This material was developed for the Live From Mars project
by Passport to Knowledge. Live
From Mars was a precursor to Mars Team Online.
Activity 3.2: Creating Craters
Teacher Background: Craters as Clocks and Clues
Almost all objects in the solar system that have solid surfaces (including
planets, satellites and asteroids) have craters. While a few are of volcanic
origin, most are the result of impacts from space. Much of the cratering
we see dates back to a "period of bombardment" in the early days of the
solar system (about 4 billion years ago) when the gravitational pull of
larger bodies attracted smaller objects which crashed into them. This
process has been important in the evolution of the planets. Cratering
caused early melting of the planets' crusts and excavated fresh sub-surface
material. Impacts from space continue, but at a slower rate. Recent examples
include the occasional meteorite fall on Earth and the collision of Comet
Shoemaker-Levy 9 with Jupiter in July, 1994.
The Earth, our Moon and the planet Mars all bear the scars of impacts
from space, but the Moon and Mars have many more craters than Earth. This
is partly because water covers almost three-fourths of our planet, and
partly because geologic processes like crustal movements and wind and
weather have eroded most of the craters over time. There is no atmosphere
or plate tectonics on the Moon, where many craters are visible. Many lunar
craters still have steep walls and are very rugged in appearance--evidence
of the lack of weathering.
Mars occupies a middle ground between Earth and the Moon in terms of
craters. Widespread cratering is visible, but more craters are seen in
Mars' Southern hemisphere than in the North. Since the initial bombardment
was presumably quite uniform across the planet, the relative lack of craters
in the north correlates well with evidence of geological activity we can
see in the region (faulting, uplifting, volcanism and flooding). All these
would have served to obliterate earlier cratering. (See Activities 1.3
and 2.2 for more on this.) Thus the presence or absence of cratering in
different parts of the planet helps date these regions relative to each
Mars also has a thin atmosphere and while no rain currently falls, there
almost certainly has been running surface water in the past. Strong regional
and even global dust storms periodically scour the surface. Martian craters
show the effects of weathering. They are shallower, have lower rims and,
generally, look much less rugged than most lunar craters.
On these and other worlds, the presence of craters within other craters,
or superimposed over the rims of other craters, or craters on top of flow
channels, or vice versa, helps create a planetary timeline.
Students will work in teams to model crater formation and to investigate
how mass, velocity and size of projectile affect an impact crater.
Students will be able to identify and name the parts of an impact crater,
and compare and contrast craters found on the Earth, the Moon and Mars.
Materials: For each team of 3 or 4 students
images of craters on Mars, Earth, and Moon
box, lined with trash bag; the sides
should be at least 4 inches high (lid to
photocopier paper box works well)
flour to fill box approximately 3" deep
three balls of the same size, about
1" across, of differing weight
(e.g. ball bearing, wooden ball, and
three marbles of different sizes
safety goggles (one for each student)
2 dark colors of dry tempera paint, e.g. purple and green--you
will need 2 colors besides the white flour. You might also try
chocolate powder to see if you think this gives better results.
scale to weigh projectiles (or teachers can supply weight information)
plant sprayer (optional)
plastic shovels or cups (for scooping flour)
Pass out images of craters on Earth, the Moon and Mars. Ask
students to identify these images, and to compare and contrast
the physical features of these environments, as can be deduced
from the images. Which environment(s) can support life? What observations
support this hypothesis? Can the lunar environment support life?
Can the Martian environment support life? How do we know? What
theories are there regarding the issue of life on Mars? What clues
do scientists look for to support the theory that water may once
have existed on Mars?
Part 1: Formation of Impact Craters:
How Mass, Velocity and Size Affect Impact Craters Explore
1. Tell students that in this Activity, they will simulate the
work of Planetary Geologists, and study craters.
2. Review directions on Activity 3.2 Student
3. Before beginning the hands-on activities, ask students to
predict what factors they think will most affect the size of the
craters they are going to make: the mass, velocity or size of
an impacting projectile? Have students record these predictions
in their Mission Logbooks.
4. After completing the Activity, compile and average student
data. Have students share their conclusions and compare these
with their pre-Activity prediction.
Students can create graphs illustrating the data gained from these
Older students can extend data to calculate potential and kinetic
energy. Potential energy represents the force of the earth's gravitational
pull. The formula for calculating potential energy is (mass) x
(gravity) x (height) where the acceleration due to gravity = 980
cm/s/s, height is in centimeters and mass is in grams. Using the
large marble, have students calculate the potential energy when
the marble is released from the three different drop heights and
finally when it is thrown from a height of 200 cm. As the marble
falls, its potential energy becomes kinetic energy (the energy
of bodies in motion). The formula for calculating kinetic energy
is (1/2) x (mass) x (velocity) x (velocity) or 1/2 m vv or 1/2
Students may also calculate the kinetic energy for each of the
above 4 drop conditions. Note: If only kinetic and potential energies
were involved in this Activity, then the energy calculated should
be equal. However, the marble in drop 4 "picked up" extra acceleration
when it was thrown into the flour, so the kinetic energy came
partly from potential energy and partly from your contribution
of additional kinetic energy! The other marbles had only kinetic
energy from their potential energy.
| Part 2: Crater Structure: |
Parts of an Impact Crater
Review the three factors affecting the initial size of a crater:
mass, velocity and size of impacting object. Ask students to sketch
a newly made crater, from both a birds-eye and cross-section perspective.
1. Have students continue procedure as outlined on Activity
3.2 Student Worksheet.
2. Have students complete a new set of sketches illustrating
the structure of craters with appropriate labels. Add to Mars
Have students go on-line and download images of craters from different
planets. Suggest they record what they find in their Mission Logbooks.
Ask them to explain how these craters may have been formed, pointing
out examples of new and older craters and looking for signs of
weathering and clues that water may have existed at these sites.
Have them revisit and annotate their predictions. Remember,
we would like to see the results, so please send them to PTK.
Research the theory about the impact that is believed to have
killed the dinosaurs
Write a "You Are There" news article about it, using the Five
"Ws"--Who, What, When, Where, and Why.