Make your own craters

Want to make craters like the ones we can see on the Moon or spacecraft have photographed on Mercury, Mars, and other solar system bodies?  First, check out this video below:


Pretty cool huh?  Although before getting too far ahead of things, a definition is in order:

Ejecta: In planetary geology, the debris that is ejected during the formation of an impact crater.

This is about how to make impact craters.  The steps required to make craters like this are pretty easy - and you don't even need an aquarium (though it makes it easier to see for larger groups).

First, find an appropriate sized shallow box, tray, pan or yes, aquarium.  Something that is in the 150 to 250 square inches range.  If it is smaller, the "soil" will be quite deep.  If it is larger than that, the "soil" may be too shallow, and not offer good results due to insufficient material.  I found even with the 200 square inches (10 gallon) aquarium that some of the larger, heavier "dropped' object hit the bottom, or were close to hitting the bottom when dropped from 5 feet up.

As an alternative, use a much larger area box, and use more flour and cocoa.  A soil that is 1 to 2 inches deep is good.

Next, spread a full, 5 pound bag (2.2kg) bag of all purpose, white flour across the bottom of the container, and spread it out evenly.  This material represents the deeper soil that is often sprayed across the upper surface, and "dug out" by the impactor.  You can see how that kind of material got sprayed across the surface of the Moon at these impact sites:

Craters on Moon with rays/ejecta

Be sure to smooth out the flour fairly well.  It doesn't need to be perfect.  A small piece of cardboard with a flat edge can make this easier to do.

On top of that, sprinkle a canister of (unsweetened) cocoa powder.  This will represent how the darkened material on the surface of the lunar maria appears, and provide contrast for when ejecta occurs from the craters to create ray systems (see below).  As an impactor hits the surface, it displaces material below it, often sending it in directions out and away from the site of impact.

Smooth out any clumps or "high points" of cocoa powder, so that it is distributed fairly evenly across the surface.

Flour craters with ejecta

Finally, choose some impactors.  I used the following ones, but others may be perfectly appropriate as well:

  • A small aquarium pebble/stone
  • A very small steel nut (10-32)
  • A Philips head driver for a drill (it made a nice oblong shaped impactor)
  • A 5/8" diameter glass bead from a craft store
  • A 3/8"-16 nut
  • A 1/2-13 nut

Feel free to use other sized rocks, pebbles, or any other material with sufficient mass to displace the flour and cocoa.  Then drop them into the "lunar soil" you have made.  For experimental purposes with children, it may be suitable to take measurements of the impactor weights and sizes, heights from which they dropped, and what size crater (diameter) they created along with how far the ejecta traveled.  

In the video above, I dropped all of my impactors from a height of 5 feet (1.5 meters), because I couldn't get any higher due to the ceiling, and I had the aquarium on a small table.  Based on calculating the velocity at impact, all of my impactors were traveling at 12.2 miles per hour when they hit.

Various other heights would incur a wide range of impact velocities.  This can be a fun way to teach physics and various equations about acceleration and velocity.  Above all, this should be memorable experiment and exercise to try.