Scientists have always wanted to know more about the universe.

Years ago, they knew many things about the moon. They knew how big it was and how far away it was from the Earth. But they wanted to know more about it. They thought the best way was to send men to the moon.

The moon is about 384,000 kilometers away from the Earth. A plane can not fly to the moon, because the air reaches only 240 kilometers away from the Earth. But something can fly even when there is no air. That is the rocket.

How does a rocket fly? There is gas (气体) in the rocket. When the gas is made very hot inside the rocket, it will rush out of the end of the rocket, so it can make the rocket fly up into the sky.

Rockets can fly out into the space. Rockets with men in them have been to the moon. Several satellites without men in them have flown to another planet much farther away than the moon. One day rockets may be able to go to any place in space.

Humans may live on another planet one day! That     1     (seem) impossible years ago. But now the idea may come true. According to Stephen Hawking, a British     2     (science), humans only have about 1,000 years to live on the earth. It means that humans     3     (fly) to another planet in 1,000 years. In fact, we have found one red planet Mars (火星). Experts have found that there     4     (be) water on it. The idea of living there looks possible. Thanks to science, the steps to Mars are getting     5     (fast) than before. For example, in 2013, Dutch experts     6     (plan) the first plan to put humans on Mars. They offered people one-way tickets to go and build a new home on Mars.     7     it was dangerous, over 200,000 people still wanted to take part in it.     8     the evening of September 21, US experts showed another plan to get humans to Mars in six years. They are also doing many     9     (prepare) to help people get back to the earth. I’m looking forward to     10     (live) on Mars. Will you join us?

The universe (宇宙) is so wide that we still don’t know much about it. It     1     the earth, the sun, the moon and the stars, and the space between them as well. Many of the stars can not be     2     because they are too far away. The moon travels around the earth. It’s our satellite. It’s the     3     to our earth. So far, humans have visited it already. And spaceships without people have reached other parts of the universe. Many countries have launched lots of man-made satellites into space. The satellites travel around the earth and help us     4     more about the earth, the weather and other things. They are used for     5     messages. With their help, TV and radio programs can be sent to countries all over the world. Satellites can also help us make telephone calls to foreign countries.

Our knowledge of the universe has been growing all the time.     6     space satellites (人造卫星), the world itself is becoming a much     7     place and people from different countries now understand each other better.

4 . Mars (火星) is a planet (行星). It is the fourth planet from the sun and is more than 200,000,000 kilometers from it. That is a very long way. Mars is also a very long way away from Earth but sometimes you can see it clearly at night. Most stars are white. But Mars is a little red. It is a very big planet. It is about half the size of Earth. The planet Earth has one moon. Mars has two moons. They are called Phobos and Deimos.

Long ago, the only way to study Mars was just to look at it. People with good eyes could see some things but not everything. Later on, it was easier, because scientists had telescopes (望远镜). They could see Mars come clearly. They learnt much more about Mars this way. In the twentieth century (世纪) things got even better. First of all, we had spacecraft. They flew close to Mars and sent back information. Then, they sent spacecraft to fly around Mars. Finally, spacecraft landed (着陆) on Mars.

Maybe one day a man will walk on Mars.

Scientists think that there has been life on the earth for hundreds of millions of years. However, we haven’t     1     life on any other planets yet.

The earth is a planet and it     2     around the sun. Seven other planets also go around the sun. None of them has an environment like that of the earth, so scientists do not     3     they will find life on them. The sun and its planets are called the solar system, and our solar system is a small part of a much larger group of stars and planets,     4     the Galaxy or the Milky Way. There     5     billions of stars in the Galaxy, and our sun is only one of them.

Scientists     6     many other galaxies in the universe already. They are very far away and their light     7     to travel for many years to reach us. So how large is the universe? It is impossible to imagine.

Scientists have sent spaceships to the planet Mars to take photos. They have even sent spaceships to travel outside the solar system . However, no spaceship has travelled far enough     8     other stars in our Galaxy. Scientists have always asked the questions: With so many stars in the universe, are we alone or is there life in space? Have there been visitors to the earth from other planets? Why has no one     9     with us? We     10     the answers yet.

9 . In the universe, as we all know, there is the sun, the moon, the earth and a good many stars. Through our geography lessons, we know the earth goes around the sun, and the moon goes around the earth. We have day and night because the earth keeps turning all the time. When our part of the earth turns to the sun, it is day. When our part of the earth turns away from the sun, it is night.

Just because the moon is closer to the earth than the sun, it looks much bigger than the sun. Big things will look smaller when they are farther, and small things also look bigger when they are nearer.

The sun is big enough to give out very strong light. The moon can’t give out any light at all, but it looks quite bright, too. Why? In fact, the light from the moon comes from the sun. The moon looks much bigger and brighter than the stars. But actually the stars are much bigger and brighter than the moon. They look smaller than the moon also because they are farther away from the earth. There are many other planets in the universe. But of all the planets, only on the earth are there living things and people can only live on the earth, too. But at 9:00 a.m., October 15th, 2003, the Chinese pilot Yang Liwei was sent up in to space. He stayed there for 21 hours. It was the first time for Chinese to get into space.

10 . Is there life on Mars (火星)? We don’t know. We are sure that people can not live on Mars. People can’t live without oxygen(氧气). There is little oxygen on Mars. Living on Mars would be like living on a very high mountain. There would be little air. It may be 50℃ at noon and -100℃ at night.

Many people think there may be plants on Mars. We know that Mars has carbon (二氧化碳). This is kind of material (物质) and we found it in all plants and animals on the earth. Mars looks red. In some places, it seems gray. Sometimes the gray color turns gray-green then brown, and then gray again. The gray-green color may be a kind of plant life changing color with seasons.

Will man go to Mars one day? If they do, they will have to take their own oxygen, food, clothing and shelter (住所) with them.