In the 1960s and 1970s, NASA astronauts who first landed on the moon made a surprising discovery: the moon has a very thin atmosphere, now known as an exosphere. Recent research using soil samples collected during the Apollo missions has revealed that meteorite impacts are the primary force behind this atmosphere.
Scientists examined nine tiny soil samples from five Apollo missions, focusing on the forms of two elements, potassium and rubidium. They discovered that meteorite impacts—both large and small—melt and vaporize lunar rocks, releasing atoms into the exosphere. This process occurs at extreme temperatures ranging from 2,000 to 6,000 degrees Celsius (3,600 to 10,800 degrees Fahrenheit), as explained by Massachusetts Institute of Technology planetary scientist and cosmochemist Nicole Nie, the lead author of the study published in Science Advances.
The lunar exosphere, in contrast to Earth’s atmosphere, is so thin that atoms rarely collide with each other. This was initially detected by instruments brought to the lunar surface during the Apollo missions, and further studied by NASA’s LADEE (Lunar Atmosphere and Dust Environment Explorer) spacecraft in 2013. LADEE identified two key processes contributing to the lunar exosphere: meteorite impacts and solar wind sputtering. The latter involves high-energy charged particles from the sun striking the lunar surface and ejecting atoms.
The recent study, however, determined that meteorite impacts contribute over 70% to the moon’s exosphere, while solar wind sputtering accounts for less than 30%. The moon’s atmosphere, consisting mainly of argon, helium, neon, potassium, and rubidium, extends up to about 62 miles (100 km) from the surface, compared to Earth’s atmosphere which reaches approximately 6,200 miles (10,000 km).
To reach these conclusions, researchers used lunar soil as a proxy to study the exosphere. They analyzed the isotopic compositions of potassium and rubidium using advanced mass spectrometers, which offer much greater precision than those available in the 1970s. The isotopic differences observed today provide insights into the ongoing processes shaping the lunar atmosphere.
As scientists continue to study the moon, they uncover new details about its fundamental processes, thanks to technological advancements. This research highlights the dynamic nature of the lunar exosphere and its reliance on external forces like meteorite impacts.