interior structure, origin and evolution of the moon

8/9/2019 Interior Structure, Origin and Evolution of the Moon

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Interior structure, origin and

evolution of the Moon

http://www.marcusmoon2022.org/


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Before and after Apollo

Prior to the Apollo Missions, some scientistsbelieved the Moon formed in the early SolarSystem along with the other planets and had

remained a primitive body.

Because of Apollo, we have learned this is notcorrect. In fact, the lunar samples brought

back by Apollo, and subsequent remote sensingmissions, have taught us a great deal about thegeologic history of the Moon.


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Implications for the origin and evolution of the

Moon from Apollo missions?

Oldest Moon rocks are 4.3 billion years old

Depletion of volatiles (H2O, K, Na, Au, etc)

Enrichment of high temperature elements (Mg,

Al, Si, Ca, Th, U, etc).

Similar oxygen isotopic ratio as the Earth.

Moons orbit lies neither in the equatorialplane of Earth or in the ecliptic plane.


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Moon quakes: Very few, and very low attenuation (i.e.,

they last for many tens of minutes).


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Moon quakes: Very low attenuation (i.e., they last for

many tens of minutes).


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S-waves do not travel through liquids, hence, the Moons

asthenosphere must be plastic.


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Moon quakes originate at the boundary between the rigid lithosphere and the plastic

asthenosphere, and on the side of the Moon facing Earth.


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The Near side: Has more mare: 32% of its

surface is mare covered

compared with 2% of the far

side (globally mare cover

17%).

The Far side:

Large basins filled on near

side, not filled on far side.

Differences: Near-side vs. Far-side


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Magma Ocean hypothesis

The Moon was molten after formation

As the molten rock cooled, it crystallized

Some crystals floated others sank


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Ages of basalts in the mare of the Apollo manned and

Luna unmanned landing sites


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Impacts are the dominant surface process on the Moon

Crater flux has decreasedwith time

It would be hard to sustain

life on Earth if flux was as

high as during the early

solar system.

Impact erode the lunar

surface

Size range 1,000km

Age data from the Apollo

landing sites allow an

estimate of the number of

craters formed over time.

Scientist can then date

surfaces by counting

craters


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Gigantic impacts during the early history of the Moon caused

formation of Multi Ring Basins


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Volcanic Features: Lava flows infill mare Impacts of comets and asteroids form huge basins

4.3-3.85 billion years ago Shock waves create fractures in the rock beneath the basin

Mountain ranges form as a result of the blast

Interior heat from radioactivity caused partial melting

Magma rose along the fractures, filling the basin

3.9 and 3.1 billion years ago and younger


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Lunar volcanoes

Lava channels

Domical hills


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Hypotheses of the origin of the Moon

giant Impact


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Fission origin of the Moon, out of the Pacific Ocean

(George Darwin)


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Giant impact hypothesis

A projectile about the size of Mars, struck the young, Earth in a

catastrophic, glancing blow nearly 4.6 billion years ago.

Material was jettisoned outward, and some fraction of this mass

remained in Earth orbit and formed the Moon.

The Moon may be mostly derived from the crust and mantle of

the Earth and/or the impacting object.

The giant impact and quick accumulation of material resulted in

a hot, molten Moon, which accounts for the relative lack of water

and other volatile elements.

After the crust cooled, impacts into the Moon scarred the

surface with numerous craters.


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Artists conception of

the Giant Impact

Hypothesis of the Moon


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Artists

conception of

the Giant

Impact

Hypothesis of

the origin of

the Moon.


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CRAY supercomputer simulation of the origin of the Moon by a

collision of Earth with a Mars-sized projectile.

Note: The Moon formed mostly from the silicate portions of the projectile and Earths

mantle, whereas the metal core of the impactor merged with Earths metallic core.

Hence, the Moon is depleted in metal and has a lower density than earth.


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Origin of the Moon: Which hypothesis is

correct?

Hypothesis Volatiles Isotopes Orbit Iron Physics

Giant

ImpactA A B+ A B+

Fission B B F A F

Capture F F A C F

Co-accretion

F A F F B

A = v. good match; C = matches some data; F = doesnt match


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http://www.marcusmoon2022.org/

interior structure, origin and evolution of the moon

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