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The moon has a thin atmosphere (artistic conception). Image source: NASA official website

Although there is no breathable air on the moon, it does have an extremely thin atmosphere. How was the moon's atmosphere formed? Scientists from the Massachusetts Institute of Technology and the University of Chicago published a paper in Science Advances pointing out that the moon's atmosphere is mainly the product of impact vaporization.

How to understand the impact vaporization process? Let's start with the lunar soil. Analysis shows that in the 4.5 billion years of the moon's history, its surface has been constantly hit, first by huge meteorites and then by dust-sized "micrometeorites". These continuous impacts lifted the lunar soil and vaporized some atoms. Some atoms were ejected into space, while others were suspended above the moon, forming a thin atmosphere that was constantly replenished as meteorites continued to hit the lunar surface. Therefore, impact vaporization is the main process that has produced and maintained the moon's extremely thin atmosphere for billions of years.

In fact, the process of determining the origin of the lunar atmosphere is not easy. In 2013, NASA launched the Lunar Atmosphere and Dust Environment Explorer, whose mission is to determine the origin of the lunar atmosphere.

"We speculate that two space weathering processes played a role in shaping the lunar atmosphere: impact vaporization and ion sputtering," says Nicole Nieh, an assistant professor in MIT's Department of Earth, Atmospheric and Planetary Sciences. Ion sputtering is a phenomenon involving the solar wind, which carries high-energy charged particles from the sun through space. When these particles strike the lunar surface, they transfer energy to atoms in the soil and sputter those atoms into the air.

To more accurately determine the origin of the lunar atmosphere, scientists collected 10 lunar soil samples, each weighing about 100 mg. They tried to first separate potassium and radium from each sample. Both elements are volatile, and each element exists in several isotopes, which means they are easily vaporized by impact and ion sputtering.

Scientists reasoned that if the lunar atmosphere is composed of atoms that evaporated and became suspended in the air, then the lighter isotopes of these elements should float more easily, while the heavier isotopes are more likely to be redeposited in the soil. Impact vaporization and ion sputtering could result in very different isotope ratios in the soil. The specific ratios of light and heavy isotopes of potassium and radium in the soil should reveal the main processes that led to the origin of the lunar atmosphere.

Further analysis results show that 70% of the lunar atmosphere may be the product of meteorite impacts, while the remaining 30% may be formed by the solar wind.

(Source: Science and Technology Daily)