Making a Comet

Astronomy:	Comet Formation
Grade Range:	Elementary School, Middle School, High School
Format:	Hands-on

Although this is a "hands-on" demonstration, don't allow younger students to actually handle the comet. This is a demonstration that students can get close to and watch, and for an older audience you might let them try to make their own comets!

Materials

• Water
• Soil and Rock Mix
• Soy Sauce
• Ammonia
• Dry Ice
• Measuring Cup
• Box with Plastic Lining
• Demonstration display poster board
• Hot plate
• Small Bowl

Safety Precautions

Please read the Cryogen Safety section of the Demonstration Safety page before performing this demonstration.

This demonstration requires: safety glasses, gloves, small blast shield

Demonstration

1. Set out your ingredients around the plastic lined box. Turn the hot plate on, and set to medium. For a younger audience (k-6th), set the small blast shield in front of the box. For an older audience (7-12th), you may ask the students if they would like to assemble the comet.
2. Assemble the comet: Put about two cups of dirt in the box, and add a half cup of water to it. Add some soy sauce sparingly, and add a small amount (one capful) of ammonia to the mix. Start mixing the ingredients with one hand, and while doing so add several pieces of the dry ice to the mix with the other. Compress the mixture into a ball, and add more dry ice as needed until the ball freezes together.
3. After explaining to the students what the ingredients represent, move your comet from the bag into the small bowl and place it on the hot plate. As it heats up, you will see the coma, or tail, of the comet form!
4. After building the first comet, you can keep it displayed for students to look at, and add dry ice as needed to keep the ball frozen. You should consider making a new comet every two hours or so, depending on the length of the event. At the end of the event, break apart the comet and lay it out for a few days to let the dirt dry out.

Why This Works

Comets are large rocky bodies in our solar system, and are easy to recognize because of the tail they create behind them. A term often used to describe comets is "dirty snowballs" because of what they are made of. Comets is made mostly of organic matter, represented by the dirt and rock mixture that we use, and will often also contain large amounts of iron in their core. Comets also contain trace amounts of complex molecules, represented with the soy sauce we added, and they often have ammonia frozen inside of them as well. Lastly, they have a lot of frozen carbon dioxide, or dry ice, on their surface as well.

We are able to find out what a comet is made of by looking at the coma of the comet. When we place our comet on the hot plate, we see the cloud of vapor coming off of the ball. This is similar to the cloud of gas and dust that we see trailing a comet as it flies close to the sun! By analyzing the tail of the comet we can find out what particles are being released, which gives us clues on what the comet is made of. A comet's tail is always pointed away from the sun, no matter what direction the comet is moving in. This is because the tail is created by the sun's solar wind, which is made of high-energy particles that are flying out and away of the sun. the solar wind blasts off gas and dust from the surface of the comet, and this gas and dust are flung away from the sun, creating the tail!

Additional Information

• Comets and Asteroids are similar in composition, and often similar in size. The main difference between the two comes from their orbits: Comets have a large elliptical orbit, and will have tails during their perihelion, or their part of the orbit closest to the sun. Asteroids have regular orbits, and larger ones can be labeled as dwarf planets. Ceres was first labeled as an asteroid, but due to its size it was promoted to dwarf planet status.
• This demonstration is a part of the Astronomy Show.