The Moon Astronomy 311 Professor Lee Carkner Lecture 13

Which of the following was not a constituent of the Earth’s original atmosphere? a)Water b)Carbon Dioxide c)Ammonia d)Methane e)Sulfur Dioxide

Why do we think the Earth’s core is liquid? a)Iron is always liquid at high pressures b)Since Venus and Mars have liquid cores, Earth should have one too c)Shear waves cannot penetrate the core d)Pressure waves cannot penetrate the core e)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 volcanism c)Where oxygen is no longer present in the atmosphere d)Where CO 2 clouds block out sunlight e)Where there are not enough icy planetesimals

The mantle, outer core and inner core are, a)Solid, liquid, solid b)Liquid, solid, solid c)Liquid, solid, liquid d)Solid all the way down e)Liquid all the way down

Temperature of Earth  Temp of Earth from energy balance  T E = [R S /(2 D S )] ½ T S  T E = [6.96X108 / (2)(1.496X1011)] ½ (5778)  T E = K  T F = 1.8T K -460 = (1.8)(278.7)-460  T F = 41.6 F  Actual Earth temp = 288 K  T = (1.8)(288)-460 = 58.4 F  How much energy does Earth emit?  P =  AT 4 =  4  R E 2 T 4  P = (5.67X10 -8 )(4  )(6.38X10 6 ) 2 (288) 4  P = 1.995X10 17 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/s 2  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 = ½mv 2  PE = KE mgh = ½mv 2 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:   billion years ago:   ~3.8 billion years ago:  large impacts produce mare basins  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)