A real comet is a mixture of several materials. While each comet has its own unique chemical signature, most of them contain water ice, organic compounds, dust, and rocky or stony chunks. It's fun to make your own comet and expose it to a simulated solar wind to observe its behavior. Here's how to make a model comet that behaves like the real deal.
This particular recipe uses solid carbon dioxide (dry ice) so that it will sublimate into a comet tail when exposed to heat. Feel free to substitute ingredients to see what effect they have on your model.
Use caution with the dry ice. It is extremely cold and can give you frostbite if you touch it. Wear gloves!
Dry Ice Model Comet Materials
- A bowl or pot large enough to hold your ingredients
- A cup of water (it will freeze into ice when mixed with the cold dry ice)
- A cup of dirt (this contains organic compounds and grit, like a real comet)
- A cup of sand (many comets contain silicates, like sand or quartz)
- Some charcoal (comets contain dark material, which can be carbon, like charcoal)
- A bit of household ammonia or window cleaner (ammonia is a nitrogen compound observed in comets)
- A couple of cups of crushed dry ice (carbon dioxide is common in comets)
- Syrup (optional: adds organic compounds and helps the comet stick together)
- Newspaper (optional: place it on your workspace to make clean-up easier)
Make the Comet
If your dry ice arrives in large chunks, you can place it in a paper bag and smash it with a hammer to crush it. If you get dry ice pellets, you can use them as they are.
Use a wooden spoon or gloved hand to mix together the ingredients and crush them together to make a lumpy ball. Like real comets, your model may break apart. One tip to help it stick together is to let it rest for a couple of moments before picking it up and examining it.
You can simulate the solar wind to make a comet tail by blowing on the model. The heat of your breath will mimic the warmth of the sun. Do you smell the ammonia? Real comets smell a bit like window cleaner!
Liquid Nitrogen Comet
Another way to simulate a comet with a tail is to use liquid nitrogen. For this comet, you dip a porous, rocky material into liquid nitrogen and remove it to see the vapor trail. Since liquid nitrogen is even colder than dry ice, you'll want to use long-handled tongs. A good material for the rocky comet is a charcoal briquette.
Compare the Simulated Comet To a Real Comet
Comets that we see come from either the Oort Cloud or the Kuiper Belt. The Oort Cloud is a sphere of material that surrounds the solar system. The Kuiper Belt is a region located beyond Neptune that contains many icy bodies within range of the Sun's gravity.
A real comet may be considered to be a sort of dirty snowball made of frozen water, dust, rocks, and dust. There are three parts to a comet:
- Nucleus - The "dirty snowball" part of the comet is its nucleus, which consists of meteoritic dirt, frozen gases (like dry ice), and water.
- Coma - As the nucleus of the comet moves close enough to the Sun, it warms and the frozen gases sublimate into vapor. The vapor pulls dust particles with it away from the nucleus. Light reflecting off the dust accounts for the fuzzy shape of a comet.
- Tail - Comets are in motion, so they leave a trail of gas and dust in their wake. The solar wind also pushes matter away from the comet and ionizes it into a bright tail. Depending on its location, a comet may have one or two tails.