Moon's atmosphere revealed through Apollo mission soil samples

In 1971, humanity stumbled upon a surprising revelation: the moon possesses an exceedingly thin atmosphere that evaded detection until after astronauts had already ventured there. While this scientific breakthrough left experts perplexed for decades, a recent study by researchers from the University of Chicago and MIT may have finally unearthed the answer. Through meticulous analysis of lunar soil samples from multiple Apollo missions, the team has discovered compelling evidence that the moon's atmosphere is primarily formed by recurrent impacts from small meteorites.

The study's author, Nicole Nie, who was a PhD candidate at the University of Chicago and is now an assistant professor at MIT, expounds on their findings. According to their comprehensive analysis, meteorite impacts contribute to at least 70% of the lunar atmosphere, while a smaller proportion is generated through solar wind abrasion on the lunar surface. Surprisingly, the answer to this longstanding question had been concealed within lunar soil samples brought back to Earth by the Apollo missions, confirms Nicolas Dauphas, professor of geophysical sciences at the University of Chicago and co-author of the study.

To gain a deeper understanding of the moon's atmosphere, it is important to acknowledge that it drastically differs from Earth's life-sustaining air. The moon's atmosphere is vastly too tenuous to facilitate respiration, merely comprising a haze of atoms scattered at a distance from its surface. Remarkably, these atoms are constantly either returning to the lunar surface or escaping into outer space, necessitating a continuous source for replenishment.

Previous efforts to identify the origin of these atoms yielded inconclusive results. Two prevailing hypotheses highlighted meteor showers as a potential driving force, given the frequent bombardment of rocks on the moon's surface, and the solar wind—an incessant flux of high-energy particles released by the sun—which collides with the lunar surface, causing dust to disperse. In 2013, NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) observed atmospheric spikes during meteor showers and decrease in the atmosphere when the moon was shielded by Earth's shadow, indicating the shielding from the solar wind. However, LADEE failed to conclusively determine the main contributing factor.

To circumvent the need for direct measurement of the lunar atmosphere, Nie and Dauphas turned to lunar soil samples collected during the Apollo missions. These samples encapsulate millions of years' worth of atoms gradually escaping into the expanse of the atmosphere and outer space. Potassium and rubidium, two elements existing in a range of isotopes or atom variations, played a pivotal role in their analysis. Influenced differently by meteor impacts and solar wind, the relative proportions of these isotopes revealed noticeable discrepancies over time.

In the past, distinguishing between these isotopes proved challenging due to a lack of appropriate techniques. However, advances in scientific methods enabled the researchers to discern distinctive patterns by painstakingly quantifying the isotope ratios. Nie elaborated on the findings, stating, "It’s actually quite a clear difference, once you are able to count them. Lunar soils display unique isotope patterns compared to other lunar rocks, shedding light on the role of meteorite impacts and solar wind bombardment as major contributors to replenishing the lunar atmosphere."

Ten lunar soil samples from various locations where Apollo missions had landed were examined, providing intriguing insights into the sources of the moon's atmosphere. The results strongly suggest that meteor showers are the predominant contributor, accounting for a minimum of 70% while solar wind comprises the remaining 30%.

Nie underscores the significance of comprehending space weather, particularly in light of the potential for human colonization of other celestial bodies: "If humans want to move to different planetary bodies someday, we will have to understand what’s going on at the surface to be able to prepare," she states. Furthermore, the scientists emphasize the importance of designing missions to collect and analyze samples from the moon and other planets onsite. This approach offers invaluable opportunities to answer complex questions that are otherwise impossible to address solely through remote spacecraft data.

Dauphas concludes by expressing enthusiasm for future research on lunar samples from the upcoming Chang'E and Artemis missions, recognizing that their team's study fundamentally contributes to the foundation for further exploration. Undoubtedly, this is an exhilarating era for moon-focused research.

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