is the focus of this module?
This remote sensing
activity introduces students to digital images, basic concepts in
remote sensing, and to software that can be used to manipulate digital
imagery. Students will learn what makes up a digital image and will
begin to use digital information to interpret information the images
is the compelling problem that students will face in this activity?
Students are challenged to find an interesting landing site on Mars.
There is no best landing site. Using the Profile tool, students
may choose any smooth spot that has interesting nearby geologic
features. The choice of landing site is secondary to learning how
to use the tools. The activity has been designed so that students
have a reason for learning how to use the tools.
Learning to use software
packages such as NIH Image or IDRISI takes some time, but after
learning some basic skills, students will soon begin to venture
forth on their own.
are some important technical details? File
Size: Two of the Mars images are about 1MB in size. To save time,
teachers may want to download these images before class or to have
them downloaded to a Network where all students can reach them.
Image Names: In this
activity we have changed the names of the images to make them a
bit more user friendly. The actual name for the Cydonia.1 image
is 673B56. The actual name for the Cydonia.2 image is 35A72. The
first numbers in the image name refer
to the orbit of the spacecraft. The letter identifies the spacecraft
that took the image: "A" identifies Viking Orbiter 1 and
"B" identifies Viking Orbiter 2. The last numbers in the
image name refer to the specific frame.
Checklist--have you thought of everything?
are some geological concepts students will encounter as they work
through this activity? As mentioned in the student section,
the area shown in the images is indeed thought to include an old
Martian shoreline. It is a transitional zone called "fretted
terrain" between the old, cratered Martian highlands to the
lower right (SE) in the regional image and the northern lowlands
to the upper left (NW). In this zone, the materials of the highlands
occur in smaller and smaller pieces towards the NW, terminating
as small, isolated mesas or mountains out on the plains. There is
a regional slope in this area: the mean elevation of the surface
in Cydonia.1 drops a few kilometers from lower right to upper left.
The mesas are thought
to be the eroded remnants of the old highland plateau: the larger
pieces look like highland materials, and the topography is consistent.
The tops of the mesas (which are typically several hundred meters
to half a kilometer above the plains) are essentially at the same
elevation as the unbroken highlands at lower right. The mesas have
been carved into complex shapes by erosion. The flat "benches"
or level "steps" seen on many of the mesas are thought
to be old wave-cut benches, similar to structures found in and around
the site of the ice-age Lake Bonneville in NW Utah (the modern Great
Salt Lake is a small remnant of this much larger and deeper ancient
lake). The angular or faceted pyramidal look to some of the mountains
is seen on terrestrial mountains, carved by prevailing winds. Note
that most of the crests of the angular mountains are oriented in
roughly the same direction, another detail consistent with wind
The plains are cut by
numerous linear depressions that form a crude polygonal pattern.
These are interpreted to be enormous "mud cracks" that
formed in the drying sediments of the old ocean floor. The ancient
mainland shoreline is indicated on Cydonia.map. It marks a definite
change in terrain, from bright and rough to dark and smooth. Students
might find it interesting to trace out the old beach in the rugged
SW parts of Cydonia.1. It can be traced in part by looking for wave-cut
terraces. The old shoreline also cuts a large (originally circular)
crater in half. Details of the crater can be brought out by restretching
that portion of Cydonia.1.
about human-made objects on Mars? These particular images
of Mars were also chosen for intrinsic student interest. Cydonia.2
contains the famous (infamous?) "Face on Mars" that has
appeared (and disappeared!) in numerous grocery store publications
and popular books on Mars and life in the universe. Your students
have almost certainly seen it before. If you look carefully near
X=580, Y=837 on Cydonia.2 (35A72), you can see what appears to be
a human-like face in one of the rock formations. This formation
has been cited many times as evidence of intelligent life on Mars.
A picture of this formation was even placed on a postage stamp in
the country of Sierra Leone.
Neither the "face"
nor its location in Cydonia.2 has been pointed out in the student
portion of the activity.
It will be interesting to see whether your students recognize the
face-like formation and comment on its presence (they probably will
- it is quite obvious if the image is properly stretched).
Assuming your students
do find the "face," it can be used as an interesting exercise
in problem solving with insufficient data. In disciplines like geology
or astronomy, which use remote sensing, it is difficult to perform
controlled experiments as in chemistry or physics. Instead, one
must act more like a detective, looking carefully at the evidence
supplied by nature to test hypotheses. Observational searches like
these often do not provide sufficient data to support or refute
a particular hypothesis, but the data can be used to constrain the
likelihood of competing hypotheses. The question of the origin of
the "face" is an example of this type of problem. To really
find out, we need to land there and look around. But we cannot.
We can consider some potential implications of assuming either a
natural or an artificial origin and look for evidence in the images
that might reflect on the likelihood of one hypothesis or the other.
Assume for a moment that
the feature is artificial. By any terrestrial standards, it is a
monumental artifact, two and a half kilometers long, two kilometers
wide, and over 400 meters (1200 feet) tall. This is about as tall
as the highest building on Earth (the Sears Tower in Chicago is
443 meters tall), but much larger in area and volume than the largest
human-made buildings, such as the Great Pyramid at Giza, the largest
structure from ancient times, or the Pentagon in Washington, DC,
one of the largest office buildings in the modern world, both shown
for comparison in the image file Face 2. Constructing such a large
artifact would require significant effort from a complex civilization.
Is there any evidence
for that civilization such as other buildings, roads, or machinery?
Some people, recognizing the improbability of an isolated artifact
of such size, have suggested that the mountains around the "face"
are parts of a "city," complete with terrestrial-type
pyramids and a "fort"(X=370, Y=630). Given this additional
assumption, how artificial do these other features look? Are they
unique? (One reason for including the regional image Cydonia.1
is to allow comparison with nearby areas. As may be seen in the
images, these types of mountains are not unique, but occur all
along the highland-lowland boundary.)
If the features of
the "face" are simply carved from a preexisting mountain
to save effort (like the Sphinx in Egypt was), is there evidence
for piles of debris or means of removal? If the materials of the
"face" were either brought to or taken away from the
site on the ground, it should show up on the images like the 2,000
year old camel paths to the ancient city of Ubar that are still
visible in satellite images (see the JPL Radar Home Page at http://southport.jpl.nasa.gov/).
help students investigate the "Face on Mars," you may
want to pose some questions such as the following:
there other features of similar complexity in the same area but
which otherwise appear natural?
Do the individual features
of the "face" (pits, ridges and flat areas) occur individually
or in different combinations on other mountains on Mars, or do such
features occur naturally on mountains on the Earth? Students could
consider Martian wind directions or erosional processes.
Is the "face"
bilaterally symmetrical, as might be expected on an artificial structure,
or is it irregular as is a natural feature? (The only other image
of the "face" is shown in the image Face 2. It is stretched
but not filtered so that no detail was lost from the original image.
It shows a little more detail on the right side of the feature than
Cydonia.2. The features appear to be only semisymmetric. This image
might be given to interested students to probe the symmetry idea.)
Might the tendency of
people to pick out familiar patterns like faces or figures of people
and animals in complex patterns such as grain on a polished piece
of wood, patterns on floor tiles, rugged mountain sides, or tree
trunks explain the "face?"
There is a "ring"
with center near X=460, Y=650 in Cydonia.2 that appears artificial.
It is a "diffraction ring" from an out-of-focus dust particle
on the camera lens. It is not on the surface of Mars. There are
also several short, nearly linear segments of channels or ridges
that some students may think are roads, but they are the above-mentioned
mud cracks and short, eroded drainage channels. It is also useful
in interpreting topography in these images to remember that the
direction of illumination is from the left. Thus, shadows of relatively
high areas trail to the right.
From the point of view
of planetary geology, the "face" is almost certainly a
natural formation. However, the image data alone cannot "prove"
it. Determined individuals can (and do) construct progressively
elaborate chains of logic or scenarios trying to support the hypothesis
of artificiality ("There are no roads or debris piles because
they flew around and carved the face using lasers...."). However,
each new assumption or scenario carries with it a new set of questions,
but the fundamental question always remains: what is the evidence?