CHAPTER 25
EARTH’S MOON
25.1 ORIGIN AND
PROPERTIES OF
THE MOON
What is the Moon?
• A natural satellite
• One of more than 150
moons in our Solar System
• The only moon of the planet
Earth
ORIGIN OF THE MOON
• SCIENTIST BELIEVE
THE MOON
FORMED WHEN A
LARGE OBJECT
ABOUT THE SIZE
OF A PLANET HIT
EARTH
YouTube How the Moon
was born!
DEVELOPMENT OF THE MOON
• SURFACE LAYERS MELTED BY FREQUENT
IMPACTS 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
MOON TODAY
• CORE INACTIVE
• IMPACTS FROM MICROMETEOROIDS
CONTINUE TO CHANGE SURFACE
THROUGH IMPACTS AND EROSION
• MOON HAS NO ATMOSPHERE TO
BURN THEM UP
PROPERTIES AND FEATURES
OF THE MOON
• Same side of moon faces
earth – geosynchronous
orbit
• About 384,000 km
(240,000 miles) 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
Far Side of the Moon
• First seen by Luna 3
Russian space
probe in 1959
• Surface features
different from near
side
– More craters
– Very few maria
– Thicker crust
Layers of the moon
Mantle
Near side
crust
(about 65
km thick)
Iron Core
Far side
crust
(about
150km
thick)
The Moon’s Surface
• No atmosphere
• No liquid water
• Extreme
temperatures
– Daytime = 130C
(265°F)
– Nighttime = -190C (310 F
Maria
• Originally thought to be “seas” by early
astronomers
• Formed from lava coming up through
cracks
• Darkest parts of lunar landscape
• Mostly basalt rock made of feldspars,
pyroxene, youngest rocks
Maria
Mascons and Rilles
• Mascons are regions
of higher gravity
• Rilles are long cracks
in the maria
RILLE
Highlands
•
•
•
•
•
Mountains up to 7500 m (25,000 ft) tall
Thought to be original crust
Formed from impacts
Lighter in color than maria
Rocks samples similar to Gabbro and
Breccia – rocks made of angular
fragments – impacts melted rocks together
Craters and Rays
• Circular hollows
formed by meteor
impacts
• Range: microscopic
to 2100 km diameter
• Most named after
people
• Same age
How did this spherule come to be on the Moon?
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.
Copernicus crater rays
Lunar soil
• Regolith – loose rock material
• Range: fine dust to sand grains 2 – 20 m
deep
• Contain no water or organics
• Formed by smashing impacts
• Composition – chips of varying minerals
and glassy beads