Impact of a Coronal Mass Ejection on the Lunar Exosphere

Chandrayaan-2 Detects Effects of Coronal Mass Ejection on Lunar Exosphere

For the first time, Chandrayaan-2's CHACE-2 payload has recorded the impact of a Coronal Mass Ejection (CME) on the Moon's exosphere. Observations revealed a sharp increase in total pressure and molecular density in the Moon’s sunlit exosphere during a CME event. This discovery reshapes our understanding of how solar activity influences airless bodies like the Moon and marks another milestone for India’s planetary science efforts.

Why This Breaks the Pattern

The idea that space weather affects an airless celestial body’s atmospheric dynamics isn’t novel — scientists have long theorized it. But until Chandrayaan-2’s observation, such interactions were speculative and largely untested in situ for the Moon. The observation quantified the physical change, recording a clear spike in density and pressure, directly demonstrating the effects of a CME on the lunar exosphere.

The shift is also notable because the Moon lacks a magnetic field. Unlike Earth, which deflects CMEs through its magnetosphere, the Moon absorbs these solar ejecta directly on its surface-bound atmosphere, creating unique interaction dynamics that contrast sharply with CMEs' effect on our planet. Chandrayaan-2’s data closes the gap between simulation models and actual measurements, elevating India’s contributions in space weather monitoring and lunar exospheric studies.

More importantly, it hints at broader implications: how solar radiation affects the sustainability of human activities on or near lunar surfaces. For future lunar habitats, high-energy CMEs could complicate resource extraction and protection from radiation. The finding introduces another variable for space governance policies concerning lunar exploration.

The Machinery Behind the Discovery

CHACE-2 (Chandrayaan-2 Atmospheric Composition Explorer-2) operates aboard the Chandrayaan-2 orbiter as one of its primary scientific payloads. Its mission objectives include studying the composition, distribution, and variability of the lunar neutral exosphere. Historically, CHACE-2 builds upon the groundwork laid by its predecessor, CHACE-1, aboard Chandrayaan-1.

Legally and institutionally, ISRO conducts these lunar missions through the space budget allocated annually by the Department of Space. The 2025 Union Budget earmarked ₹12,543 crore for space programs, of which planetary exploration constitutes a modest portion. With Chandrayaan-2 launched in 2019, on a GSLV Mk-III rocket costing approximately ₹978 crore, it aligns with India's growing ambitions in competitive space research amidst modest fiscal outlays.

The absence of legal frameworks concerning solar interactions with celestial bodies in international treaties also merits attention. Neither the Outer Space Treaty (1967) nor the Moon Agreement (1979) specifically tackles space weather's implications on lunar exploration or exospheric dynamics, showing a gap in global regulatory mechanisms.

What the Data Actually Says

The data reveals fascinating contradictions. While the Ministry of Earth Sciences’ public statements emphasized the immediate rise in pressure and molecular density within the exosphere, these spikes are temporally fleeting — dissipating within hours. It underscores that the lunar exosphere’s atoms rarely engage in molecular collisions due to extremely low densities.

During normal conditions, densities in the lunar exosphere are estimated at around 10^6 particles per cubic centimeter — a figure that balloons during CMEs but rapidly stabilizes. With most released particles being hydrogen and helium ions, CHACE-2 documented densities increasing by over 200%, pushing the boundaries of theoretical predictions made during Chandrayaan-1.

What the data doesn't address is the longer-term impact. Could sustained CME exposure alter the Moon’s surface-bound exosphere permanently? Or worse, affect its regolith composition? Current models cannot definitively address these concerns, leaving room for future missions to investigate residual effects more comprehensively.

The Uncomfortable Questions

While this observation is groundbreaking, the institutional critique comes from two angles: funding limitations and the lack of scientific continuity post-mission. Despite the nearly ₹978 crore allocated for Chandrayaan-2, India’s planetary exploration budget remains a fraction of global peers like NASA or ESA. The volume of data generated from CHACE-2 deserves follow-up research, yet no planned missions post-Chandrayaan-3 explicitly focus on lunar exospheric studies.

Secondly, ISRO’s coordination with other international bodies remains limited concerning collaborative solar interaction studies. A coordinated approach, similar to how NASA and the European Space Agency jointly conduct heliophysics missions, could amplify Indian findings beyond episodic breakthroughs. Without this scaling, leveraging lunar weather observations across global Lunar Gateway initiatives and human habitat design misses a critical scientific opportunity.

The oversight also extends to regulatory concerns — given these CMEs' direct impact on future lunar installations, can treaties like UNCOPUOS evolve to mandate stronger protocols for solar radiation protection? Much depends on whether India will push for lunar governance talks beyond exploratory science directives.

Comparative Anchor: South Korea’s Space Weather Approach

South Korea’s Korean Astronomy and Space Science Institute (KASI) provides a sharp contrast. Unlike ISRO's episodic mission designs, KASI launched its space weather forecast program in 2018 as a continuous effort, pairing terrestrial observations with lunar simulations supported by the Korea Pathfinder Lunar Orbiter (KPLO). KPLO’s instruments, including advanced plasma analyzers, offer continuous mapping of solar wind interactions with lunar plasma structures — an institutional rigor India lacks.

While Chandrayaan-2 succeeds in groundbreaking in situ observation, South Korea’s continuous feedback models create refinements in real-time for cross-disciplinary governance, bridging space weather from exploration science to broader policy concerns for Moon-bound human activity.

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