CHAPTER 25
EARTH’S MOON
25.1 ORIGIN AND
PROPERTIES OF
THE MOON
DAHS MR. SWEET
1
OBJECTIVES
• EXPLAIN VARIOUS HYPOTHESES
ABOUT HOW THE MOON FORMED.
• DESCRIBE THE FEATURES AND
PROPERTIES OF THE MOON.
2
WHAT IS THE
MOON?
• A NATURAL SATELLITE
• ONE OF MORE THAN 96
MOONS IN OUR SOLAR
SYSTEM
• THE ONLY MOON OF THE
PLANET EARTH
3
ORIGIN OF THE MOON
• SCIENTIST BELIEVE THE MOON FORMED
WHEN A LARGE OBJECT ABOUT THE SIZE
OF A PLANET HIT EARTH.
1. Earth is hit offcenter by a planetsized object.
2. The impact
heats and deforms
both bodies. Some
rocky debris
remains in orbit
around Earth.
3. The debris ring,
made of rock from the
outer layer of both
objects, gradually
coalesces, forming the
moon.
4
DEVELOPMENT OF THE MOON
• METEOROID IMPACTS MELTED MOONS
SURFACE AND CREATED CRATERS
• FORMED MAGMA OCEAN
• LIGHTER MATERIALS ROSE TO SURFACE –
COOLED AND HARDENED
• 4.0 – 3.5 BILLION YEARS AGO IMPACTS
DECREASED
• OVER MILLIONS OF YEARS MAGMA RICH IN
IRON ERUPTED FILLING LARGE BASINS
CREATING MARIA
5
YouTube - How the Moon was
born!
Observe images illustrating the
impact theory of the moon's
formation.
6
MOON TODAY
• CORE INACTIVE
• IMPACTS FROM MICROMETEOROIDS
CONTINUE TO CHANGE SURFACE
THROUGH IMPACTS AND EROSION
• MOON HAS NO ATMOSPHERE TO
BURN THEM UP
7
LAYERS OF THE MOON
Mantle
Near side
crust
(about 65
km thick)
Far side
crust
(about
150km
thick)
Iron Core
8
UPDATE
• National Geographic Moon
9
PROPERTIES AND FEATURES
OF THE MOON
• SAME SIDE OF THE
MOON FACES EARTH GEOSYNCHRONOUS
ORBIT
• ABOUT 384,000 km
(240,000 mi.) FROM
EARTH
• 3,476 km (2,155 miles) IN
DIAMETER
– ABOUT ¼ THE SIZE OF
EARTH
• DENSITY 3.3g/cm3
• 1/6 EARTH’S GRAVITY
10
FAR SIDE OF THE MOON
• FIRST SEEN BY
THE LUNA 3
RUSSIAN SPACE
PROBE IN 1959
• SURFACE
FEATURES ARE
DIFFERENT FROM
THE NEAR SIDE
– MORE CRATERS
– VERY FEW MARIA
– THICKER CRUST
11
THE MOON’S SURFACE
• NO ATHMOSPHERE
• NO LIQUID WATER
• EXTREME TEMPS.
– DAYTIME = 130C
(265°F)
– NIGHTIME = -190C
(-310 F)
121212
MARIA
• ORIGINALLY
THOUGHT TO BE
“SEAS” BY EARLY
ASTRONOMERS
• DARKEST PARTS OF
THE LUNAR
LANDSCAPE
• MOSTLY BASALT
ROCK MADE OF
FELDSPARS AND
PYROXENE
• YOUNGEST ROCKS
Maria
13
MASCONS
• MASCONS MEANS MASS
CONCENTRATIONS
• AREAS IN MARIA WITH
– HIGHER DENSITY ROCKS
– HIGHER GRAVITY READINGS
• DISCOVERED IN 1960’S
14
RILLES
• TRENCHLIKE VALLEYS
RUNNING THROUGH
MARIA
• MAY HAVE FORMED
FROM A RIVER OF
LAVA
• THE RIVER SURFACE
HARDENED
• THE LAVA DRAINED
AWAY
• THE SURFACE
COLLAPSED
RILLE
15
HIGHLANDS
•
•
•
•
•
MOUNTAINS UP TO 7,500 m (25,000 ft) TALL
THOUGHT TO BE THE ORIGINAL CRUST
FORMED FROM IMPACTS
LIGHTER IN COLOR THAN MARIA
ROCK SAMPLES SIMILAR TO GABBRO AND
BRECCIA
– ROCKS MADE OF ANGULAR FRAGMENTS
– IMPACTS MELTED ROCKS TOGETHER
16
17
CRATERS
• CIRCULAR
HOLLOWS FORMED
BY METEOR
IMPACTS
• SIZE RANGE IS
MICROSCOPIC TO
2100 km DIAMETER
• MOST NAMED
AFTER PEOPLE
18
19
20
21212121
RAYS
• CONSIST OF
SHATTERED ROCK
AND DUST
• SPLASHED OUT BY
METEROID
IMPACTS
• COPERNICUS IS 93
km CRATER WITH
RAYS 100’S km
LONG
22
LUNAR SOIL
• REGOLITH
– LOOSE ROCK MATERIALS
• RANGE FROM FINE DUST TO SAND GRAINS
2 – 20 m DEEP
• CONTAIN NO WATER OR ORGANICS
• FORMEDY BY SMASHING IMPACTS OF
METEORS
• COMPOSED OF
– ROCK AND MINERALS CHIPS
– GLASSY BEADS
23
24
How did this spherule come to be on the Moon?
25
Explanation: When a meteorite strikes the Moon,
the energy of the impact melts some of the
splattering rock, a fraction of which might cool
into tiny glass beads. Many of these glass beads
were present in lunar soil samples returned to
Earth by the Apollo missions. Pictured above is
one such glass spherule that measures only a
quarter of a millimeter across. This spherule is
particularly interesting because it has been
victim to an even smaller impact. A miniature
crater is visible on the upper left, surrounded by
a fragmented area caused by the shockwaves of
the small impact. By dating many of these
impacts, astronomers can estimate the history of
cratering on our Moon.
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25.1 SECTION REVIEW
• PAGE 560
• 1-2 WITH QUESTIONS
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