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What causes the big mass anomaly under the moon?

The dark blue South Pole Aitken Basin. The dotted line represents the mass anomaly.
Credit: NASA / Goddard Space Flight Center / University of Arizona

On the other side of the moon, at the South Pole, there is an enormous and very strange structure. And scientists believe they know the cause of this anomaly.

The South Pole Aitken Basin is a huge crater created by an ancient impact on the Moon and its longest axis would range from New York City to Omaha (Nebraska). Beneath that pool is a strange anomaly ̵

1; a mass surplus that extends at least 300 kilometers into the depth and is more than ten times the Earth's crust. Scientists suspect that this is a remnant of the impactor that created the crater.

Two data sets contributed to the study: Lunar Orbiter Laser Altimeter (LOLA) topographical data aboard the Lunar Reconnaissance Orbiter (LRO) and global gravitational data from the pair of small spacecraft for gravity and interior restoration (GRAIL). The analysis of the two, according to the article published in Geophysical Research Letters, found a "noticeable mass surplus in the mantle" under the pelvis with an additional mass of about 2.18 trillion (that is 10 ^ 18) kilograms. That's about the size of a decent sized asteroid.

How much extra mass landed there? The team presented two ideas. Possibly, a process caused certain materials to concentrate under the pelvis as the lunar mantle cooled. Interestingly enough, the extra mass might indicate that there is a huge metal core in the lunar mantle left behind by the impact. Either way, should this mass anomaly persist under further observation, it will be significant implications for the understanding of lunar history scientists. If the mass was created by an impact, the location about 400 kilometers southeast of the crater center could help improve our understanding of how craters are created by impact. If it was caused by the uneven crystallization of a magma ocean, scientists will want to understand why and how it happened.

Lately there has been a lot of excitement around the moon, also thanks to the fact that China has reached its Chang'e-4 mission on the other side of the moon and because the US is working to bring people to the lunar surface return. And research has shown that the South Pole Aitken Basin is a very interesting place. Only recently, the 4 mission scientists from Change found clues about mantle material in the pelvis, possibly posed by another impactor.

The moon is a very strange place. Who knows what we will find on our return?

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