The Moon

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The Moon
Apollo
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The Moon

• Moon almost uniquely preserves evidence of early
  planetary evolution
• Large enough to differentiate produce a variety
  of rocks over time
• Small enough to have cooled and preserved this
  early history
• Early Earth (Venus, Mars?) history lost
  Asteroids cooled early

• Three Major Early Evolution Questions
• Nature of early magma ocean and initial lunar
  differentiation.
• Evolution of internal reservoirs that produced
  highland and basaltic rocks (age and
  geochemistry).
• Nature (time flux) of early bombardment and
  effects on rocks.

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Four Hypotheses for the Formation of the Moon

1. Fission Moon derived from spinning Earth bulge.
2. Co-accretion Earth-Moon formed in place as
   mini-solar system.
3. Capture Passing Moon captured by Earths
   gravity.
4. Giant Impact Collision of proto-Earth with
   Mars-sized object.

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Formation of the Earth-Moon
Giant Impact
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Why Giant Impact?
The Earth has a large iron core, but the moon
does not. This is because Earth's iron had
already drained into the core by the time the
giant impact happened. Therefore, the debris
blown out of both Earth and the impactor came
from their iron-depleted, rocky mantles. The iron
core of the impactor melted on impact and merged
with the iron core of Earth, according to
computer models. The moon has exactly the same
oxygen isotope composition as the Earth, whereas
Mars rocks and meteorites from other parts of the
solar system have different oxygen isotope
compositions. This shows that the moon formed
form material formed in Earth's neighborhood. If
a theory about lunar origin calls for an
evolutionary process, it has a hard time
explaining why other planets do not have similar
moons. (Only Pluto has a moon that is an
appreciable fraction of its own size.)
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First Lunar Tides, an artists conception of
the Moon as seen from Earth about 4.2 billion
years ago.
The heavily cratered Moon is in close Earth
orbit, and mare basalts have not yet filled the
crater bottoms. The oceans have recently
condensed on the cooling surface of Earth and are
experiencing the first tides. It is not known if
life existed in these early seas. Likewise, the
size and frequency of impact events are
uncertain, as is the effect of these events on
the emergence or extinction of life. The ravages
of tectonics will destroy most evidence of this
time on Earth, but the lunar surface remains.
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Lunar Landing Sites
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Lunar Surface
There are two primary types of terrain on the
Moon the heavily cratered and very old highlands
and the relatively smooth and younger maria. The
maria (which comprise about 17 of the Moon's
surface) are huge impact craters that were later
flooded by molten lava. Most of the surface is
covered with regolith, a mixture of fine dust and
rocky debris produced by meteor impacts. For some
unknown reason, the maria are concentrated on the
near side.
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Lunar Mineralogy
Only four minerals - plagioclase feldspar,
pyroxene, olivine, and ilmenite - account for
about 98 of the crystalline material of the
lunar crust.
Some of the most common minerals at the surface
of the Earth are rare or have never been found in
lunar samples. These include quartz, calcite,
magnetite, hematite, micas, amphiboles, and
certain sulfide minerals.
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Lunar Rocks
Most of the lunar crust, often called the
highlands, consists of rocks that are rich in a
particular variety of plagioclase feldspar known
as anorthite. As a consequence, rocks of the
lunar crust are said to be anorthositic because
they are plagioclase-rich rock with names like
anorthosite, noritic anorthosite, or anorthositic
troctolite.

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Lunar Anorthosite
When the moon first formed it probably had a
surface composed mostly of feldspar-rich igneous
rocks. This rock type still exists today and
makes up the lunar highlands, which is the
lighter-colored part of the moon visible from
Earth. This 4.4-billion-year-old rock sample is
an anorthosite collected from the lunar highlands
of the moon by Apollo 16 astronauts.
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Lunar Breccias
The crust of the Moon began to form about 4.5
billion years ago. While it was forming and for
some time afterwards, it experienced intense
bombardment from meteors, many of which were
huge. The rocks of the crust have been repeatedly
broken apart by some impacts and glued back
together by others. As a consequence, most rocks
from the lunar highlands are breccias, a word
meaning a rock composed of fragments of older
rocks.
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Mare Basalts
Mare basalts cover about 17 of the surface of
the Moon, but it is estimated that they account
for only about 1 of the volume of the crust.
Apollo 15 sample 15016
Apollo 11 sample
Starting about the time of the period of intense
bombardment, the lunar mantle partially melted.
The resulting magmas rose through the crust to
the surface, ponding in low spots. These low
spots were mainly the huge craters and basins.
When filled with lava-filled they are usually
called mare (singular) and maria (plural).
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Volcanic Fire Fountain
Apollo 17 Orange Glass 40-60 microns
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Apollo 17 Orange Soil
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From Wentworth et al. (2008)
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Lunar Samples

• Lunar Sample Laboratory at NASA JSC in Houston is
  chief repository for samples from Apollo
  11,12,14,15,16,17
• 382 kg
• 2196 original samples
• Now subdivided into 86,000 samples
• Samples distributed to scientists and educators
  worldwide
• 80 by weight remains pristine

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Lunar Sample Laboratory
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JSC Lab for Lunar Sample Curation
Positive pressure Stainless glovebox Nitrogen Chem
ically Clean
Level D 0.15"
Restricted Materials Chemically "Clean"
Level C 0.10"
Airlock
Change Room
Level B 0.05"
Airlock
Security
Level A 0.00" H2O
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15 of Apollo Moon Rocks at White Sands Test
Facility
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Top Ten Discoveries from Lunar Samples
1. The Moon is not a primordial object -- it is
a differentiated terrestrial planet made of
igneous rock.    2. The Moon has an ancient
crust that preserves its early history impact
crater record has been calibrated using absolute
ages of rock samples.    3. The youngest Moon
rocks are virtually as old as the oldest Earth
rocks. The earliest processes and events that
probably affected both planetary bodies can now
only be found on the Moon.     4. The Moon and
Earth may be genetically related and formed from
different proportions of a common reservoir of
astromaterials -- the Moon is highly depleted in
iron and in volatile elements that are needed to
form atmospheric gases and water.   5. The Moon
is lifeless it contains no living organisms,
fossils, or native organic compounds.  
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Top Ten Discoveries from Lunar Samples
6. All Moon rocks originated through
high-temperature processes with little or no
involvement with water. They are roughly
divisible into three types basalts,
anorthosites, and breccias.    7. Early in its
history, the Moon was melted to great depths to
form a magma ocean. The lunar highlands contain
the remnants of early, low density rocks that
floated to the surface of the magma ocean.     8.
The lunar magma ocean was followed by a series
of huge asteroid impacts that created basins
which were later filled by lava flows.     9. The
surface of the Moon is covered by a rubble pile
of rock fragments and dust, called the lunar
regolith, produced by innumerable meteorite
impacts through geologic time.   10. The regolith
contains a unique radiation history of the Sun to
a degree of completeness that we are unlikely to
find elsewhere.
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Moons Early History

• Formation likely from an impact of Mars-size
  proto-planet with the Earth
• Similar material in Moon to crust material of the
  Earth
• Small core implies different total composition
  the Earth (lacking Earth's core material
  abundance ratio)
• Surface solidifies quickly
• Captures early composition and character of Moon
  solar system
• Bombardment from planetesmals at beginning of
  formation is easily seen in impact craters
• Internal heating increases because of radiation
  and crust formation
• Forces the interior liquid rock to flow into
  large craters
• Forms the Mare (volcanic seas)

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• Lunar Surface Chronology
• 4.6 By
• Layer of plagioclase-rich crust floats on more
  dense liquid magma during early lunar formation
• Heavier olivine, pyroxene, and ilmenite (FeTiO3)
  sank to form source areas for mare basalts
• 4.4 By
• KREEP rocks form as upper liquid mantle
  crystallizes
• Partial melting events are probably responsible
  for the Mg-rich highland rock. This is indicated
  by some similarities in composition of Mg-rich,
  plagioclase and KREEP compositions. Partial
  melting could have also been at deeper depths.
• Intense meteoric bombardment reduces much of
  highlands to rubble - as seen in Apollo samples
• FeO-rich material remaining after magma
  solidifies moves into lower crust, making
  KREEP-like basalt regions in later basalt flows
• 3.9 By
• Remelting or partial melting produces maria
  volcanism (effusive, not eruptive). These flows
  fill large basins produced by earlier, intense
  bombardment. Remelting/partial melting due to
  radioactive processes in the interior.
• 3 By
• End of most igneous activity (including mare
  formation)
• Continuing but reduced meteoric bombardment
• Mass range of bombarding material from 10-15 to
  1020 g
• 3 By to present Surface processes include
  meteoric activity (fracturing of surface rock and
  formation of regolith) and radiation (solar wind
  and cosmic rays), some magmatism.

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Lunar Asymmetry
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Orientale Viewed from Orbit
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Lunar Geologic Time Scale
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Geologic Map of the Moon
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Pre-Nectarian
South Pole Aiken Basin
Imbrium
Nectarian
Orientale
Copernican
Mare Basalts
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South Pole Aitken Basin (Giant South Polar
Basin)

• Very Large (d2500 km) and Very Old (gt4 Ga)
• Deep-seated Mantle as clasts within breccias and
  impact melt.
• Old basalts derived from different mantle
  composition.
• Old highland rock not modified by younger impact
  basin.
• Away from influence of areas of moon rich in U,
  Th, K, REE.

• Far removed from other sampled sites on moon
  Different rock types?

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Farside of the Moon albedo (left) and topography
(right) derived from Clementine data.The outer
ring of South Pole-Aitken (SPA) Basin is shown
with a dotted line (after Wilhelms, 1987). The
enormous SPA Basin is not located at the South
Pole, but derives its name from the fact that it
extends from the South Pole to the crater Aitken
near the equator.
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Lunar South Pole

• Ice in lunar cold traps may provide history of
  volatiles in the solar system
• Water ice (gt 1010 tons) could exist in permanent
  shadow
• (gt 20,000 km2)
• Terrain in south polar sites may provide nearly
  continuous sunlight (gt80)
• Low sun elevation provides nearly constant and
  benign surface temperatures (-50ºC vs. -170º to
  120ºC at equator)
• Region proximate to large permanently shadowed
  areas
• (-230ºC)

After D.B.J. Bussey, et. al., 1999
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Mare Nectaris
The Nectaris Basin, in the southeastern quadrant
of the lunar nearside, is about 860 kilometers
across. It is more degraded than the other
basins, indicating that it is older than Imbrium
and Orientale. Samples returned by the Apollo 16
mission suggest an age of 3.92 billion years for
this basin.
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Mare Imbrium
The Imbrium Basin is the largest basin on the
nearside of the Moon, with a diameter of 1160
kilometers The Imbrium Basin is also the second
oldest basin on the Moon. Based on samples
returned by Apollo 15, it formed about 3.85
billion years ago.
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Mare Orientale
The Orientale Basin occurs near the western limb
of the lunar nearside and is only partially
visible from telescopes on Earth. This classic
multi-ring basin is 930 kilometers in diameter.
Material from this basin was not sampled by the
Apollo program, so the basin's precise age is not
known. However, it is the freshest impact basin
on the Moon and is believed to be slightly
younger than the Imbrium Basin, which formed
about 3.85 billion years ago.
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Copernicus
The crater Copernicus, 93 kilometers in diameter,
is one of the most prominent features on the
Moon's nearside. It is a relatively fresh crater,
believed to have formed less than 1 billion years
ago. Its system of bright rays is quite prominent
at full Moon.
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Tycho
The crater Tycho, 85 kilometers in diameter, is
the youngest large impact crater on the Moon's
nearside. Ejecta from this crater was spread
across much of the nearside of the Moon and is
visible in the form of bright rays at full Moon.
One such ray crosses the Apollo 17 landing site,
2000 kilometers from Tycho. Laboratory analysis
of samples from this landslide suggest that
Tycho's age is about 100 million years.
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Lunar Interior
   The Moon's crust averages 68 km thick and
varies from essentially 0 under Mare Crisium to
107 km north of the crater Korolev on the lunar
far side. Below the crust is a mantle and
probably a small core (roughly 340 km radius and
2 of the Moon's mass). Unlike the Earth,
however, the Moon's interior is no longer active.
The Moon's center of mass is offset from its
geometric center by about 2 km in the direction
toward the Earth. Also, the crust is thinner on
the near side.
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Lunar Interior
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Mare Basalts

• Sample data for TiO2 in mare basalts
• TiO2 of lunar maria derived from Galileo
  Clementine
• Results
• Titanium contents of lunar basalts are unimodal
  and broadly distributed
• Lunar basalt compositions are not well
  represented by samples
• Remote sensing data provide new perspective on
  lunar volcanism

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Natural radioactivity on the lunar surface as
determined by the gamma-ray spectrometer on Lunar
Prospector
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Lunar Prospector gamma-ray Thorium map

• Calibrated to Apollo data
• Heat-producing elements concentrated in
  Imbrium-Procellarum region
• Strongly non-uniform crustal differentiation

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Lunar Prospector gamma-ray Thorium map
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• The Feldspathic Highlands Terrane (FHT) which
  includes its somewhat different outer portion
  (FHT,O) this terrane has low FeO and Th.
• The Procellarum KREEP Terrane (PKT),
  characterized by high Th.
• South Pole Aitken Terrane (SPA Terrane), which
  has modest FeO and Th. These do not correspond to
  the traditional divisions into highlands and
  maria.

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Some Vital Statistics

• Averages 236,000 miles from the earth.
• Closest distance (perigee) is about 220,000
  miles,
• Greatest distance (apogee) is about 255,000
  miles.
• Diameter about 2160 miles, roughly 1/4 that of
  the earth
• Mass 1/81 that of earth. Surface gravity 1/6 that
  of earth
• Takes 29-1/2 days to circle earth.

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Summary of Significant Features
Rays around more recent craters Highlands and
Maria Crust of Moon is largely anorthosite and
gabbro (or norite) Maria are mostly basalt
Maria almost exclusively on earth-facing
side Tidally locked to earth Same side always
faces earth Moon slightly elongated Small
moonquakes occur when moon nearest earth Moon
causes tides on Earth Most marked in oceans but
a small tide occurs in the solid earth, too.
Tides are slowing Earth's rotation - Earth
rotated about 400 times/year 500,000,000 years
ago. As Earth slows, it transfers its rotation
(angular momentum) to the Moon, causing it to get
farther from Earth.
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Summary of Significant Features
Moonquakes occur about 800 mi. deep in Moon, just
outside core Small molten core, probably
magnesium-iron silicate or iron sulfide but may
be nickel-iron like Earth's. Core boundary not
sharp. Diameter of core about 500 miles. No
magnetic field now but seems to have had one
early in its history. Moon differs chemically
from Earth Very poor in water Depleted in
volatile elements Richer in some metals, such as
titanium No surface water, life or atmosphere
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Constellation Program Humans back to the Moon and
on to Mars
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Ares Launch Vehicles
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Orion Crew Vehicle
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Lunar Lander 2018