A10 Report

Exploring Planetary Atmospheres Name: Dasol Lee Introduction: In this lab you investigate planetary atmospheres and how they affect in-falling bodies. Learning Goals: Students will  Atmospheric compositions of Earth’s, Mars’, Venusian, and Titan’s atmospheres  Learn how atmospheres thins out using concept of scale height.  Learn what kind of objects can penetrate an atmosphere and fall to the ground and which will burn out in the atmosphere Learning tools: 1. Simulation: https://astro.unl.edu/mobile/scaleheight/sim1/sim1.html 2. Simulation: https://astro.unl.edu/mobile/scaleheight/sim2/sim2.html 3. Simulation: https://astro.unl.edu/mobile/scaleheight/sim3/sim3.html 4. Excel spreadsheet (provided) Part 1: Scale height Background: Atmosphere is a layer of gas surrounding a planet or a moon, that is held in place by the gravity of that planet or moon. An atmosphere is more likely to be retained if planet’s or moon’s surface gravity it is high and the temperature of the atmosphere is low. This layer of gas pushes down on the surface of a body with its weight resulting in atmospheric pressure. Pressure is defined as a force (weight of the vertical column of atmosphere above that location. In case of atmospheric pressure) divided by area over which the force is applied. As elevation increases, there is less overlying atmospheric mass, so that atmospheric pressure decreases with increasing elevation. Also density drops with elevation: the greater the elevation the thinner the atmosphere. There are many units used for pressure. Her we’ll use the SI unit called Pascal: 1 Pascal = 1 Newton/ 1 square meter or 1000 Pascals = 1 kiloPascals = 0.145 psi. Scale height H is commonly used to describe the atmosphere of a planet it is a general way to describe how a value of a given property, in case of atmospheric pressure, decreases with increased elevation. Scale height is the vertical distance over which the pressure falls down to about 37% of what is originally was i.e. drops by 67%. The nature of the decline is such that these values fall by an additional factor of 67% for each additional scale height. Thus, scale height describes the degree to which the atmosphere “hugs” the planet: the shorter the scale height, the more atmospheric gasses are concentrated near the surface.

Figure 1. Procedure: Click on https://astro.unl.edu/mobile/scaleheight/sim1/sim1.html to open the simulation. You should see a window that looks like that shown in figure 1. Study figure 2 to see what controls need adjusting and how to use the sim. Use the sim to collect the data for Earth altitude, pressure, and density for elevations listed in worksheet table (worksheet called scale height). You can either move the red dot to the desired elevation by hand, or type the value (multiplying scale height) into the rectangle next to Scale Height in the upper right. Make a graph (scatter graph with smooth lines and markers – see Appendix A for detailed instructions of how to do it) of pressure versus altitude. Complete the statement: As the altitude increases the pressure decreases (enter: increases, decreases, or doesn’t change). Make a graph (scatter graph with smooth lines and markers – see Appendix A for detailed instructions of how to do it) of density versus altitude. Complete the statement: As the altitude increases the density of gas decreases (enter: increases, decreases, or doesn’t change) Figure 2.

1. Switch to the simulation linked here: https://astro.unl.edu/mobile/scaleheight/sim2/sim2.html . You should see a window that looks like that shown in figure 3. Study figure 3 to learn how to use this sim. Identify composition of each body’s atmosphere and fill in the data in worksheet tab “composition” and for each of set bodies: Earth, Mars, Titan, and Venus. In addition, record body mass and radius, temperature, surface gravity and scale height for each object. For each of the four celestial bodies make a pie chart showing the composition of its atmosphere (see Appendix B for how to make a pie chart) Copy your charts here: Copy your Excel table here: Figure 3.

Select Earth again. Record its current scale height here : 8.38 km. It is thought that Earth’s original atmosphere was composed of hydrogen and helium, because these were the main gases comprising the protoplanetary disk around the young Sun from which the planets formed. Find the scale height for earth’s original atmosphere Earth if its composed of 75% hydrogen (H 2 ) and 25% helium. To do that, move the sliders for nitrogen oxygen and argon to zero and move up the sliders for hydrogen (to 75%) and helium (to 25%). Leave the remaining settings at Earth’s default values Scale height for Earth’s original atmosphere is 97.04 km. How does it compare with the current Earth’s scale height? A lot bigger, nearly 12 times bigger than the original scale height (is it the same, bigger or smaller, a lot bigger or a lot smaller, a little bit bigger or a little bit smaller) Part 3. Meteoroid impacts Background Meteoroids regularly enter Earth's atmosphere at high speeds. Whether they are stopped by Earth's atmosphere, burn up, or plow into Earth's surface depends very much upon how their mass compares to the mass of the column of air that they would pass through. Scale height is a useful tool to help you identify both extremes in behavior. Most treatments of meteors categorize the outcome into 4 categories (see Landstreet, Physical Processes in the Solar System , 2003, pp. 118). Realize that these bins are only an approximation and meteor behavior depends greatly upon its initial velocity, composition/density, and mechanical strength. Still, we can often determine the outcome of a meteoroid encounter by comparing the mass of the meteoroid to the mass of the column of air that it will pass through.  Very low-mass meteoroids – These meteoroids are smaller than a dust grain and never display any meteor phenomena.

1. Set meteoroid density to that of iron (Fe). Set the Meteor Radii to 0.010 m. Then, gradually increase the radius of the meteor and find what is the smallest radius of the meteor for which the ratio of the mass of the column of air to the mass of the meteor M AC /M m is 10 i.e. meteor will likely reach the ground. The minimum radius for the iron meteor to reach the Earth’s surface is : 0.098 m . 2. Adjust the density of the meteorite to that of stone and set the Meteor Radii to 0.020 m. Then adjust the radius and find what is the smallest radius of the meteor for which the ratio of the mass of the column of air to the mass of the meteor M AC /M m is 10 i.e. meteor will likely reach the ground. The minimum radius for the stony meteor to reach the Earth’s surface is : 0. 2418 m . How do the sizes of those two meteors compare? Which is bigger ? Iron Why? Iron meteor requires a lesser radius but can still reach the Earth’s surface. By how much? Find the ratio of their radii R iron /R stone = 0.40 3. Take your stony meteor to Venus, Mars, and Titan. Will it reach the surface there? Yes What is the minimum size of a stony meteor that can reach Martian surface? Cant reach What is the minimum size of a stony meteor that can reach Titan’s surface ? 4.45m What is the minimum size of a stony meteor that can reach Venusian surface? 24.8m 4. Switch back to iron. What is the minimum size of an iron meteor that can reach Martian surface? Cant reach What is the minimum size of an iron meteor that can reach Titan’s surface? 1.80m What is the minimum size of an iron meteor that can reach Venusian surface ? 10.05 Rank the four celestial bodies in order from the one which atmosphere allows the smallest meteors to pass through to the surface, to the one that allows the biggest ones . Earth, Titan, Venus, Mars What does this ranking tell us about those four object’s atmospheres? Neither an iron meteor or a stony meteor cannot penetrate the atmosphere of Mars. Conclusion question: On February 15, 2013, a meteoroid exploded in the atmosphere over Chelyabinsk, Russia. The energy released produced window breaking shockwaves, intense heat, and scattered numerous small fragments of ‐ the original meteoroid. This resulted in over 1500 injuries people despite the fact that this is not a densely populated area. (The meteor’s explosion was well documented-see embedded YouTube footage). The meteor ‐ gained significant media attention, in part because of how visually impressive and damaging it was, but also because it caught everyone by surprise. Although astronomers attempt to track large near Earth objects which could potentially become damaging meteoroids, ‐ the Chelyabinsk meteor was not detected prior to its atmospheric entry. 18 m

Figure 6. Because the meteor was destroyed in the atmosphere, attaching numbers to it is difficult; the best estimate of its mass is about 10 million kilograms and 18 meters in diameter (thus radius of about 9 meters). For visual size comparison with some familiar landmarks see figure 5. Use the simulation from Part 3 to find out the composition of the Chelyabinsk meteor. Select Earth, enter the radius and try different densities to see which results in the mass for this meteor that matches most closely the estimated value of 10 million kilograms. Begin by adjusting the slider that controls meteor density. Once you get close, adjust the numbers in ρ M = window till you get as close to 10 million kilograms as possible. Your estimate of the density of the Chelyabinsk meteor is ρ M = 410 kg/m 3 . Based on your estimate of its density, was Chelyabinsk meteor mostly metallic, rocky, or icy? Metallic What is the value for the ratio of the mass of the column of air to the mass of the meteor for Chelyabinsk meteor? M AC /M m = 0 Based on this value would it be considered a low, medium, or high mass meteor? Medium Based on tis classification, what would you predict its fate upon approaching the Earth to be? There is a chance that it might hit Earth, but not anytime soon. Does your prediction agree with the its actual fate: atmospheric disintegration very near Earth’s surface? No Submission details: Submit into this lab’s drobox on Blackboard:  MS Word report (this document with your entries)  Excel worksheet Appendix A: making scatter graphs 1. Make a graph of pressure vs. altitude: select cells D2 through D18, press Ctrl and hold it down while you also select cells B2 through B18. Then click on “Insert” tab and select scatter graph option smooth lines and markers see figure below. 2. Repeat for density: select cells E2 through E18, press Ctrl and hold it down while you also select cells B2 through B18. Follow the same procedure as above. Make sure to label axis (including units) and, since we have more than one chart, add chart titles. Appendix B: making a pie chart Figure 5.