Question Over Theory Of Lunar Formation

[Michaelangelica]

chemical analysis of lunar rocks may force scientists to revise the leading theory for the Moon's formation: that the satellite was born when a Mars-sized body smacked into the infant Earth some 4.5 billion years ago.

 

If that were the case, the Moon ought to bear the chemical signature of both Earth and its proposed 'second' parent. But a study published today in Nature Geoscience¹suggests that the Moon’s isotopic composition reflects only Earth's contribution.

 

Junjun Zhang at the University of Chicago in Illinois and her colleagues used a mass spectrometer to make the most precise measurement so far of the relative abundance of titanium-50 and titanium-47 in Moon rocks gathered by the Apollo missions in the 1970s. The authors report that the lunar ratio of the two isotopes is identical to that found in Earth’s mantle, within about 4 parts per million

http://www.nature.com/news/question-over-theory-of-lunar-formation-1.10300?WT.mc_id=FBK_NPG

 

 

[Turtle]

i don't see a conflict with the impact formation theory if the impacting body had a composition similar to earth's. given that the earth and and the impacting body formed in the same solar system, having similar compositions would be well within expectations. :ebomb: :moon: (the body of the linked article says as much & the headline is just that; a headline.)

[CraigD]

i don't see a conflict with the impact formation theory if the impacting body had a composition similar to earth's. given that the earth and and the impacting body formed in the same solar system, having similar compositions would be well within expectations. :ebomb: :moon: (the body of the linked article says as much & the headline is just that; a headline.)

I don’t think the main and sub headline,

“Question over theory of lunar formation

Titanium signature poses puzzle for popular theory of Moon’s origin”

or the first paragraph

“A chemical analysis of lunar rocks may force scientists to revise the leading theory for the Moon's formation: that the satellite was born when a Mars-sized body smacked into the infant Earth some 4.5 billion years ago.”

are really misleading, just subject to being easily misinterpreted: it’s easy to misinterpret “puzzle” as “major problem”, and “revise” as “reject”, when the article clearly show that neither of these interpretations are the accurate. New data really does seem to demand some revision for the specifics of the giant impact hypothesis.

 

The gist I gather of Zhang and colleagues of the U of Chicago recent analysis and Canup of Southwest Research Institute recent modeling work is that Zhang and team’s new, more accurate mass spectroscope measurement of the abundance of titanium isotopes in Moon rock raise problems for the giant impact model roughly hypothesized mass parameters,

 

Earth (0.905) + Theia (0.107) [imath]\to[/imath] Earth (1.000) + Moon (0.012)

 

, where the number in parenthesis is mass, because the model can’t account for Earth and the Moon’s current Ti isotope ratios being so nearly identical.

 

Canup suggests that new mass parameters,

 

Earth (0.798) + Theia (0.214) [imath]\to[/imath] Earth (1.000) + Moon (0.012)

 

can, by allowing for a longer, hotter vapor cloud, where Ti isotopes destine for the Earth and Moon’s crusts mixed more thoroughly.

 

Note that I’ve shown the mass parameters to 3 significant digits, and assumed a Theia mass of exactly 1 or 2 times Mars’s, just to allow them to add up to the present, precisely known Earth and Moon values. The giant impact hypothesis isn’t this precise in defining these parameters. The key point is that Canup’s new parameters roughly double the mass of Theia, with a corresponding reduction in the mass of pre-collision Earth.

 

With my amateur’s appreciation of the subject, these results and hypotheses give me an appetite for some super-precise measurements of the crust not only of Earth, the Moon, and some asteroids (many of which we’re pretty sure came from Mars), but of Mars and Venus (which may be a good analog for pre-collision Earth). A sample extract and return spaceflight mission is the most obvious way to get this, and is planned for 2018-2023 for Mars, but I wonder if robotic in-place analysis could get the data faster and cheaper? In either case, though Mars missions are not easy thing, getting data from Venus is even more challenging.