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Minor Bodies of the Solar System
Section 1: Earth’s Moon
Preview
• Key Ideas
• Exploring the Moon
• The Lunar Surface
• The Interior of the Moon
• The Formation of the Moon
• Formation of the Moon
Section 1
Minor Bodies of the Solar System
Section 1
Exploring the Moon
• satellite a natural or artificial body that revolves around a
celestial body that is greater in mass
• moon a celestial body that revolves around a body that is
greater in mass; a natural satellite
• Six of the planets in our solar system have natural
satellites, or moons. Our moon is Earth’s satellite.
• The Apollo space program sent six spacecraft to study the
moon. Scientists were able to gather data about the
moon’s weak gravity and its effect on astronauts, as well
as data about the moon’s surface.
Minor Bodies of the Solar System
Section 1
The Lunar Surface
• Any feature of the moon is referred to as lunar.
• Light and dark patches on the moon can be seen with the
unaided eye.
• The lighter areas are rough highlands composed of rocks
called anorthosites. The darker areas are smooth, reflect less
light, and are called maria.
• mare a large, dark area of basalt on the moon
• Maria are plains of dark, solidified lava which formed more
than 3 billion years ago when lava slowly filled basins that
were created by impacts of massive asteroids.
Minor Bodies of the Solar System
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The Lunar Surface, continued
Craters, Rilles, and Ridges
• crater a bowl-shaped depression that forms on the surface of
an object when a falling body strikes the object’s surface or
when an explosion occurs
• The surface of the moon is covered with craters, rilles, and
ridges. Most of the craters formed when debris struck the
moon about 4 billion years ago.
• Rilles are long, deep channels that run through the maria.
Rilles are thought to be leftover lava channels from the
formation of the maria.
• The moon’s surface also has several ridges, which are long,
narrow elevations of rock that rise out of the surface and
criss-cross the maria.
Minor Bodies of the Solar System
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The Lunar Surface, continued
Regolith
• More meteorites have reached the surface of the moon
than have reached Earth’s surface because the moon
has no atmosphere for protection.
• Over billions of years, these meteorites crushed much of
the rock on the lunar surface into a layer of dust and
small fragments called regolith.
• The depth of regolith layer varies from 1 m to 6 m.
Minor Bodies of the Solar System
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The Lunar Surface, continued
Lunar Rocks
• Lunar rocks are igneous, and most rocks near the
surface are composed mainly of oxygen and silicon.
• Rocks from the lunar highlands are light-colored, coarsegrained anorthosites rich in calcium and aluminum.
• Rocks from the maria are fine-grained basalts and
contain titanium, magnesium, and iron.
• Breccia is found in both maria and the highlands. Lunar
breccia formed when meteorites struck the moon.
Minor Bodies of the Solar System
Section 1
The Interior of the Moon
• The interior of the moon is less dense than the interior of
Earth.
• Most of the information about the interior of the moon
comes from seismographs that were placed on the moon
by the Apollo astronauts.
• More than 10,000 moonquakes have been detected.
From these moonquakes, scientists learned that the
moon’s interior is layered.
Minor Bodies of the Solar System
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The Interior of the Moon, continued
The Moon’s Crust
• The side of the moon that faces Earth is called the near
side. The other side of the moon that faces away from
Earth is called the far side.
• The pull of Earth’s gravity during the moon’s formation
caused the crust on the far side of the moon to become
thicker than the crust on the near side.
• The crust on the near side is about 60 km thick. The
crust on the far side is up to 100 km thick.
Minor Bodies of the Solar System
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The Interior of the Moon, continued
The Moon’s Mantle and Core
• Beneath the crust is the moon’s mantle. The mantle is
thought to be made of rock that is rich in silica,
magnesium, and iron.
• Scientists think that the moon has a small iron core that
has a radius of less than 700 km.
• Studies of the core have shown that the moon’s rotation
is not uniform and that the core is neither completely
solid nor completely liquid.
Minor Bodies of the Solar System
Section 1
The Formation of the Moon
• Most scientists agree that the moon formed in three stages.
The Giant Impact Hypothesis
• The giant impact hypothesis states that the formation of the
moon began when a large object collided with Earth more
than 4 billion years ago.
• The collision ejected chunks of Earth’s mantle into orbit
around Earth. The debris eventually clumped together to form
the moon.
• This hypothesis explains when moon rocks share many of the
chemical characteristics of Earth’s mantle.
Minor Bodies of the Solar System
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The Formation of the Moon, continued
Differentiation of the Lunar Interior
• Early in its history, the lunar surface was covered by an
ocean of molten rock.
• Over time, the densest materials moved toward the
center of the moon and formed a small core.
• The least dense materials formed an outer crust.
• The other materials settled between the core and the
outer layer to form the moon’s mantle.
Minor Bodies of the Solar System
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The Formation of the Moon, continued
Meteorite Bombardment
• As the outer surface of the moon cooled to form the
crust, debris struck the solid surface and produced
craters and regolith.
• About 3 billion years ago, less material struck the lunar
surface, and few new craters formed.
• Craters that have rays formed during the most recent
meteor impacts. During this stage, virtually all geologic
activity stopped on the moon.
Minor Bodies of the Solar System
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The Formation of the Moon, continued
Minor Bodies of the Solar System
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The Formation of the Moon, continued
Lava Flows on the Moon
• After impacts on the moon’s surface formed deep basins, lava
flowed out of cracks, or fissures, in the lunar crust.
• This lava flooded the crater basins to form maria.
• The presence of maria suggest that fissure eruptions once
characterized the moon.
• Because of the uneven thickness of the moon’s crust, more
maria formed on the near side of the moon than on the far
side.
Minor Bodies of the Solar System
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The Formation of the Moon, continued
Lava Flows on the Moon
• Scientist do not yet know how magma formed in the lunar
interior or how magma reached the surface.
• There is no evidence of plate tectonics or convection currents
in the moon’s mantle.
• Some scientists think the energy needed to produce magma
may have come from a long period of intense meteorite
bombardment. Other scientists think radioactive decay of
materials may have heated the moon’s interior enough to
cause magma to form.
Minor Bodies of the Solar System
Formation of the Moon
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Section 1