By Will Dunham
WASHINGTON Reuters) – NASA astronauts who became the first people to land on the surface of the Moon in the 1960s and 1970s also discovered a previously unknown lunar feature: It has an atmosphere, albeit a rather tenuous one. Recovered soil samples now reveal the main physical process driving this atmosphere.
By analyzing which forms of two elements – potassium and rubidium – were present in nine small soil samples from five Apollo missions, researchers determined that the lunar atmosphere was created and is sustained primarily by the effects of meteorites, large and small, that hit the Earth. surface of the Moon.
“Meteorite impacts generate high temperatures ranging from 2,000 to 6,000 degrees Celsius (3,600 to 10,800 degrees Fahrenheit). These extreme temperatures melt and vaporize rocks on the lunar surface, similar to the way heat vaporizes water, releasing atoms into the atmosphere.” , said the Massachusetts Institute. by planetary scientist and cosmochemist Nicole Nie, lead author of the study published Friday in the journal Science Advances.
The lunar atmosphere is extremely thin and technically classified as an exosphere, meaning that atoms do not collide with each other because they are so few in number, in contrast to Earth’s thick, stable atmosphere.
“The Apollo missions carried instruments to the lunar surface that detected atoms in the air,” Nie said.
In 2013, NASA sent the LADEE (Lunar Atmosphere and Dust Environment Explorer) robotic spacecraft to orbit the moon to study its atmosphere and surface environment. He identified two processes, known as space weathering, at work – meteorite impacts and a phenomenon called solar wind sputtering.
“Solar winds transport high-energy charged particles, mainly protons, through space. When these particles reach the Moon, they transfer their energy to atoms on the lunar surface, causing them to be ejected from the surface,” Nie said.
Solar wind refers to the constant flow of charged particles from the sun that permeates the solar system.
LADEE has not determined the relative contributions of these two processes to the lunar atmosphere. The new study showed that impacts account for more than 70% of its composition, while solar wind sputtering contributes less than 30%.
The Moon has been constantly bombarded by meteorites – early in its history, by large meteorites that punched holes in craters visible on the lunar surface, and more recently by smaller meteorites, including dust-sized micrometeorites. Some of the atoms lifted by these impacts fly into space. The rest remains suspended above the surface in an atmosphere that is regularly replenished as more meteorites land.
The lunar atmosphere contains mainly argon, helium and neon, along with potassium and rubidium and possibly other elements at lower levels. It extends from the surface of the Moon to a height of about 62 miles (100 km). Earth’s atmosphere extends approximately 6,200 miles (10,000 km).
Instead of investigating the actual atoms in the lunar atmosphere, researchers used lunar soil, called regolith, as a substitute. They used an instrument called a mass spectrometer to examine the ratio of different isotopes of potassium and rubidium in the soil. Isotopes are atoms of the same element with slightly different masses due to different numbers of subatomic particles called neutrons.
“This is possible because the soil on the lunar surface has been interacting with the exosphere since the formation of the Moon, and the different processes leave distinct marks on the isotopic composition of the lunar soil,” said planetary scientist and study co-author Timo Hopp of the Institute Max Planck for Solar System Research in Germany.
There are three isotopes of potassium and two isotopes of rubidium.
After decades of studying the Moon, scientists are still learning about some of its basic processes.
“Many important questions about the lunar atmosphere remain unanswered. We are now able to answer some of these questions due to advances in technology,” Nie said. “When Apollo samples were returned from the Moon in the 1970s, the isotopic compositions of potassium and rubidium in the lunar soils were measured using mass spectrometers. However, at that time, no isotopic differences were observed. Today’s mass spectrometers offer much greater precision.”
(Reporting by Will Dunham; Editing by Daniel Wallis)
