Ch. 30.1 The Earth’s Ch. 30.1 The Earth’s MoonMoon

Satellite—a body that orbits a larger Satellite—a body that orbits a larger body.body.

The The moonmoon is earth’s natural satellite. is earth’s natural satellite. The moon has weaker gravity (1/6The moon has weaker gravity (1/6thth

that of earth) because it has less that of earth) because it has less mass than earth.mass than earth.

Moon’s gravity too weak to hold Moon’s gravity too weak to hold gasses, so no atmosphere.gasses, so no atmosphere.

Moon’s temp. ranges from 134 C Moon’s temp. ranges from 134 C during the day to -170 C at night.during the day to -170 C at night.

Moon rotates once every 27.3 days, Moon rotates once every 27.3 days, but a lunar day is 29.5 earth days but a lunar day is 29.5 earth days because the moon is also travelling because the moon is also travelling around the sun at the same time.around the sun at the same time.

The Lunar SurfaceThe Lunar Surface

Observers from earth see light and Observers from earth see light and dark patches.dark patches.

Light areas are called Light areas are called highlandshighlands, and , and consist of light-colored rock.consist of light-colored rock.

Dark areas are called Dark areas are called mariamaria (latin for (latin for seas) and are smooth and reflect seas) and are smooth and reflect little light. Made of dark solidified little light. Made of dark solidified lava, from ancient volcanic eruptions.lava, from ancient volcanic eruptions.

Rilles Rilles are long deep channels that are long deep channels that run through the maria. Probably lava run through the maria. Probably lava channels.channels.

CratersCraters

Cover moon’s surface. Most formed Cover moon’s surface. Most formed about 4 billion years ago.about 4 billion years ago.

Object striking moon leaves bowl-Object striking moon leaves bowl-shaped depression. Displaced shaped depression. Displaced material settles out in streaks, called material settles out in streaks, called raysrays..

Since no erosion on the moon, its Since no erosion on the moon, its surface has changed little since it surface has changed little since it formed.formed.

Lunar RocksLunar Rocks

Much of moon’s surface crushed into Much of moon’s surface crushed into dust and fragments by meteorite dust and fragments by meteorite impacts.impacts.

RegolithRegolith—the layer of dust and —the layer of dust and fragments (1 m to 6 m) that covers fragments (1 m to 6 m) that covers the lunar surface.the lunar surface.

Surface lunar rocks composed mainly Surface lunar rocks composed mainly of oxygen and silicon.of oxygen and silicon.

Highland rocks are light-colored, Highland rocks are light-colored, course-grained course-grained anorthosites, anorthosites, rich in rich in calcium and aluminumcalcium and aluminum..

Maria rocks are fine-grained, dark Maria rocks are fine-grained, dark colored basalts, high in titanium, colored basalts, high in titanium, iron, and magnesium.iron, and magnesium.

BrecciaBreccia—fragments of other rocks —fragments of other rocks melted together after meteorite melted together after meteorite impacts. Common all over. impacts. Common all over.

The Interior of the MoonThe Interior of the Moon

Info from seismographs placed by Info from seismographs placed by Apollo astronauts.Apollo astronauts.

Weak moonquakes recorded.Weak moonquakes recorded. Crust is 60 to 100 km thick.Crust is 60 to 100 km thick. Underneath is denser mantle, to a Underneath is denser mantle, to a

depth of about 1000 km.depth of about 1000 km. Possibly slightly molten or small iron Possibly slightly molten or small iron

core. Almost no magnetic field. core. Almost no magnetic field.

Development of the MoonDevelopment of the Moon

Giant-impact hypothesisGiant-impact hypothesis– Mars-sized – Mars-sized object struck the earth and ejected object struck the earth and ejected fragments into orbit, which fragments into orbit, which eventually joined to form the moon.eventually joined to form the moon.

22ndnd Stage—surface of moon covered Stage—surface of moon covered by ocean of molten rock. Denser by ocean of molten rock. Denser parts separated and sank to the core.parts separated and sank to the core.

33rdrd Stage—surface cooled to form Stage—surface cooled to form crust. Meteorites struck and broke crust. Meteorites struck and broke through, causing molten rock to flow through, causing molten rock to flow up and form the smooth maria.up and form the smooth maria.

About 3 billion years ago, impact About 3 billion years ago, impact activity decreased, and geologic activity decreased, and geologic activity stopped due to cooling. activity stopped due to cooling. Rayed craters formed by most recent Rayed craters formed by most recent impacts.impacts.