# Evaluate parameters affecting crater formation.

Make your own series of craters, to observe the “geological” results.Look at and evaluate images of craters on other planets/celestial bodies.
cratering_lab_rev.doc

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Craters
Overview
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Evaluate parameters affecting crater formation.
Make your own series of craters, to observe the “geological” results.
Look at and evaluate images of craters on other planets/celestial bodies.
Materials You Will Need
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Two contrasting colors of sand (or similar; see Activity 1)
Box or tray to contain sand (higher sides will help contain the sand best!)
Various small objects to simulate impactors (rocks, a marble, small ball, dice, etc., and at
least one irregular shaped object)
Prelab
1.
What factors could affect an impact crater’s shape and size?
2.
What effect do you expect varying these factors will have on the craters?
3.
Explain how you could test these hypotheses.
Introduction
One look at the surface of the Moon should convince you that “empty space” is not so empty
after all. There is actually a wide range of objects floating between the planets, from tiny
particles to asteroids that can be a hundred miles across, debris left behind when the planets were
formed. These objects can be perturbed from their orbits (by a close passage by a planet, a
passing star, any number of things) and onto paths that cross ours — or any other planet or moon.
When that happens, a collision occurs and an impact crater is formed.
The size and shape of the crater depend on the impactor: its size, shape, speed, and the angle is
hits the ground with. Specifically, the size of the crater depends on the energy of the impactor.
However, the relationship is not linear, but rather is a power law:
where D is the diameter, E is the energy of the impactor when it hits the ground, n is the power,
and k is a constant.
The energy when the impactor strikes the ground is all kinetic,
where m is the mass of the impactor, and v is the speed it’s going when it hits the sand.
Unfortunately, v is inconvenient to measure in our classroom. Fortunately, energy is conserved,
so we can give the impactor a known energy and know it will hit the sand with that amount of
energy. The total energy of a falling object is the sum of the kinetic and potential energy. If you
drop the impactor so it starts with v = 0, the total energy is just potential (called gravitational
potential energy):
where m is still the mass, g is the acceleration due to gravity = 9.81m/s2 at the surface of the
Earth, and h is the height above the ground.
Activity 1: History of Cratering
Craters can be used to find out information about conditions on the planet or moon. An active
planet will have few craters because tectonics and volcanism recycle the planet’s surface. On a
planet with an atmosphere, craters can be worn away due to wind or water erosion. A
geologically dead planet with no atmosphere has no way to remove craters, except through more
cratering.
To demonstrate cratering, you’ll have a box of sand. There should be a thick base of white sand
which you’ll add a thin regolith of colored sand to. (Note if the sand in the box isn’t white, you
should get colored sand with a good contrast). Be sure to make the layer of colored sand very
thin, since you want to see the pattern of ejecta when you make the crater. [You may use other,
similar materials, e.g. flour and cinnamon, flour and fine layer of potting soil are combinations
some have used.]
Smooth the surface of the sand and apply a thin layer of colored sand. Try throwing a ball
bearing sideways into the sand and see what shape it makes. Get some of the other objects and
throw them in. Make a bunch of craters without wiping the sand clean, to see how they pile up
on top of each other (be careful not to mess up your craters pulling the objects back out!) Look
carefully at the patterns in the sand and in the colored sand on top of the white sand — around the
crater you should see a crater rim and a little further away, rays of ejecta thrown out by the
objects.
Activity #1 Questions:
1. As you dropped the marbles from different heights, how did the ejecta (material tossed
out of the crater) change?
2. When you dropped non-spherical objects, or threw the marble at an angle, how did the
shape and ejecta change? How does this relate to craters seen on other planets/moons?
3. If you were to look at another group’s sandbox, could you tell which craters were made
first (older)? How?
4. Describe the transformation of energy that takes place during the formation of an impact
crater (from approach of the meteorite to after the crater is formed).
5. By looking at craters astronomers can get an idea of conditions on another planet/moon
without even going there. Below are images of the four Galilean moons of Jupiter.
[Make sure you study all four pictures!]
a) Place them in order from oldest to youngest surface terrain.
b) Explain how you figured out what order to put them in.
c) Based only on the pictures, which one(s) are most likely to be geologically active?
Why (note none of them have a substantial atmosphere)?
Callisto
Europa
Ganymede
Io

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