Comet Nucleus: Linking a Comet's Composition to Its Properties
Purpose/Hypothesis
In this project, you will construct a comet* using either the same or similar ingredients that make up a real comet. Comets are composed of bits of dirt or dust, held in place by ice. The ice is a combination of water and carbon dioxide ice. Comets contain carbon-based or organic molecules and ammonia. Sodium or salt was found to be in the comet Hale-Bopp. Trapped gas and an uneven surface are other features of a comet.
It is these materials in the nucleus that form the brilliant head and tail when they come close to the Sun. Once you have constructed the comet, you can then observe its behavior.
*Adapted from "Making A Comet in the Classroom" by Dennis Schatz, Pacific Science Center, 1985.
Level of Difficulty
Moderate (because of the number of trials and careful measurements needed).
Approximate Budget
$15.
Timetable
45 minutes for initial setup; several hours observation time.
How to Work Safely
Dry ice is carbon dioxide frozen at -110%F (-79%C). If you touch a piece of dry ice too long, it will freeze your skin and feel like a burn. Wear gloves when working with dry ice and do not place dry ice in your mouth. Also be careful when you pour the ammonia into the spoon to prevent it from splashing into your eyes.
Materials Needed
- 2 cups (500 milliliters) of water
- 2 cups (500 milliliters) of dry ice, broken into pieces if possible (dry ice is available at ice companies and some butcher shops)
- 2 to 3 spoonfuls of dirt (a small dinner spoon is fine; the exact size is not important)
- 1 spoonful of ammonia
- 1 spoonful of organic material (dark or light corn syrup works, or Worcester sauce works well)
- thick gloves
- large plastic bowl
- 2 heavy-duty garbage bags
- self-sealing plastic bag
- hammer or mallet
- mixing spoon
- salt
- paper towels
Step-by-Step Instructions
- Cut open one garbage bag and use it to line your mixing bowl.
- Add the water and dirt in the mixing bowl. Stir well.
- Add a dash of ammonia
- Add a sprinkle of salt and a spoonful of the organic material. Stir well.
- Put on gloves and place the dry ice in the self-sealing plastic bag. Zip the bag closed and place the bag inside the second garbage bag. Pound the dry ice with a hammer until it is crushed.
- Add the dry ice to the ingredients in the mixing bowl and stir rapidly. Continue stirring until the mixture is slushy and almost totally frozen.
- Lift the garbage bag with the comet out of the bowl and shape it like a snowball. Shape the plastic bag and not the snowball. Wear gloves.
- Unwrap the comet and place it on the bag.
- After you have observed the comet for several hours, break it apart and look at the inside.
Summary of Results
Draw a picture of the comet and note how it appears. Gently blow on the comet and note your observation. After two hours have passed, note your observations of the comet and compare it to your first description. What has happened to the carbon molecules in the organic substance? Write a brief explanation of how this miniature comet relates to what occurs during a comet's orbit.
Troubleshooter's Guide
Below is a problem that may arise during this project, a possible cause, and a way to remedy the problem.
Problem: The comet fell apart during the snowball formation.
Possible cause: You may not have broken up the dry ice into small enough bits. Try the experiment again, pounding the dry ice thoroughly.