In News:

• In a landmark discovery, the Indian Space Research Organisation (ISRO) announced that Chandrayaan-2’s orbiter has, for the first time, recorded the impact of a Coronal Mass Ejection (CME) from the Sun on theMoon’s exosphere — the thin, outermost layer of its atmosphere.
• The finding, made using the CHACE-2 (Chandra’s Atmospheric Composition Explorer-2) payload, marks a significant step in understanding how solar activity influences airless celestial bodies like the Moon.

About the Observation

• The CHACE-2 instrument, aboard Chandrayaan-2’s orbiter, detected a sharp rise in total pressure and molecular density in the Moon’s sunlit exosphere during a CME event on 10 May 2024.
• This observation confirmed, for the first time, theoretical predictions about how high-energy solar emissions affect the Moon’s extremely tenuous atmosphere.
• The findings were published in the journal Geophysical Research Letters (August 2025) under the title “Impact of a Coronal Mass Ejection on the Lunar Exosphere as Observed by CHACE-2 on the Chandrayaan-2 Orbiter.”

Understanding Coronal Mass Ejections (CMEs)

• CMEs are massive bursts of charged particles — primarily ionized hydrogen and helium — ejected from the Sun’s corona.
• When directed toward planetary bodies, these particles can interact with their atmospheres or surfaces, causing chemical and physical changes.
• On Earth, CMEs are often linked with geomagnetic storms and auroras, but their influence on airless bodies like the Moon had remained largely unobserved until this study.

The Lunar Exosphere: Nature and Composition

• The Moon’s atmosphere is so thin that it is classified as an exosphere — a region where individual gas atoms and molecules rarely collide.
• The boundary of the lunar exosphere directly touches the Moon’s surface, making it a “surface-boundary exosphere.”
• It is primarily composed of trace elements such as helium, argon, sodium, and potassium, released through processes like:
  • Solar wind interactions (bombardment by charged particles),
  • Photon-stimulated desorption (solar radiation freeing surface atoms), and
  • Micrometeorite impacts (which vaporize surface material).
• Since the Moon lacks a global magnetic field, its exosphere is directly exposed to solar wind and CMEs, making it a natural laboratory for studying space-weather effects.

Chandrayaan-2 Mission Overview

• Launch Date: 22 July 2019, by GSLV-Mk III-M1 from Sriharikota.
• Components: Orbiter, Lander (Vikram), and Rover (Pragyan).
• Although communication with the lander was lost during descent on 7 September 2019, the orbiter remains fully operational in a 100 km × 100 km lunar orbit.
• Objective of CHACE-2: To analyse the composition, distribution, and temporal variability of the Moon’s neutral exosphere.

Key Findings of the Observation

• During the May 2024 CME event, CHACE-2 recorded a ten-fold increase in the number density of neutral atoms and molecules in the Moon’s dayside exosphere.
• The total pressure in the exosphere rose sharply, indicating enhanced release of surface atoms due to direct CME particle bombardment.
• The results provided empirical validation for long-held theoretical models on solar-lunar interactions.
• This was the first direct evidence of how the Moon’s atmospheric conditions respond dynamically to solar events.

Significance of the Discovery

• Scientific Advancement:
  • Deepens understanding of space weather phenomena and their effects on airless celestial bodies.
  • Offers valuable insights into Sun–Moon interactions and how charged solar particles shape planetary exospheres.
• Operational Relevance:
  • Enhances the ability to predict and model space-weather impacts on future lunar missions and human habitats planned by 2040.
  • Helps design radiation-resistant systems for lunar surface operations.
• Strategic and Technological Implications:
  • Reinforces India’s growing expertise in planetary science and space environment monitoring.
  • Demonstrates the long-term operational success of the Chandrayaan-2 orbiter, even years after its launch.
• Global Collaboration Potential:The findings can inform international lunar missions, including NASA’s Artemis and JAXA’s SLIM, contributing to a shared understanding of lunar space weather dynamics.