Activity adapted from NASA 'Impact craters':https://www.nasa.gov/wp-content/uploads/2009/07/impact-craters.pdf
This is most easily run as a group activity, with one or two trays on a carpet, with students circling the tray(s).
It can also be run with a tray for each table group.
Introduce the activity:
In the solar system, chunks of rock sometimes collide with planets or moons.
These stray small chunks of rock and metal most often come from the asteroid belt (between Mars and Jupiter), when a collision between asteroid belt bodies sends an asteroid out of the belt into the rest of the solar system.
Asteroids come in various shapes (as they are not large enough for gravity to pull them into a sphere): https://en.wikipedia.org/wiki/Asteroid#/media/File:Asteroidsscale.jpg
Impact craters, from when a "meteoroid" hits the surface, are the dominant geographic features on many solid Solar System objects. (Early in the history of our solar system, asteroid impacts were much more common. Now, many of these stray chunks of rock have been caught by the gravity of big planets.)
Shake a tray of flour back and forth so that the surface of the flour is relatively flat. Do not press the surface down - allow it to settle with its own weight. Place the tray on the floor.
Sprinkle cinnamon over the flour to make an even coat of brown over the flour.
Optionally ask students to make asteroid-shaped pieces with their modelling clay. (Show them shapes from here: https://en.wikipedia.org/wiki/Asteroid#/media/File:Asteroidsscale.jpg)
Allow students to drop the marble/clay ball from a height above the tray, taking turns.
Name the parts of the crater that are formed:
The floor of the crater (the bottom of the hole), the rim (the raised edges ringing the hole), ejecta (material projected out of the crater - it will look white in contrast to the brown cinnamon), rays (long lines extending away from the crater; a pattern made by the ejecta).
(See p.3 of Activity adapted from: https://www.nasa.gov/wp-content/uploads/2009/07/impact-craters.pdf)
Students can observe that different clay asteroid shapes all make circular impact craters (as long as they are going fast enough).
Students, or a teacher demonstration, can model an 'oblique impact' crater - an asteroid hitting a planet surface at an angle (either with a throw from the side, or by tipping the tray). The crater made has ejecta concentrated on one side (see last photo). Easier to see properly on a new layer of cinnamon.
Students can try dropping their 'asteroids' from different heights (therefore different impact speed), to observe the difference in the crater sizes made.
Optional: ask students to measure the heights they are dropping from and to measure the diameter of the crater from rim to rim in each case. (Note that this data is messy and there is not a huge amount of difference between high and low drop heights, but it demonstrates graphing data, and how to draw lines of best fit. See worksheet attached.)
Once the flour and cinnamon is covered in impacts and it is hard to see the patterns, stir up the flour and cinnamon to make an even colour, then reapply the cinnamon..
Discussion points and more information:
1. Students should find that the crater diameter is always larger than the asteroid. When the surface of a real planet or moon is hit by a chunk of rock (more precisely called a meteoroid, or the "impactor"), the shock fractures the surface rock and makes a large cavity which is larger than the impactor. The impact sprays material ("ejecta") in all directions. (Any remaining rock pieces are called meteorites.) Asteroids hit the moon at an average of 20 kilometers per second, and make a crater 10 t0 20 times larger than the impacting object.
2. Point out to students that the marble/clay stays in the hole - for a real crater the impact rock has gone. It has shattered and been distributed with the ejecta. Or if the impact generates enough heat, the impactor melts or vapourizes.
3. Either through eye-balling the difference in patterns, or by graphing data collected, the size of the crater and the average ray length increases with impact speed. (See graph of data - it is messy, but a line of best fit shows the trend.)
4. Show students an image of real craters and ask if theirs looked similar
e.g. on Mercury: https://assets.science.nasa.gov/content/dam/science/psd/photojournal/pi… and https://science.nasa.gov/resource/the-impressive-rays-of-hokusai/
e.g. on the Moon: https://myearthscience.com/wp-content/uploads/2017/11/crater-rays-moon….
Next time students see a full moon, they might be able to find the crater rays on it: https://upload.wikimedia.org/wikipedia/commons/2/2d/Full_Moon_%28159847…
5. Show students a real oblique impact crater: http://lroc.sese.asu.edu/posts/595
What do craters tell astronomers?
Scientists figure out the speed of an impact by the size of the crater formed. They also look at other features that are made with the very high speeds of meteorites hitting moons and planets - sometimes craters have central uplifts and terraced walls that give more information about the impact, and the rock on and under the surface of the planet.
Craters with different features are sometimes formed. e.g. Rampart Craters on Mars (https://en.wikipedia.org/wiki/Rampart_crater). There are no rays. Water or ice present under the impact site melted with the impact, then flowed away instead of being thrown away from the crater. This pattern of ejected material can be used as a way to identify areas with possible water or ice in the surface layers of a planet.
The number of craters on a surface can tell scientists about a planets geology and atmosphere:
Many craters indicate that there is no atmosphere to burn up the rocks as they come down. (e.g Mercury). It also may indicate that there are no plate tectonic movements or erosion turning over the planet’s surface. Earth and Venus have an atmosphere, which burns up rocks as they hit it (called "meteors" or "shooting stars"). Earth also has moving tectonic plates and erosion that recycle the rocks, so removing craters. (The craters on the Moon are good for studying crater formation, as the Moon has no atmosphere, plate tectonics, or moving water (which all erode a surface and erase all but the most recent impacts).
http://mars.nasa.gov/education/modules/GS/GS38-49.pdf
