Live From Mars was active July 1996-December 1997.
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 other.
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.
Materials: For each team of 3 or 4 students
should be at least 4 inches high (lid to
photocopier paper box works well)
1" across, of differing weight
(e.g. ball bearing, wooden ball, and
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:
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 Worksheet.
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 investigations.
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 mv2.
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 Mission Logbooks.
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.