Moon's crust underwent resurfacing after forming from magma ocean

November 21, 2017, University of Texas at Austin
Moon crust formation graphic. Credit: The University of Texas at Austin/Jackson School of Geosciences

The Earth's Moon had a rough start in life. Formed from a chunk of the Earth that was lopped off during a planetary collision, it spent its early years covered by a roiling global ocean of molten magma before cooling and forming the serene surface we know today.

A research team led by The University of Texas at Austin Jackson School of Geosciences took to the lab to recreate the magmatic melt that once formed the and uncovered new insights on how the modern moonscape came to be. Their study shows that the Moon's crust initially formed from rock floating to the surface of the magma ocean and cooling. However, the team also found that one of the great mysteries of the lunar body's formation - how it could develop a crust composed of just one mineral - cannot be explained by the initial crust formation and must have been the result of some secondary event.

The results were published on Nov. 21 in the Journal for Geophysical Research: Planets.

"It's fascinating to me that there could be a body as big as the Moon that was completely molten," said Nick Dygert, an assistant professor at the University of Tennessee, Knoxville who led the research while a postdoctoral researcher in the Jackson School's Department of Geological Sciences. "That we can run these simple experiments, in these tiny little capsules here on Earth and make first order predictions about how such a large body would have evolved is one of the really exciting things about mineral physics."

The experimental apparatus in the synchrotron facility. The researchers used the machine to recreate moon magma in the lab. Credit: Nick Dygert

Dygert collaborated with Jackson School Associate Professor Jung-Fu Lin, Professor James Gardner and Ph.D. student Edward Marshall, as well as Yoshio Kono, a beamline scientist at the Geophysical Laboratory at the Carnegie Institution of Washington.

Large portions of the Moon's crust are made up of 98 percent plagioclase—a type of mineral. According to prevailing theory, which the study calls into question, the purity is due to plagioclase floating to the surface of the magma ocean over hundreds of millions of years and solidifying into the Moon's crust. This theory hinges on the having a specific viscosity, a term related to the magma's "gooiness," that would allow plagioclase to separate from other dense minerals it crystallized with and rise to the top.

Dygert decided to test the plausibility of this theory by measuring the viscosity of directly. The feat involved recreating the molten material in the lab by flash melting mineral powders in Moon-like proportions in a high pressure apparatus at a synchrotron facility, a machine that shoots out a concentrated beam of high energy X-rays, and then measuring the time it took for a melt-resistant sphere to sink through the magma.

"Previously, there had not been any laboratory data to support models," said Lin. "So this is really the first time we have reliable laboratory experimental results to understand how the Moon's crust and interior formed."

Moon's crust underwent resurfacing after forming from magma ocean
Video of a melt-resistant sphere falling through a magma sample. The researchers calculated the viscosity of the magma sample by measuring how quickly the sphere sank through the magma. Credit: Nick Dygert

The experiment found that the magma melt had a very low viscosity, somewhere between that of olive oil and corn syrup at room temperature, a value that would have supported plagioclase flotation. However, it would have also led to mixing of plagioclase with the , a process that would trap other minerals in between the plagioclase crystals, creating an impure crust on the lunar surface. Because satellite-based investigations demonstrate that a significant portion of the crust on the Moon's surface is pure, a secondary process must have resurfaced the Moon, exposing a deeper, younger, purer layer of flotation crust. Dygert said the results support a "crustal overturn" on the lunar surface where the old mixed was replaced with young, buoyant, hot deposits of pure plagioclase. The older cruse could have also been eroded away by asteroids slamming into the Moon's .

Dygert said the study's results exemplify how small-scale experiments can lead to large-scale understanding of geological processes that build planetary bodies in our solar system and others.

"I view the Moon as a planetary lab," Dygert said. "It's so small that it cooled quickly, and there's no atmosphere or plate tectonics to wipe out the earliest processes of planetary evolution. The concepts described here could be applicable to just about any planet."

Explore further: Rock samples indicate water is key ingredient for crust formation

More information: Nick Dygert et al, A Low Viscosity Lunar Magma Ocean Forms a Stratified Anorthitic Flotation Crust With Mafic Poor and Rich Units, Geophysical Research Letters (2017). DOI: 10.1002/2017GL075703

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14 comments

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Nik_2213
5 / 5 (1) Nov 21, 2017
How does this relate to the 'Late Heavy Bombardment' which caused major resurfacing of much of Moon ??
Parsec
3 / 5 (1) Nov 22, 2017
It is exceedingly unlikely that the moon's crust has eroded so evenly everywhere to expose an underlying layer. What we see is almost certainly what has been there for eons. What an interesting mystery!
szore88
2 / 5 (4) Nov 22, 2017
MIT's Dr. Sean C. Solomon wrote,
"the Lunar Orbiter experiments vastly improved our knowledge of the moon's gravitational field... indicating the frightening possibility that the moon might be hollow."

10. Moon Echoes: On November 20, 1969, the Apollo 12 crew jettisoned the lunar module ascent stage causing it to crash onto the moon. The LM's impact (about 40 miles from the Apollo 12 landing site) created an artificial moonquake with startling characteristics - the moon reverberated like a bell for more than an hour.

This phenomenon was repeated with Apollo 13 (intentionally commanding the third stage to impact the moon), with even more startling results.

Seismic instruments recorded that the reverberations lasted for three hours and twenty minutes and traveled to a depth of twenty-five miles, leading to the conclusion that the moon has an unusually light - or even no - core.
Nik_2213
5 / 5 (2) Nov 22, 2017
If you check out the document rather than his sound-bite, it *specifically* refers to porosity.
http://adsbit.har...000.html

Remember the moon's surface is being endlessly 'plowed' by impactors ranging from nano- to bus or larger...
Nik_2213
5 / 5 (1) Nov 22, 2017
From Wiki...

Several lines of evidence imply that the lunar core is small, with a radius of about 350 km or less.[3] The size of the lunar core is only about 20% the size of the Moon itself, in contrast to about 50% as is the case for most other terrestrial bodies. The composition of the lunar core is not well constrained, but most believe that it is composed of metallic iron alloyed with a small amount of sulfur and nickel. Analyses of the Moon's time-variable rotation indicate that the core is at least partly molten.[4]
Nik_2213
5 / 5 (2) Nov 22, 2017
More from Wiki...

In 2010, a reanalysis of the old Apollo seismic data on the deep moonquakes using modern processing methods confirmed that the Moon has an iron rich core with a radius of 330 ± 20 km. The same reanalysis established that the solid inner core made of pure iron has the radius of 240 ± 10 km. The core is surrounded by the partially (10 to 30%) melted layer of the lower mantle with a radius of 480 ± 20 km (thickness ~150 km). These results imply that 40% of the core by volume has solidified. The density of the liquid outer core is about 5 g/cm3 and it could contain as much 6% sulfur by weight. The temperature in the core is probably about 1600–1700 K.[5]
Solon
1.8 / 5 (5) Nov 22, 2017
"The Earth's Moon had a rough start in life. Formed from a chunk of the Earth that was lopped off during a planetary collision, it spent its early years covered by a roiling global ocean of molten magma before cooling and forming the serene surface we know today".

Pure fantasy.

Nik_2213
5 / 5 (1) Nov 22, 2017
"Pure fantasy."

#S, please justify how you came to that conclusion. I've seen Plate Tectonics, the Big Bang, quarks, neutrino non-zero mass etc etc validated. I'm open to robust proof.
rrwillsj
2.8 / 5 (4) Nov 22, 2017
{Insert cheesy joke here}
Solon
1 / 5 (4) Nov 22, 2017
#N
"I'm open to robust proof."

Me too. How do you intend to prove their claim? I say the lunar surface has been thrashed by major solar storms, which would include iron ions, and provide an explantion for the patches of high iron content surface material. I can't prove it, can you disprove it?
StudentofSpiritualTeaching
1 / 5 (2) Nov 25, 2017
@Solon: about that current scientific belief versa knowledge, that the moon must be a spin-off from Earth, solely based on a probability perspective, due to the high similarity of substance, is anyone still studying alternate explanations? I mean, like this one ow.ly/85R130gO0WW
Nik_2213
5 / 5 (2) Nov 25, 2017
#S, the solar wind is mostly electrons, protons and alpha particles. If you want iron, it must be part of the deep moon brought up by lava-floods following mega-impacts, or delivered directly to surface by nickel-iron-rich impactors which may range in size from nano-dust to 'bus' or larger...

You claim, against best available evidence, that the moon did NOT form from a mega-impact, did NOT have a magma ocean. Please do not just splutter 'Pure Fantasy', please explain, show working.
Nik_2213
not rated yet Nov 25, 2017
#SoST, IIRC, the as-is capture hypothesis was discarded when calculations showed there was no way for the two interacting bodies to quickly lose the excess energy to establish an orbit.
==
Having tangled with 'Technical German' and its 'Reverse Polish' format, I would beg to differ on its claim to be 'beautiful'. Translating syntheses was like doing huge cryptic crosswords. A core sentence often 'ran on' for a complete page, with umpteen agglutinative technical expressions scattered through the text and ALL the verbs at the end. It often took much longer to figure the recipe than to do the work. I have similar issues with Latin...
StudentofSpiritualTeaching
1 / 5 (1) Nov 25, 2017
@Nik: Interesting information on the capture hypothesis. Do you have the link to that study? I wonder, if it will see a correction one future day. On the qualities of German, I had also been surprised when reading this claim of it being the best language there is on this planet. Although, one aspect is obvious, you can translate a no matter how complicated foreign language text loss-less into German, but the opposite is rarely true.

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