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.