Apollo samples help unlock secrets of Moon's atmosphere
A groundbreaking study led by Nicole Nie, an assistant professor at MIT's Department of Earth, Atmospheric, and Planetary Sciences, has shed light on the formation of the Moon's exosphere. The research was conducted in collaboration with a team from the University of Chicago and NASA's Goddard Space Flight Center. The team discovered that impact vaporization is primarily responsible for creating the lunar atmosphere. To reach these conclusions, researchers analyzed samples of lunar soil collected during NASA's Apollo missions.
Impact vaporization: A key process in lunar atmosphere formation
Impact vaporization is a phenomenon that occurs when meteorites strike the lunar surface, causing soil and materials to vaporize. These vaporized materials either escape into space or remain suspended in the Moon's atmosphere, continuously renewing its exosphere. "We give a definitive answer that meteorite impact vaporization is the dominant process that creates the lunar atmosphere," stated Nie.
Meteorite impacts have shaped lunar atmosphere over billions of years
Nie further explained that over the Moon's 4.5 billion-year history, its surface has been continuously bombarded by meteorites. This has led to a steady state of thin atmosphere replenished by small impacts all over the Moon. The study also revealed that most atoms stay in the lunar atmosphere due to impact vaporization, whereas ion sputtering — another space weathering process involving solar wind — would eject many atoms into space.
Impact vaporization vs ion sputtering
"From our study, we now can quantify the role of both processes, to say that the relative contribution of impact vaporization versus ion sputtering is about 70:30 or larger," Nie added. The researchers isolated two volatile elements — potassium and rubidium — from each sample and measured their isotopes using a mass spectrometer.
Study's findings could have implications for understanding other celestial bodies
The results showed that soils contained mostly heavy isotopes of both elements, indicating that impact vaporization was the dominant process contributing to the lunar atmosphere's formation. Justin Hu, a lunar soils researcher at Cambridge University, commented on the study's significance: "The discovery of such a subtle effect is remarkable." He added that these findings could have implications for understanding processes on other moons and asteroids, which are the focus of many planned return missions.
