In a study published in Science Advances, scientists from MIT and the University of Chicago have identified the primary process responsible for forming and sustaining the moon’s extremely thin atmosphere. Through analyzing samples of lunar soil collected by astronauts during the Apollo missions, the team discovered that impact vaporization is the main process by which the moon has generated and maintained its delicate exosphere over billions of years. The constant bombardment of meteorites and micrometeoroids has kicked up lunar soil, vaporizing certain atoms on contact and lifting them into the air, creating a tenuous atmosphere that is continually replenished by meteorite impacts.
The Lunar Atmosphere and Dust Environment Explorer (LADEE) mission conducted by NASA in 2013 aimed to determine the origins of the moon’s atmosphere. With the remote measurement of soil and atmospheric composition, scientists hoped to correlate these findings with space weathering processes such as impact vaporization and ion sputtering. Preliminary data suggested that both processes play a role in shaping the lunar atmosphere, but the exact contributions were unclear and not quantifiable. By examining Apollo samples, more precise answers could be obtained to pinpoint the origins of the moon’s atmosphere.
By isolating and analyzing potassium and rubidium isotopes in lunar soil samples, the researchers were able to determine the ratios of heavy to light isotopes to differentiate between impact vaporization and ion sputtering. The results showed that mostly heavy isotopes of both potassium and rubidium were present in the soil, indicating that impact vaporization is the dominant process in generating the moon’s atmosphere. The team could quantify the relative contribution of impact vaporization versus ion sputtering and found that impact vaporization accounts for 70% or more of the lunar atmosphere, with the remaining percentage attributed to the solar wind.
The innovative approach of combining potassium and rubidium isotope measurements allowed the researchers to make a groundbreaking discovery regarding the formation of the moon’s atmosphere. This finding has implications beyond the moon’s history, as similar processes could be significant on other moons and asteroids, which are the focus of upcoming return missions. The discovery underscores the importance of studying samples from the moon and other celestial bodies to gain a clearer understanding of the solar system’s formation and evolution, highlighting the critical role of sample return missions in advancing planetary science research.
The study’s lead author, Nicole Nie, emphasized the importance of lunar samples in providing precise data that can be quantitatively analyzed to gain a deeper understanding of celestial bodies’ geological processes. The discovery of the subtle effect of impact vaporization on the moon’s atmosphere showcases the critical role of combining innovative techniques with careful quantitative modeling to unravel complex planetary phenomena. The research was supported by NASA and the National Science Foundation, underscoring the collaborative efforts of various institutions in advancing our knowledge of the moon’s atmospheric processes and the broader implications for planetary science.