Martian Topography

Objective

Given high-resolution maps of Mars, students will explore the Martian surface and identify, measure, and describe the major geological landforms. These include large, individual objects (Olympus Mons and Valles Marineris), global features (the north-south dichotomy), and high-resolution surface images (erosion possibly due to flowing water).

Background and Theory

Mars, the third planet in our solar system, is similar to Earth in a number of ways. The coldest temperatures on the surface (-140 Celsius) are not far below polar temperatures here on Earth, and the high temperatures get up to a balmy 20 Celsius for short periods of time. Mars also has a thin but active atmosphere with clouds, weather systems, and winds that erode the surface. Both water and CO₂ ice collect at the poles, giving Mars polar caps much like Earth's polar regions (see picture above).

There are some striking differences. First, the thin atmosphere prevents water from existing on the surface as a liquid, so there are no large oceans (only ice at the poles). Second, since the surface has not been recycled by plate tectonics, it provides a record of Mars stretching back to the late heavy bombardment. Finally, dust and wind dominate the erosion on Mars, with some dust storms reaching global scales.

You will explore some of the unique geological features on the surface of Mars, starting with two famous, large objects and dominant global features, and ending with high-resolution images at a much smaller scale.

Procedure

Using the appropriate images linked in the sections below, answer the following questions. Record your answers on the worksheet provided.

Part A: Volcanoes and Valleys

1. Visit the Viking Orbiter Clickable Map of Mars.

   Note: a new browser window will open, so be sure to return to this window when you go on to question No. 2.

   This composite map of Mars generates images from the Viking orbiter for display. Identify and examine images (click on the region of the map; you may need to zoom out on most of them) of the following features:
   • The large volcano, Olympus Mons by noting an approximate latitude and longitude
   • The large rift valley, Valles Marineris by noting an appoximate latitude and an estimate the range in longitude

2. Olympus Mons is the largest volcano in the entire solar system (at 24 km in height, it is about 3 times higher than Mt. Everest, at 8 km). It is surmounted by a complex summit caldera, and surrounded by a prominent scarp several kilometers high.
   1. Using this image, find the radius of Olympus Mons (the image scale factor is 1.8 km/pixel).

      Your value will be approximate; measure from the center of the complex crater to the "prominent scarp" or cliff-like ledge that marks the edge. (Note: if you keep the "x" or "y" coordinate about the same for both clicks, you can avoid the use of Pythagorean's theorum at this step.)

   2. Using the fact that Olympus Mons is 24 km high, what is the slope of the volcano? (Remember: opposite/adjacent = tangent of the angle. The angle is thus the inverse tan of opposite/adjacent. Make sure your calculator is working in "degrees" and not "radians.")

      Need a scientific calculator?

   3. Compare it to our national highway standard of a maximum 6% slope. Comment on your comparison by relating what it is like to drive up or down a 6% grade (slope), where you see truck run-outs, for example, or the absolutely steepest highway you've ever driven up or down. The average grade to the top of Snoqualmie Pass is probably less than 1%!

3. Valles Marineris is a rift valley formed when the Martian crust cooled. The entire valley is over 5000 km long (longer than the United States is wide).
   1. Using this image, measure the width of Valles Marineris (the image scale is 0.93 km/pixel). Use any criteria you wish, just state what you chose to measure as the "Valley."

      (Note: if you keep the "x" coordinate about the same for both clicks, you can avoid the use of Pythagorean's theorum at this step.)

   2. Because Mars is smaller than Earth and therefore has greater surface "curvature," if you were standing on one side of the valley, you would not be able to see the other side. (On a clear Mars day, you can see about 15 km away.) Recall pictures you have seen of the Grand Canyon. How does the view across the Valles Marineris compare?

1. Return the the Viking Orbiter Clickable Map of Mars. As soon as the first detailed images of Mars came back to the Earth, planetary scientists noticed the terrain in the north differed dramatically from the terrain in the south.
   • Pick five areas in the north (it is best to work between the equator and 45 degrees north) and record their crater density:
     1. Count the total number craters in the image in each of the five areas you pick. Record in the table.
     2. Find the average number of craters (average count).
     3. Determine the image size (in pixels) and use the scale factor to convert the height and width into kilometers. (If you accept the default scaling, this should be (256 x 256) pixels or about (238 x 238) km. (Check the scaling information at the bottom of the page after clicking on the map to make sure.)
     4. Compute the area in square kilometers: Area = height x width
     5. Divide the total number of craters by the area, and record this on your data sheet under "Average Density." This number represents the average number of craters per square kilometer.
   • Repeat this for the south (staying below the equator but above about 45 degrees south).
   • Comment on your results, remembering that you are randomly selecting areas.
   • What conclusions can you draw from your results? Write a short hypothesis that might explain the differences. If your results are not what you expect, then be sure to comment on this as well.

The Global Surveyor Mars Orbiting Camera (MOC) has radically changed our view of Mars. The high resolution camera returns images where the smallest visible feature is about 2 meters in size (about the size of you!).

1. All of the images from MOC are available from Malin Space Science Systems. Take a moment to check out some of the images.

2. The polar regions of Mars are of great interest to scientists. The poles record, in layering of ice and dust, periods of climate change on the red planet. These layers are about 10 to 100 meters thick. During the history of Mars, the climate has changed several times such that different layers have different amounts of ice and dust, changing their appearance. Look at these images. If each layer represents 100,000 years of accumulated ice and dust, approximately how much of Mars' climate history is recorded in these layers? Recall (or find out) how atmospheric scientists use cores drilled in Antarctica for their studies. What do these cores (sometimes kilometers in length), tell us about the history of the Earth? Here we have another example of how comparative planetology works. (If we could only get to Mars to drill!)

3. Early in the year 2000, researchers discovered what appear to be recent evidence of flowing water on Mars. Take a look at this sequence of images and answer the following questions.
   1. Identify the alcoves, channels and aprons identified in the images. Using MOC2-234 as a model, draw and label a schematic (geologic map) of a gully.
   2. Pick one of the other images. Draw a geologic map of the image and identify the same features. Be sure to indicate which image you chose.
   3. Compare these (337 kbytes) two images of Mars and Mt. St. Helens. Name one similarity and one difference you see between these images.
   4. What is the main problem with the "recent flowing water" hypothesis used to explain these features? (Hint: recall Mars' atmospheric pressure.)