See two ways of making a model comet. Learn how the the model comet simulates a real comet. The dry ice model comet is more realistic, both in terms of composition and behavior. But, a foil or paper comet is a safe and simple project for kids that still teaches the parts of a comet and how they work.
Dry Ice Model Comet
The dry ice comet is a realistic simulation of a comet’s chemistry, including the way it smells. Dry ice is very cold, so only handle it with tongs or gloves. Store dry ice in a paper bag or in an ice chest. If you use an ice chest, don’t seal it or else the sublimating dry ice will build up dangerous pressure.
- 2 cups dry ice
- 2 cups water
- 1 cup dirt or sand
- 1 tablespoon corn starch
- splash of vinegar
- dash of corn syrup
- dash of rubbing alcohol
- ice chest
- plastic bag (trash bag or shopping bag)
- large plastic mixing bowl
- large wooden spoon
- mallet or hammer
Construct a Dry Ice Comet
- Line the mixing bowl with a plastic bag.
- Add the dry ice and crush it into small pieces using the mallet.
- Stir in the other ingredients.
- Wearing insulating gloves, pick up the trash bag and mold it around the “comet” to make a rounded shape. Add a bit more water if you have trouble making the comet stick together.
- Now, unwrap the comet and observe it. Note how it smells, how it reacts if you apply heat or air (as from a blow dryer) to one side, and how it changes over time. As the comet melts, small gas jets appear. Carbon dioxide escapes through the jets, sometimes taking bits of ice with it.
How the Dry Ice Comet Simulates a Real Comet
A dry ice comet mimics the chemical composition and behavior of a real comet. Sometimes scientists call comets “dirty snowballs.” This is a fairly accurate name, since comets consist of water ice, with bits of rock and organic compounds.
- The solid mixture represents the nucleus of the comet. Dry ice makes the comet cold. Comets contain a lot of water. The dirt represents the minerals and dust comets contain. Starch binds the parts of the comet together. Corn syrup represents the organic molecules in the comet, while vinegar simulates a comet’s amino acids. Rubbing alcohol represents the alcohol in comets (although that is usually toxic methanol).
- The vapor surrounding the comet is its coma.
- If you move the model comet or apply blow dryer heat, the vapor trails represent the comet’s tail.
Eventually, the model comet breaks into pieces. Real comets also break apart as they lose mass orbiting their star.
Make a Model Comet Without Dry Ice
Another fun model comet uses a solid ball for the comet’s nucleus and coma and ribbons for its tails.
- Meter stick, long straw, or other stick
- Sheet of paper or aluminum foil
- Fan or blow dryer (optional)
Construct the Model Comet
- Tie or tape one end of the ribbons to the end of the stick.
- Wrap the paper or foil around the end of the stick, leaving the ribbons free to flow. You may have to cut or tear the paper or foil to accommodate the ribbons.
- The fan or blow dryer blows the ribbon tail.
How the Model Comet Simulates a Real Comet
The foil or paper ball acts as the comet’s nucleus and coma. The ribbons are the comet’s tails. If you like, use different colors of ribbons for each type of tail. The two tails are the dust tail, which trails out out behind the direction of the comet’s movement, and the gas or ion tail, which is lighter and blows in the direction of the solar wind.
A few comets have a third, smaller tail. This tail is between the dust trails and the gas trail and consists of salt. The salt moves behind the comet, but the solar wind also ionizes it and affects its direction.
The fan or blow dryer acts like the Sun. The solar wind blows the comet’s tail away from the Sun. When the comet is far from the wind, it has a dust tail, but not much of an ion tail. Both tails become more prominent as the comet nears the star.
If you don’t have a fan, run around with the comet. This illustrates the way the dust tail moves behind the comet nucleus.
- Brandt, John C.; Chapman, Robert D. (2004). Introduction to Comets (2nd ed.). Cambridge University Press. ISBN 978-0-521-80863-7.
- Erickson, Jon (2003). Asteroids, Comets, and Meteorites: Cosmic Invaders of the Earth. The Living Earth. New York: Infobase. ISBN 978-0-8160-4873-1.
- Ishii, H. A.; et al. (2008). “Comparison of Comet 81P/Wild 2 Dust with Interplanetary Dust from Comets”. Science. 319 (5862): 447–50. doi:10.1126/science.1150683
- Randall, Lisa (2015). Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe. New York: Ecco/HarperCollins Publishers. ISBN 978-0-06-232847-2.