Let’s Make a Comet!

(These are Dennis' notes. - JAG)

Who remembers comet Hale-Bopp from a few years ago? (Ask for a show of hands)

What do you remember most about it? (Ask a few volunteers)

What I’d like to do today is talk about what comets are made out of. But rather than just list a bunch of ingredients, I’d like to make one for you today!

Comets have three main parts: The nucleus, the coma, and the tail.

The nucleus is the comet’s distinct, solid center.

The coma is a hazy cloud of dust and gas that surrounds the nucleus.

But perhaps most recognizable portion of a comet is the tail, which is nothing more than the coma being pushed away from the nucleus by the Sun’s light pressure and solar wind.

What do you think that the nucleus is made out of? (Wait for responses)

Okay, let’s put one together!

First of all, one of the main ingredients is water. In fact, approximately 80-90% of the comet is nothing more than water! (Add water to plastic-lined container)

The nucleus also contains rocks and solid materials similar in composition to meteorites, which we’ll represent with this dirt. (Add dirt to the water and stir)

Comets also contain a number of organic compounds such as methane, ammonia, cyanide, and formaldehyde. Now, most of these chemicals are fairly noxious, so I’m using another complex organic compound— Worcestershire Sauce, straight from the kitchen! (Add sauce to the mix and remind them that comets do NOT have Worcestershire Sauce in them! )

Believe it or not the other major ingredient found in comets is frozen carbon dioxide. Does anyone know another name for frozen carbon dioxide?

Right! We call it dry ice. Does anyone know why we call it dry ice?

Well, it’s because it doesn’t melt—instead it changes from a solid directly into a gas. We call this process sublimation.

(Add dry ice to the cloth bag and bang away while explaining safety precautions for handling dry ice).

Now that we have all our ingredients ready, let’s put them all together.

(Pour dry ice from bag into the bowl and explain what you’re doing)

(Remove the comet from the bowl and hold it up for all to see.)

Okay, here’s our comet nucleus. You probably can’t hear it, but it is fizzing and sizzling as the dry ice sublimates away in our nice warm auditorium.

If this were out in space, the sublimating carbon dioxide would also carry away some of the other ingredients and eventually for a hazy coma around the nucleus.

After a while, the pressure of the sunlight would start pushing against the coma and would eventually form the tail.

One thing that is important to remember is that comets do not produce their own light, but only reflects sunlight, just like the Moon.

Does anyone have any other questions about comets? (Answer or tapdance)

(If demo is toward the end of the hour, mention that people can come up and take a closer look after the rest of the presentations).

Thank you very much!

SuperScienceSaturday: MakeComet (last edited 2010-01-21 02:50:57 by localhost)