Cook Up a Comet

Learn About Comets By Making One

About the Activity

The Cook Up a Comet activity gives insight into the "dirty snowball" model of comets-
composed of material from the early solar system in the form of frozen water and gases,
simple organic compounds, and dust. Using dry ice and simple household materials, this
comet concoction is a big hit with kids and adults alike.
Topics Covered
• What a comet is made of
• How the Solar System formed

Participants
This activity can be done as a
demonstration with families, the general
public, and school groups ages 9 and up.
To have school groups make their own
comet, it is recommended that each group
have adult supervision. See more tips on
leading this as a group activity, see the
Materials Needed Helpful Hints.
• Measuring cup
• Large spoon
• Mixing bowl
• 4 black garbage bags Location and Timing
• Hammer (use one for many comets) You can make a comet in a classroom, at
• Work gloves and protective goggles a star party, with youth groups, and the
• Dry Ice – 2 cups per comet general public. It can get a bit messy so it
• To find dry ice in your area: is good to have newspaper to put down if
http://www.dryiceinfo.com/ you are inside. The demonstration takes
• Ammonia (window cleaner) – 2 Tbs. about 10-15 minutes.
• Dark corn syrup (or cola) – 1 Tbs.
• Water – 2 cups
• Dirt - 1/4-cup
• (Optional) Overhead projector and glass
Included in This Activity
bowl or a heat lamp to show comet tail Preparation Instructions
Detailed Activity Description
Helpful Hints
Background Information

© Copyright 2000 Regents of the University of California

Copies for educational purposes are permitted.
Additional astronomy activities can be found here: http://nightsky.jpl.nasa.gov
Preparation Instructions
Collect all ingredients/materials in advance. It is strongly advised that you
try the activity yourself first.

Detailed Activity Description

Activity Notes:
You can run this activity as a demonstration or as an activity where groups of
participants get to make their own comet. Follow all safety guidelines below and
make sure that your audience can follow directions or have adult supervision.
See Helpful Hints at the end of the activity.

Instructions Narrative
Step 1: Everyone needs to be conscious about
Begin this activity by arranging all the safety! We'll be using dry ice today. It
ingredients and utensils in front of you can cause cold "burns" and flying chips
on a sturdy worktable. You will need a can be damaging to eyes, so whoever
helper who is wearing goggles and handles the dry ice must always wear
gloves. (If you will have each group protective gloves and goggles.
make their own comet, see the Helpful
Hints at the end of the activity.)
Step 2: In our solar system, comets were part
Open up one garbage bag and use it to of what nature didn't clean up after the
line your mixing bowl. This will help you solar system was formed from a
shape your comet, and make cleaning swirling disk of gas and dust called the
up easier at the end. solar nebula. As this nebula of gas and
dust swirling around the sun cooled, it
formed small rocks or planetesimals,
which then gathered together to make
bigger rocks, which ended up forming
the planets and moons. Comets were
the leftovers. You can think of them as
the bits of dough left in the bowl when
you make cookies.
Step 3: Comets have water in them. Water is
Add the 2 cups of water to the mixing made from just 2 elements – hydrogen
bowl. and oxygen. The gases hydrogen and
oxygen, as well as water vapor were
probably all present in the solar nebula.
Step 4: You can't buy interplanetary dust at the
Add 1/4-cup sand or dirt, stirring well. store, so we have to use sand and dirt
in its place. Sand and dirt have the
minerals, and simple compounds that
are found in comets. But dirt also
contains bacteria, and mold, which are
not found in comets. These living
things have been created over the
eons since the earth was formed.
Step 5: Organic material means anything made
Next, add a dash of organic material up of carbon, hydrogen, nitrogen, and
(e.g. corn syrup or cola), stirring until oxygen. Sugar, alcohol, and methane
well mixed. are all organic compounds. All living
things are also made mostly of these
four substances. Scientists have
discovered that our Milky Way galaxy
actually contains a very simple kind
sugar that probably existed before the
planets were formed! Corn syrup
represents the simple organic
compounds that were probably present
in the solar nebula, and these helped
form life later on.
Step 6: Ammonia, the same compound we use
Add about 1/8 cup (2 Tablespoons) of to clean windows, is another organic
ammonia and stir some more. You compound that existed in the solar
should have a muddy, slightly icky- nebula. The atmospheres of the giant
smelling, sludge. planets Jupiter and Saturn contain
large amounts of ammonia.
Step 7: Dry ice is frozen carbon dioxide, the
Make sure your helper is wearing same gas that makes bubbles in soda
goggles and heavy gloves to handle pop. Most of the atmosphere of Mars is
the dry ice. carbon dioxide. When a comet is far
from the sun, its carbon dioxide is
frozen into dry ice.
Step 8: We crush the dry ice to make it mix
(If your dry ice has already been with the water, dirt and organic
crushed, read the narrative and go material. All the "ingredients" in the
immediately on to Step 9.) Put the dry original solar nebula were pretty evenly
ice inside several plastic bags and mixed, so our comet's ingredients
crush it by pounding it with a hammer. should be well mixed with no really big
You will need 2 cups of the crushed dry lumps.
ice.
Step 9: Stirring is like the rotation of the solar
.Have your helper scoop up 2 cups nebula that "mixed" the original batch of
of the dry ice and add the dry ice to comets as it whirled through space. Mixing
the other ingredients in the mixing also brings all the ingredients to the same
bowl while stirring vigorously. Be temperature.
sure to mix the ingredients quickly,
for about 30 seconds. Move fast, as
the dry ice will start to freeze the
water right away.
Step 10: Although most of our ingredients are at the
Now take the spoon out and just let same temperature as the surrounding air,
the comet sit for a minute or two. the dry ice is about -79 degrees Celsius (or
-110 degrees Fahrenheit). The dry ice
cools the other ingredients until they are
frozen solid. In space, real comets are
usually so far away from the sun, they are
even colder than this.
Step 11: If the person holding the bag shuts it too
Lift the comet out of the bowl by the tightly, the bag starts to blow up, or inflate.
plastic liner. Have one person hold This is because some of the carbon dioxide
the bag loosely. The person with is sublimating, or turning from dry ice into
the gloves should use their hands to carbon dioxide gas. It's called "dry" ice
compress and mold the contents for because it never becomes a liquid. If a
at least a minute. If you have more comet's orbit takes it near the sun and the
gloves, get others to help. sun heats it up, the surface of the comet
starts to disintegrate and break down.
Some comets go so near the sun that they
completely fall apart and burn up.
Step 12: Don't worry if our comet doesn't look round
Unwrap your comet from the plastic and smooth. Real comets aren't either.
bag, and you're done! Comets orbit the sun and have a variety of
different orbital periods, ranging from a few
years, to hundreds of thousands of years.
Step 13 (optional): If a comet's orbit takes it near the Sun and
Place the comet in a glass bowl on the Sun heats it up, the surface of the
an overhead projector that has comet begins to change directly from a
been heating up for awhile. You can solid into a gas and starts to form a long
also use a heat lamp or very hot gossamer tail. As it heats up, and the ice
light bulb. See the Helpful Hints. that is holding it together disappears, it will
shed some of its material leaving a trail of
dust and small rocks in its wake. Some of
these can contain ice.
Helpful Hints

If you would like to do this demonstration as an activity with many groups

making their own comets, it is important that these groups are over the
age of 9 and able to follow directions closely to reduce risk of injury. With
school and youth groups, it is recommended that an adult supervise each
group. You will need to supply the materials list for each comet. (One
overhead projector or heat lamp is sufficient for the whole group.)

If you set up a heat lamp to demonstrate the how a comet's coma forms,
point the lamp at the ceiling and hold a comet over it (with gloves on!) and
you may see plumes of steam coming off. This steam is really water vapor
that is condensed by the super-cold CO2 sublimating (changing directly
from a sold to a gas) from the surface.

The disappearance of the comet might raise questions about what

happens to real comets. You then have a chance to discuss how comets
get close to the sun, how they are heated and "shed" material as they get
close to the Sun in the form of gas, dust, and meteoroids, and thus
gradually disintegrate.

Clean Up: The comets themselves can be placed in a large container like
a detergent bucket. Students should not touch the comets with bare hands
except very briefly. After they have melted again, dispose of the sludge in
a well-lined garbage can or a toilet.

Background Information

Comets have a variety of different orbital periods, ranging from a few years, to
hundreds of thousands of years, while some are believed to pass through the
inner Solar System only once before being thrown out into interstellar space.
Short-period comets are thought to originate in the Kuiper Belt, or associated
scattered disc, which lie beyond the orbit of Neptune. Long-period comets are
believed to originate at a very much greater distance from the Sun, in a cloud
(the Oort cloud) consisting of debris left over from the condensation of the solar
nebula. Comets are thrown from these outer reaches of the Solar System
inwards towards the Sun by gravitational perturbations from the outer planets (in
the case of Kuiper Belt objects) or nearby stars (in the case of Oort Cloud
objects), or as a result of collisions.

An astronomer named Fred Whipple suggested in 1950 that comets were a lot
like "dirty snowballs." He was right--they are mostly frozen water, with some
other gases and dirty stuff. Comets spend most of their time as frozen
globs traveling far away from the sun on huge orbits, that may or may
not go near the sun. However we also know that a few times each
century, we see one in sky, often with long fiery tails. You might want
to discuss what your audience thinks causes these drastic changes.
This activity is adapted from a classroom activity, for use in schools and with
further explorations. Learn more here:
http://cse.ssl.berkeley.edu/SegwayEd/lessons/cometstale/com.html

The bits of comets that fall off when they get close to the Sun are what often
cause meteor showers here on Earth. When that happens, we are passing
through the trail where a comet once passed. You can find out which comets
produce some of the annual meteor showers here:
http://ssd.jpl.nasa.gov/?meteor_streams

For some great activities to use with younger audiences, see NASA's Solar
System Exploration site. It also talks about how the tail of a comet always points
away from the Sun:
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Comets&Display=Kids

To learn about how NASA's LCROSS mission is investigating water that may
have been left on the Moon from comet impacts, see their website:
http://lcross.arc.nasa.gov/