Homework
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Is there a good scientific question?
Is there a good explanation for why the
topic/question is worthy of research?
Is there a good hypothesis (if / then)?
Are there at least 10 quality sources?
Will the project need special approval?
What questions or comments do you have
for the person?
The Earth’s Moon
09.10.07 / 09.11.07
Concept: The Moon
► EQ:
What hypotheses have been developed
to explain the evolution of the Moon?
Earth's Moon
General characteristics
• Size
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•
unusually large relative to the Earth
Most satellites are much smaller than their
parent planets.
• Density
Comparable to Earth's crust
• Too low to contain a significant iron core
•
Earth's Moon
General characteristics
• No atmosphere
• Tectonics no longer active
• Surface is bombarded by small meteorites
which slowly smoothes the landscape
• Oldest rocks are about 4.5 by, in contrast
to Earth’s oldest rock, which 3.8 by
Lunar topography
Lunar Surface
Two types of terrain
• Maria (singular, mare), Latin for "sea“
• Highlands, English for land that is
high
Lunar surface
Maria
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•
Dark region
Fairly smooth lowlands
Originated from asteroid impacts and lava
flooding the surface
Form most of the near side of Moon
Were once thought to be seas because of their
dark color
Formation of Maria
Lunar surface
Lunar highlands
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Bright, densely cratered regions
Bright, densely cratered regions
Make up most of the Moon
Make up nearly all of the far side of the
Moon
• Older than maria
Craters
► Produced
by an impact from a meteoroid
which produces
 Ejecta
 Rays (associated with younger craters)
► Craters
within craters are common
► Crater layering can be used for relative
dating
A 20-kilometer-wide crater
on the Moon
The Copernicus crater is 93 km wide.
Graphic: from Lunar and Planetary Institute
Earth’s Moon
► Central
Peaks
The physics of large impacts are mind-boggling….
The rocks are subjected to stresses hundreds of
times their failure strengths. This means that the
rocks effectively behave as if they were water….
They flow plastically as if they were fluids.
Source: http://www.uwgb.edu/dutchs/planets/cratform.htm
Source: http://www.uwgb.edu/dutchs/planets/cratform.htm
Check up
► How
are central peaks formed?
► What are maria?
► Why are highlands more cratered than
maria?
► What is a major visual difference between
the near side and far side of the Moon?
Lunar Regolith
 Regolith
means “blanket”
• Covers all lunar terrains
• Gray, unconsolidated debris
• Soil-like layer produced by meteoric
bombardment
• Varies in depth from about 2 – 20 meters
 Regolith
on earth produced by
weathering
Lunar Regolith
Where did it come from?
► Hypothesis
1: fission (daughter)
 Moon was ejected from Earth
 Mathematical models show it is impossible
► Hypothesis
2: coaccretion (sister)
 Earth and Moon formed together from same material
 Cannot explain Moon’s lack of core
► Hypothesis
3: capture (spouse)
 Moon was another planet caught by Earth’s gravity
 Cannot explain why Moon and Earth are so chemically
similar
 This is very unlikely to ever happen
Giant Impact Hypothesis
►A
Mars-sized object hit the Earth in our
planet’s early history
 Material was ejected into orbit and formed
Moon
 Has been supported by mathematical model
 Explains why the Moon:
►is
very similar in age to Earth
►has identical materials to Earth’s crust
►does not have an iron core
Check up
► Describe
the three models of Lunar
evolution that were replaced by the giant
impact hypothesis.
► Describe evidence for the giant impact
hypothesis
► Why are regolith on highlands thicker than
on maria?
► How can scientists determine relative ages
of Lunar craters?