Nature paper on Moon's initial evolution - Tidally driven remelting

[Astronuc]

a study in the journal Nature argues for the earlier age, saying that the ancient Moon also went through a period when it got hot and partially remelted, producing new rocks about 4.35 billion years ago.

https://www.npr.org/2024/12/18/nx-s...-35-billion-heres-the-moons-anti-aging-secret

Astronomers have long known that the Earth and Moon are younger than 4.6 billion years, because that's when the solar system got its start.

A huge cloud of dust and gas collapsed inward, forming a new star. Leftover clumps of matter started crashing into each other, glomming together and gradually building up planets.

During this chaotic time, an object the size of Mars smashed into the proto-Earth.

"It would surely have been spectacular," says Nimmo. "It was just so energetic that it's really hard for us to conceive of what it must have looked like."

The paper on Nature - Tidally driven remelting around 4.35 billion years ago indicates the Moon is old
https://www.nature.com/articles/s41586-024-08231-0

The last giant impact on Earth is thought to have formed the Moon1. The timing of this event can be determined by dating the different rocks assumed to have crystallized from the lunar magma ocean (LMO). This has led to a wide range of estimates for the age of the Moon between 4.35 and 4.51 billion years ago (Ga), . . . . Here we argue that the frequent occurrence of approximately 4.35-Ga ages among lunar rocks and a spike in zircon ages at about the same time is indicative of a remelting event driven by the Moon’s orbital evolution rather than the original crystallization of the LMO.

I have yet to read the paper. I'm curious about the interpretation of the Moon's and Earth's geology.


Meanwhile - The first rocks from the Moon’s far side are in this geologist’s hands
https://www.nature.com/articles/d41586-024-03893-2

On 25 June, Li Chunlai watched eagerly as a capsule carrying the first pieces of the far side of the Moon landed on Earth. “Sample, I finally got you,” he thought, as if speaking to an adversary he had spent years trying to outwit.

That moment capped decades of hard work for Li, deputy chief designer for China’s Chang’e-6 mission, which blasted off to the Moon on 3 May. The 3,200-kilogram lander — about as heavy as a pickup truck — spent two days drilling and scooping material on the lunar surface before sending the samples back to Earth.

 

[D H]

The paper on Nature - Tidally driven remelting around 4.35 billion years ago indicates the Moon is old
https://www.nature.com/articles/s41586-024-08231-0

I have yet to read the paper. I'm curious about the interpretation of the Moon's and Earth's geology.

That first paper is quite interesting. It appears to resolve discordant estimates for the Moon's age, but also (in my mind) may raise some new issues.

The discordant estimates of the Moon's age are a fairly solid ~4.5 billion years old based on some lunar zircons versus a very solid estimate of 4.35 billion years old based on several other lunar zircons. The article marks the discrepancy down to tidal heating the occurred 100 to 200 million years after the Moon first formed. The author claims the heating was driven by huge tidal resonances as the Moon passed through a key resonance point, the Laplace plane transition, during its initial rapid recession from the Earth.

A key new issue (to me): How did the Moon retain its frozen shape from before this heating event during this tidal heating? Aside: The Moon is well known to not be in hydrostatic equilibrium. Its shape is more reflective of when the Moon was significantly closer to the Earth. This apparently occurred when the Moon was even closer than the Laplace plane transition that the author claims as the source for this tidal heating. The authors suggest this is due to the partial melt nature of the Moon's mantle during the heating event that left the crust more or less intact.