Collision Model of Moon's Formation Apparently Wrong

Someone · #1 by **Someone** » Mar 26, 2012 9:20 pm

The until now believed to be more likely scenario for the formation of the Moon, that it resulted from collision by a Mars-sized body and called the 'Collision Hypothesis', while not conclusively incorrect, appears to have now a very strong piece of evidence against it. The second likely scenario, that the Moon was spun off from Earth (or the two spun apart from each other) and called the 'Fission Hypothesis', would, if this study is accurate, have to be considered to be more likely unless the vaporization in a collision was at a level high enough to explain the result away.
http://www.nature.com/news/question-ove ... id=FBK_NPG

SafeAsMilk · #2 by **SafeAsMilk** » Mar 26, 2012 9:33 pm

Interesting stuff.

So they seem sure that the moon came from Earth, and isn't a caught satellite because their compositions are so similar? Why would the composition of the object that might have slammed into Earth be so different?

Weaver · #3 by **Weaver** » Mar 26, 2012 9:35 pm

I think your use of "apparently wrong" and "more likely" aren't yet justified by the current level of scientific understanding, including this latest study.

While it's a very interesting hypothesis, I don't think that it's conclusive enough to justify the level of certainty you've assigned with those phrases.

Someone · #4 by **Someone** » Mar 27, 2012 2:13 am

Weaver wrote:I think your use of "apparently wrong" and "more likely" aren't yet justified by the current level of scientific understanding, including this latest study.

While it's a very interesting hypothesis, I don't think that it's conclusive enough to justify the level of certainty you've assigned with those phrases.

I actually am back so soon just to say what you said. I think if we are dealing with Lunar surface material, there might be reasons to expect vaporization from initial impact to result in the Lunar surface having Earth's, rather than a mix of the two colliding bodies', material. It is premature, but it is interesting that this unsettles things a little.

Someone · #5 by **Someone** » Mar 27, 2012 2:17 am

SafeAsMilk wrote:Interesting stuff.

So they seem sure that the moon came from Earth, and isn't a caught satellite because their compositions are so similar? Why would the composition of the object that might have slammed into Earth be so different?

They don't have to be hugely different, but they would be expected to differ by quite a lot more than indicated by this particular research result, based on the older empirical data discussed in the linked article. If you want to see a Nature magazine article (or is it a letter?--anyway, simple for that there too) about as simple as they get, just read it.

DavidMcC · #6 by **DavidMcC** » Mar 27, 2012 10:38 am

I wouldn't abandon the giant impact hypothesis just yet, because Zhang's "fission" alternative has problems of its own, and they are not obviously less severe than that of the giant impact model, at least in its latest version:

But Canup says that although the collision model may need revision, it need not be abandoned.

http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question38.html

The Fission Theory: This theory proposes that the Moon was once part of the Earth and somehow separated from the Earth early in the history of the solar system. The present Pacific Ocean basin is the most popular site for the part of the Earth from which the Moon came. This theory was thought possible since the Moon's composition resembles that of the Earth's mantle and a rapidly spinning Earth could have cast off the Moon from its outer layers. However, the present-day Earth-Moon system should contain "fossil evidence" of this rapid spin and it does not. Also, this hypothesis does not have a natural explanation for the extra baking the lunar material has received.

Someone · #7 by **Someone** » Mar 27, 2012 7:19 pm

The new result we are discussing may merely lead to refinement of the Collision Model or its timing. For instance, it may only be consistent with having occurred when the Earth was still entirely molten.

Someone · #8 by **Someone** » Apr 03, 2012 9:23 pm

I have sent an email to a Wendy Zhang at the University of Chicago that I assume is the Junjun Zhang of a brief note saying that the Collision Hypothesis probably needs to be revisited in today's New York Times Science Times section. I brought up the refining idea I just put forward here. Though I assume she is inundated with emails, if I get a response I will say something here. It may not even be the right person, unfortunately, though. Sounds like her area of expertise, but there is a male Junjun Zhang on Facebook, so I wonder if the author of the NYTimes note might have made an identifying error.

Collision Model of Moon's Formation Apparently Wrong

Collision Model of Moon's Formation Apparently Wrong

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