Our Moon May Have Formed From Multiple Small Ones, Says Report (go.com)

An anonymous reader quotes a report from ABC News: A series of cosmic collisions may have spawned multiple moonlets that morphed into the one big moon we know today. Rather than one giant impact that knocked off part of early Earth and created the moon, a number of smaller collisions may have produced lots of mini-moons, Israeli scientists reported Monday. And those mini-moons, over millions of years, may have clumped together to make one large one. The researchers conducted nearly 1,000 computer simulations and estimate about 20 impacts could do the job. They say that would explain why the moon seems to be composed of material from Earth, rather than some other planet, too. It's actually an old theory revitalized now by the Weizmann Institute of Science's Raluca Rufu in Rehovot, Israel, and his team. Their findings were published in Nature Geoscience.

Comments

Basically, the mainstream theory, or not?

[Mostly a lurker]

As I understand it, the Giant Impact Hypothesis has Theia's impact creating debris that gradually coalesced into the moon. That this debris formed several smaller moons before they joined up seems plausible, but I am not sure what is really different about what they are proposing.

Re:Basically, the mainstream theory, or not?

[NotAPK]

I read the article.

The main problem is that they claim "the problem" with the impact is that we can't find any evidence or residue from Theia. Well, a lot of the models show that the impacter's core (which would have already differentiated and have a metal core) mostly goes into the core of the earth, and the silicate portion mixes with the bulk silicate earth (BSE). The moon is mostly formed from the earth's mantel, not from the impactor, and this is why the moon has the same composition as the BSE. The problem is working out why there is little to no isotopic fractionation between the moon and the earth, since conventional wisdom suggests a hot violent process such as the giant impact would have resulted in such fractionation.

The most useful part of the article is the suggestion that we go to venus. The similarities and differences in isotopic fractionation between the moon and the earth can only really be interpreted with a greater understanding of isotopic variation among the terrestrial planets, and failed planets (e.g. Vesta) in the asteroid belt.

For more information I recommend reading this paper which is fortunately funded to be open access.