1. Chapter 19: Chapter 19: The Search for Extraterrestrial Life

2. WHAT DO YOU THINK? How do astronomers search for extraterrestrial life? Have astronomers located any extraterrestrial civilizations? If advanced alien civilizations exist, is there any way they might know of our existence?

3. You will discover… what qualities scientists believe are necessary for life to exist how scientists estimate the number of planets orbiting other stars that could support complex life how scientists search for life beyond our own solar system—and the results of those searches how we are trying to communicate with extraterrestrial life

4. Creating Complex Molecules When an atom such as carbon (C), can combine with more than two other atoms (in carbon’s case, with four atoms), then the complex, nonlinear chains essential for life can form.

5. Non-Carbon Organic Molecules? When any molecule that can make three or more strong bonds (other than carbon) combines, it makes compounds that are either too soft (left) or too hard (right), or too reactive or too inert, to be useful in supporting life.

6. A Carbonaceous Chondrite Carbonaceous chondrites date back to the formation of the solar system. Analysis of newly fallen carbonaceous chondrites discloses that they are rich in organic compounds (arrow).

7. Miller-Urey Experiment Modern versions of this classic experiment prove that numerous organic compounds important to life can be synthesized from gases that were present in Earth’s primordial atmosphere.

8. Miller-Urey Experiment A slime of organic material created in the original Miller- Urey experiment.

9. The Water Hole The “water hole” is a noise-free region perfect for interstellar communication.

10. Radio Telescope Used for SETI NASA Deep Space Radio Telescope, Mojave Desert, California

11. Region of the Search for Extraterrestrial Intelligence

13. Human Memorabilia in Space A visual version of the signal sent in 1974 from the Arecibo radio telescope toward the globular cluster M13.

14. Human Memorabilia in Space Pioneer plaque

15. Human Memorabilia in Space Voyager 1 & 2 digital record

16. WHAT DID YOU THINK? How do astronomers search for extraterrestrial intelligence? They search for radio signals from other advanced civilizations. Have astronomers located any extraterrestrial civilizations? No extraterrestrial civilizations have yet been discovered. If advanced civilizations exist, is there any way they might know of our existence? Yes, they might detect our intentional radio broadcasts into space, our everyday radio and television broadcasts, or possibly one of our spacecraft traveling in interstellar space.

17. Key Terms Drake equation organic molecule SETI water hole