To distinguish between the highlands and maria of the Moon.
To identify various lunar features.
To descrihe features as the result of impact, volcanic or tectonic action.
To use the method of superposition to date lunar features relative to each other.
Read your textbook section on lunar geology. I f you have an opportunity, look at the Moon
through a pair of binoculars or a telescope. The following are some definitions you may need.
Highlands are mountainous regions of the lunar surface, chiefly made up of anorthositic rock as
opposed to the basaltic rock of the flat, darker, lower maria. The maria are large impact basins
formed early in the lunar history by huge meteorites crashing into the lunar surface and exploding. The
basins were filled by vulcanism from about 3.9 to 3.2 billion years ago. Molten lava from beneath the
lunar crust flooded the maria basins and formed other volcanic features such as rilles. Rilles are wavy
or sinuous valleys formed by collapsed lava tubes in the maria. Sometimes times the lava tubes collapsed
in pockets to form chains of craterlets which look like a windy row of sinkholes. Lava flows on the
surface of the maria cooled at the edge of the flow forming wrinkle ridges.
Smaller meteorites formed other impact features such as craters and their ejecta which formed
rays. Craters are the usually circular depressions formed by the explosion of the impacting meteorite.
The explosions throw out other material, called ejecta, which may form smaller craterlets near the
original impact. Streaks of fine, whitish dust thrown out from impact features are called rays because
they radiate from the crater.
The third major process that changes the lunar surface is tectonic activity. Any cmstal crack or
uplift caused by moonquakes or other subsurface shifts on the Moon is called tectonic activity. Tectonic
activity usually results in straight features while vulcanism results in curved or sinuous features. As
most quake activity is now very far beneath the lunar surface, the Moon is now virtually tectonically
You have now nearly finished the preparation for the laboratory. If you are unsure of the material,
please reread the preparation, consult your textbook or ask questions of your instructor. Answer the
questions on the next page and be ready to hand them to your instructor at the start of lab.
THE MOON PRE-LAB
Using your lecture textbook and/or any other acceptable source of information, answer each question
in complete sentences. Be sure to define any relevant terms.
Explain the following terms relating to lunar surface features.
a. Maria (singular "Mare"):
d. Wrinkle Ridge:
Explain the following terms relating to processes that shape the lunar surface.
d. Dating by Superposition:
THE MOON LAB EXERCISE
In completing this lab, you will view images found on the Astronomy lab website. Your instructor
will direct you to the location.
The Earth, the Moon and the Sun are the most familiar astronomical objects in the sky. Of these,
the Moon has been historically the most studied and most photographed by astronomers. Even a small
telescope reveals an incredible profusion of lunar features. The most prominent are the lunar maria.
which show as dark smooth areas surrounded by mountains. Almost all of the maria are on the earthside
of the Moon and have lower elevation than the lighter highlands. The worksheet is a sketch of the
Moon, the meandering lines outline maria and highlands.
Examine the images of the near and far sides of the moon on the website. Describe the similarities and differences.
Look carefully at the image of the near side of the Moon and the map of the moon on your table.
Place M's on the worksheet at the center of the major maria. How many maria did you find?
Estimate the fraction of the Earth side of the Moon that is maria.
Describe the general shape of the maria. Are there any major exceptions? I f so, which ones?
Wrinkle ridges are sinuous, low, irregular ridges which are associated with the maria. Examine
the image of Mare Serenitatis. Find a prominent wrinkle ridge in the maria, sketch it on your
worksheet, and label it w.r.
Suggest how wrinkle ridges may have formed.
Based on the appearance of the maria, explain how they might have been formed.
Examine the image labeled 'LeMonnier.' How does the appearance of the crater LeMonnier in
Mare Serenitatis confirm your answer to question 7?
Craters are the circular depressions which are scattered over the lunar surface. They range in size
from a hundred or so kilometers, such as Copernicus, Tycho and Kepler, to those so small they were
seen only at ground level by the astronauts.
Locate Copernicus on the worksheet and note it by a small c.
Just northeast of Copemicus are the Appenine Mountains which form a southern border to Mare
Imbrium. The image labeled 'moonmap' represents a region 10° in every direction centered on 20°N
latitude and 0° longitude.
In this region there are many impact craters. Generally they can be divided into three main
profiles. Examine the images labeled crater-a, crater-b, and crater-c.
Name an example of each of these crater types found in this region represented in the 'moonmap
Which type of crater is Copemicus?
a. Which of the three types of craters in question 10 tend to be the smallest? Which are the largest?
b. Do each of the three types occur in both the highlands and the maria?
Look carefully at the image labeled 'Copemicus.' It was taken by the Apollo 15 command module. The large crater to the far right near the horizon is Copemicus. Using the map, find the
location of this image on the Moon and note it on the worksheet with a square.
The prominent large crater just to the left of the photo center is
ing toward the compass direction of
Account for the appearance of the long, jumbled, gradual slope outside the crater rim by explaining how the crater might have been formed.
State how the activity that formed the crater might also explain the higher-than-normal number
of small craterlets in the foreground of the photograph.
and you are look-
17. Between the crater identified in question 14 and Copemicus there is a winding line of small craterlets. Find these craterlets on your moon map. List two ways in which these are different from
the craters studied previously. (Hint: Look at their arrangement and shape.)
Which of the Moon's major surface-modifying processes produced this sinuous line of craterlets?
Rays are light streaks radiating from craters. Name a crater with extensive rays.
Give three reasons why you would not expect to find a crater with such an extensive ray system
on the Earth.
RILLES AND FAULTS
Rilles are narrow channels, some straight, some sinuous, often mnning hundreds of kilometers.
Faults are cracks or dislocations of the lunar cmst. Many straight rilles are faults, but faults also include
The Alpine Valley (also known as Valles Alpes) near 50°N, 0°, and The Straight Wall (also known as
Rupes Recta) near 20°S, 10°W.
Locate and name one prominent straight rille that is obviously a crustal fracture.
Sketch this rille on the worksheet.
Suggest how rilles and faults may have been formed.
Look at photograph B which was also taken by the Apollo 15 command module. It features two
sinuous rilles as well as a long, oval depression and numerous craters.
With the exception of the lower right of the photograph, the terrain seems to be
The craters in a string near the center of the photo are like those of question 17. Thus, they are
(impact/tectonic/volcanic) in origin.
Can you suggest how the two sinuous rilles were formed?
Lunar features can be classified by the means which formed them.
1) Impact features are caused by a very large size range of meteoroids crashing into the lunar surface.
The larger objects penetrate the surface then explode. 2) Vulcanism causes flows of liquid magma
from beneath the crust out onto and across the surface. Sometimes it is also responsible for uplifted
features such as domes. 3). Tectonic activity results from moonquakes or other cmstal shifts.
Some features show two processes, such as the maria. The general shapes of the maria wer
determined by gigantic meteoritic impacts which formed impact basins. The maria were then filled by
Characterize the following features as impact, tectonic, volcanic or some combination.
The Alpine Valley
The crater of question 14
The craterlets of question 17
The rille of question 21
The sinuous rilles of photograph B
Determining the relative dates of two features is simplest when they are superimposed. The most
recently formed feature modified the shape, stmcture or color of the older. One example is a more
recent cmstal fault cutting through a mountain range such as The Alpine Valley. Another example is
an older crater filled with ejecta or maria lava. Rays are excellent indicators of age as they cover large
regions of the Moon. If a crater is superimposed on top of the rays, it is younger than the crater from
which the rays emanate. If the rays blanket the crater, the crater is the older feature. Further explanation
is given at the beginning of the Mars Laboratory. By comparing the absolute ages of lunar rocks (as
determined by radioactive analysis) with the relative dating of features from which these rocks came,
a fairly thorough history of the Moon can be written.
By looking at the map, determine which of each pair is older.
Arrange in order of age the following features seen in photograph B: the long, oval depression
to the left; the small, round craters in the depression; the left sinuous rille; the maria whose edge
can be seen in the photo.
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