In a groundbreaking new study that challenges long-held assumptions about the Moon’s atmospheric composition, researchers have revealed intriguing daily and sporadic variations in carbon, nitrogen, and oxygen ions above the lunar surface. This discovery unveils a previously underappreciated dynamic in the faint and elusive lunar exosphere, offering fresh insights into the Moon’s volatile element reservoirs and their interaction with solar activity. The findings, derived from measurements made by the Kaguya satellite, fundamentally reshape our understanding of how the Moon retains and processes volatile compounds despite its harsh and airless environment.
For decades, the giant impact hypothesis has served as the dominant explanation for the Moon’s formation, positing a largely volatile-poor origin. According to this model, the violent collision that birthed the Moon would have expelled most volatiles, leaving behind a dry, barren world in terms of elements like carbon, nitrogen, and oxygen. However, contrary to this expectation, data collected in situ during lunar missions have repeatedly indicated the presence of volatile elements on and near the Moon’s surface. These observations have prompted scientists to explore the mechanisms that supply and maintain these elements within the lunar exosphere, an exceedingly thin atmosphere composed primarily of ionized particles.
Utilizing an ion mass analyzer aboard the Japan Aerospace Exploration Agency’s (JAXA) Kaguya satellite, the research team conducted highly sensitive measurements of ion species, focusing on C⁺, N⁺, and O⁺ ions. The study identified irregular spikes in the ratio of ionized carbon to oxygen following periods of intensified meteoroid activity. More intriguingly, the data revealed consistent daily fluctuations in both the C⁺/O⁺ and N⁺/O⁺ ratios. These observations suggest a complex interaction between lunar surface reservoirs and external space weather influences, challenging earlier assumptions that micrometeoroid impacts and photoionization are the primary drivers of lunar atmospheric compositions.
Digging deeper into the source of these volatile ions, the researchers proposed two scenarios grounded in the observed data. On one hand, the fluctuating nitrogen-to-carbon ratios suggest the presence of a nitrogen-rich reservoir within the lunar regolith—a hypothesis supported by Apollo sample analyses that detected indigenous nitrogen-bearing compounds. On the other hand, the data could also be explained by emissions of carbon monoxide (CO) and carbon dioxide (CO₂) gases, which would release carbon but negligible nitrogen into the exosphere. These two possibilities indicate previously overlooked reservoirs or processes that replenish volatiles above the lunar surface in tandem with solar wind interactions.
Perhaps most notably, the study attributes the daytime generation of C⁺, N⁺, and O⁺ ions predominantly to solar wind sputtering. This process involves energetic particles emitted by the Sun colliding with the lunar surface, ejecting atoms and molecules into the exosphere. Unlike micrometeoroid impacts or photon-induced ionization, sputtering directly interfaces with the lunar soil’s chemical composition and reveals that the lunar surface itself serves as a volatile source. This finding fundamentally reframes our understanding of the Moon’s tenuous atmosphere by emphasizing the role of extraterrestrial plasma interactions rather than sporadic impact events.
The research team’s findings bear significant implications for planetary science and lunar exploration. The ability of the Moon to retain nitrogen-rich materials and carbonates within its regolith despite billions of years of hostile solar radiation opens new questions about the evolution of lunar volatiles. It also challenges assumptions that the Moon’s atmosphere is a closed, static system. Instead, the lunar exosphere appears remarkably dynamic, responding not only to diurnal solar activity but also to episodic meteoritic influxes, which trigger transient chemical changes visible in ion ratios.
Further, the identification of indigenous volcanic gases as a potential source of volatiles highlights the enigmatic persistence of outgassing processes on the Moon. Apollo mission samples already hinted at sporadic volcanic activity and trapped gases within basaltic rocks, but this study provides vital in situ evidence linking those findings to active replenishment mechanisms. The interplay between ancient volcanic reservoirs and contemporary surface processes could provide a model for similar volatile cycling on other airless bodies in the solar system.
From a technical perspective, the use of ion mass analyzers in lunar orbit marks a sophisticated advance in exospheric measurements. Previous remote sensing methods struggled to tease apart the chemical complexity of such a thin atmosphere, with ionized species often existing at densities too low for ground-based observation. The Kaguya satellite’s instrumentation allowed for real-time, high-resolution detection of ion fluxes, enabling the discovery of temporal fluctuations on a daily scale and during meteoroid shower events. This advancement underscores the critical role of state-of-the-art space instrumentation in unraveling the subtle processes shaping planetary environments.
The implications of these findings extend beyond academic curiosity. As space agencies worldwide gear up for renewed lunar exploration, understanding the Moon’s volatile inventory becomes pivotal to sustaining human presence and resource utilization. Nitrogen, carbon, and oxygen are essential elements for life support systems, and their availability and replenishment mechanisms could influence the design of future lunar bases. Moreover, the study’s insights into volatile cycling provide a science-based foundation for assessing lunar soil processing techniques to extract valuable resources, potentially reducing reliance on Earth-bound supply chains.
Despite the exciting progress, many questions remain open for further investigation. The exact chemical identity and spatial distribution of the nitrogen-rich reservoir require deeper exploration via lander missions and sample return campaigns. Additionally, the interplay between solar wind intensity, micrometeoroid flux, and exospheric composition suggests complex feedback loops that are not yet fully understood. Future missions equipped with enhanced ion detectors and surface instruments could illuminate the processes governing these episodic changes in volatile ion ratios, informing broader models of airless body atmospheres.
The study also rekindles discussion about the preservation of volatiles in extreme environments, illuminating broader themes pertaining to planetary habitability and volatile migration across the solar system. If the Moon can maintain such reservoirs despite its lack of atmosphere and magnetic field, could similar mechanisms operate on other small bodies such as Mercury, asteroids, or even icy moons with tenuous atmospheres? Understanding the underlying physics and chemistry of sputtering and volatile retention on the Moon lays groundwork for comparative planetology and guides expectations for the distribution of life-essential elements elsewhere.
Moreover, the revelation that solar wind sputtering plays a dominant role in ion generation invites renewed scrutiny of charged particle interactions with planetary surfaces. This coupling influences not only exospheric chemistry but also space weathering—the gradual alteration of surface materials due to exposure to space environments. Deciphering how sputtering modifies the lunar regolith’s chemical and physical properties over time could inform interpretations of remote sensing data and geological histories derived from orbital and surface studies.
In summary, this innovative research breathes new life into lunar science by demonstrating that the Moon’s atmosphere is neither inert nor uniformly sparse in volatiles. Instead, it is a dynamic and chemically diverse environment shaped by solar wind sputtering acting on a nitrogen-rich regolith and volcanic gas sources. These results challenge prevailing models of lunar formation and atmospheric evolution and open multiple avenues for ongoing and future scientific exploration. As humanity prepares for its return to the Moon, such discoveries deepen our connection to our closest celestial neighbor and spark exhilarating possibilities for unraveling the mysteries of planetary bodies across the cosmos.
The continuous monitoring of lunar volatile ion ratios through missions like Kaguya represents a vital step toward comprehensively mapping the Moon’s exospheric chemistry and volatile cycling. These findings serve as a compelling reminder that even our nearest astronomical companion holds secrets that defy long-standing assumptions. With advancements in spacecraft instrumentation and renewed scientific focus, the Moon stands poised to reveal its intricate and evolving atmospheric story, enriching our broader understanding of planetary science.
Subject of Research:
Chemical composition and daily variations of carbon, nitrogen, and oxygen ions in the lunar exosphere.
Article Title:
Daily variations of carbon, nitrogen and oxygen ions in a thin lunar atmosphere.
Article References:
Terada, K., Nishihira, R., Yokota, S. et al. Daily variations of carbon, nitrogen and oxygen ions in a thin lunar atmosphere. Nat. Geosci. (2026). https://doi.org/10.1038/s41561-026-01933-2
