurled by the Sun. This increased quantity of the solar coronal mass that impacted on the Moon enhanced the process of knocking off the atoms from the lunar surface, thereby liberating them to the lunar exosphere, which manifested as the enhancement of the total pressure in the sunlit lunar exosphere.

This observation would provide scientific insight into the understanding of the lunar exosphere and space weather effects on the Moon. Apart from pushing the edge of our scientific understanding about the Moon and the lunar space weather (the effect of the Sun's emissions on the Moon), this observation also indicates the challenges of building scientific bases on the Moon. Lunar base architects need to account for such extreme events, which would temporarily alter the lunar environment, before the effects subside.

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