The Moon

Our nearest neighbor

Info about the Moon◼ Diameter: 3,476 km (0.27 earth) (5th largest, 2nd in density)

◼ Distance from Earth: 384,000 km (239,000 miles)

◼ Surface gravity: 0.16

◼ Roughly same surface area as Africa

◼ Orbital period: 27.3 days

◼ Day: 27.3 days (tidally locked)

◼ No atmosphere◼ Daytime Temp = 224F, night= -244F

◼ Surface features: ◼ Heavily cratered, old uplands

◼ Maria, or lava flows, 16% surface

◼ Water on the Moon?

◼ Crust is 60-70 km (3x earth’s)

◼ Mantle

◼ Core is probably iron, > 450km in diameter (25% lunar diameter)

Lunar Interior

Moonquakes

1) Deep earthquakes from mantle

region (700 km deep) – tides

2) Vibrations from impacts

3) Thermal quakes from expansion

of crust

4) Shallow quakes 20-30 km deep,

can last for 10 minutes, mag 5.5

Near and Far Sides of the Moon

North and South Poles

Phases of the Moon

Map of Sunlight on the North Pole

The Surface of the Moon

Maria (seas) – dark areas

– solidified pools of ancient

lava reflect less light

Terrae (highlands) – light

areas – very ancient surface

of moon

Impact craters – “spots”

Maria

1) Solidified pools of basaltic lava – lava

flowed into old impact basins

1) Thin crust allowed lava flows

2) High iron content

3) Evidence for old shield volcanoes

4) Found mostly on near side – 31% of

surface on near side

5) Most 3-3.5 billion years old, a few as

young as 1.2 billion years

Volcanoes on the Moon

Volcanoes on Earth, Io, Moon

Lunar Surface

Lunar Highlands

• Heavily Cratered

• Ancient – as old as 4 billion

years

• Shows dominance of

impacts in early history of

solar system – 300k craters

larger than 1 km

• Evidence that formed from

magma ocean

• “mountains” do not have

same origin as earth

Impact Craters

◼ ~0.5 million craters

◼ Can be used to

estimate age

Crater Formation

Crater Formation 2

Copernicus Crater

Age: 800 million

years (Apollo 12)

Size: 93 km

Fresh Crater Showing Ejecta

Copernicus

Tycho Crater

• 110 Million years

• 85 km

• Bright ejecta make

it a prominent

feature

Piece of Ejecta from Tycho

Other Lunar Features

Graben: trench that forms due to expansion of lunar surface

Evidence that

the moon is still

contracting

Topographical Map of Graben

Lobate Scarps – More evidence of contraction

• Known as a thrust fault –

where crust of the moon is

pushing together.

• Steep face on one side, gentle

slope on the other

Rilles – Canyons/Trenches on the Moon

Rille – from a

collapsed lava

tube?

Longest Rille on the Moon

160 km x 10 km

Wrinkle Ridges

160 km x 10 km

• Formed when lava

cools and

contracts

Wrinkle Ridges in the Sea of Tranquillity.

Lunar Soil (regolith)

Regolith

• Mechanical disintegration of

basalt and other rocks on the

moon due to meteor impacts

and bombardment by solar

and cosmic high energy

particles.

• No organic components.

• Rock fragments, glass,

volcanic and impact

spherules

Water

Apollo 11 Landing Site

Views from the lunar surface

Apollo 12

Apollo 13 Views of Far Side of the Moon

Apollo 14

Apollo 17

Orbit of the Moon

Plane of Earth’s equator: Celestial equator – tilted 23.5 deg wrt Solar system

Tilt of moon’s equator wrt its orbit – 6.68 deg

Tilt of moon’s axis wrt solar system = 1.53 deg

Axis of moon – tilted 1.53 deg wrt moon’s orbit

Orbit of the Moon

Barycenter = underneath the surface of the earth

Barycenter = ∑(rimi)/∑(mi)

Lunar Libration

Evolution of Moon’s orbit◼ Tides

◼ Neither the moon or the earth is perfectly symmetric

◼ When formed, Earth/moon much closer together and rotated much faster◼ Moon 12,000-29,000 miles away

◼ Orbital period ~4hrs

◼ Earth’s day a few hours less (dinosaur day about 2 hrs shorter)

◼ Tides are transferring momentum from Earth to the moon

◼ Means – moon is moving further away from Earth (1.5 in/yr)

◼ Earth’s rotation period slowing about 0.002 s/century

◼ Final solution = ◼ Orbital period and Earth’s day ~ 47 days.

◼ Moon’s distance 348,000 miles instead of 239,000

◼ 10s of billions of years

Formation

◼ Fission Hypothesis

◼ Capture

◼ Co-Formation

◼ Impact

Collision