How does water change the Moon's origin story?

February 27, 2018, Carnegie Institution for Science
Screen shot from a video simulation of the canonical model of the Moon's formation, in which the proto-Earth was hit by a Mars-sized object between 4.4. and 4.5 billion years ago. Credit: Miki Nakajima and Dave Stevenson.

It's amazing what a difference a little water can make. The Moon formed between about 4.4 and 4.5 billion years ago when an object collided with the still-forming proto-Earth. This impact created a hot and partially vaporized disk of material that rotated around the baby planet, eventually cooling and accreting into the Moon.

For years, scientists thought that in the aftermath of the collision hydrogen dissociated from water molecules and it and other elements that have low boiling temperatures, so-called "," escaped from the disk and were lost to space. This would lead to a dry and volatile element-depleted Moon, which seemed to be consistent with previous analyses of lunar samples.

But ongoing research about the Moon's chemistry is revealing that it may be wetter thaninitially thought, which raises questions about some aspects of this origin story.

"This is still very much an area of active research, so there is much that scientists, including our Department of Terrestrial Magnetism staff scientist Erik Hauri, as well as many other Carnegie colleagues and alumni, are figuring out about how much water exists in the Moon. This is a highly important and challenging question to answer given that we have limited knowledge on the history and distribution of lunar water," explained Carnegie's Miki Nakajima who, together with Caltech's Dave Stevenson, set out to determine whether prevailing Moon-formation theories needed to be adjusted to account for the more recent higher estimates of lunar water content.

A video simulation shows the canonical model of the Moon's formation, in which the proto-Earth was hit by a Mars-sized object between 4.4. and 4.5 billion years ago. Credit: Miki Nakajima and Dave Stevenson.

The work is published by Earth and Planetary Science Letters.

They created detailed models to determine whether existing theories about the Moon-forming collision could explain a wet Moon that's still depleted in other volatile elements like potassium and sodium.

They modeled different conditions and water abundances of the Moon-forming disk. At higher temperatures, their disk was dominated by silicate vapor, which came from evaporation of the mantles of both the proto-Earth and the impactor, with a relatively small abundance of hydrogen dissociated from water. At lower temperatures, their disk was dominated by water, from which hydrogen did not disassociate under this temperature range, making its escape mechanism very inefficient.

"The good news is that our models show that observations of a wet Moon are not incompatible with a giant impact origin," Nakajima explained.

However, it also means that scientists need to come up with other explanations for why the Moon is depleted of potassium, sodium, and other volatile elements. Other possibilities exist, such as the volatile elements in the disk falling onto Earth rather than escaping or being part of the Moon's formation. Or potentially they were part of the Moon when it first accreted from the post-collision disk but were later lost.

Explore further: A dash of water on the lunar rocks

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FieryFly
not rated yet Feb 27, 2018
There has been quite a few studies done about how the moon was formed.. One Theory suggested a impactor struck the early Earth with just enough force to "Burp" enough of the mantle into orbit around earth.. and this burped mantle material became the moon. This mantle material lacks the core metal to give the moon its own gravitational ability to spin, so it became tidal locked to the earth.
rrwillsj
1 / 5 (2) Feb 27, 2018
I'm not certain whether to blame the researchers or the writer & editor for the level of ridiculous reached in this article?

To me, the assumptions and incoherence of the conclusions are the same logic as:

"Your bladder wakes you up in the middle of the night. Still half-asleep, you stumble through the dark, to your toilet. And let fly with a 'whoosh!' of relief.

To suddenly realize that you are pissing all over your own feet!

Then blaming your aimlessness on what your parents were up too, sixty years ago. When they conceived you."

Whatever archaic water was captured by the nascent Moon? Is deeply buried under billions of years of infalling debris and tectonic activities. Most likely locked up in minerals.

What is being detected is the remnant outgasing from recent captures of material from system-wide flotsam. And by recent, I mean the last tens of millions of years.

yaridanjo
1 / 5 (1) Feb 28, 2018
The Earth/Moon system was formed as a double planet:

http://yaridanjo....lan.html
OUR SOLAR SYSTEM

WarrenPlatts
5 / 5 (1) Feb 28, 2018
What is being detected is the remnant outgasing from recent captures of material from system-wide flotsam. And by recent, I mean the last tens of millions of years.


The problem with that is the LCROSS volatiles are more consistent with that found in the early hot disk, rather than with comets. That would seem to entail that outgassing would be true juvenile material present at the formation.
TheGhostofOtto1923
1 / 5 (1) Feb 28, 2018
I'm not certain whether to blame the researchers or the writer & editor for the level of ridiculous reached in this article?
Let me add a totally ad hom observation...

What a fucking pissant you are.

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