Making a Comet

Materials

   Water 
   Soil 
   Soy sauce 
   Ammonia 
   Dry ice 
   Small blast shield 
   Box with plastic lining that can be used to compress mixture 
   Gloves 
   Safety glasses 
   Demonstration display poster board 
   Hot plate 

Preparation

Set up blast shield to keep kids from getting their hands into the dry ice.

Demonstration

The demonstrator will mix together the ingredients that represent the components of a comet, being careful not to hurt themselves or anyone else with the dry ice. Once the ingredients are mixed the demonstrator then compresses the mix together to form a sort of ball.

What to Say

Start by asking if anyone has seen a comet. Show the pictures of various comets on the display board and point out the various features: nucleus, coma, dust tail and plasma tail. Point out in the diagram of the comet orbiting the sun that the tail is always pointing AWAY from the sun. Ask if any of the kids can explain why that is. Likely no one will know why so explain that this demo will help illustrate why that is and what comets are like in general.

Mix the ingredients together and describe what each ingredient represents. The water will represent (once frozen) the ice found in comets, the soil represents the dark organic material, the soy sauce represents the other complex chemicals found in comets, the dry ice represents the frozen carbon dioxide locked into comets and the ammonia is the same as the ammonia found in comets. After the ingredients have been pressed into a sort of ball, show the comet to the kids and explain that it is similar to the nucleus of a comet.

Use a hot plate to demonstrate the effect of the sun on the “comet”. It should start to evaporate more quickly and create more of a coma. Explain that the sun is really really hot and when a comet gets close to it, it starts to heat up and evaporate. This stuff that's evaporating away is what makes the long tail that you see in pictures.