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Ever since their discovery by the Apollo 12 crew, scientists have been puzzled by strongly magnetized rocks found on the Moon. Most Moon rocks that were brought back by the Apollo missions have very little iron, and therefore lack the ability to be strongly magnetized. At first, the magnetic oddities didn’t appear to be related to any lunar geology such as craters or lava flows. Over time, additional lunar missions have provided more data showing that only some portions of the Moon’s crust have magnetic fields. A team of scientists now theorize that the magnetized “patches” on the lunar surface may be the remains of an asteroid that crashed into the Moon shortly after its formation nearly 4.5 billion years ago. The impact crater, known as the South Pole-Aitken basin is one of the largest known in our Solar System.

Mark Wieczorek (Paris Institute for Global Physics), describes the South Pole-Aitken basin as, “this huge, whopping crater that’s roughly half the size of the U.S,” and says it may hold the answers to the mystery of the Apollo 12 rocks.

Studies of the basin show that it is elliptical which suggests the impact was by a large object that hit at an oblique angle. Wieczorek speculates that the impactor was 10% to 30% iron by weight and about 100 times more magnetic than the lunar regolith. Interestingly enough, the theorized impact angle would have flung debris from the object in a pattern very similar to the observed magnetic anomalies. The material could have been magnetized as it cooled by a magnetic field that may have existed early in our Moon’s history.

Wieczorek and his team set out to test their theories with computer simulations of different types of impacts. The research led to a scenario where an object struck the Moon at about a 45 degree angle with a velocity of 15 kilometers per second. The team’s best impact model was described as normal by Wieczorek who stated, “We don’t require improbable conditions.”

Now the team needs to address one other question: How and when did a magnetic field develop on the Moon?

Wieczorek offers a simple solution: Go back to the moon and collect samples.

Source: NASA Lunar Science Institute