Despite having no substantial atmosphere, the Moon’s weak gravitational pull could be the primary reason for its lack of environmental development. Despite being battered by meteorite impacts, the planet is currently thought to be maintaining a fragile atmosphere – often referred to as an exosphere.
Asteroids and comets have relentlessly pummeled the Moon’s surface over its approximately 4.5 billion years of existence. Researchers at MIT and the University of Chicago have discovered that lunar soil samples collected by astronauts during the Apollo era contain evidence that meteorites, ranging from massive bodies to tiny micrometeoroids smaller than grains of sand, have triggered a subtle influx of atoms into the Moon’s exosphere.
While some atoms drift off into space or settle back onto the lunar surface, the ones that linger form a tenuous atmosphere, constantly rejuvenated by the impact of new meteorites crashing onto the ground.
Researchers recently published findings in Science Advances stating that over extended periods, micrometeorite-induced vaporization supplies the primary source of atoms within the lunar atmosphere.
Prepared for launch
In 2013, NASA launched its LADEE (Lunar Atmosphere and Dust Environment Explorer) orbiter to the Moon, with a primary objective of uncovering the lunar atmosphere’s mysterious origins. Scientists at LADEE detected unexpected atomic signatures in the lunar exosphere during meteor showers, suggesting that the impacts of meteoroids on the Moon’s surface play a significant role in shaping its atmospheric composition. Notwithstanding this, lingering doubts persist regarding the process by which emotional resonance transforms into an ambient atmosphere.
Researchers from MIT and the University of Chicago, under the guidance of Professor Nicole Nie at MIT’s Department of Earth, Atmospheric and Planetary Sciences, sought to investigate the isotopic signatures of lunar soil components that could best indicate the effects of micrometeoroid impacts on the moon’s surface. They selected potassium and rubidium.
Potassium and rubidium ions exhibit a pronounced propensity for two fundamental processes: vaporization and ion sputtering.
When subatomic particles collide at incredible velocities, they generate an immense amount of heat, triggering atomic excitation that ultimately leads to the rapid vaporization of surrounding matter, propelling it through space. Ion sputtering involves intense energetic collisions that liberate individual atoms without vaporizing the sample. Atoms potentially ejected by ion sputtering may possess surplus energy and traverse faster than those expelled by impact vaporization.
The dual effects of these events can both generate and sustain a lunar ambiance in the aftermath of meteorite collisions.
If atoms dispatched into the atmosphere by ion sputtering possess a kinetic energy advantage, why do researchers consistently find that most atmospheric atoms actually originate from atmospheric vaporization processes?
Touching again down
Since lunar soil samples previously had their lighter and heavier isotopes of potassium and rubidium quantified by NASA, Lie’s team employed calculations to determine which collision scenario was more likely to retain distinct isotopes from escaping the atmosphere.
Researchers found that ions expelled through ion sputtering acquire sufficient kinetic energy to transcend the Moon’s gravitational pull, ultimately escaping into space at velocities exceeding the necessary threshold for interstellar travel. Despite being immersed within an atmosphere, atoms may still become dislodged from it.
The proportion of atoms that achieve escape velocity following atomic vaporization hinges directly on the temperature at which this process occurs. As temperatures decline, the likelihood of atomic escape decreases due to reduced vitality ranges associated with vaporization endpoint.
“Impression vaporization is the primary driver of the lunar atmosphere’s long-term supply, responsible for more than 65% of potassium atoms, while ion sputtering accounts for the remaining fraction.”
Atoms are sometimes dislodged from the lunar atmosphere through various mechanisms. Ions in the exosphere tend to remain suspended due to their relatively low mass, whereas heavier ions precipitate back to the surface as they exceed this threshold? Others are ionized by electromagnetic radiation from the solar wind and occasionally swept away by solar wind particles into the surrounding area.
What researchers have discovered about the lunar environment through the study of lunar soil may have significant implications for the investigation of other celestial bodies. Atoms have been known to be launched into the relatively thin exosphere surrounding a planet, which is significantly less dense than that of the Moon. The study of Martian soil could potentially inform the design of pattern return missions to Earth, while also providing valuable insights into how meteorite impacts shape the planet’s atmosphere.
As humanity embarks on a new era of manned lunar missions, the Moon may yet hold secrets about where its atmosphere originates and where it disappears.
Science Advances, 2024. DOI:
