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Chapter 9
Tides

Tides and the Earth’s Rotation
 Rise and fall of crust and water causes friction
 Like a hand on a spinning tire
 Causes day to lengthen 0.0015 s/century
○ 481 days/year 900 MYA

Tides and the Moon’s Orbit
 Earth drags tidal bulges ahead of where they
would be if the Earth weren’t spinning
 Causes Moon to accelerate, increasing its
angular momentum, causing it to recede from
the Earth about 3 cm/year
The Moon’s Surface

Observations from the
Earth
 1400s – Jan Van Eyck
 1500s – Leonardo da Vinci
 1609 – Galileo
○ Used telescopes
○ Two types of lunar terrain
 Maria – Meaning “seas”, dark
areas
 Terrae – Meaning land, lighter,
cratered regions
The Moon’s Surface

Exploration of the Moon
 1957
○ Soviets send Sputnik and scare US into the “Space Race”
 1966
○ First robot lander – sends pictures back
 1969
○ Apollo 11 lands on Moon – Neil Armstrong, Buzz Aldrin
 2020
○ NASA plans to return to Moon

Lunar Craters
 Formation of Craters
○ Meteors falling toward the Moon
 Regolith
○ Surface debris caused by impacts
The Moon’s Surface

Volcanic Features
 The Maria
○ Impact causes deep basin
○ Fracture allows magma to come up
○ Movement of dense material into
fracture creates a mass called a
mascon
 Sinous Rilles
○ Sinous (winding) – looks like a dried
riverbed
○ Straight
Lunar Samples

Chemical Composition
 Very similar elements to the Earth
 More abundant: Al, Ti, U
 Less abundant: Na, Cl, Zn, Pb

Ages of Lunar Samples
 Oldest are 4.5 billion
 Most are younger
○ Magma flooded, eruptions occurred until 3.2 billion
years ago (not much rock formation since)
Lunar Samples

Ages and Cratering
 Crater Density – craters per given
amount of lunar surface
 Crater Saturation – New impacts would
destroy the same amount it creates
 History of the Lunar Surface
○ Uses density, rate of crater formation
○ Surface has been quite stable for last 3.2
billion years aside from heavier cratered
maria
 Crater Densities on Other Planets and
Satellites
○ Based on crater densities
○ Can not do radioactive dating
The Moon’s Atmosphere

Density
 Almost no atmosphere
 Mostly He, Ne, Ar, H
 Temperature from -280°C to 260°C due to
poor insulation
 Planets and stars always visible due to dark sky

Gain and Loss of Gases
 Gain
○ H, He due to solar winds
 Loss
○ He, Ar due to radioactive decay of rocks
 Water from comets vaporizes then reforms at poles
The Moon’s Interior

Mass
 Determined by orbital period and distance of satellites
around Moon
 Found to be 1/81 the mass of Earth

Density of the Moon
 Less dense than Earth
 Near density of Earth’s crust
 Possibly came from same material

Lunar Seismology and Internal Structure
 Used to probe interior of the Moon
 Four seismometers placed during Apollo landings
 Thicker on far side of the Moon
 Heat flow much lower as well
The Origin of the Moon

Fission, Accretion, Capture
 Fission Theory
○ Idea: Moon and Earth were one, but Moon broke off
○ Good: Explains how Moon is similar to Earth’s crust
○ Bad: Assumption that Earth rotated fast enough to fling Moon off of it
 Binary Accretion Theory
○ Idea: Moon and Earth formed at same time
○ Good: Formation from same material explains similarity of material on
both
○ Bad: Abundance of iron is too different for this to work
 Capture Theory
○ Idea: Moon formed elsewhere in solar system but captured by Earth’s
gravity
○ Good: Explains differences in materials on both
○ Bad: Moon would have gone past too quickly
○ Bad: Can’t explain similarities in chemical composition of the Moon
and Earth
Origin of the Moon
 Giant
Impact Theory
 Gaining wide acceptance in past 25
years
 Idea: Moon formed from debris when
Earth was struck by a body larger than
Mars which cooled and orbited Earth
 Good: Accounts for similarities AND
differences between Earth and Moon
Activity

Create a blueprint for a lunar base
 Be sure to include all necessary facilities for
human life to exist for a long period of time

Write out a description for each part of
the lunar base