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What version of NIH Image is required? "Mars Landing" was created with NIH image version 1.58. The functions described in this activity should be retained in new versions of the software, but the menu items may change from version to version of NIH Image.

What important technical concepts will students encounter as they work through this activity?

Digital Image: A picture made of a large array of pixels in a specified order. Digital images can be easily sent across great distances and can be manipulated on a computer.

Pixel: A pixel is the smallest element of a digital image. It is a square with no detail other than a single shade of color.

Pixel Value: Every pixel in an image is assigned a Digital Number (DN) value in accordance with its color or shade of gray. In this activity, the pixels of the "8-bit" images have any one of 256 (0 to 255) different shades of gray.

Histogram: A graph detailing the frequency, or number of occurrences, of pixel values. Users can determine from a histogram the range of values in an image, and can monitor changes made to pixel values by different enhancement processes.

Plot Tool: A feature that allows users to reveal pixel values in the path of a line drawn on the image. By using this tool, students can make inferences about the topography of the surface of Mars.

Look-Up Table (LUT): Visual key that shows what color or shade of gray is assigned to each pixel value.

Pseudo-Color Images: Images that are created by changing grayscale images to arbitrary color schemes by applying different color palettes to the LUT. This process does not change the pixel values; it merely assigns a color scheme to the LUT, potentially enhancing features on the images.

Filtering: The process of changing pixel values to emphasize or deemphasize certain pixels or groups of pixels. This process will help bring out some of the "hidden" features that have meaning to us. Filtering can be a powerful tool. However, remember that every time a filter is used, some pixel values are changed and some information is lost. Be aware of overprocessing.

Stretching: The process of emphasizing a small range of pixel values by concentrating the visible contrast. In this activity, students concentrate the visible contrast by using the Contrast and Brightness scales.

What is meant by the term "Resolution" in this remote sensing activity? This activity introduces the fundamental notion of resolution. It is possible that students may ask questions about this concept. Resolution refers to the discernibility or clarity of objects in an image. Resolution is a function of the distance of the camera from the objects being imaged and characteristics of the camera itself. Imagine sitting in a football stadium, looking for a friend. Your eyes are your "camera." They have a fixed angular field of view (unless you squint, of course), and a set number of pixels in the image determined by the number of rods and cones on your retina (on the order of several million). If your friend is sitting on the other side of the field, you may have difficulty in seeing her because as you gaze at objects far away, your absolute field of view is large and the area detected by each rod or cone in your eye will be large: your friend's face will be only a few "pixels" across and not distinguishable from the many other faces around her. Now let's assume you can walk directly across the field toward her. As you approach her, the absolute field of view of each rod or cone becomes smaller, and details become clearer. As you get very close, you see her quite well because your absolute field of view has become quite small and each rod or cone records only a very small area: the resolution has increased. The same thing is happening with the images provided in this activity. Cydonia.1 was taken from an orbit high above the surface of Mars, while Cydonia.2 was taken by a similar camera in a much lower orbit. Thus, Cydonia.2 has a much better resolution image than Cydonia.1.


Image of that says Module Notes: Mars Landing.

What 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 provide.

What 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.

What 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.

Preparation Checklist--have you thought of everything?

What 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 erosion.

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 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.

What 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. So:

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

To help students investigate the "Face on Mars," you may want to pose some questions such as the following:
Are 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?"

Note: 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?

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Grade Level: 7-12

Resources for this module

Images of Mars: Teachers wanting to find additional images of Mars can obtain them on CD-ROM from the National Space Science Data Center. The address is:

NSSDC/Coordinated Request and User Support Office (CRUSO)
Mail Code 633.4

Goddard Space Flight Center

Greenbelt, Maryland 20771

ph: (301)-286-7355
fax: (301)-286-1635

Maps of Mars: Shaded relief and photomosaic maps of Mars are available in many formats and scales. The maps provide local and regional contexts, and place names, and can lead to further studies about Mars. Specific maps containing the landing area include the Mare Acidalium Quadrangle (MC-4, scale of 1:5 million) and Mare Acidalium SE (MC-4 SE, 1:2 million). Mars maps can be obtained for a nominal fee from:

U.S. Geological Survey
Branch of Distribution
Box 25286
Federal Center
Denver, CO 80225

Providing for Reflection
Despite a limited level of commitment while working on a module, students can still experience significant learning if they enter into the reflection process. Ideally, reflection occurs at various points during the module; however, reflection done only at the close of a module can also be a powerful learning experience.


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