The Moon Astronomy 311 Professor Lee Carkner Lecture 13

Which of the following compounds was the source of the main component of the earth’s atmosphere? a)Carbon Dioxide b)Water c)Ammonia d)Sulfur Dioxide e)Methane

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

Luna -- The Goddess of the Moon   Since ancient times the Moon has been thought to affect behavior (“lunatic”, “moonstruck”) 

Features of the Moon

Principle Features of the Moon  Maria   maria is Latin for seas  arrangement of maria produces the “man-in-the- moon”  Highlands   Craters   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

Apollo Command, Service, and Lunar Modules

The Apollo Program  Explored the Moon from 1968 (Apollo 8 orbiter) to 1972 (Apollo 17)   Left behind many instrument packages and brought back 842 pounds of rocks

Why is the Moon Airless?  An air molecule is in a tug-of-war between two forces  Gravity   Thermal motions    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    Highlands:  covered with light colored anorthosite    Entire Moon is also covered in dust from meteor bombardment called regolith

Mare Basalt and Anorthosite

Heavy Bombardment Period   For about 800 million years this material bombarded everything in the solar system   This is when the vast majority of Moon craters were formed

Forming a Crater   Material in crater is compressed and pushed outwards (rim walls)   Middle floor of crater often rebounds (central peak)

The Moon’s Interior   Moon is much less active than the Earth   Moon once had a magnetic field but does not today, indicating the presence of a small iron core that has solidified  Moon also has a lower density than the Earth

Inside The Moon

How Did The Moon Form?  What does our formation theory need to explain?   Moon is much less dense than the Earth, with only a small iron core

Moon Formation Theories

Collisional Ejection Theory    The collision put large amounts of debris in orbit, which formed into the Moon  Explains the similarities between Earth and Moon rocks   The ejected material was mostly mantle rock so the Moon has a very small core

Moon Creation Simulation

A History of the Moon  4.6 billion years ago:  Giant impactor hits Earth, ejected material forms the Moon  billion years ago:   ~3.8 billion years ago:  large impacts produce mare basins  billion years ago:  mare basins fill with lava  3 billion years ago- present   small amounts of crating 

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)