Are There Other Neighborhoods Like Our Own?

Transcription

1 Are There Other Neighborhoods Like Our Own? Searching for Abodes of Life in the Universe This lesson is taken from an education module developed for Challenger Center s Journey through the Universe program. Journey through the Universe takes entire communities to the space frontier. Start the Journey at Support for this work was provided by NASA through grant number ED A from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS Challenger Center, Challenger Center for Space Science Education, and the Challenger Center logotype are registered trademarks of Chal leng er Cen ter for Space Science Education. No portion of this module may be re pro duced with out written permission, except for use within a Journey com mu ni ty. 2001, Challenger Center for Space Science Education. January 2001

2 CHALLENGER CENTER S JOURNEY THROUGH THE UNIVERSE 38 Grade Level 5-8 Exploring the Neighborhood of the Solar System Overview One of the most exciting goals in exploration of the Solar System is to search for life. Several missions to planets throughout the Solar System have supported this search, from the attempt to confirm the existence of liquid water within Jupiter s moon Europa, to testing Martian soil for traces of organic materials. In recent years, an entirely new field of science, called astrobiology, has emerged around this goal. ESSENTIAL QUESTION Why search for life in the solar system, and where might we expect to find it? But why is it important to prove or disprove that life is present elsewhere in the Solar System? On a philosophical level, the search for life is an attempt to answer the question, What is our place in the cosmos? If we are alone, we are compelled to wonder why we are so special. On the other hand, if the universe is teeming with life, what other varieties of life exist? If life is rare, we can come to a better understanding of the delicate harmony that exists on our planet and the importance of preserving it. If life does exist elsewhere, then learning about an alien biology may even help us to better understand the nature of our own biology. With these motivations in mind, this activity takes us one step further in the exploration for life forms. As we are driven to search for life within the Solar System, where should we look? From our own investigations on Earth, we know that life spans a variety of habitats. We can find it at extreme pressures below the ocean s surface, exposed to high levels of radiation within nuclear reactors, and extracting nutrients and energy from nearly every available source. Similarly, life s presence encompasses a broad range of temperature. Life has been found in the frigid climes of Antarctica to the scalding thermal pools (115 C or 231 F) in Yellowstone National Park. However, while the range may be wide, it is not infinite. In frozen water, the chemicals and molecules that are essential to the processes of life cannot be dissolved or move. Penguins and polar bears that survive in seriously sub-freezing temperatures use stored fat and insulation to maintain a high OBJECTIVES Students will: Read data tables. Graph data. Use the graphs to interpret how planetary temperatures that may be suitable for life derive from many factors.

3 CHALLENGER CENTER S JOURNEY THROUGH THE UNIVERSE 39 internal temperature and depend upon an unfrozen environment nearby to provide food for example, penguins can tolerate the Antarctic winter (-60 C = - 76 F) only because they can gorge beforehand on fatty fish in the relatively warm and unfrozen ocean. Antarctic ice-fish, on the other hand, really live and function at a body temperature below freezing (-3 C = 27 F) by virtue of a biochemical anti-freeze and the fact that salty ocean water has a freezing temperature a bit below 0 C. Some life thrives at 115 C (239 F), but not at higher temperatures, possibly because enzymes and proteins necessary for life cannot exist at higher temperatures. The temperature range for life on Earth may prove to be an adequate rule of thumb to judge the likelihood of life s presence on a foreign world. MATERIALS Data tables Graph paper Colored pencils Ruler Intuitively, one of the most significant influences on a planet s temperature is the distance from its parent star. In our case, the Sun is our parent star. A planet absorbs energy from the light radiating from the Sun, which should raise the planet s temperature. It re-radiates that energy into space as infrared light, which should lower the planet s temperature. Since both these processes are occurring simultaneously, the planet s temperature reflects an equilibrium between the energy absorbed and the energy re-radiated into space. You might think that the closer the planet is to the Sun, the higher its equilibrium temperature. However, several factors can reduce or enhance a planet s ability to retain the energy of sunlight, causing the actual temperature to differ from our expectations. One factor which is familiar to us on Earth is the greenhouse effect. The carbon dioxide in our atmosphere will let visible light from the Sun in, but it doesn t like to let infrared light (emitted by warm objects) out. On Earth, the greenhouse effect raises the average temperature on the planet to be about C (54 72 F) higher by retaining energy. While this makes the Earth comfortable to those living here, the greenhouse effect can be taken to harsh extremes. On Venus, which has a thick atmosphere of carbon dioxide and high-altitude clouds of noxious chemicals, the greenhouse effect is so pronounced that the planet has a nearly constant temperature of around 460 C (about 860 F). The reflectivity of a planet termed its albedo also can influence its temperature. If an object is perfectly black (called a blackbody), it absorbs all light falling on it. On the other hand, reflective objects absorb only some of the light energy that falls upon them. If a black object and a reflective object were located at the same distance from the Sun, the black object would have a higher temperature. This isn t too mysterious. On a sunny day, the hood of a black car will have a higher temperature than the hood of a white car. Jupiter s moon Europa, which is covered in a white layer of ice, reflects much of the light that

4 CHALLENGER CENTER S JOURNEY THROUGH THE UNIVERSE 40 falls on it and is therefore cooler than a dark object would be at the same location. There is no such thing as a perfectly black object; everything reflects at least a little light. However, some objects, like asteroids, are a fairly good approximation to a blackbody because of their low reflectivity. Another temperature-altering influence is tides. On Earth, we are familiar with the tides of the ocean, where the Moon tugs on one side of the Earth more strongly than the other, distorting the shape of the Earth. The fluid part of the Earth (the oceans) distorts more easily than the solid parts (the continents) causing a tidal bulge to slosh around the Earth. The moons of Jupiter each experience tidal forces due to Jupiter itself and also due to all the other moons. The forces on the inner moons Io and Europa are strong enough that the tides bend and flex the rock of the crust and core, creating heat. On Io, the heat is great enough to produce volcanoes and evaporate any water it once had. On Europa, the heat may be enough to melt a global ocean beneath a crust of water ice. The moons Ganymede and Callisto are similarly affected, but to a much lesser extent due to their large size and greater orbital distance. In this activity, students will come to a better understanding of some of the factors that influence a planet s temperature. First, their intuition will be tested as they hypothesize how the temperature of a blackbody (in this case, a small very dark rock) should vary as it is moved farther from the Sun. Then they will use actual data to plot the temperature of a blackbody object at different distances from the Sun, and will compare these data to the temperatures at which life is found on Earth. This will allow them to estimate the orbital limits in which they think a life-bearing planet could be found. Finally, they will plot the observed temperatures of the planets at their actual orbital distances from the Sun and discover that in most cases, reality differs significantly from the simple blackbody-equilibrium model. With this information, the students will present hypotheses regarding the differences between expected and actual temperatures, and will use this information to propose a plan for future searches for life in the Solar System.

5 CHALLENGER CENTER S JOURNEY THROUGH THE UNIVERSE 41 Procedures 1. Prior to this activity, review data tables and graphing skills with the students. 2. Students will begin by labeling the x- and y-axis on each of two graphs. X will be Distance from the Sun and y will be Temperature. The range of temperatures for both graphs will be 250 C up to 500 C. Graph #1 will cover the entire solar system out to Pluto. Label this Graph #1: Entire Solar System. Graph #2 will cover only the inner solar system, as far as mid-way between Mars and Jupiter. Label this Graph #2: Inner Solar System. Students will use the Distance from the Sun information in Data Table #2 to determine the range for the x-axis for both graphs. Distances from the Sun in this activity are given in AU (Astronomical Units). Students should determine an x-axis from 0 to 40 AU for Graph #1, and 0 to about 3 AU for Graph #2. 3. The temperature limits of life observed on Earth are 60 C to +115 C ( 76 F to 239 F). The coldest is observed for Emperor penguins in the Antarctic winter; the hottest is for bacteria living in geysers, hot springs, and deep sea vents. In between, Antarctic ice-fish have the coldest body temperature and year-round environmental temperature, at 3 C (27 F). Have students draw a red line across both graphs at -60 C, and another at 115 C. The temperatures between these two extremes represent a life zone, and students should label it on their graphs. 4. At this point it is important to introduce to the students the concept of a blackbody in space and how the temperature changes as you move away from the Sun. Have the students lightly pencil-in a line on the graphs that they feel represents the temperature of a blackbody as you move out from the Sun. 5. Next, with a blue pencil plot the actual temperatures of the blackbody object vs. Distance from the Sun on both graphs, drawing a smooth curve to connect the points. These data are found in Data Table #1. Discuss with the students how their prediction compares with what happens to an actual blackbody as it is moved farther from the Sun. 6. Using the distances (not the temperatures) from Data Table #2, have the students mark a point on the curved line at the distance of each of the worlds, labeled by the first letter of the name of each world. Do this on both graphs. 7. At this point students should stop to discuss which worlds appear to fall in the life zone. The temperature of Earth should be near the freezing point of water. Have students list all of the worlds that fall within the life zone the region of survivable temperatures.

6 CHALLENGER CENTER S JOURNEY THROUGH THE UNIVERSE Students may wonder why the temperature of the Earth is so low. Have them brainstorm ideas for the cause. 9. Using Data Table #2, and with a different colored pencil, have students plot the actual temperature ranges of each the inner planets (through Mars) on Graph #2. Do the same for the outer planets on Graph # Students will plot both the high and low temperature for each world. Once they have plotted the temperatures, have them connect the points with a vertical line. 11. Have students compare the actual temperature ranges to the blackbody temperatures. 12. Students will find that despite where the world falls on the blackbody line, several worlds have temperatures that apparently could support life. There are many reasons why these worlds have these significant temperature ranges. For example, the greenhouse effect, tidal heating, localized volcanic activity, etc. 13. Have students research each world that has a temperature range within the life zone, but a blackbody temperature outside the life zone, to learn why the temperature is different from a blackbody object. [As an example, a small dark rock at Mercury s orbit would have a very high temperature and lie outside the life zone. But Mercury is sometimes found to have temperatures inside the life zone, even temperatures too cold for life. As the Sun sets on Mercury, temperatures plummet. At night, and at the poles, Mercury is frigid.] 14. Students should develop creative ways to report their findings to the rest of the class. Discussion Have the class discuss those worlds which have temperature ranges inside the life zone but whose blackbody temperature is outside the life zone. Could these worlds have environments supporting life? Is a temperature inside the life zone the only consideration for life elsewhere (see the activity titled Earth versus Other Worlds )?

7 CHALLENGER CENTER S JOURNEY THROUGH THE UNIVERSE 43 ASSESSMENT Students work can be evaluated using the following rubric: 4 Points All qualities of an excellent graph are present. Writing is clear and understandable. Uses data to lead to logical conclusion. Restates results of graphs. Includes personal analysis and comments. 3 Points Missing one quality of an excellent graph. Acceptable use of data to support conclusion. Comments are few, but acceptable. 2 Points Missing two qualities of an excellent graph. Data is used, but conclusion is not well supported by the data. 1 Point Missing more than two qualities of an excellent graph. Conclusion does not refer to the data. Does not include thoughts. 0 Points No graph complete. Off topic or unrelated. Writing is unreadable. Transfer and Extensions 1. Have students research different climates around the globe. Students can compare this information to species population maps to see where different species live. Students can then research the characteristics of different species to see if they have adaptations appropriate for their environments. 2. Research different NASA missions to other planets and how the environmental conditions affected the construction of the spacecraft used for these missions. 3. Discuss with your students the motivations for exploring other worlds. Some answers may include: curiosity; to find useful resources; to find a new place to colonize; if intelligent life forms exist, to see if we could learn about them; to find out whether we are alone in the universe; or to better understand our place in the universe. 4. Discuss the ethical implications of exploring other worlds. Possible topics: Do we have the right to move to places where life already exists or places where life could exist; transform another world into a more Earth-like environment; use natural resources from other worlds; or alter the natural beauty of other worlds.

8 Student Worksheet Data Table #1 Distance from Center of Sun (AU) Temperature of Blackbody ( C) Student Worksheet: page 1 of 2

9 Data Table #2 Approximate Distance from Center of Sun (AU) Temperature Range ( C) Mercury to +257 Venus Earth 1 89 to +55 Earth s Moon to +127 Mars to +27 Jupiter (cloud-tops) Europa to 149 Io to +727 Ganymede to 149 Callisto to 149 Saturn (cloud-tops) Titan (surface) Uranus (cloud-tops) Neptune (cloud-tops) Pluto to 213 Student Worksheet: page 2 of 2

10 Challenger Center Programs The internationally acclaimed Challenger Learning Center Network currently consists of state-ofthe-art, innovative educational simulators located at 49 sites across 29 states, Canada, and the United Kingdom. Staffed by master teachers, the core of each Center is a two-room simulator consisting of a space station, complete with communications, medical, life, and computer science equipment, and a mission control room patterned after NASA s Johnson Space Center. See for information. A joint initiative of Challenger Center for Space Science Education, the Smithsonian Institution, and NASA, Voyage A Journey through our Solar System is a space science exhibition project that includes permanent placement of a scale model solar system on the National Mall in Washington, DC, and at locations all over the world. See for information. Space Day SM launches new Design Challenges created by Challenger Center each school year. The inquiry-based challenges are designed to inspire students in grades 4-8 to create innovative solutions that could aid future exploration of our solar system. See for information. Challenger Center s Journey through the Universe program provides under-served communities with diverse national resources, including K-12 curriculum materials, teacher workshops, classroom visits by scientists from all over the country, and Family Science Nights. See for information. The MESSENGER spacecraft (MErcury Surface, Space ENvironment, GEochemistry and Ranging) is to be launched in 2004 and go into Mercurian orbit in Challenger Center is one of the partner organizations charged with MESSENGER education and public outreach activities. See for information. Through the Challenger Center Speakers Bureau, Voyages Across the Universe, staff members speak to student audiences of 30-1,000, conduct workshops for educators, give keynote and featured presentations at conferences, as well as conduct Family Science Nights at the National Air and Space Museum, and other facilities across the nation, for audiences of 300-1,000 parents, students, and teachers. See for information. For information about other Challenger Center programs, or to purchase our classroom resources, visit