Meteorite Strikes Are the Primary Creator of the Moon’s Thin Atmosphere, Study Finds

The moon has a thin atmosphere that needs constant replenishing, as its atoms often escape to space due to the weakness of lunar gravity. Scientists know that various weathering processes can send particles from the moon’s surface into its atmosphere, but what’s been less clear is which process is the dominant one.

In a study published last week in the journal Science Advances, researchers report that micrometeorite impacts, which vaporize atoms in the lunar soil, are the primary force contributing to the moon’s atmosphere.

“Our findings provide a clearer picture of how the moon’s surface and atmosphere interact over long timescales [and] enhance our understanding of space weathering processes,” Nicole Nie, co-author of the new study and a planetary scientist at MIT, tells the Guardian’s Nicola Davis.

The moon’s atmosphere is technically called an exosphere because it’s so thin. “It is essentially a sparse collection of atoms, so tenuous that they rarely collide with each other,” Nie says to Astronomy.com’s John Wenz.

Researchers have considered two main reasons for the creation of the moon’s atmosphere: micrometeorite strikes and solar wind. When asteroids or meteoroids traveling at high speeds slam into the moon’s surface, creating craters, they lift vaporized particles into the air, some of which join the moon’s atmosphere. And without a magnetic field, it’s also bombarded by solar wind, a stream of energetic charged particles expelled by the sun.

“When these particles impact the moon, they transfer their energy to lunar surface atoms, causing them to be ejected from the surface,” Nie tells Reuters’ Will Dunham.

In 2013, NASA sent an orbiter to the moon called the Lunar Atmosphere and Dust Environment Explorer (LADEE). The spacecraft studied both the effects of meteorites and solar wind on building the moon’s atmosphere.

“Based on LADEE’s data, it seemed both processes are playing a role,” Nie says in a statement from MIT. “For instance, it showed that during meteorite showers, you see more atoms in the atmosphere, meaning impacts have an effect. But it also showed that when the moon is shielded from the sun, such as during an eclipse, there are also changes in the atmosphere’s atoms, meaning the sun also has an impact. So, the results were not clear or quantitative.”

To better understand the role of these phenomena, researchers studied soil collected from the moon’s surface during the Apollo missions in the 1960s and 1970s. They looked at ten samples, each weighing less than one-thousandth of a pound. They dissolved the crushed soil in acid, allowing them to isolate isotopes—or various versions—of potassium and rubidium.

How much meteorites and solar wind contribute to the atmosphere should affect the concentrations of isotopes in the soil. While both processes would eject lighter isotopes into the atmosphere, leaving primarily heavier isotopes on the ground, finding the exact ratio would illuminate whether meteorites or solar wind played a larger role. So the researchers measured the isotope ratios for both potassium and rubidium.

Based on the results, the team determined that at least 70 percent of the moon’s atmosphere is due to meteorite impacts. Solar wind is responsible for the remaining roughly 30 percent.

The findings help us better understand how the moon works, Simeon Barber, who researches the moon at the Open University in England and did not contribute to the new paper, tells the Guardian. “The moons of Mars, Phobos and Deimos, would be fascinating places to do this kind of study on next,” he adds.

Myriam Lemelin, an Earth scientist at the University of Sherbrooke in Canada who wasn’t involved in the study, tells the Canadian Broadcasting Corporation’s Nicole Mortillaro that while this and previous studies have focused on the moon’s equatorial region, future missions will look at the area around the south pole.

“The samples that will be brought back from the south polar region can definitely be used to look into the same isotopes and see if we can measure different things,” she tells the publication.

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Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.