Ch. 30.1 The Earth's Moon
Ch. 30.1 The Earth’s
Moon
Satellite—a body that orbits a larger body.
The moon is earth’s natural satellite.
The moon has weaker gravity (1/6 th that of earth) because it has less mass than earth.
Moon’s gravity too weak to hold gasses, so no atmosphere.
Moon’s temp. ranges from 134 C during the day to -170 C at night.
Moon rotates once every 27.3 days, but a lunar day is 29.5 earth days because the moon is also travelling around the sun at the same time.
The Lunar Surface
Observers from earth see light and dark patches.
Light areas are called highlands, and consist of light-colored rock.
Dark areas are called maria (latin for seas) and are smooth and reflect little light. Made of dark solidified lava, from ancient volcanic eruptions.
Rilles are long deep channels that run through the maria. Probably lava channels.
Craters
Cover moon’s surface. Most formed about 4 billion years ago.
Object striking moon leaves bowlshaped depression. Displaced material settles out in streaks, called
rays.
Since no erosion on the moon, its surface has changed little since it formed.
Lunar Rocks
Much of moon’s surface crushed into dust and fragments by meteorite impacts.
Regolith—the layer of dust and fragments (1 m to 6 m) that covers the lunar surface.
Surface lunar rocks composed mainly of oxygen and silicon.
Highland rocks are light-colored, course-grained anorthosites, rich in calcium and aluminum.
Maria rocks are fine-grained, dark colored basalts, high in titanium, iron, and magnesium.
Breccia—fragments of other rocks melted together after meteorite impacts. Common all over.
The Interior of the Moon
Info from seismographs placed by
Apollo astronauts.
Weak moonquakes recorded.
Crust is 60 to 100 km thick.
Underneath is denser mantle, to a depth of about 1000 km.
Possibly slightly molten or small iron core. Almost no magnetic field.
Development of the Moon
Giant-impact hypothesis– Mars-sized object struck the earth and ejected fragments into orbit, which eventually joined to form the moon.
2 nd Stage—surface of moon covered by ocean of molten rock. Denser parts separated and sank to the core.
3 rd Stage—surface cooled to form crust. Meteorites struck and broke through, causing molten rock to flow up and form the smooth maria.
About 3 billion years ago, impact activity decreased, and geologic activity stopped due to cooling.
Rayed craters formed by most recent impacts.
