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The Search for Other Solar Systems

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The Search for Other Solar Systems APPENDIX A The Search for Other Solar Systems Outcomes: 1. explain the roles of evidence, theories and paradigms in the development of scientifi c knowledge (114-2) 2. analyse why and how a particular technology was developed and improved over time (115-5) 3. describe and evaluate the design of technological solutions and the way they function, using scientifi c principles (116-6) 4. analyse why scientifi c and technological activities take place in a variety of individual and group settings (117-6) 5. analyse examples of Canadian contributions to science and technology (117-11) Introduction How do we fi nd other solar systems? For most of human history we have looked at the night sky and pondered the question “Are Nearly 1500 other solar systems have been detected we alone in the universe?” Medieval scholars so far. There are fi ve methods to detect the presence speculated that other worlds must exist and that of planets orbiting other stars. some would harbour other forms of life. New technologies have allowed us to begin the fi rst steps in the search for extraterrestrial life. The Radial velocity method fi rst step in this process is the detection of solar The tug of gravity on a star by the planets orbiting it systems around stars other than our own sun. causes it to wobble back and forth. This wobble can Most of the planets we have found orbiting other be detected by measurements of the Doppler shift stars have been large gas giants like Jupiter. of the light emitted from the star. The shift of the Some of them have also been found very close stars spectrum towards the blue as it moves toward to their parent star, unlike our own solar system. us and then towards the red as it moves away can be However, for the fi rst time, we have been able detected easily by large telescopes. to detect earth sized planets orbiting inside the habitable zone of other solar systems, where liquid water can exist on their surfaces. New observations have forced us to re-examine our theories of solar system formation and expand the range of possible solar systems that could support life. Figure 1: Spectral shifts. (Source: http://innumerableworlds.wordpress.com/2009/03/) EARTH SYSTEMS 3209 INTERIM CURRICULUM GUIDE 171 APPENDIX A Transit photometry method This method detects planets by measuring the dimming of a star as the orbiting planet passes between it and the Earth. The passage of a planet between a star and the Earth is called a “transit.” If such a dimming is detected at regular intervals, then it is very probable that a planet is orbiting the star and passing in front of it once every orbit. Figure 4: Microlensing method. (Source: http://wise-obs.tau.ac.il/news/exoplanets.html) Direct imaging Extrasolar planets are relatively small and do not make their own light. They are easily lost in the brilliant glare of the stars they orbit. Scientists have used a coronograph to block most of the star’s Figure 2: Transiting planet and dip in star brightness central light to directly photograph an exoplanet for (Source: http://www.astro.wisc.edu/~townsend/static. the fi rst time. php?ref=diploma-2) Astrometry method The wobble of a star due to the gravitational tug of a planet as it orbits the star is seen directly by making very precise observations of the star as it slowly moves across the sky. Figure 3: Wobble of a star. Courtesy: NASA/Kepler mission. Microlensing method Einstein predicted that when a heavy object passed in front of a distant star the gravity of the Figure 5: Direct imaging of 3 planets orbiting a star. Courtesy: Gemini Observatory/Association of Universities for Research in planet could bend the light and act like a lens. Astronomy This would magnify the star’s image and make it briefl y look brighter. Large telescopes have been able to measure this brightening in very distant stars. 172 EARTH SYSTEMS 3209 INTERIM CURRICULUM GUIDE APPENDIX A Gemini North Kepler Mission Canada has been leading the search for extrasolar The Kepler Satellite Mission was specifi cally planets through the operation of the Gemini designed to survey a portion of our region of the Observatory Program. This program consists of Milky Way galaxy to discover Earth-sized planets twin 8.1 metre diameter optical/infrared telescopes in or near the habitable zone and determine how located on two of the best observing sites on many of the billions of stars in our galaxy have such the planet. From their locations on mountains planets. in Hawaii and Chile, the Gemini telescopes can collectively access the entire sky. Figure 6: Gemini North, Maunakea, Hawaii. Courtesy: Gemini Observatory/Association of Universities for Research in Astronomy. The telescopes use adaptive optics systems which Figure 8: Computer rendition of Kepler spacecraft. Courtesy: fl ex the mirror to correct the blurring effects of the NASA/Kepler mission/Wendy Stenzel atmosphere which we see as the ‘twinkling’ stars do when we look up on a clear night. They also It has proven to be very successful at using the use a coronagraph to remove approximately 99% transit photometry method, having found over of the star light, while still letting the planet’s light 1500 extrasolar planets to date. Its location in orbit, pass through. It enables the scientists to directly above the Earth’s distorting affects enables it to see observe planets orbiting other stars. extremely fi ne drops in a star’s light. It is the fi rst The image below shows a star which lies about program that is capable of fi nding planets that are as 500 light-years from Earth and an orbiting planet. small as the Earth. The planet is much larger than the planet Jupiter Up until recently most of the planets the Kepler and it mission had found were much larger than the planet orbits its Earth. Now scientists using Kepler have found 58 star at a satellites within the ‘Goldilock Zone’ where it is distance neither too hot nor too cold for liquid water to exist. about It is believed that these planets are our best hope 300 times for fi nding life outside our solar system. Also, for farther the fi rst time, fi ve of these planets were found to be than Earth roughly earth the size of the Earth! does from our own star. Figure 7: Star with visible planet to the northeast. Courtesy: Gemini Observatory/Association of Universities for Research in Astronomy EARTH SYSTEMS 3209 INTERIM CURRICULUM GUIDE 173 APPENDIX A that it also has at least 5 planets larger than earth that orbit very close to the parent star. If placed in our solar system they would all lie within the orbit of Mercury! The Nebular Hypothesis is still thought to apply to the formation of the early planets into roughly the confi guration seen in our own solar system. The neat, ordered process of turning large discs of gas and dust into stable solar systems like our own appears to be too simplistic to explain what we have been observing outside our own system. It is now assumed Figure 9: Numbers of planet candidates. Courtesy: that although the basic principles still apply, the NASA/Kepler Mission/Wendy Stenzel chaotic nature of gravitational interactions between the components may be the determining factor in the process of developing a series some of the unusual What do the extrasolar planetary arrangements seen below. systems look like? The accepted theory of solar system formation - the “Solar Nebular Hypothesis” - infers that a solar system should have rocky inner planets and larger gaseous planets much farther out. Many of the solar systems we have discovered however do not always appear to follow this pattern. Many solar systems have very large planets orbiting very close to their parent star. It is now theorized that larger planets may migrate inwards due to gravitational interactions between each other and the leftover dust and gas in the solar nebula from which they formed. Some Figure 10: Planetary arrangements around various stars. planets may be gravitationally ‘slingshot’ Courtesy: NASA/JPL-Caltech into different orbits, fi red into the parent star or ejected from the system entirely. Friction within the gas and dust surrounding the What’s next? early protoplanet may also create drag on the planets, changing their orbital velocity, thus causing them to spiral inwards towards It appears that wherever we look in the heavens there their parent star or into collisions with other are solar systems just waiting to be explored. The planets. next step is to use our largest telescopes to try and isolate the light coming from the planets to determine One such system labelled Kepler – 11 the chemical composition of their atmospheres. contains a star similar to our own nearly 2000 light years from earth. It has been discovered Certain gases are known to be essential indicators of the presence of life, such as water, methane or ozone. Detailed spectrography could tell us if life - as we know it exists. 174 EARTH SYSTEMS 3209 INTERIM CURRICULUM GUIDE APPENDIX A Conclusion References Until now we could not prove that other solar Science programs at the Gemini Observatory. systems existed outside our own. Advancements Available: http://www.gemini.edu in scientifi c methods and technology have not Kepler Satellite Mission to fi nd earth – like planets. only let us directly observe other systems but like Available: http://kepler.nasa.gov all scientifi c explorations they have forced us to re-examine our theories of solar system formation.
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