The Moon

Astronomy 311Professor Lee

CarknerLecture 13

Which of the following was not a constituent of the Earth’s original atmosphere?

a) Waterb) Carbon Dioxidec) Ammoniad) Methanee) Sulfur Dioxide

Why do we think the Earth’s core is liquid?

a) Iron is always liquid at high pressuresb) Since Venus and Mars have liquid cores,

Earth should have one tooc) Shear waves cannot penetrate the

cored) Pressure waves cannot penetrate the coree) From computer modeling of convection

What defines the outer edge of the habitable zone?

a) Where planets are too small to have plate tectonics

b) Where it is too cold for volcanismc) Where oxygen is no longer present in

the atmosphered) Where CO2 clouds block out sunlighte) Where there are not enough icy

planetesimals

The mantle, outer core and inner core are,

a) Solid, liquid, solidb) Liquid, solid, solidc) Liquid, solid, liquidd) Solid all the way downe) Liquid all the way down

Temperature of Earth Temp of Earth from energy balance

TE = [RS/(2 DS)]½ TS

TE = [6.96X108 / (2)(1.496X1011)]½ (5778) TE = 278.7 K TF = 1.8TK -460 = (1.8)(278.7)-460 TF = 41.6 F

Actual Earth temp = 288 K T = (1.8)(288)-460 = 58.4 F

How much energy does Earth emit? P = AT4 = 4RE

2T4

P = (5.67X10-8)(4)(6.38X106)2(288)4

P = 1.995X1017 W

Luna -- The Goddess of the Moon

Since ancient times the Moon has been thought to affect behavior (“lunatic”, “moonstruck”) There is no good evidence

for this however

Principle Features of the Moon Maria

maria is Latin for seas arrangement of maria produces

the “man-in-the-moon” Highlands

Craters circular impact structures range in size from few hundred

km to microscopic

Moon Facts

Size: 3476 km diameter

Orbit: 384,000 km

Description: small, airless, cratered surface is similar to Mercury

Timeline of Moon Exploration

Luna 1 (USSR, 1959) first spacecraft to fly by the Moon

Luna 2 (USSR, 1959) Luna 9 (USSR, 1966) first lunar lander Luna 10 (USSR, 1966) Apollo 8 (USA, 1968) first manned orbiter Apollo 11 (USA, 1969) Luna 16 (USSR), 1970) first automated sample

return

Near and Far Sides of the Moon

Why is the Moon Airless?

Gravity

Thermal motions

All molecules have a velocity proportional to their temperature

The Moon has no atmosphere because this velocity is too large for its gravity to overcome

The Surface of the Moon Maria:

covered with dark colored mare basalt similar to lava on Earth

Highlands: covered with light colored anorthosite very old (more than 4 billion years)

Moon rocks are similar in many ways to Earth rocks, but are depleted in volatiles

Mare Basalt and Anorthosite

Tycho and Rays

Falling Bodies Real impactors get their energy from their very high

orbital velocities

A body a height h above a surface has potential energy:

PE = mgh

1000 grams = 1 kg

g = 9.8 m/s2

h is the height above the surface in meters

Energy When the object hits the surface, all of the

potential energy is converted into kinetic energy:

PE = KE = ½mv2

PE = KEmgh = ½mv2

v = (2gh)½

If g and h are in meters, v is in m/s

The Moon’s Interior

Moon is much less active than the Earth

Moon is much less dense than the Earth

Moon once had a magnetic field but does not today, indicating that the core has solidified

Inside The Moon

Moon Formation Theories

Collisional Ejection Theory The collision put large amounts of debris in

orbit, which formed into the Moon

Energy from impact depleted the Moon in volatiles

The ejected material was mostly mantle rock, so the Moon has a very small core

A History of the Moon 4.6 billion years ago:

4.6-3.8 billion years ago:

~3.8 billion years ago: large impacts produce

mare basins

3.8-3.1 billion years ago:

3 billion years ago-present core solidified, no more

magnetic field small amounts of

cratering

Next Time

Read Chapter 10

Summary

Moon was formed 4.6 billion years ago when large impactor hit the Earth

Moon has a low density because it has only a small iron core

Moon has become tidally lock so that only the near-side faces Earth

Most of our information about the Moon comes from the Apollo missions

Summary: Surface Maria

large impacts produced basins which then filled with lava

darker, denser and younger than the highlands Highlands

regions that have not experienced large impacts or lava

lighter, less dense and older than the Maria Large numbers of impacts have covered the

surface with craters and regolith (dust)