Contents CHAPTER 1 What Are Extraterrestrials CHAPTER 2 Looking for Life CHAPTER 3 Clues on Earth CHAPTER 4 Exploration Tools CHAPTER 5 Strange Sightings CHAPTER 6 What’s Next ACTIVITY Your Space Science Mission Glossary Learning More Index and About the Author 4 10 20 28 34 40 44 46 47 48
CHAPTER 1 What Are Extraterrestrials For thousands of years people have wondered if there is life beyond Earth For more than 100 years scientists have been trying to answer that question People on Earth are terrestrials a word that comes from the Latin terra which means earth or land An extraterrestrial is a life form that exists beyond Earth Our Solar System Astronomers are scientists who study the stars planets and other aspects of space Some astronomers are searching for life beyond our planet Earth is one of eight planets in our Solar System This is a system in which planets orbit or travel around a star Earth’s star is the Sun Astronomers are studying these other planets and their moons but the search does not end there Our Solar System is part of a spiral-shaped galaxy called the Milky Way Our Solar System lies within one curved part of the spiral called the Orion Arm Earth’s Solar System belongs to a spiral galaxy or collection of stars similar to this galaxy M33 4
Radio telescopes scan space for signals that might be signs that intelligent life exists elsewhere in the universe There may be as many as 400 billion stars in the galaxy Many of these stars have at least one planet orbiting them This means that there are billions of possible places for scientists to look for life in the Milky Way alone There are billions of other galaxies in the universe and they also have billions of stars orbited by planets Extraterrestrial Experts Earth’s galaxy is so vast that many people believe that life must exist somewhere in it other than on Earth What kind of life could this be Extraterrestrials may take a form that we do not recognize Astrobiologists are scientists who are looking for extraterrestrial life They study the beginnings and future of life in the universe as well as its evolution and distribution or where it is found Astrobiology has become an important part of space science In 1998 the National Aeronautics and Space Administration NASA established the NASA Astrobiology Institute NAI to search for signs of life One part of astrobiology is the search for intelligent life Its scientists are looking for signs of thinking life forms in the universe In the late 1970s NASA began the Search for Extraterrestrial Intelligence SETI The SETI Institute founded in 1984 is a leading research center that works with NASA NASA and the SETI Institute are two leading U S organizations but the search for extraterrestrial life involves astrobiologists astronomers engineers and many others around the world Together they may find it 5
