Did the moon ever have a magnetosphere?

In a few years, NASA will send astronauts to the moon again for the first time since the Apollo era (1969-1972). The long-term goal of the Artemis program is to create the necessary infrastructure for a “sustainable lunar exploration program”. The associated opportunities for lunar research are far-reaching and will likely lead to new discoveries about the formation and evolution of the moon.

In particular, the scientists hope to solve the long-standing mystery of whether or not the moon had a magnetosphere. In anticipation of what scientists might find, an international team of geophysicists led by the University of Rochester examined samples of lunar material brought back by the Apollo astronauts. Based on the composition of these samples, the team determined that the moon’s dynamo was short-lived.

The research was led by John A. Tarduno, William R. Kenan Jr., Professor of Geophysics and Dean of Research for Art, Science and Technology at the University of Rochester. He was supported by researchers from the Rochester Department of Earth and Environmental Sciences, Planetary Science Institute (PSI), Michigan Technological University (MTU), Geological Survey of Japan, and universities in the US, UK, Canada and France.

The moonglass samples tested by Rochester scientists were collected during NASA’s Apollo 16 mission in 1972. (Photo by University of Rochester / J. Adam Window

For their study, the team examined samples of moon glass from a young impact crater (around 2 million years old). This impact caused material on the surface to mix with the material in the mantle, which was formed shortly after the moon was formed (around 4.5 billion years ago). In the past, examination of lunar rocks has revealed evidence of strong Earth-like magnetization, suggesting exposure to a magnetic field.

In the case of Earth, our planetary magnetic field (also known as the magnetosphere) is the result of a geodynamo deep within our planet’s core. This is created by the movement of the molten outer core around the solid inner core, which creates the powerful electrical currents that make up the Earth’s magnetic field. For some time now, scientists have understood the important role our magnetic field plays in maintaining habitability here on earth.

Without this field, the surface of our planet would be bombarded by intense amounts of solar radiation and cosmic rays. In addition, the interaction with charged particles from the sun (solar wind) would have slowly stripped our atmosphere over the course of eons (which happened on Mars). Although the moon has no magnetic field to speak of today, it once did, which begs the question of how long it existed.

In addition, scientists have many unresolved questions about how the moon, given its size and mass, could have maintained a magnetic field. As Tarduno stated in a recent press release from Rochester Newscenter:

“This is a new paradigm for the lunar magnetic field. Since the Apollo missions, there has been the idea that the moon had a magnetic field that was as strong or even stronger than the earth’s magnetic field about 3.7 billion years ago.

The core of the moon is really small and it would be difficult to actually drive such a magnetic field. In addition, the previous measurements, which record a high magnetic field, were not carried out with heating experiments. They used other techniques that may not accurately record the magnetic field. “

A partial sample of the moon glass is placed in a 2 x 2 millimeter square quartz glass tube (insert) and then analyzed with the laboratory’s superconducting quantum interference device (SQUID) magnetometer. The results provide information about the moon’s floor – and could help support a new wave of lunar experiments. Photo credit: University of Rochester / J. Adam Window photos

Tarduno has been a leader in paleomagnetism for years, where geophysicists study the evolution of the Earth’s magnetic field to learn more about planetary evolution, environmental changes and their interrelationships. Tarduno and his team briefly heated the moon glass samples with carbon dioxide lasers (CO2) and then measured their magnetic signals with highly sensitive superconducting magnetometers.

This allowed them to get more accurate readings of their magnetization without changing it, which in the past was possibly a factor and led to misleading results. Unfortunately, the researchers found that the readings they obtained could be the result of meteorite or comet impacts, rather than a magnetic field. Similarly, their examination of other samples showed that they had the potential to record strong core dynamo-like magnetic fields.

However, these samples showed no magnetization, further evidence that the moon never had a long-lived magnetic field. Said Tarduno:

“One of the problems with lunar samples was that the magnetic carriers in them are quite susceptible to change. By heating with a laser there is no sign of a change in our measurements so we can avoid the problems people have had in the past.

If there had been a magnetic field on the moon, the samples we examined would all have received magnetization, but that’s not the case. It is quite conclusive that the moon did not have a long-lived dynamo field. ”

A new study suggests that the moon’s magnetic field from a dynamo in its liquid metallic core (inner red sphere) lasted 1 billion years longer than expected. Photo credit: MIT / Hernán Cañellas / Benjamin Weiss

These results contradict previous research conducted by MIT’s Department of Earth, Atmospheric and Planetary Sciences, in which analysis of lunar rocks collected from the Apollo 15 mission suggested the moon was before 1 and 2.5 Had a magnetic field billions of years ago. Scientists previously suspected that the moon’s magnetic field disappeared about 1 billion years after it was formed (about 3 to 3.5 billion years ago).

The implications of these results are of great importance for our understanding of the composition and evolution of the Moon. Without the protection of a magnetic field, the moon would be vulnerable to solar wind, which could cause volatile compounds to nestle in the lunar floor. This includes carbon, hydrogen, water, but also compounds such as helium 3, which are not available in abundance here on earth. Said Tarduno:

“Our data suggests that we should look at the high end of the helium-3 estimates, since a lack of magnetic shielding means more solar wind is reaching the lunar surface, resulting in much deeper helium-3 reservoirs than that People so far thought.

“Against the background of our research, scientists can better think about the next lunar experiments. These experiments can focus on the current lunar resources and their use, as well as the historical records of what is trapped in the lunar soil. “

Illustration of Artemis astronauts doing research on the lunar surface. Credits: NASA

When astronauts begin long-term sojourns on the lunar surface, they must rely on local ice sources and other resources to support their operations – a process known as In-Situ Resource Use (ISRU). This research could help inform field research, essential infrastructure creation, and meeting electricity needs. For example, helium-3 is currently used in medical imaging and cryogenics and could one day be used as fuel for fusion reactors.

A short-lived magnetosphere also means that the lunar surface has a more complete record of solar wind emissions. This could allow scientists to reconstruct a record of solar activity and the evolution of the sun by examining soils at different depths. The study, titled “Absence of a long-lived lunar paleomagnetosphere,” describing the team’s findings, recently appeared in Science Advances.

Further reading: Rochester University

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