How do craters form?

Contributed by Ezequiel Contreras Martinez

Introduction

Take a quick glance at the moon. Can you see all the circular shapes all across the face of the Moon and the lines extending from them? Those, in fact, are what planetary scientists call the “craters” and the “ejecta rays” that extend from them – which are all made from material blasted out of the crater when an asteroid impacts the surface of the Moon.

These craters form when rocks or comets from space smash into the surface of the Moon. And, as a result, it can pulverize the ground and create what we call “regolith” – which is what forms those “ejecta rays”.

Lucky for you, we can recreate this entire process with materials that you may have at home!

Materials

• Cake pan or tin
• Flour
• Cake sprinkles
• Cocoa
• Spoon or shifter
• Towel, newspaper, or paper towels
• 2 or 3 different sized spherical objects (small rubber ball, rocks, etc)

Procedure

1. Prepare the Moon’s sub-surface
   • Spread about an inch of flour into your cake pan. The flour represents the parts of the Moon’s crust that an impactor will pulverize and blast out.
2. Add rocks and minerals
   • Add a layer of cake sprinkles to represent rocks and minerals buried under the surface.
3. Create the Moon’s surface
   • Add a thin layer by sprinkling cocoa over the top with a spoon. You can also use a sifter for an even coating. The cacao will represent the surface layer on the Moon.
4. Prepare for impact
   • Now, find a spot where you can safely and easily drop and/or safely throw some ball of mass into your cake pan. You may want to put down a newspaper or a towel to catch any baking ingredients that come out of the pan as well.
5. Make a Moon crater
   • Simulate a rock impacting the Moon by holding a small rock, for example, above your head and dropping it into the cake pan. Observe the “ejecta pattern” created by the impact. Did any of the sprinkles get ejected out of the crater?
6. Time to experiment!
   • Try dropping different sizes of balls of masses from different angles, heights, and speeds if you can. How does the eject pattern differ from one impact to the next?
     

Physics Concepts and Questions

• Throughout this at-home experiment, you will take your first steps as scientists but, most importantly, as experimentalists. You will experience how changing certain things at the beginning of your experiment will impact the overall outcome of your experiment. Or, how, no matter how many attempts you make, there will always be some factor of uncertainty with your measurements. This will surely prepare you for the larger world of experiment as you venture throughout your career as a young scientist. 
• Furthermore, this experiment will serve as an early introduction to concepts such as energy (kinetic or potential), collisions (elastic or inelastic), or conservative central forces (gravitational attraction) – all prevalent explicitly and/or implicitly in this at-home experiment. And albeit it may be years till you finally fully explore these concepts in-depth, you can check out additional demonstrations and at-home experiments that talk about, for example, elastic and inelastic collisions.

Conclusions and Further Investigations

• What are other features of the moon and how do they form? (e.g. lunar marias and highlands)
• Explore the formation process and the many theories behind how the Moon formed

Citations

“Student Project: Make A Moon Crater.” NASA, NASA, 29 June 2021, https://www.jpl.nasa.gov/edu/learn/project/make-a-moon-crater/. 

“Explore – to the Moon – Crater Creations: Moon.” Lunar and Planetary Institute (LPI), https://www.lpi.usra.edu/education/explore/LRO/activities/craterCreations/. 

“Craters in the Classroom.” Craters in the Classroom | Las Cumbres Observatory, https://lco.global/education/activities/craters-in-the-classroom/.