Investigating the Dynamic Martian Polar Caps
On-Line Student Instruction and Answer Sheet

In this activity, you will be investigating the changing polar ice cap on the planet Mars and comparing the change to Earth's changing polar ice cap.  Before you begin, print out a copy of this on-line instruction and answer sheet to record your data and observations.  

NASA scientists want to know, "How much does the polar ice cap on Mars change?"  Let's use NASA Hubble Space Telescope images to find out.  

View the on-line movie, Mars Changing Polar Ice Caps Movie (mpg, QT, or anim_GIF) serveral times.  In the space provided, carefully sketch: (i) the maximum extent of ice coverage; (ii) the minimum extent of ice coverage; and (iii) the average or middle extent of ice coverage.  
 

Maximum extent of ice coverage	Average extent of ice coverage	Minimum extent of ice coverage

Why?   (Always write in complete sentences.) 
 
 
 

NASA scientists use computers to conduct scientific investigations everyday. One procedure frequently used is called IMAGE PROCESSING.  Today, we are going to learn how to process images of Earth and Mars on your computer.  In this activity, we are going to measure the areas of the polar caps, and how they change over time.  

Be sure you have the following items on your computer before you begin.  

• image processing software (Mac or PC)
• image format converters (Mac or PC)
• saved TIF images of Mars 1 and 2 on your computer's hard drive.
• saved TIF images of Earth 1 and 2 on your computer's hard drive.
• Movie, Mars Changing Polar Ice Caps Movie (mpg, QT, or anim_GIF), saved on your computer's hard drive.

Note: GIF and JPG images can be converted easily into TIF images using image format converters, such as Gif Converter (Mac) or Paint Shop Pro (PC). 

3. Set the Image Scale: Move the pointer to the Analyze pull-down menu at the top of the screen, depress the mouse button, drag down to Set Scale, and let go.  A new window will open.  In the center of the window is a box labeled Units. Click on the down arrow in the box and select kilometers as your unit of measurement.  At the top of the window enter 292 in the Measured Distance box and 4362 in the Known Distance box (this corresponds to a scale of 292 pixels = 4362km).  Click OK and start measuring!  

4. Draw a Diameter: Using the Segment Tool (Tools window, 5th icon from the top in the right hand column), draw the longest segment you can across the diameter of the white ice cap.  Once the segment is drawn, return to the Analyze pull-down menu, drag down to Measure, and release the mouse button.  Again, click on Analyze, drag down to Show Results, and release the mouse button.  A Results window will appear with your answer in the column marked length.  

5. Freehand Tool to Measure Perimeter and Area: This image processing program has 4 tools for selecting regions for study.  The first tool in the right hand column of the tool window is used to drag out rectangular areas.  The second tool in the right hand column of the tool window is used to define oval or circular areas.  Using the third tool in the right hand column of the tool window, you can connect a sequence of points with line segments, to create a polygon of your own design.  To close the polygon (connect your last point to your first point), just click the mouse twice in rapid succession.  The fourth selection in the right hand column of the tool window allows you to freehand any curve you want (this is called the Freehand Tool and looks like a heart).  Determine the area of the polar ice cap using the freehand tool to trace the outside.  Select Analyze and Show Results to view the measured value for perimeter and area.  Record your results below.  

6. How big is the winter Martian Polar Ice cap compared to the state (or country) in which you live?  

7. Now that you know how to measure various aspects of Mars, lets get data for both the maximum and minimum extent of the Martian northern polar ice cap.  The minimum extent image is mar97_mars.tif and available for viewing through your WWW-browswer as mar97_mars.gif.  

Record your data here:  

 

MARS	maximum extent	minimum extent	difference between
diameter	km	km	km
perimeter	km	km	km
area	km2	km2	km2

 

9. Does anything on Earth compare to these sizes?  
What?  
 
 
 

In the previous section you learned about the changing polar ice cap on Mars.  Now, lets apply what you have learned to the study of Earth's northern polar ice cap.  

Determine the maximum, minimum, and average extent of snow and ice coverage for Earth's north pole.  Use the following images 02.tif and 08.tif. (These can be viewed through your WWW-browser as 02.gif and 08.gif.)  Set the scale to be 248 pixels = 12756 km using the same procedure you used for Mars in the previous section.  

Record your data below:  
 

Why or why not?  
 
 
 

Note that the largest extent of ice coverage is in August, yet the first day of summer is in June.  A similar situation occurs in winter; the first day of winter is in December, yet the maximum ice coverage is in February.  

How might you account for this difference?  
 

It isn't that way on Mars; why not?  
 
 
 

Does this observation change your answer to the previous question?  

• Which planet has a larger ice cap during the winter?
• Which planet has the smaller ice cap during the summer?
• Which planet has the largest change in the polar ice cap?
• Why does a "thermal lag" exist on Earth but not on Mars?
• If you know the scale, you can make similar measurements for any planet or moon.  However, most images on the WWW are in GIF or JPG format.  What do you need to do in order to use these image processing programs?