The Moon has no breathable air, but it does have a thin atmosphere resulting from the impact of micrometeorites over billions of years, a process explained Friday in a study published in Science Advances.
A team from the Massachusetts Institute of Technology (MIT) and the University of Chicago reported that the process that formed the atmosphere of Earth’s natural satellite and still maintains it is primarily contact vaporization during meteorite impacts.
The researchers studied lunar soil samples collected by Apollo astronauts and data from NASA’s LADEE lunar probe.
LADEE was designed to determine the origins of the satellite’s atmosphere.
Analysis suggests that throughout the Moon’s 4.5 billion-year history, its surface has been continuously bombarded, first by massive meteorites and, more recently, by smaller, dust-sized micrometeorites.
These impacts lift up the lunar soil, vaporizing certain atoms on contact and launching the particles into the air.
While some are ejected into space, others remain suspended, forming a tenuous atmosphere that is constantly renewed as meteorites continue to reach the surface.
“We provide a definitive answer that vaporization by meteorite impacts is the dominant process in creating the lunar atmosphere,” said study lead author Nicole Nie of MIT in a statement.
Data from the LADEE mission, launched in 2013, indicate that two processes play a role in creating the lunar atmosphere: impact vaporization and ion sputtering.
Sputtering is a phenomenon related to the solar wind, which transports energetically charged particles from the Sun through space.
When these particles collide with the lunar surface, they can transfer their energy to atoms in the soil and send them into the air.
To more precisely determine the origins of the lunar atmosphere, the team used ten samples of lunar soil to first attempt to isolate two elements from each sample: potassium and rubidium.
Both elements are volatile, meaning they are easily vaporized by impact and ion spray.
The team analyzed the presence of potassium and rubidium isotopes. Each element exists as several isotopes, which are variations of the same element, with the same number of protons but slightly different numbers of neutrons.
The scientists tested the theory that impact vaporization and ion sputtering should result in very different isotopic ratios in the soil.
The specific ratio of light to heavy isotopes remaining in the soil, for both potassium and rubidium, should reveal the main process contributing to the origin of the lunar atmosphere.
Analysis of lunar soil samples showed that the surface contained mostly heavy isotopes of potassium and rubidium.
Using modeling, the researchers quantified the ratio of heavy to light isotopes of potassium and rubidium and, comparing the two elements, found that impact vaporization was “in all likelihood the dominant process by which atoms vaporize and rise to form the lunar atmosphere,” the study noted.
Finally, the team quantified the contribution of both processes and established that 70% or more of the lunar atmosphere is the product of meteorite impacts, while the remaining 30% is a consequence of the solar wind.…Read more by Blaine
