4 Life Out There

Unit 4 VOCABULARY 1 1 Listen and read. Earth is a planet that moves around the sun. Other planets also orbit the sun. The sun and planets make up our solar system. The sun is a star like the stars you see in the sky at night. Some stars have solar systems with planets, too. There may be another planet out there that has an atmosphere with oxygen to breathe. A star and the planets that orbit around it make up a solar system. Stars and solar systems make up a galaxy. Our galaxy is the Milky Way. It has about 100 billion stars. The Milky Way isn’t the only galaxy. There are more galaxies in the universe than there are stars in a galaxy! How many? We don’t know. There are too many to count, and many are too far away to see. A comet is a cloud of rock, ice, and gas that orbits the sun. Many earth years pass in its journey around the sun. Scientists keep data on comets to know when they will appear. Think of the many galaxies in the universe. Think of the many stars in each galaxy. Think of the many planets that orbit the stars. Do you think that extraterrestrials may live on one of the planets? Many people debate this question. an orbit a planet a comet space a galaxy 2 Listen and repeat. a planet Earth is a planet. orbit Earth orbits the sun. a solar system Earth is the third planet in our solar system. atmosphere The atmosphere on Earth lets us breathe and survive. a galaxy Our galaxy is called the Milky Way. the universe There are many galaxies in the universe. a comet A comet is made up of rock, ice, and gas. a journey A journey to another planet could take many years. data Scientists collect data on the universe. space There is no air in space. an extraterrestrial Some people think that extraterrestrials live on other planets. debate Scientists debate whether there is life on other planets.

SONG 1 Listen, read, and sing. Deep in Outer Space Let’s all take a journey past the atmosphere, beyond our solar system, far away from here. We might find a new planet. We might find a new place. We might find things we’ve never seen deep in outer space. Deep in outer space, who knows what we might find? Deep in outer space, deep in outer space! Somewhere in the universe we might find a moon where flowers grow. You never know, but I wish we’d get there soon! Deep in outer space, who knows what we might find? Deep in outer space, deep in outer space! But right here on planet Earth life is all around. Our world is full of color, texture, light, and sound. We can take a journey right outside our door and see the wonder of life on Earth and so much more! Deep in outer space, who knows what we might find? Deep in outer space, deep in outer space! Deep in outer space.

GRAMMAR 1 May and might If a planet has an atmosphere, it may have life. Do you think astronauts might go to the moon again? There might be life on other planets. Yes, but it may be very simple life.

VOCABULARY 2 1 Listen and repeat. a rocket A rocket has enough power to reach space. a spacecraft A spacecraft has traveled to the moon. an astronaut An astronaut travels in space. a space station A space station orbits the Earth. search The search for life on other planets is important. communicate Astronauts communicate with Mission Control for directions. 2 Listen and stick. Work with a partner. Take turns describing the rocket liftoff. Ready to begin the liftoff! Mission control is about to start the count down. Start the engines! They have started the rockets. 10, 9, 8 . . . The rockets are burning. They will soon lift the spacecraft from Earth. . . . 4, 3, 2, 1. We have liftoff! The spacecraft is moving! And the two astronauts are leaving Earth! Can you imagine the excitement for those two astronauts? It’s not their first time in space. Both astronauts lived on the space station for four months. They returned to Earth from the space station just one year ago. Soon Mission Control will be able to communicate with them. They can’t communicate during liftoff. After orbiting the Earth, the ship will land on the moon. GRAMMAR 2 Indefinite pronouns Did everyone see that comet? Does anyone want to be an astronaut? Someone will go to Mars one day. No one can see all the stars in the universe.

READING 1 Listen and read. Listening for Life If extraterrestrials live on other planets, we can’t see them. Planets in other solar systems are extremely far away. We can’t see the planets, even with our biggest telescopes. But what if the extraterrestrials want to communicate with us? What if they are sending messages? This signal would travel through space. After many years, it might reach our solar system. It would be hidden in the noise from other places in space. We would need special tools to hear it. Scientists at SETI (Search for Extraterrestrial Intelligence) have made a tool for listening. It uses 42 satellite dishes that are connected together. Scientists plan to have 350 dishes one day. They point all the dishes at the same place in the sky. Then they search for any data they can hear. The dishes can hear very weak signals. For example, they could hear a cell phone on a planet in our solar system. (That’s if someone had a cell phone on Jupiter!) The dishes pick up noise from radios on Earth, too. Scientists must be careful to avoid this noise. We have not heard from an extraterrestrial yet. But is it possible that they are listening to us? If they are, most could not have heard us yet. We have used radios for less than 100 years. That’s not much time for the big distances in the universe. In that time, our signal could only reach a small number of stars. Extraterrestrials from nearby solar systems would not hear us for thousands of years.