2. The Traveling Exhibit Science Background Part D: Search for Life prepared by Dr. Cherilynn Morrow for the Space Science Institute Boulder, CO

3. D. Search for Life KEY QUESTIONS: Does life exist on an extra-solar planet? How can we find it? The SETI Allen Telescope Array NASA’s Terrestrial Planet Finder

4. Life as we know it requires: 1.liquid water; 2.some form of energy (e.g. sunlight, chemical, volcanic); 3.access to organic materials (e.g. carbon compounds); 4.a sufficiently stable environment (i.e. time to originate and evolve). The search for life beyond Earth is informed by what we know about life on Earth.

5. On planet Earth life has evolved.  15 Courtesy NASA’s Navigator Program

6. Most of the life on Earth is microbes, not animals or plants! Animals and humans make up only 1% of the life on Earth. Humans could not survive without microbes! Alien Earths: Weighing Life Interactive We’ve discovered that microbes are vital to every other living thing on Earth! Cool!

7. Why Search for Life Beyond Earth? In the past couple of decades, the study of life on Earth has revealed the existence of life in “extreme” environments that were generally thought to be uninhabitable. The organic chemicals needed for life as we know it are found pervasively in and between the stars of the galaxy. In the past decade we have been detecting more and more planets orbiting other stars. It is a compelling question whether we are alone or other life (especially self-aware life) is out there. Either answer is amazing! Tube worms near deep ocean hydrothermal vent Star forming region Sun-like star with Earth-like planet Artist concept

8. Searching for Signs of Life Beyond Earth What are scientists doing? Kepler 1.Astrobiology: Studying life on Earth to aid the search for life beyond Earth — microbial life in “extreme environments” 2.Planetary Exploration: Exploring planets in our solar system with robots — Mars rovers seeking signs of past surface water 3.Finding Extra-solar planets: Searching for Earth-like planets orbiting distant stars— NASA’s Kepler Mission. 4.Looking for Signs of Life: Learning how to measure the composition of the atmospheres of extra-solar planets to detect signs of life. 5.SETI: Seeking electromagnetic signals from a technological civilization Mars rover Artist concept Parkes Radio Telescope

9. Life Changes its Environment Note the presence of ozone (O 3 ), and water vapor in the spectrum of Earth’s atmosphere – indirect evidence of life!  Life needs a suitable environment to flourish. It also feeds back and changes its environment.  The way life changes its environment is known as a biosignature – a sign of the presence of life.  Oxygen in Earth’s atmosphere is a biosignature of life. Looking from afar, we cannot see plants and bacteria directly, but we can infer the presence of photosynthetic life if there is atmospheric oxygen.

10. Microbial Mats Microbial mats are complex colonies of different types of microbes. When exposed to light they emit gases that over time can transform the composition of a planetary atmosphere. There is a microbial mat in the Alien Earths exhibit. Life Changes its Environment

11. “Hollywood Alien” Cyanobacteria like the one below may represent a more likely type of alien whose presence might be detected via its transformative effect on the atmosphere of an extra-solar planet.

12. How will we know a planet supports life? Look for evidence of oxygen Look for liquid water Analyze the reflected light from the planet to see if the planet has an atmosphere Look for signs of biological activity (methane) and rule out other explanations. 17 Courtesy NASA’s Navigator Program

13. NASA’s Terrestrial Planet Finder Does life exist on an extra-solar planet? How can we find it? In a decade or so, TPF's spectroscopy should allow atmospheric chemists and biologists to use the relative amounts of gases like carbon dioxide, water vapor, ozone & methane to find whether an extra-solar planet may support life. Artist Conception of NASA’s Terrestrial Planet Finder (TPF) spacecraft

14. The SETI Search The SETI Institute uses radio and optical telescopes to search for signals that might be emitted by technologically advanced life. The Allen Telescope Array is being developed at Hat Creek, CA to greatly expand the SETI search. Allen Telescope Array Dish Parkes Radio Telescope

15. The Drake Equation What do we need to know about to discover life in the galaxy? N = R * f p n e f l f i f c L R* = rate of formation of stars suitable for the development of intelligent life. f p = fraction of those stars with planetary systems. n e = number of planets, per solar system, with an environment suitable for life. f l = fraction of suitable planets on which life actually appears. f i = fraction of life bearing planets on which intelligent life emerges. f c = fraction of civilizations that develop a technology that releases detectable signs of their existence into space. L = length of time such civilizations release detectable signals into space. N = estimated number of civilizations in the Milky Way Galaxy whose electromagnetic emissions are detectable. LOTS OF THINGS!

16. N = estimated number of civilizations in the Milky Way Galaxy whose electromagnetic emissions are detectable. The Drake Equation N = R * f p n e f l f i f c L The Alien Earths exhibit has a computer kiosk where you can play with the numbers of the Drake Equation! Our Milky Way galaxy may look like this one. It is home to more than100 billion stars!

17. R * = rate of formation of stars suitable for the development of intelligent life. N = R * f p n e f l f i f c L f p = fraction of those stars with planets

18. number of planets, per solar system, with an environment suitable for life. n e = number of planets, per solar system, with an environment suitable for life. N = R * f p n e f l f i f c L fraction of suitable planets on which life actually appears. f l = fraction of suitable planets on which life actually appears.

19. N = R * f p n e f l f i f c L f i = fraction of life-bearing planets on which intelligent life emerges (may not be life with technology) f c = f c = fraction of civilizations that develop a technology that releases detectable signs of their existence into space.

20. N ≈ L L = length of time such civilizations release detectable signals into space. N = R * f p n e f l f i f c L

21. Now the challenge is to discern whether any of these signals could be signs of a technologically advanced, extraterrestrial civilization. Alien Earths: SETI Interactive A current SETI scientist A future SETI scientist ? “I’m detecting different kinds of spacey signals!” Me too!

22. The search for life beyond Earth is shaped by what we know about life on Earth. Life on Earth requires liquid water, energy, organic materials. Most life on Earth is microbial. Life changes its physical environment in ways that are more easily detected from afar than the life forms themselves. Knowledge of these changes determines how we look for life elsewhere (e.g. oxygen in a planetary atmosphere or radio signals from technological beings). D. Search for Life SUMMARY

23. The “Origins” Timeline in Pictures (As best we currently know it) Can you trace the symbolic steps from the Big Bang to life? BIG BANG Sun & planets forming LIFE! Habitable worlds Heavier elements needed for life created in massive stars and spewed into the galaxy via supernova explosions Organic materials

24. CONCLUSION Re-visiting the Big Ideas of the Introductory Presentation We are developing extraordinary new tools, techniques, & insights for exploring the age-old question of whether there is life beyond Earth. Our search for habitable worlds and signs of life in our galaxy is guided by our study of how stars and planets form & our understanding of life on Earth.

25. Parting Points to Ponder The natural processes in our universe have resulted in life forms (e.g. humans) capable of reflecting on their own origins and on the possibility of life elsewhere.

26. There are two possibilities: Maybe we’re alone… Maybe we’re not… Both are equally amazing…

27. We shall not cease from exploring, And the end of all our exploration Will be to arrive where we started And to know the place for the first time. - T.S. Eliot, Little Gidding