18. Making a Comet in the Classroom
(Activity E-3, Grade Level: 4-9+)
"Making a Comet in the Classroom" reprinted by permission from
Dennis Schatz (Copyright ©1985 by Dennis Schatz). No reproduction
of this activity of any sort is permitted without written permission.
Dennis Schatz can be reached at the Pacific Science Center, 200 Second
Ave., N., Seattle, WA 98109. Phone (206) 443-2001
Whatís This Activity About?
Comets are wonderfully mysterious things for our students. Since Halleyís
return in 1985, the only widespread images of comets have been artistic
pictures prompted by the Shoemaker-Levy 9 impact at Jupiter in 1994. This
activity give students a chance to observe the uneven surface, dark composition,
delicate character, and even venting of trapped gas of a "mock"
comet. All of these traits are based on the information scientists have
gathered from watching comets over the years, and especially from the
fly-by of Halley. "Making a Comet in the Classroom" can be done
as a teacher demonstration or a student activity and is one of the most
fun and accurate activities about comets.
What Will Students Do?
Students will observe as a comet is created from common ingredients (dry
ice, dirt, water). For later grades, with appropriate facilities and enough
dry ice, students can make their own comets.
Tips and Suggestions
ï	Be careful with the dry ice. Always use gloves, or oven mitts!
If students handle the dry ice, review proper safety procedures and
what to do if the ice contacts skin.
ï	For lower grades, use this activity as a demonstration. Ask
students to note the proportions of ingredients, the color and surface
characteristics, the jets, and the slow disintegration.
ï	For later grades, have the students create their own comets
by mixing all of the ingredients in a plastic bag. If youíre brave,
allow the students to let their comets "fly" by throwing them
outside in an open area.
ï	To simulate movement of the comet through the solar system,
carry the comet as you walk around a bright bulb (the Sun) in a darkened
room. Far from the bulb, walk very slowly, and comment on the low temperature
and feeble light. Closer to the bulb, describe passing Saturn and Jupiter,
and near Mars warming up so much that the tail begins to form. Walk
more quickly toward the bulb (the increasing gravitational pull between
the Sun and the comet causes the comet to travel faster), swing around
it, and head away, tumbling the comet as you go. Follow up this activity
with pictures of Halleyís comet, taken by the Giotto spacecraft as it
ï	Places to get dry ice: ice cream stores, grocery stores, butcher
The "ingredients" for a six-inch comet
Other materials you should have on hand include
An ice chest
A large mixing bowl (plastic if possible)
4 medium-sized plastic garbage bags
A hammer, meat pounder, or rubber mallet
A large mixing spoon
Dry ice is available from ice companies in most cities (look under "ice"
in the Yellow Pages for a local source). Day-old dry ice works best, so
you might want to buy it the afternoon before the day you do the activity.
Keep the dry ice in an ice chest packed with newspaper and tightly closed.
Most ice companies have a minimum on the amount of ice they will sell
(usually 5 pounds). But having extra dry ice on hand will be useful because
some will evaporate and also because it is advisable to practice this
activity at least once before doing it with the class.
Here are the steps for making a 6-inch comet (students make good bakerís
assistants for this exercise!):
1)Cut open one garbage bag and use it to line your mixing bowl.
2) Have all ingredients and utensils arranged in front of you.
3)Place water in mixing bowl.
4)Add sand or dirt, stirring well.
5)Add dash of ammonia.
6)Add dash of organic material (e.g. corn syrup), stirring until well
7)Place dry ice in 3 garbage bags that have been placed inside each
other. (Be sure to wear gloves while handling dry ice to keep from being
8)Crush dry ice by pounding it with a hammer.
9)Add the dry ice to the rest of the ingredients in the mixing bowl
while stirring vigorously
10)Continue stirring until mixture is almost totally frozen.
11)Lift the comet out of the bowl using the plastic liner and shape
it as you would a snowball.
12)Unwrap the comet as soon as it is frozen sufficiently to hold its
Now you can place the comet on display for the students to watch during
the day as it begins to melt and sublimate (turn directly from a solid
to a gasñwhich is what carbon dioxide does at room temperature and comets
do under the conditions of interplanetary space when they are heated by
The comet is reasonably safe to touch without getting burned by the dry
ice, but it is still best to have a spoon or a stick for the students
to use while examining it. As the comet begins to melt, the class may
notice small jets of gas coming from it. These are locations where the
gaseous carbon dioxide is escaping through small holes in the still-frozen
water. This type of activity is also detected on real comets, where the
jets can sometimes expel sufficient quantities of gas to make small changes
in the orbit of the comet.
After several hours, the comet will become a crater-filled ice ball
as the more volatile carbon dioxide sublimates before the water ice melts.
Real comets are also depleted by sublimation each time they come near
the Sun. Ultimately, old comets may break into several pieces or even
completely disintegrate. In some cases, the comet may have a solid, rocky
core that is then left to travel around the cometís orbit as a dark barren