Contents CHAPTER 1 What Is the Solar System CHAPTER 2 The Sun CHAPTER 3 Talking About Planets CHAPTER 4 Space Telescopes CHAPTER 5 New Discoveries CHAPTER 6 What’s Next ACTIVITY Your Space Science Mission Glossary Learning More Index and About the Author 4 8 18 28 34 40 44 46 47 48
4 CHAPTER 1 What is the Solar Sistem A solar system is a star and the A galaxy is a clump of billions of solar objects that travel around it systems Our Solar System is in the including planets asteroids and Milky Way galaxy This is a spiral-shaped comets Our Solar System centers on spiral-shaped galaxy that contains several the Sun The Sun's gravity a force that hundred billion stars including our attracts objects holds Earth and other Sun The Milky Way is about 100,000 planets and objects in orbit around it light years across A light year is the Some planets are orbited by moons distance light travels in a year which is Mercury is the closest planet to the around 5 9 trillion miles 9 5 trillion km Sun One of the most distant objects is On a dark night you can sometimes see Sedna It is not classified as a planet the Milky Way as a thick band of stars It is one of the many objects in the in the sky Our Solar System is in one of outer reaches of our Solar System the galaxy's four spiral arms Neptune Uranus Saturn Jupiter Mars Earth Venus Mercury This artwork shows the order of the planets in our Solar System in relation to the Sun
In a galaxy such as the Milky Way stars and their solar systems are bunched in long arms that form a flat spiral shape Many stars have planets circling around them There could be billions of other planets in the Milky Way alone Some solar systems possess more than one star Binary star systems have two stars Multi-star systems have three or more stars in one solar system Chasing Space In the United States the National Aeronautics and Space Administration NASA improves our understanding of the Solar System by exploring the planets their moons and small bodies such as comets Its research seeks to learn about the origin or beginning and history of our Solar System NASA scientists are also looking out for the possibility that life exists elsewhere in space The 2018 Global Exploration Roadmap is a document that shows the plan of 14 space agencies that have come together with a common goal to expand human presence in our Solar System The plan starts with missions to the International Space Station ISS which orbits Earth then advances to the Moon and then to Mars Cooperation between the agencies will be the key to success 5
