CHAPTER 28: THE MOON

Moons Are Natural Satellites Satellite – a body that orbits another

body

7 planets in our solar system have smaller orbiting bodies

Artificial satellites – satellites of Earth Space telescopes Weather data equipment

Moon Vocabulary – Mare (Maria)

Mare Latin for “sea”

Large dark area of basalt on the moon

Dark solidified lava

Formed more than 3 billion years ago

Moon Vocabulary - Craters

Bowl-shaped depressions

Cover surface of moon

Formed from leftover debris during solar system’s formation

Moon Vocab – Ridges and Rilles

Rilles Long deep channels that

run through maria

Ridges Long narrow elevations

of rock Rise out of surface Criss-cross maria

Moon Vocab - Regolith

Layer of gas and dust

Covers most of the lunar surface

Formed from crushing of lunar rocks by meteorites

Lunar Rocks

Similar to Earth rocks Contains many of same

elements

Igneous rocks Rocks that form when

magma cools

Sides of the Moon…

Near Side Always faces Earth

Far Side Always faces away

Lunar Layers 3 layers

Crust Outer layer

Thicker on Far Side 60-100 km thick

Mantle Beneath crust Made of silica, magnesium, iron

Core Small, made of iron Neither completely solid nor completely liquid

Why Moon has almost no gravitational field

How Was the Moon Formed? Giant Impact Hypothesis

Large Mars-sized object collided with Earth Over 4 billion years ago

Chunks of Earth’s mantle ejected into orbit

Debris eventually clumped together to form the Moon

Differentiation of Lunar Interior

When Moon formed…

Surface was covered by ocean of molten rock

Over time:

Denser material moved to center formed core

Less dense material cooled formed crust

Meteorite Bombardment

Meteorites had hit the Moon over time

Bombardment decreased significantly 3 billion years ago

Stopped all geologic activity on Moon

Moon has looked the same since then

Other Minor Bodies Other satellites that orbit the Sun

Leftover debris from formation of solar system

Include Asteroids Meteoroids Meteorites Comets

Asteroids Fragments of rock and metal

Orbit the Sun in ellipses

Largest of the minor bodies Known as “minor planets”

Largest asteroid in solar system: Ceres

Other examples: Earth-grazers – pass within 2x distance to

the Moon Trojan asteroids

Located on either side of Jupiter

Meteoroids

Called meteors when enter Earth’s atmosphere

Small pieces of rock or metal in space Meters to

millimeters in size

Meteorites Any part of a meteor that is left

when it hits Earth

3 types:

Stony

Iron

Stony-Iron

Comets Bodies of rock, metals, gases, and ice

Orbit the Sun Long period – orbit lasts longer than 100 years Short period – orbit lasts shorter than 100 years

3 major parts of a comet

Nucleus core

Coma spherical cloud of gas and dust around core

Tail evaporating gas and dust Faces away from Sun

Comets, Cont’d Originate in the Oort Cloud

Spherical cloud of gas and dust

Lies beyond Pluto’s orbit

Contains nuclei of billions of comets