the moon astronomy 311 professor lee carkner lecture 13
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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)