Except Pluto (冥王星), there 【小题1】 eight planets in the solar system now, including Earth. By the distance from the Sun from close to far, they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Pluto used to be known as 【小题2】 smallest planet in our solar system, and the furthest planet from the Sun.

Pluto was discovered in 1930, and was named by an eleven-year-old girl from England. Pluto is only half 【小题3】 wide as the United States. This planet takes 248 earth years to travel around the Sun. It means we need 6. 5 earth days to spend a day on Pluto. Pluto is about 40 times farther from the Sun than Earth is. Pluto is in an area of space called the Kuiper Belt 【小题4】 has thousands of small, icy objects. The temperature on Pluto is 【小题5】 low that Earth air would turn into ice soon. The gravity on Pluto is less stronger than that on Earth. So fat persons may prefer to move there, they would weigh much less on Pluto.

Scientists think that there has been life on the earth for millions 【小题1】 years. However, we 【小题2】 found life on any 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 【小题3】 planets are called the solar system. The solar system is a small part of the universe.

Scientists has 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 【小题4】.

Why has no one from other planets sent us a message? Have they tried 【小题5】 send information to us? With so many stars in space, are we alone, or is there life on other planets in space?

We see the sun every day. If it is 【小题1】（sun）, we can see the moon at night, too. The moon is near us. So far astronauts 【小题2】（visit） the moon several times. The moon is almost 【小题3】 nearest satellite（卫星） to the earth in space.

Light 【小题4】（travel）at 300,000 kilometers a second. Light reaches us from the moon in less than a second and a half. The moon is about 382,000 kilometers away.

Light from the sun arrives in the earth in about 8.5 【小题5】（minute）. The sun is about 149,640,000 kilometers away 【小题6】 the earth. Other stars are much 【小题7】（far） away than the sun. Light from the nearest star reaches 【小题8】（we）in about four years. When you look at a star, it is very small. 【小题9】 in fact many of them are much bigger than the sun. They look small only because they are 【小题10】（real） far away.