2024-08-06 06:20:34
On the Moon, there is no atmosphere, at least not in the sense that we understand it on Earth. There is also no magnetic field to protect its surface from cosmic and solar radiation impacting it. Therefore, one could say that the Moon is “naked” and exposed to the vacuum of space. However, our favorite satellite has something very similar to our atmosphere, a kind of mantle of gases that has so far been a mystery to science. MIT has just solved it.
Stones from outer space. This thin and tenuous atmosphere that was known to exist on the Moon is called the exosphere. The problem is that, as we mentioned earlier, the satellite lacks a magnetic field that provides a restrictive influence like on Earth, so its exosphere should have been stripped away by solar activity quite some time ago.
Therefore, it seemed clear that something was, in some way, “replenishing” these gases as they were used up. A new study conducted by MIT seems to have resolved the mystery: the source of this replenishment is micrometeorites no larger than grains of dust, tiny rocks that constantly collide with the lunar surface, lifting and vaporizing lunar dust and releasing atoms into the space surrounding the Moon.
The statement. As explained in a statement by Nicole Nie, a geochemist at the Massachusetts Institute of Technology (MIT), “we have provided a definitive answer: meteoritic impact-induced vaporization is the dominant process that creates the lunar atmosphere. The Moon is about 4.5 billion years old, and during that time, its surface has been continuously bombarded by meteoroids.”
Not only that, according to the researcher, the study has also shown that over time, a thin atmosphere reaches a stable state “because it is continually replenished through small impacts across the entire Moon,” Nie says.
The problem of the lunar “atmosphere.” Basically, their study always encountered the same barrier: it was too diffuse. It was known to be there because the detectors left by the Apollo missions found different atomic components in it, but researchers have had difficulty determining exactly how it originates.
They report in the new work that micrometeorite impacts were one of the main avenues of study through models, as was a process called ‘ionic sputtering’ in which atoms are ejected from the lunar surface when bombarded with charged particles carried by the solar wind.
A lunar orbiter, key. To reach the conclusion about micrometeorites, they conducted a new analysis. They carefully focused on data from a lunar orbiter called Lunar Atmosphere and Dust Environment Explorer (LADEE), which operated for seven months between 2013 and 2014. “Based on LADEE data, it seemed that both processes play a role,” Nie explains. “For example, it showed that during meteor showers, more atoms are seen in the atmosphere, which means impacts have an effect.”
Additionally, the analysis also showed that when the Moon is protected from the Sun, as during an eclipse, there are also changes in the atoms of the atmosphere, “which means the Sun also has an impact. Therefore, the results were neither clear nor quantitative,” the researcher clarifies.
So what did they do? To narrow it down further, they examined actual samples of lunar dust collected during the Apollo program for two elements: potassium and rubidium, both known to be present on the Moon and which vaporize easily.
Results. These two elements and their particularities proved crucial. When solar particles or micrometeorites collide with the lunar surface, the rubidium and potassium found there vaporize. However, being heavier elements, they fall back to the lunar surface quite quickly. Essentially, the ratios of the isotopes of each element vary depending on whether they are vaporized by micrometeorite impact or by ionic sputtering.
Thus, the next step was to grind the lunar dust down to a fine layer and analyze the results using a mass spectrometer. They found that both processes play a role in generating the lunar exosphere, although the contribution from micrometeorites is more than twice that of the solar wind.
Implications. According to Nie, after the study, it is possible to quantify the role of both processes, “to state that the relative contribution of impact vaporization versus ionic sputtering is approximately 70:30 or greater.” Not only that. The result, in addition to deciphering one of the great mysteries of the Moon, has implications beyond that. For example, if similar processes are occurring in other parts of the Solar System, such as in asteroids and other moons, we could detect them in samples.
“Measuring the isotopes of potassium and rubidium in the regolith of those objects will help us understand how they were affected by meteoritic bombardments and the sputtering of solar wind over geological timescales and how space erosion differs throughout the Solar System,” the researchers conclude.
Image | NASA
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