Article: The Moon
Website: Enchanted Learning
http://www.enchantedlearning.com/subjects/astronomy/moon/Craters.shtml
October 24, 2012
Impact Craters on the Moon
Impact craters are the remains of collisions between an asteroid, comet, or meteorite and the Moon. These objects hit the
Moon at a wide range of speeds, but average about 12 miles per second (20 kilometers per second).
The surface of the moon is scarred with millions of impact craters. There is no atmosphere on the moon to help protect it
from bombardment from potential impactors (most objects from space burn up in the Earth's atmosphere). Also, there is no
erosion (wind or water) and little geologic activity to wear away these craters, so they remain unchanged until another new
impact changes it.
These craters range in size up to many hundreds of kilometers, but the most enormous craters have been flooded by lava,
and only parts of the outline are visible. The low elevation maria (seas) have fewer craters than other areas. This is because
these areas formed more recently, and have had less time to be hit.
Different Types of Impact Craters
The size, mass, speed, and angle of the falling object determine the size, shape, and complexity of the resulting crater.
Small, slow objects have a low energy impact and cause small, simple craters. Large, fast objects release a lot of energy
and form large, complex craters. Very large impacts can even cause secondary cratering, as ejected material falls back to
the ground, forming new, smaller craters, or a series of craters.
Most of the craters on the Moon are circular. The few craters that are not circular, like
Messier and Messier A (pictured at the left) in the Mare Fecunditatis, are an enigma.
Scientists do not know exactly how these oddly-shaped craters were formed.
Bibliography Information:
Note: You won’t fill in every item. Information depends on the type of source.
This source is a:
Magazine
Book
Author’s Last Name
Title of Book/Article/Website
Newspaper
Website
First Name
Other:
Middle Initial
nd
2 Author:
(periodicals, textbooks, encyclopedias, websites)
Place Published
(books only)
Publisher
Edition
Volume Number
(if applicable)
(periodicals or encyclopedias)
Publication or
Copyright date
Editor
(if applicable)
Page Number(s)
Type of Website: (Educational, business/company, personal, etc.)
The URL is http:// www.enchantedlearning.com/subjects/astronomy/
(websites only)
moon/Craters.shtml
Computer Internet (no author)
“Title of Article or Website.” <Internet address> Date.
Last Date of Access
(websites only)
Article: Impact Cratering
Website/Organization: Lunar and Planetary Institute
http://www.lpi.usra.edu/education/explore/shaping_the_planets/impact_cratering.shtml
October 24, 2012
Impact Cratering
Impact cratering is the excavation of a planet's surface when it is struck by a meteoroid.
Impacts are instantaneous events. They leave very characteristic features.
What are craters?
Craters are roughly circular, excavated holes made by impact events. The circular shape is due to material flying out in all directions as
a result of the explosion upon impact, not a result of the impactor having a circular shape (almost no impactors are spherical). Craters
are the most common surface features on many solid planets and moons—Mercury and our Moon are covered with craters.
What happens when an impactor hits?
When an impactor strikes the solid surface of a planet, a shock wave spreads out from the site of the impact. The shock wave fractures
the rock and excavates a large cavity (much larger than the impactor). The impact sprays material — ejecta — out in all directions. The
impactor is shattered into small pieces and may melt or vaporize. Sometimes the force of the impact is great enough to melt some of
the local rock. If an impactor is large enough, some of the material pushed toward the edges of the crater will slump back toward the
center and the rock beneath the crater will rebound, or push back up, creating a central peak in the crater. The edges of these larger
craters also may slump, creating terraces that step down into the crater.
What influences the size and shape of a crater?
The size and shape of the crater and the amount of material excavated depends on factors such as the velocity and mass of the
impacting body and the geology of the surface. The faster the incoming impactor, the larger the crater. Typically, materials from space
hit Earth at about 20 kilometers (slightly more than 12 miles) per second. Such a high-speed impact produces a crater that is
approximately 20 times larger in diameter than the impacting object. Smaller planets have less gravitational "pull" than large planets;
impactors will strike at lower speeds. The greater the mass of the impactor, the greater the size of crater.
Craters most often are circular. More elongate craters can be produced if an impactor strikes the surface at a very low angle — less
than 20 degrees.
Bibliography Information:
Note: You won’t fill in every item. Information depends on the type of source.
This source is a:
Magazine
Book
Author’s Last Name
Title of Book/Article/Website
Newspaper
Website
First Name
Other:
Middle Initial
nd
2 Author:
(periodicals, textbooks, encyclopedias, websites)
Place Published
(books only)
Publisher
Edition
Volume Number
(if applicable)
(periodicals or encyclopedias)
Publication or
Copyright date
Editor
(if applicable)
Page Number(s)
Type of Website: (Educational, business/company, personal, etc.)
The URL is http://www.lpi.usra.edu/education/explore/shaping_the_planets/
(websites only)
impact_cratering.shtml
Computer Internet (no author)
“Title of Article or Website.” <Internet address> Date.
Last Date of Access
(websites only)
Source: Earth Science Textbook: Chapter 19, Section 4 (pgs. 680-681)
In 1609, the Italian scientist Galileo Galilei heard about a telescope, a device built to observe distant objects by making
them appear closer. Galileo made his own telescope by putting two lenses in a wooden tube. When Galileo pointed his
telescope at the moon, he was able to see much more detail than anyone had ever seen. Recent photos of the moon show
much more detail than Galileo could see with his telescope.
Features on the moon’s surface include craters, maria, and highlands.
The moon’s surface has dark, flat areas, which Galileo called maria, the Latin word for “seas.” Galileo incorrectly thought
that the maria were oceans. The maria are actually hardened rock formed from huge lava flows that occurred between 3
and 4 billion years ago.
Galileo saw that the moon’s surface is marked by large round pits called craters. Some craters are hundreds of kilometers
across. For a long time, many scientists mistakenly thought these craters had been made by volcanoes. Scientists now
know that these craters were caused by the impacts of meteoroids, chunks of rock or dust from space.
Galileo correctly inferred that some of the light-colored features he saw on the moon’s surface were highlands, or
mountains. The peaks of the lunar highlands and the rims of the craters cast dark shadows, which Galileo could see. The
rugged lunar highlands cover much of the moon’s surface.
The moon is dry and airless. Compared to Earth, the moon is small and has large variations in its surface
temperature. To stay at a comfortable temperature, protect against sunburn, and carry an air supply, you would have to
wear a bulky spacesuit if you visited the moon. The moon is 3,476 kilometers in diameter, a little less that the distance
across the United States. This is about one-fourth Earth’s diameter. However, the moon has only one-eightieth as much
mass as Earth. The moon has no liquid water. However, there is evidence that there may be large patches of ice near the
moon’s poles. Temperatures in these regions are so low that ice there would remain frozen.
Bibliography Information:
Note: You won’t fill in every item. Information depends on the type of source.
This source is a:
Magazine
Book
Author’s Last Name
Title of Book/Article/Website
Newspaper
Website
First Name
Other:
Middle Initial
nd
2 Author:
(periodicals, textbooks, encyclopedias, websites)
Place Published
(books only)
Publisher
Edition
Volume Number
(if applicable)
(periodicals or encyclopedias)
Publication or
Copyright date
Editor
(if applicable)
Page Number(s)
Type of Website: (Educational, business/company, personal, etc.)
The URL is http://
Last Date of Access
(websites only)
(websites only)
Citation, Book: Two or more authors:
First author’s last name, first name and second author’s first name and last name. Title of book.
Place of publication: Publisher, publication or copy right date.
Name:
Impact Crater Lab Research Note Cards
Period:
As you read the background information, look for interesting facts or quotes that you think could be useful in a
report about impact craters. Write one fact/quote and the name of the source on each “note card” below. Be
ready to share with the class.
Fact/Quote:
Fact/Quote:
Source:
Source:
(Pg. #
)
(Pg. #
Fact/Quote:
Fact/Quote:
Source:
Source:
(Pg. #
)
)
Fact/Quote:
Fact/Quote:
Source:
Source:
(Pg. #
(Pg. #
)
)
(Pg. #
)