A Study of the Moon’s Internal Structure

A Study of the Moon’s Internal Structure

Apollo Data revealed the Internal Structure of the Moon.

When NASA sent the Apollo Mission to the moon in 1969, they placed the world’s first seismographs there. As a result of the data collected by these seismographs, researchers determined that the moon’s structure was made up of a thin crust measuring approximately 65 kilometers in thickness, a mantle measuring approximately 100 kilometers in thickness, and a core measuring approximately 500 kilometers in radius. At the time, seismic data processing technology was not mature enough to ascertain the features of the core’s composition.

According to recent findings by NASA experts, who used state-of-the-art seismological tools to Apollo-era data, it is likely that the moon has a core that is quite similar to the Earth’s.

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The magnetic field and formation of the Moon

Understanding the lunar core’s composition and structure is essential for building accurate models of the moon’s genesis. The data gives insight into the formation of a lunar dynamo, a natural mechanism our moon may have used to produce and sustain its strong magnetic field throughout its early history.

The team’s results suggest a solid, iron-rich inner core with a radius of almost 150 miles. In contrast, the team’s findings suggest a fluid, predominantly liquid-iron outer core with a radius of around 200 miles. A partly molten boundary layer surrounding the core, with a radius estimated to be about 300 miles in radius, distinguishes it from the Earth in this regard. The study’s findings show that the core includes a tiny amount of light elements such as sulfur, consistent with recent seismology studies on Earth, which reveal the existence of light elements such as sulfur and oxygen in a layer around our core.

Seismometer data from the Apollo era

The researchers anatomized many data obtained during the Apollo lunar flights to develop their findings. The Apollo Passive Seismic Experiment comprised four seismometers installed between 1969 and 1972 and recorded continuous lunar seismic activity until late 1977. The experiment was a collaboration between NASA and the United States Geological Survey.

According to Renee Weber, chief researcher and space scientist at NASA’s Marshall Space Flight Center in Huntsville, Ala., “We utilized tried and reliable approaches from terrestrial seismology to this historical data collection to reporting the first-ever direct discovery of the moon’s core.”

The scientists also used array processing to examine the seismograms from the Apollo missions, which is a method for identifying and distinguishing the signal sources of moonquakes and other seismic activity. The researchers determined how and where seismic waves went through or were reflected by parts of the moon’s core, which provided information about the composition and status of layer interfaces at various depths on the moon.

Results from the Apollo era

Even though sophisticated satellite imaging missions to the moon have made significant contributions to the study of the moon’s history and topography, the deep interior of Earth’s only natural satellite has remained a source of speculation and conjecture since the era of the Apollo space missions. Researchers have previously inferred the presence of a core based on indirect estimations of the moon’s internal characteristics. Still, they were divided on the core’s size, composition, and radius, among other things.

Previous lunar seismic investigations were hampered by a wash of “noise” created by overlapping signals repeatedly bouncing off features in the moon’s fractionated crust, which was a major source of error. To overcome this obstacle, Weber and his colleagues used a technique known as seismogram stacking, also known as digital partitioning of signals, to collect data. When the researchers used stacking, they enhanced the signal-to-noise ratio, which allowed them to more clearly monitor the travel and behavior of each signal as it went through the lunar interior.

According to Weber, the team hopes to continue working with the Apollo seismic data to enhance their estimations of core qualities and define lunar signals and possibly help interpret data returned from future flights.

GRAIL Mission Data

Future NASA missions will aid in the collection of more specific information. This year will see the launch of the Gravity Recovery and Interior Laboratory (GRAIL), a NASA Discovery-class mission that will explore our planet’s interior. Two spacecraft will be involved in the project, which will travel in tandem orbits around the moon for many months to analyze the moon’s gravitational field in unprecedented detail. The project will also give scientists answers to long-standing concerns about the moon, allowing them better to understand the satellite from its crust to its core, exposing underlying structures and, indirectly, the moon’s thermal history.

The Analysis Group

Besides Weber, the team included scientists from Marshall, the University of Arizona University, the University of California, and the Institut de Physique du Globe de Paris in France, among other institutions. Their results have been published in the journal Science’s online version, which you can see here.

Space organizations such as NASA and other space agencies have been examining possibilities for establishing a Multinational Lunar Network, which would consist of a robotic network of geophysical monitoring stations on the moon, as part of attempts to coordinate international missions over the next decade.

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