Build Your Own Planet
Lesson 4: Atmosphere
Group: _____________________________
Does the atmosphere of a planet affect its surface temperature? If so,
how? This lesson will explore that question.
The gases that surround a planet are called its “atmosphere.” A planet’s
atmosphere creates pressure at its surface, because gravity is constantly trying to
pull all the gases down toward the center of the planet. If an atmosphere is too
thick it may create crushing pressures, like on Jupiter. If there is too little
atmosphere there will not be enough pressure at the surface to keep water as a
liquid. As atmospheric pressure drops, the boiling point of water drops. At
extremely low pressures the boiling point drops below the melting point. This
means that water can never exist as a liquid—it changes directly from a solid to a
gas. This is what happens on Mars.
Before we do the experiment, discuss the following question with your
group and make a prediction: How might an atmosphere affect a planet’s
average surface temperature?
Prediction: A planet’s atmosphere keeps ________________ heat at its
surface.
(more or less)
Experiment: Test the Effect of the Atmosphere on Temperature
You will need:
This worksheet
A clear plastic two liter pop bottle
2 small thermometers
Step 1: Cut off the top of the plastic bottle at the top of the label. Remove the
labels.
On a sunny day:
Step 2: Place the thermometers in a refrigerator for at least 5 minutes (longer is
fine).
Step 3: Remove the thermometers from the refrigerator. Bring this worksheet,
both thermometers and the bottle outside into the Sun.
Step 4: Place both thermometers on the ground near each other in the Sun.
Cover one of the thermometers with the clear bottle. (If the thermometer is
longer than the diameter of the bottle you will need to stand the thermometer
up inside the bottle.) Be sure that the other thermometer does not lie in the
shadow of the bottle. Wait at least three minutes.
Step 5: Lift up the bottle and check the temperature on the thermometer. Record
the temperature here: _________ º F / C (circle).
Note: Circle “F” if you recorded the temperature in degrees Fahrenheit. Circle “C”
if you recorded it in degrees Celsius. Make sure to use the same temperature
scale throughout this experiment.
Step 6: Check the temperature of the other thermometer. Record the
temperature here: _________ º F / C (circle).
Because there might be small differences in the thermometers, we need to swap
the thermometers and repeat the experiment, so continue on to Steps 7 - 9.
Step 7: Take the thermometer that was under the bottle and place it on the
ground. Put the other thermometer under the bottle. Wait at least three minutes.
Step 8: Lift up the bottle and check the temperature on the thermometer. Record
the temperature here: _________ º F / C (circle).
Step 9: Check the temperature of the other thermometer. Record the
temperature here: _________ º F / C (circle).
Step 10: Add the temperatures under the bottle recorded in Steps 5 & 8.
Total temperature under the bottle: ______________ º F / C (circle).
Add the temperatures outside the bottle recorded in Steps 6 & 9.
Total temperature outside of the bottle: _______________º F / C (circle).
Questions:
1) Was the temperature under the bottle higher or lower than the temperature
outside of the bottle? __________________________.
2) Which thermometer—the one outside of the bottle or the one under the
bottle—represents the effect of the atmosphere?
__________________________.
3) How does the atmosphere affect a planet’s temperature?
_____________________________________________________________.
You should have discovered that the temperature under the bottle was
warmer than the temperature outside the bottle. Heat energy from the Sun
bounces off a planet’s surface and radiates back into space. The bottle acted as a
kind of greenhouse atmosphere around the thermometer. It trapped the heat
around the thermometer, making the temperature even higher. You’ve probably
felt the same effect if you’ve ever gotten into a car with its windows rolled up on
a hot, sunny day.
The ability of an atmosphere to trap heat is called the GREENHOUSE
EFFECT. Not all the gases in an atmosphere are greenhouse gases, that is, gases
that trap heat. Carbon dioxide, methane, and ozone are three greenhouse gases
that we have in Earth’s atmosphere, but there are others.
On Earth, nitrogen and oxygen make up 99% of the gases in our
atmosphere. Neither of these gases traps heat. Most of Earth’s greenhouse effect
comes from carbon dioxide and methane. But only 0.03% of our atmosphere is
carbon dioxide, and methane makes up only 0.002%. Yet both of these gases
have a great effect on our average surface temperature.
Check the Planet Temperature Calculator to see how important these tiny
amounts of carbon dioxide and methane are in warming our planet.
(www.astro.indiana.edu/~gsimonel/temperature1.html) Enter normal Earth
values for MASS (1), DISTANCE (1), and BOND ALBEDO (29), but set the
GREENHOUSE EFFECT to “0,” (no effect).
4) What is Earth’s average surface temperature with no GREENHOUSE EFFECT?
_________ º F / C (circle).
Venus has a GREENHOUSE EFFECT 200 times as powerful as Earth’s.
Because of this, Venus’ average surface temperature is around 460ºC, much too
hot to support life as we know it. What would Venus be like without any
GREENHOUSE EFFECT? We can find out by entering Venus’ values for distance
and albedo into the planet temperature program and setting its GREENHOUSE
EFFECT to 0. Enter these values into the program:
MASS: 1
DISTANCE: 0.72
BOND ALBEDO: 75
GREENHOUSE EFFECT: 0
5) What is Venus’ average surface temperature with no GREENHOUSE EFFECT?
_________ º F / C (circle).
6) Would Venus still be too hot to support life with no GREENHOUSE EFFECT?
__________.
7) Would Venus be habitable with no GREENHOUSE EFFECT?
__________. Why or why not? ___________________________________
_____________________________________________________________.
8) Now think about the average surface temperature of the planet you are
exploring. Based on what you have discovered with the planet temperature
program, is the average surface temperature of your planet too hot, too cold or
about right? ______________________________.
9) Based on what you now know about greenhouse effect, do you want your
planet to have a strong or weak effect? ____________.
Look at number 6 of the planet preference survey to find out the type of
atmosphere on your planet. The thickness of the atmosphere you chose will
restrict the range of numbers that you may enter for GREENHOUSE EFFECT in
the planet temperature program.
If you chose “Trace” choose a number between 0 and 0.4.
If you chose “Thin” choose a number between 0.4 and 3.
If you chose “Thick” choose a number between 3 and 300.
Our planet has a GREENHOUSE EFFECT of ___________.