Science for Kids: Make a comet

I shared a post a couple weeks ago about taking my first photo of a comet.  Comets are amazing when you think about them as a big ball of ice and gas travels through space.  As it gets closer to the sun it begins to heat up and that gas and ice leaves a big tail that we associate with comets.

To understand exactly what a comet is, you can make a small scale version.  This was a project I had done last year at my son's school when they were learning about space.  The best part is you get to play with dry ice, which you can buy at certain stores.

There are a couple safety concern with this project.  Dry ice is is very cold so you should have the appropriate gloves to handle it.  It can cause burns very easily if it stays on exposed skin.  When dry ice sublimates it makes carbon dioxide which can displace oxygen in an enclosed space.  Make sure you are working in a large room.  As long as you are careful it is safe to work with.

The supplies you need are:

2-3 cups of dry ice
2 cups of water
Small handfull of dirt or sand
Garbage bags
Mixing bowl
Wooden mixing spoon
Hammer
Safety glasses and gloves

To make your comet you just need to follow these steps:

1.  Crush you dry ice.  Most dry ice comes in a block or in pellets.  Place the dry ice in a garbage bag.  Double bagging works best in case you have a hole.  Take a hammer and gently hit the ice in the bag.  This is easy done with the bag on a garage floor or a sidewalk.  It will crush easily.

2.  Place the ice in a mixing bowl that is lined with a garbage bag.   If the garbage you just used to crush the ice is still in good shape then just place it in the the bowl.  Open the bag so the ice is exposed.  Or you can pour the crushed dry ice in a new garbage bag that is lining a bowl.

3.  Add the sand or dirt and mix it into the ice.  The dirt is another component of the comet and will give it that dirty look.

4.  Pour the water into the mixture.  Quickly take the garbage bag and wrap it around the ice/water mixture.   The dry ice is so cold it will freeze the water and make your comet.    Shape the mixture into a big snowball comet.

5.  Unwrap the comet to see it's unique shape.  Make sure you still have some cold resistant gloves to hold the comet.


Just like a real comet, as this miniature iceball heats up the carbon dioxide gas from the dry ice will smoke.  This is just like the gas from a real comet forming a tail.  You make even hear popping as large pockets of carbon dioxide that were trapped are released.  The surface of a real comet would be highly unstable just like this.


If you demo this, practice it first.  You may find that certain rations of water to dry ice give you the best results.