This lesson is based on California's Middle School Integrated Model of NGSS.
MS-ESS1-1 Earth's Place in the Universe
PE: MS-ESS1-3 Analyze and interpret data to determine scale properties of objects in the Solar System.
DCI: ESS1.B Earth and the Solar System - The Solar System consists of the Sun and a collection of objects including planets, their moons, and asteroids that are held in orbit around the Sun by its gravitational pull on them.
SP2: Developing and Using Models - The model in this activity is a simulated comet made by household kitchen chemicals. It reinforces the notion that the ingredients that are found on Earth are also the ingredients found in space.
CCC: Systems and System Models - Students will use a model of a comet constructed with household kitchen chemicals to understand the physical and chemical composition of comets found in the outer reaches of our Solar System.
This lesson provides a model of an ordinary comet found orbiting the Sun. Comets have very elongated elliptical orbits that carry them far from the Sun, only to return to sweep through the Inner Solar System. When comets near the Sun, the Sun's radiation causes them to outgas and form a coma (thin atmosphere) and tails. The tails point away from the Sun.
By building a model of a comet which will outgas and evaporate in their presence they are able to understand the makeup of distance objects in our Solar System. Following the demonstration the student will create a diagram and an explanation of a comet in their Science Interactive Notebook.
Other Needed Materials
Comets are composed of water and carbon dioxide (dry ice) with smaller amounts of carbon (charcoal), silicon (sand), organic material (corn syrup), and ammonia. Comets originate from the Kuiper Belt, a spinning cloud of ice and dust particles that revolve around the Sun beyond the orbit of the planet Neptune, part of the Outer Solar System (Jupiter, Saturn, Uranus, Neptune, Kuiper Belt, Oort Cloud)
When gravitational conditions are just right, a chunk of ice can be pulled free from the Kuiper Belt and begin a solitary orbit of the Sun. The large gas giants of the Outer Solar System (Jupiter, Saturn, Uranus, Neptune) have enough gravitational pull that they can actually yank a chuck of ice free from the Kuiper Belt. Once free the Sun's gravity pulls them toward the Inner Solar System (Mercury, Venus, Earth, Mars), creating a new orbital path.
These new orbits are highly elliptical, meaning they spend most of their time far away from the Sun and then swing in rather close. As comets near the Sun they begin to melt and off-gas carbon dioxide. This carbon dioxide forms a coma (thin atmosphere) around the comet and produces a tail that always points away from the Sun regardless of the comet's direction of travel.
This means that as the comet approaches the Sun, its tail stretches to the rear; while the comet rounds the Sun and continues out into deep space the tail proceeds the comet. The tail is highly reflective and is what is typically seen on Earth.
I build the comet in the classroom, demonstrating each ingredient that goes into the trash bag. I then set it aside to let it form together. The trick to building a solid classroom comet is to let it sit for about 10 minutes in order to allow the ingredient to freeze together.
As the ingredients are freezing together I spend these 10 minutes discussing with the kids the ingredients of the kitchen comet, chemical composition of a comet, scientific significance of studying comets, typically orbits, the behavior of the comet's tail(s), and historical significance of comet observations. All the while making sure to highlight relevant vocabulary. With the remaining time I have my students search the web on their school issued Chromebooks for information that will assist them in their assignment (see below).
I suggest they research:
After the comet is ready, I pass it around so that students can closely observe it. Almost immediately, the kids notice that the comet is hissing and expelling carbon dioxide gas. I remind the students that the comet is starting to melt and the expelled gas they see is similar to what happens when a comet travels close to the Sun. When the Sun heats up the comet, and causes the comet to warm up enough to release dust and gases, that forms into a giant glowing "head" that is larger than most planets. The dust and gases form a tail that stretches for millions of kilometers.
Listen as one of our classroom comets begins to warm up.
Here's you'll notice that I allow students to use their cell phone cameras to capture their classroom comet. I explain the use of this strategy in Using Technology Strategy
Student Work Sample
The students had to create a scientific drawing of both the anatomy of a comet and describe the orbit of a typical comet (necessitating the web research while the kitchen comet was freezing together). The drawing had to include at least three colors and three comet facts.
I require multiple colors to ensure that my students take their time and create a high quality drawing. If I didn't require as many colors, most of my students would just draw something sloppy in pencil and argue with me that they completed the assignment. The more colors they use the more involved they become with this assignment and hopefully that involvement will translate to better knowledge retention.