Live From Mars was a precursor to Mars Team Online.
Activity 1.2: Mapping the
Topography of Unknown Surfaces
| Teacher Background: Mapping Mars with Global Surveyor
The Viking orbiters provided wonderful pictures, and subsequent
image processing created mosaics of most of Mars. But much important
information is still missing. An example is something as basic as
the elevation of future landing sites. Because Mars' atmosphere
is so thin, parachutes are relatively less effective than here on
Earth. (There's less resistance to slow the spacecraft down: Newton's
Laws, once more!) So, it's critical to know how thick a layer of
Martian atmosphere you're traveling through before you reach the
surface. If the landing sites are too high up, there'll be too little
atmosphere, and you may design a braking system that won't work
well enough to slow your descent! Ouch... back to the drawing board.
Current uncertainties about Martian elevations are as large as 3
kilometers, enough to make spacecraft designers very nervous. Enter
One of the six instruments on board Mars Global Surveyor will
be the Mars Orbiter Laser Altimeter (MOLA). MOLA's laser will fire
pulses of infrared light 10 times each second. By measuring the
length of time it takes for the light to reflect off the Martian
surface and return to the spacecraft, scientists can determine the
distance to the planet's surface. (Spacecraft navigation data gives
the distance of MGS from the center of the planet, so putting the
two data sets together will yield Martian surface elevation with
a precision of a few tens of meters.) MOLA will provide information
to construct the first full topographic map of Mars, showing fine
details of plains, valleys, craters and mountains.
Note: Since topographic maps use sea level to define zero elevation,
we Earthlings measure the height or depth of all landforms relative
to sea level. Of course there's no sea on Mars, so scientists describe
elevations relative to a zero level that is called the "datum" surface.
Objectives Students will be able to describe in words and graphic displays
the elevation or depression profile of sections of Mars' Olympus
Mons and/or Valles Marineris.
Students will demonstrate the ability to describe the operation
of the MGS laser altimeter, and simulate its operation.
Students will be able to explain how orbiting spacecraft build
up global maps one data slice at a time.
Students will use contour maps to create 3-dimensional Martian
Students will transform numerical measurements into 3-D representations
of hidden landforms.
| Materials: for each team of 3/4 students
1 shoebox with lid
1 grid support constructed by gluing one complete 16 cm x 30 cm grid paper onto a piece of cardboard
Altimeter rod (10 cm length, cut from a coat hanger or wooden
an awl, leather punch or other sharp object to punch holes in
top of shoebox
17 sheets of cm grid paper (16 cm x 30 cm)
papier mache, plaster of paris, or small pieces of rocks, wood,
aluminum foil that can be used to make a Martian terrain inside
bottom of shoebox
contour map of Olympus Mons and Valles
Marineris (provided with this Guide: duplicate and scale up
to give the best "fit" with a standard shoebox); you may wish to
duplicate this and cut into "jigsaw puzzle" pieces, covering up
place names, in order to increase the challenge aspect of this Activity.
Explain why NASA needs elevation data from Mars, and how MOLA
operates, or have teams go on-line and research MOLA and report
back. As noted above, the altitude of a landing site can be crucial
for spacecraft safety.
Tell students that they represent a NASA Mission team specializing
in mapping the elevation of a little known planet. This Activity
simulates the process of gathering data about a surface which can't
be measured directly. Working in teams, students will first construct
a segment of Mars-in 3 dimensions-from current contour maps, without
revealing its exact topography to other teams. This Challenge landscape
will be hidden inside a securely-closed shoebox. Each team, in turn,
will receive a Challenge landscape created by another team, and
unknown to them. Their mission is to collect simulated altimeter
data on the Challenge landscape, and create a 3-D paper profile
map of what they think is hidden in the box (the "Result" landscape).
At the end of the Activity, they'll see how accurately Challenge
and Result landscapes match.
Note: Ideally, this is a two stage Activity: you can do just the
measuring activity, but the students will benefit both from creating
the Challenge and Result landscapes (scaling, plotting, cooperation
and model-making skills) which will let them literally get their
hands on two sections of Mars.
Making the Challenge landscape
1. Working from the sections of contour maps you provide, each
team should make a three-dimensional Mars landscape covering the
bottom of the shoebox.
2. Tape or glue a piece of cm grid paper to box lid. Label horizontal
and vertical axis 0, 1, 2, 3, etc.
3. Using a sharpened awl or leather punch, punch small holes at
intersections of the grid. Be careful!
4. Seal box with tape. Exchange the closed Martian Challenge boxes.
Tell students that they will now simulate the Mars Orbital Laser
Altimeter using the "Altimeter rod" and collect data representing
the Mars terrain hidden in the shoebox. The teacher might want to
demonstrate the following procedure:
1. Find the coordinates (0,0) on the box top.
2. Insert the Altimeter rod into the hole at (0,0), until it comes
in contact with the landform inside.
3. Keeping the rod upright, measure how much is showing above
the lid. Subtract this from its full 10 cm. length to find the distance
from "orbit" (lid) to surface (or use a piece of easily removable
paper tape as a marker, and remove and measure the rod.)
4. On the graph paper plotting grid, locate the (0,0) coordinate
and count down the number of centimeters which the rod measured.
Plot this point on the grid.
5. Repeat this procedure across the row (0,1), (0,2) (0,3), (0,4),
etc. to (0,30).
6. Connect the altimeter readings across the row.
7. Cut along this data line.
8. Fold along the dotted line (row 10) and glue on the appropriate
row (0,0 for the example above) of the grid support. You now have
the first row of your three dimensional Mars landscape. (See Diagram)
Note: to move things along, in a team of 3-4 students, one might be
MOLA and collect and measure altitude, one might plot the data points,
and another might cut out and assemble the profile sheet once each row
of data has been collected. Students should rotate through tasks to expose
each of them to all parts of the process.
Repeat this procedure for:
- the second row, coordinates (1,0), (1,1), (1,2), (1,3), (1,4), etc.
- the third row, coordinates (2,0), (2,1), (2,2), (2,3), (2,4), etc.
to (2,30); and so on, up to the sixteenth row, coordinates (16,0), (16,1),
(16,2), (16,3), (16,4), etc. to (16,30).
After class has completed the hands-on procedure:
1. Look at the Challenge and Result profiles. Ask students to determine
which "Result" corresponds to which "Challenge."
2. If you have had students create sections of Valles Marineris and
Olympus Mons as the Challenge landscapes, assemble them and enjoy the
3. Suggested discussion questions:
How could a more detailed map of the surface be made? (more holes,
holes closer together, thinner probes)
Where else could this map-making technique be used? (other planets
and their moons, ocean floors, remote areas that are difficult to reach
What other techniques beside lasers could be used? (e.g. radar-as on
NASA's Magellan spacecraft which surveyed Venus, or sonar, as in submarines.)
In what ways will future Mars Missions use MOLA information?
4. Locate a topographical map of your area: what is the scale? What
symbols are used?
5. Invite a Surveyor (perhaps a student's parent) to class: What tools
do they use? Do they ever work with GPS (Global Positioning Satellite)
which now provides altitude data, as well as latitude and longitude?
6. Record in Mission Logbooks successes or problems in completing
laser will fire infrared pulses every ten seconds. These pulses of energy
travel at the speed of light (186,000 miles per second). NASA scientists
can determine the distance from the spacecraft to the land form below
by timing how long it takes the pulse to travel from the spacecraft
to the surface and back to the spacecraft (which you can think of as
a kind of echo). Distance = Speed x Time (e.g., travel at 50 miles per
hour for 3 hours and you have gone a distance of 150 miles.) If we divide
this distance by 2, we have the distance from the spacecraft to the
Teachers of older students might have them calibrate their measuring
rods in seconds instead of length. Then, remind students of the velocity
of light and have them calculate the distances to the various points
in their topographical models. As a starter, MGS's orbit is X kilometers
(go on-line and find out...) above Mars. Given that the standard shoe
box is Y centimeters high (measure one), and that the base of the box
can be considered Mars' datum (see above) then each cm on the Altimeter
represents Z seconds (here's the math challenge!)
Research how laser
altimeters operate and report to class. Construct a visual (poster,
3-D mock-up, etc.) to use in your report.
Research the use of sonar in other technologies and in the animal
kingdom (dolphins, whales, bats).
Adapting this Activity to Higher or Lower Grades
Younger students may find this Activity still works well with arbitrary
landforms, rather than those modeled on actual Martian topography. In
this case, simply have each team create an interesting mountain/valley
shape, which then becomes the challenge for other teams to survey and
a sturdy model which you'll be able to use multiple times, create the
surface by crumpling newspaper and covering it with aluminum foil. Pour
plaster of paris or apply papier mache over the foil, and spread the
plaster all the way to the box sides to anchor the surface. It's best
to have 1-3 "mountains" or one complex feature in each box; try to make
the highest and lowest points about 10 cm different in length.