- 3289 - MOON - Apollo moon rock discoveries? Geologist studying the Earth’s and Moon’s magnetic field that is captured in rock formations could offer a clear picture of just what type of magnetic field the Moon possessed before it mysteriously switched off around 900 million years ago.
--------------------- 3289 - MOON - Apollo moon rock discoveries?
- Most of the Moon rocks brought back by Apollo crews were ejected from their origins by meteor impacts. Without knowing their original orientation as they cooled in lava flows billions of years ago, the magnetic particles inside can’t reveal much about the Moon’s ancient magnetic field.
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- Geologists were able to combine a couple of Apollo-era samples with newer NASA imaging of the Moon’s surface. They gained new insights into the strength and shape of the lunar magnetic field.
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- The interaction between the movement of materials within a planet, like molten rock and lava, and a planet’s rotation creates a planetary magnetic field. The molten material within Earth’s outer core possesses electrical currents. Its movement produces the magnetic field, which extends from the interior of the planet to space, deflects cosmic radiation and particles emitted by the Sun, and causes fantastic-looking polar auroras.
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- Other planets have magnetic fields of various strengths. Earth’s magnetic field is weaker than those belonging to Jupiter, Saturn, Uranus, and Neptune.
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- Today, while the Moon doesn’t have an internal magnetic field, it has some magnetic spots. Geologists were able to determine the angle, or the steepness, of the Moon’s ancient magnetic field from rock samples extracted from an Apollo 17 landing site and compared it to predictions based on assumptions of what the Moon’s magnetic field should have looked like.
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- The field angle matched exactly what they predicted it should be if the Moon’s magnetic field looked like the Earth’s, one with a North and South pole.
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- Because the Moon rotates so slowly and is tidally locked to the Earth, the magnetic field should actually be highly complicated. It should have a field with multiple poles. However, this study shows they looked more like a bar magnet.
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- It is actually surprising the Moon had a magnetic field at all because the lunar core is much smaller than Earth’s. But the findings show the Moon’s field not only resembled Earth’s it may have also been similar in strength.
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- They determined the Moon's magnetic field may have averaged around 50 microTeslas in strength, whereas Earth’s field averages around 25 to 65 microTeslas.
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- Some of the rocks the mission had collected had not been impact ejecta, but rocks that had slumped down from a crater wall. By analyzing both orbiter and Apollo era photos, the rocks’ original orientations could be calculated. They can see the layering that implies the horizontal lava flows within it and that it hasn't moved much from its original position.
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- The Moon’s magnetic field is important because it provides the nearest comparison to Earth for understanding how, why, and when planetary bodies generate magnetic fields and what that means for life. We think that magnetic fields are important for having a habitable planet because they provide shielding in the atmosphere.
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- This study is compatible with theories of polar wander, where the Moon might have shifted its axis of spin to compensate for changes in surface density due to ancient volcanism.
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- Researchers are looking forward to NASA’s Artemis missions, which could return humans to the lunar surface by 2024. We need to have oriented samples, then we can answer a lot more questions.
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- What we learned from the Apollo samples indicate that the Moon generated a magnetic field for at least 2 billion years. However, the geometry of the lunar magnetic field is still largely unknown because the original orientations of essentially all Apollo samples have not been well constrained.
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- Determining the direction of the lunar magnetic field over time could show the mechanism by which the lunar dynamo was powered and whether the Moon experienced true polar wander.
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- Measurements of the lunar magnetic field 3.7 billion years ago as recorded by Apollo 17 mare basalt samples 75035 and 75055 found a mean palaeo-intensity of 50 μT, micro-Teslas
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- The inclination of the magnetic field at the time was 34 ± 10°. Our recovered inclination is consistent with a ‘seleno-centric axial dipole” (SAD) field geometry which is a dipole in the center of the Moon and aligned along the spin axis. Amazing how science works!
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- October 2, 2021 MOON - Apollo moon rock discoveries? 3289
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