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EI2GYB > ASTRO 31.08.21 11:44l 153 Lines 7195 Bytes #999 (0) @ WW
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Subj: Lunar samples solve mystery of the moon's supposed magnetic
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Lunar samples solve mystery of the moon's supposed magnetic shield
Research may help inform a new wave of lunar experiments based on data
that will be gathered by the Artemis mission
Tests of glass samples gathered on Apollo missions show magnetization
may result from impacts of objects like meteors, not as a result of
magnetization from the presence of a magnetic shield.
In 2024, a new age of space exploration will begin when NASA sends
astronauts to the moon as part of their Artemis mission, a follow-up
to the Apollo missions of the 1960s and 1970s.
Some of the biggest questions that scientists hope to explore include
determining what resources are found in the moon's soil and how those
resources might be used to sustain life.
In a paper published in the journal Science Advances, researchers at the
University of Rochester, leading a team of colleagues at seven other
institutions, report their findings on a major factor that influences
the types of resources that may be found on the moon: whether or not the
moon has had a long-lived magnetic shield at any point in its 4.53
billion-year history.
The presence or absence of a shield matters because magnetic shields
protect astronomical bodies from harmful solar radiation.
And the team's findings contradict some longstanding assumptions.
"This is a new paradigm for the lunar magnetic field," says first author
John Tarduno, the William R. Kenan, Jr., Professor of Geophysics in the
Department of Earth and Environmental Sciences and dean of research for
Arts, Sciences & Engineering at Rochester.
Did the Moon Ever Have a Magnetic Field?
For years, Tarduno has been a leader in the field of paleomagnetism,
studying the development of Earth's magnetic shield as a means to
understanding planetary evolution and environmental change.
Earth's magnetic shield originates deep within the planet's core.
There, swirling liquid iron generates electric currents, driving a
phenomenon called the geodynamo, which produces the shield.
The magnetic shield is invisible, but researchers have long recognized that it
is vital for life on Earth's surface because it protects our planet from solar
wind -- streams of radiation from the sun.
But has Earth's moon ever had a magnetic shield?
While the moon has no magnetic shield now, there has been debate over
whether or not the moon may have had a prolonged magnetic shield at
some point in its history.
"Since the Apollo missions, there has been this idea that the moon
had a magnetic field that was as strong or even stronger than Earth's
magnetic field at around 3.7 billion years ago," Tarduno says.
The belief that the moon had a magnetic shield was based on an initial
dataset from the 1970s that included analyses of samples collected
during the Apollo missions.
The analyses showed that the samples had magnetization, which researchers
believed was caused by the presence of a geodynamo.
But a couple of factors have since given researchers pause.
"The core of the moon is really small and it would be hard to
actually drive that kind of magnetic field," Tarduno explains.
"Plus, the previous measurements that record a high magnetic
field were not conducted using heating experiments.
They used other techniques that may not accurately record the
magnetic field."
When Lunar Samples Meet Lasers
Tarduno and his colleagues tested glass samples gathered on previous
Apollo missions, but used CO2 lasers to heat the lunar samples for a
short amount of time, a method that allowed them to avoid altering
the samples. They then used highly sensitive superconducting magnetometers
to more accurately measure the samples' magnetic signals.
"One of the issues with lunar samples has been that the magnetic
carriers in them are quite susceptible to alteration," Tarduno says.
"By heating with a laser, there is no evidence of alteration in our
measurements, so we can avoid the problems people may have had in the past."
The researchers determined that the magnetization in the samples could
be the result of impacts from objects such as meteorites or comets --
not the result of magnetization from the presence of a magnetic shield.
Other samples they analyzed had the potential to show strong magnetization
in the presence of a magnetic field, but didn't show any magnetization,
further indicating that the moon has never had a prolonged magnetic shield.
"If there had been a magnetic field on the moon, the samples we studied
should all have acquired magnetization, but they haven't," Tarduno says.
"That's pretty conclusive that the moon didn't have a long-lasting
dynamo field."
Lack of Magnetic Shield Means an Abundance of Elements
Without the protection of a magnetic shield, the moon was susceptible to
solar wind, which may have caused a variety of volatiles -- chemical
elements and compounds that can be easily evaporated -- to become implanted
in the lunar soil. These volatiles may include carbon, hydrogen, water,
and helium 3, an isotope of helium that is not present in abundance on Earth.
"Our data indicates we should be looking at the high end of estimates
of helium 3 because a lack of magnetic shield means more solar wind
reaches the lunar surface, resulting in much deeper reservoirs of
helium 3 than people thought previously," Tarduno says.
The research may help inform a new wave of lunar experiments based on
data that will be gathered by the Artemis mission. Data from samples
gathered during the mission will allow scientists and engineers to
study the presence of volatiles and better determine if these materials
can be extracted for human use. Helium 3, for instance, is currently
used in medical imaging and cryogenics and is a possible future fuel source.
A lack of magnetic shielding also means that ancient lunar soils may
hold records of past solar wind emissions. Analyzing cores of soil
samples could therefore provide scientists with a better understanding
of the evolution of the sun.
"With the background provided by our research, scientists can more
properly think about the next set of lunar experiments to perform,"
Tarduno says. "These experiments may focus on current lunar resources
and how we could use them and also on the historical record of what is
trapped in the lunar soil."
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