Venus (金星) is close to the earth. It is the second planet from the sun. The earth is the third planet from the sun. Venus is similar (相似的) to the earth in size and mass (质量). It is often described as the earth’s “sister”.

Scientists have been learning about Venus for a long time. First they looked at Venus through telescopes (望远镜). But Venus is covered with thick clouds. Scientists could not see Venus well through the clouds. So they made guesses about it.

For a long time, scientists thought that Venus had water and plants. They thought Venus might have animals too. But they didn’t know for sure.

Then scientists found a way to learn more about Venus. In the 1960s, they began sending probes (航天探测器) to Venus. The probes flew through the thick clouds. They took pictures of Venus up close. They found out many things too. The probes sent the pictures and things they found out back to the scientists.

The scientists learned a lot from the probes. First they learned that most of their guesses were not right. And they learned that Venus is very hot.

After that, scientists knew they could not send people to Venus. But they still wanted to know more about it. So they sent new probes. These new probes took great pictures of the planet. The pictures showed that Venus has plains (平原) and mountains! And in some ways, Venus looks like the earth.

Hey! The people of the earth. Can you hear this radio message? Do not be afraid! We come in peace from another planet— and why not? We are your cousins. We are men, as you are. We have been here before.

You will see a huge spaceship, a few hours from now. We are flying towards the solar system (太阳系) almost as fast as this radio message. Your sun is already in sight. Our ancestors (祖先) and yours shared the sun ten million years ago. I’m sure you have forgotten your history while we have remembered ours.

Our ancestors lived on the Earth when dinosaurs were dying. Sadly, they could hardly save the beasts. Your planet was very warm then. Our ancestors believed it would make a nice home for them.

They were wrong. Though we were masters of space, we knew so little about the Earth.

For millions of summers — there were no winters in those ancient days — the Earth had rapid (飞速的) development. It took about thirty years to fly from one planet to another, so our ancestors seldom travelled in space. But they never felt lonely. They kept in touch with their relatives and friends on other planets. Three or four times every century, starships would call and bring them space news.

But two million years ago, the Earth began to change. The temperatures fell quickly. The ground was covered with snow and ice. At that time, however, our ancestors knew little about that. Those who had called the Earth their home believed there was just a strange disease spreading on the earth. The disease wouldn’t cause death to them, but it would bring much pain and do harm to men’s health.

Scientists think that there has been life on earth for millions of years. However, we haven’t found life on other planets yet. The earth is a planet and it goes around the sun. And there are seven other planets that also go around the sun. The sun and its planets are called the solar system. The solar system is a small part of the universe.

Scientists have launched many spaceships to explore other planets in the solar system. Some spaceships have gone beyond the solar system. However, no one has discovered any life in space yet.

Why has no one from other planets sent us a message? Have they tried to send information to us? With so many stars in space, are we alone, or is there life on other planets in space?