Hawai'i Space Grant College, Hawai'i Institute of Geophysics and
Planetology, University of Hawai'i, 1996
To determine the factors affecting the appearance of impact craters
The circular features so obvious on the Moon's surface are
impact craters formed when impactors smashed into the surface.
The explosion and excavation of materials at the impacted site created
piles of rock (called ejecta) around the circular hole as well as
bright streaks of target material (called rays) thrown for great
Two basic methods that form craters in nature are:
1) impact of a projectile on the surface and 2) collapse
of the top of a volcano creating a crater termed caldera.
By studying all types of craters on Earth and by creating impact craters
in experimental laboratories, geologists concluded that the Moon's craters
are impact in origin.
The factors affecting the appearance of impact craters and ejecta
are the size and velocity of the impactor, and the geology of the target
By recording the number, size, and extent of erosion of craters,
lunar geologists can determine the ages of different surface units
on the Moon and can piece together the geologic history. This technique
works because older surfaces are exposed to impacting meteorites
for a longer period of time than are younger surfaces.
Impact craters are not unique to the Moon. They are found on all
the terrestrial planets and on many moons of the outer planets.
On Earth, impact craters are not as easily recognized because
of weathering and erosion. Famous impact craters on Earth are Meteor Crater
in Arizona, U.S.A.; Manicouagan in Quebec, Canada; Sudbury in Ontario,
Canada; Ries Crater in Germany, and Chicxulub on the Yucatan coast in Mexico.
Chicxulub is considered by most scientists as the source crater of the
catastrophe that led to the extinction of the dinosaurs at the end of the
Cretaceous period. An interesting fact about the Chicxulub crater is that
you cannot see it. Its circular structure is nearly a kilometer below the
surface and was originally identified from magnetic and gravity data.
Lunar Impact Crater
Typical characteristics of a lunar impact crater are labeled on
this photograph of Aristarchus, 42 im in diameter, located West of Mare
bowl shaped or flat, characteristically below surrounding ground
level unless filled in with lava.
blandet of mateial surrounding the crater that was exzcavated during
the impact event. Ejecta becomes thinner away from the crater.
rock thrown out of the crater and deposited as a ring-shaped pile
of debris at the crater's edge during the explosion and excavation of an
characteristically steep and may have giant stairs called terraces.
bright streaks starting from a crater and extending away for great
distances. See Copernicus crater for another example.
mountains formed becuase of the huge increase and rapid decrease
in pressure during the impact event. They occur only in the center of craters
that are larger than 40 km diameter. See Tycho crater for another example.
In this activity, marbles or other spheres such as steel shot,
ball bearings, or golf balls are used as impactors that students drop from
a series of heights onto a prepared "lunar surface." Using impactors of
different mass dropped from the same height will allow students to study
the relationship of mass of the impactor to crater size. Dropping impactors
from different heights will allow students to study the relationship of
velocity of the impactor to crater size.
Review and prepare materials listed on the student sheet.
The following materials work well as a base for the "lunar surface."
Dust with a topping of dry tempera paint, powdered drink mixes glitter
or other dry material in a contrasting color. Use a sieve, screen , or
flour sifter. Choose a color that contrasts with the base materials for
most striking results.
all purpose flour
Reusable in this activity and keeps well in a covered container.
It can be recycled for use in the lava layering activity or for many other
science activities. Reusable in this activity, even if colored, by adding
a clean layer of new white baking soda on top. Keeps indefinitely in a
covered container. Baking soda mixed (1:1) with table salt also works.
Reusable in this activity but probably not recyclable. Keeps only in freezer
in airtight container.
sand and corn starch
Mixed (1:1), sand must be very dry. Keeps only in freezer in airtight container.
Pans should be plastic, aluminum, or cardboard. Do not use glass. They
should be at least 7.5 cm deep. Basic 10"x12" aluminum pans or plastic
tubs work fine, but the larger the better to avoid misses. Also, a larger
pan may allow students to drop more marbles before having to resurface
and smooth the target materials.
A reproducible student "Data Chart" is included; students will
need a separate chart for each impactor used in the activity.
Begin by looking at craters in photographs of the Moon and asking students
their ideas of how craters formed.
During this activity, the flour, baking soda, or dry paint may fall onto
the floor and the baking soda may even be disbursed into the air. Spread
newspapers under the pan(s) to catch spills or consider doing the activity
outside. Under supervision, students have successfully dropped marbles
from second-story balconies. Resurface the pan before a high drop.
Have the students agree beforehand on the method they will use to "smooth"
and resurface the material in the pan between impacts. The material need
not be packed down. Shaking or tilting the pan back and forth produces
a smooth surface. Then be sure to reapply a fresh dusting of dry tempera
paint or other material. Remind students that better experimental control
is achieved with consistent handling of the materials. For instance, cratering
results may vary if the material is packed down for some trials and not
Allow some practice time for dropping marbles and resurfacing the materials
in the pan before actually recording data.
Because of the low velocity of the marbles compared with the velocity of
real impactors, the experimental impact craters may not have raised rims.
Central uplifts and terraced walls will be absent.
The higher the drop height, the greater the velocity of the marble, so
a larger crater will be made and the ejecta will spread out farther.
If the impactor were dropped from 6 meters, then the crater would be larger.
The students need to extrapolate the graph out far enough to read the predicted
Have the class compare and contrast their hypotheses on what things
affect the appearance of craters and ejecta.
As a grand finale for your students, demonstrate a more forceful impact
using a slingshot.
What would happen if you change the angle of impact? How could this be
tested? Try it! Do the results support your hypothesis?
If the angle of impact is changed, then the rays will be concentrated
and longer in the direction of impact. A more horizontal impact angle produces
a more skewed crater shape.
To focus attention on the rays produced during an impact, place a paper
bulls-eye target with a central hole on top of a large, flour-filled pan.
Students drop a marble through the hole to measure ray lengths and orientations.
Use plaster of Paris or wet sand instead of dry materials.
Videotape the activity.
Some people think the extinction of the dinosaurs was caused by massive
global climate changes because of a meteorite impact on Earth. Summarize
the exciting work that has been done at Chicxulub on the Yucatan coast
Some people think Earth was hit by an object the size of Mars that caused
a large part of Earth to "splash" into space, forming the Moon. Do you
agree or disagree? Explain your answer.
Physics students could calculate the velocities of the impactors from various
heights. (Answers from heights of 30 cm, 60 cm, 90 cm, and 2 m should,
of course, agree with the velocity values shown on the "Impact Craters
- Data Chart".
Go to Impact Craters Student
Go to Impact Craters Data
Go to Impact Craters Graph.
Return to Impact
Craters Activity Index.
Return to Hands-On
Activities home page.
This activity has been copied, with permission, from the University of
Hawaii's School of Ocean & Earth Science & Technology server to ours,
to allow faster access from our Web site. We encourage you to explore
Return to Reach Out!
To Reach Out!
volunteer organization at the University of Michigan