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The Earth's Moon
● The Earth's Moon, in many
ways, is prototypical of a
substantial fraction of the
objects in the Solar System.
– Like many other moons and
planets it exhibits a heavily
cratered surface that
preserves a history of internal
geological activity.
● All that being said, as we'll
see, the Moon is also a truly
bizarre object,
unrepresentative of most
other Solar System objects!
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The Earth/Moon as a Double Planet
● With the exception of Earth, all planets in the Solar System have
much smaller Moons.
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The Earth/Moon as a Double Planet
● The Earth and Moon are more similar in size.
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The Earth/Moon as a Double Planet
● The Earth and Moon are more similar in size.
Seen from Mars orbit by
Mars Reconnaissance
Seen from a distance Orbiter
(Galileo spacecraft on its
way to Jupiter)
True orbital separation
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Tidal Coupling
● Tides have worked to slow the
rotation rate of the Earth and
Moon.
– The Moon's rotation has been
slowed to the point where it
always keeps the same
hemisphere turned to Earth.
– We only ever see one side of
the Moon.
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Tidal Coupling
● Tides have worked to slow the
rotation rate of the Earth and
Moon.
– The Moon's rotation has been
slowed to the point where it
always keeps the same
hemisphere turned to Earth.
– We only ever see one side of
the Moon.
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Tidal Coupling
● Tides have worked to slow the
rotation rate of the Earth and
Moon.
– The Moon's rotation has been
slowed to the point where it
always keeps the same
hemisphere turned to Earth.
– We only ever see one side of
the Moon.
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General Features of the Moon
● It's round...
– Gravity plays a significant role
in shaping large objects in the
Solar System
– Rocks (e.g small asteroids) are
cohesive and strong and do not
change shape under their
internal gravitational stresses.
– If an object is large enough,
gravity provides enough force
to deform rock and make it
flow. The object behaves like
a liquid/plastic droplet and
becomes spherical.
Note that this asteroid is 500
times smaller relative to the
Moon than depicted here.
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General Features of the Moon
● Contrast between distinct
“dark” and “bright” terrains.
– Dark regions (the Maria) are
relatively crater free and at a
lower elevation than the bright
terrain.
– Bright regions (the Highlands)
are heavily cratered.
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The Lunar Highlands
● The heavily battered lunar highlands represent the oldest surviving crust
of the Moon.
– These regions are saturated with craters since they have been exposed to
infalling debris since nearly the beginning of the Solar System.
– Rocks brought back by the Apollo astronauts indicate an radioactive dating age
of about 4.2 billion years for highland rocks – indicating the formation age of
the original lunar crust.
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The Lunar Highlands
● The heavily battered lunar highlands represent the oldest surviving crust
of the Moon.
– These regions are saturated with craters since they have been exposed to infall
debris since nearly the beginning of the Solar System.
– Rocks brought back by the Apollo astronauts indicate an radioactive dating age
of about 4.2 billion years for highland rocks – indicating the formation age of
the original lunar crust.
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The Lunar
Maria
● The Lunar Maria are huge impact
basins where the previous history
of cratering has been erased by
lava flows.
– Radioactive dating of rocks brought
back from the maria indicate ages
of about 3.5 billion years.
– The highlands and maria were
shaped in the first billion years of
lunar history. The Moon has been
largely geologically dead since
then.
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The Lunar Maria
● The maria are dark because the
lavas that filled them are dark,
comparable to basaltic lava flows
on Earth.
● The highlands are brighter
because
– the original crust of the
Moon consisted of a
lighter colored material
(anorthosite)
– the roughness of these
regions also makes them
appear brighter.
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The Lunar
Maria
● Huge impacts fractured the crust
enabling the flow of magma from
deep inside the relatively young
Moon.
– The Moon has since cooled to the
point where it has nearly
completely solidified.
– Little or no geologic activity since
3 billion years ago!
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The Lunar
Maria
● The huge impacts fractured the
crust enabling the flow of magma
from deep inside the relatively
young Moon.
– The Moon has since cooled to the
point where it has nearly
completely solidified.
– Little or no geologic activity since
3 billion years ago!
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Lunar History
● Early crust formation
● Heavy bombardment
● Huge impacts
● Filling of Basis with lava flows
● Geologic death and light
subsequent cratering
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Lunar History
● Early crust formation
● Heavy bombardment
● Huge impacts
● Filling of Basis with lava flows
● Geologic death and light
subsequent cratering
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Bombardment History
● Few craters have accumulated
since the maria were resurfaced.
● What does this say about the
history of bombardment in the
Solar System??
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Cratering History
● Cratering has tapered off to a drizzle from the time of the “heavy
bombardment”
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Crater Counting and Surface “Age”
● Turn this around, and the degree of cratering of a surface can
reveal the “age” of the surface (if you know the cratering rate).
– Where “age” means the time since last resurfacing.
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Crater Counting and Surface “Age”
● Turn this around, and the degree of cratering of a surface can
reveal the “age” of the surface (if you know the cratering rate).
– Where “age” means the time since last resurfacing.
Saturn's
moon
Enceladus
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The Lunar Farside
● Farside not Darkside!
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The Lunar Farside
● The far side of the Moon is completely dominated by highland
terrain. There are virtually no maria???
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The Lunar Farside
● The crust is thicker on the far side.
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An Explanation for the Lunar Farside??
Two moons originally
formed from the
debris of the moon-
forming collision.
Not long thereafter
these two Moons
collided at relatively
low velocity,
plastering one face
of the Moon with an
extra later of material
(click on the left
image for the article
in Nature).
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Shaping the Lunar Surface
● Overall, impacts both large and small have been responsible for
sculpting the Lunar surface.
● Even the Moon's mountains are piles of impact debris.
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Shaping the Lunar Surface
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Regoliths and Breccia
● Impacts have fractured and pulverized the surface and fused
previously fractured rocks together.
– An impact fractured planetary surface is a “regolith” (blanket rock
literally)
– An impact fused rock made of different rock types is a “breccia”.
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Lunar Exploration
● A dozen humans walked on the Moon in six separate missions
flown between 1969 and 1972.
Apollo 11 30th anniversary site
Apollo mission summaries and images
Landing sites
Top 10 Apollo results
First person history
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Going Back?
● A return to the Moon was under discussion, but an expensive
proposition.
● The most recent set of plans have been scrapped by the
administration as too unrealistic.
● At the same time lunar exploration continues – especially the
search for water.
44
Going Back?
● A return to the Moon is under discussion, but an expensive
proposition.
● The most recent set of plans have been scrapped by the
administration as too unrealistic.
● At the same time lunar exploration continues – especially the
search for water (rocket fuel!).
45
Going Back?
● A return to the Moon is under discussion, but an expensive
proposition.
● The most recent set of plans have been scrapped by the
administration as too unrealistic.
● At the same time lunar exploration continues – especially the
search for water (i.e. rocket fuel!)
46
The Latest...from NASA
This is the beginning of a new era in space exploration
where we will build the capabilities to send humans
deeper into space than ever before.
We will use the International Space Station as a test
bed and stepping stone for the challenging journey
ahead. We are changing the way we do business,
fostering a commercial industry that will safely service
low Earth orbit so we can focus our energy and
resources on sending astronauts to an asteroid and
eventually to Mars. The road ahead is challenging but
this approach and space exploration architecture puts
us in a position to go where no human has gone
before..
