Overview

There are many different kinds of planets in the galaxy, including many which are not found in our own Solar System. In this lab, we will explore the vast diversity of other worlds.

Science Question

What are the properties of exoplanets of different masses, compositions, and distances to their star?

Materials

• Styrofoam spheres (in at least two different sizes; ideally four)
• Toothpicks
• Paint in “natural” colors
• Drop cloths
• Paper plates
• Paint brushes
• Paper cups with water in them
• Yellow “sun” balloons
• A long strip of white paper

Astronomy

There are several types of planets out in the galaxy in solar systems which do not look like our own. They include the following:

• Hot Jupiter systems. Planets which are the size of Jupiter, but live very close to their star, are often so close that their year is only a day long. Hot Jupiters are so massive that they often fling any other smaller planets out of the solar system. They are almost always found alone. Hot Jupiters are believed to form the same way planets in our solar system formed, from the bottom up (i.e. the accretion of materials onto small rocky cores)
• Sub-Neptunes. These planets are about 4-6 times larger than the Earth, and have thick hydrogen-helium envelopes (atmospheres). Like Uranus and Neptune, trace amounts of gasses like methane may give them a blue color. Sub-Neptunes are found at all distances from their star.
• Super-Earths: These planets are 2-10 times more massive than Earth, and 1-2 times larger. Gravity is very strong on these objects. They may have a thin atmosphere, like Earth, or no atmosphere at all, or they may be covered in vegetation, or water oceans.
• Earths. Little is known about the diversity of Earth-like planets outside our Solar System. Like their more massive cousins, they could look like Mercury, Venus, Earth, or Mars, or millions of possible variations.

Activity

Each person should get one large styrofoam sphere and one small styrofoam sphere. These represent a rocky planet and a gas giant planet. On a paper plate, put a little bit of paint in the colors you choose for your planets, and grab one or two paint brushes. Fill a cup with water to rinse off your paint brush.

1. Using what you know about what colors a gas giant can be, paint the large sphere to resemble a possible gas giant. Use the toothpicks to hold on to the planets as you paint them. They can have horizontal stripes, or one face of the planet can be different from the other if the planet is close-in (tidally locked). Gas giants in our solar system are blue (Neptune and Uranus) from methane, yellow (Saturn) from hydrocarbons, or stripes of brown (Jupiter) from ammonia. Gas giants can be different colors, but you must justify your color choice with physical phenomena.
2. Then, paint the small sphere to look like a rocky planet. There are a lot of choices for rocky planets: water clouds (white), carbon dioxide clouds (yellow), rust surface like Mars (orange/red), living surface like Earth (green), water oceans (blue), anthocyanin foliage surface (purple), barren surface like the Moon/Mercury (white/gray), dark surface like an asteroid (gray/black), or combinations thereof.
3. Design a solar system! Roll out the long piece of white paper as your background. Then choose a small, medium or large sun (balloons). Break up some leftover plain spheres to represent asteroids and comets in your system, if there are any. Line up the sun and planet(s) roughly to scale. Label on the paper where the Habitable Zone is. The Habitable Zone is the range of distances around a star that liquid water can exist on the surface of a planet.

QUESTIONS

1. Which of the four types of planets did you choose?
2. Justify all color and design (i.e. stripes, solid, etc) choices for:
3. Describe how the planets in your solar system formed. Did they accrete from smaller bodies, or did they form directly from the solar nebula (massive, far-out planets do this, but others don’t)
4. Draw the four types of planets roughly to scale.
5. Is your rocky planet habitable? Why or why not?
6. Can you think of any reasons a planet might be in the habitable zone but not suitable for life?
7. Your rocky planet may have started with a primary atmosphere. What are those made of?
8. Now, it may have a secondary atmosphere. What kinds of gasses might be in a secondary atmosphere?
9. How does a planet come to have a secondary atmosphere?