1 . We have seen lots of science fiction movies about aliens (外星人). People travel to stars and even fight with aliens in the movies. But are there real aliens in the universe (宇宙)? Most of us think it is impossible, just like fairy tales. But the answer of some scientists is yes. So they have been searching for aliens in outer space for many years. They hope to find life signs of aliens.

Some scientists are used to using radio telescopes (望远镜) to search for aliens in space. In order to find aliens, they have worked hard for over half a century, but so far they have found nothing. Then some scientists guessed aliens might not want to connect us, but aliens could answer our messages. So some scientists sent radio signals into the universe. They hope one day they would be picked up by alien technology. These scientists want to prove (证明) that we are not alone in the universe.

But what should we do if the “alien phone” rings one day? Should we answer it? Stephen Hawking, the famous physicist, thught it could be dangerous to connect aliens. He said that the main purpose of aliens’ visit to the earth could be searching for our resources (资源). But other scientists think we have no need to worry. David Morrison, a NASA scientist, said, “If an alien radio signal reaches the earth from a planet thousands of light-years away, then they almost surely have solved all the problems we still have including the short of resources. Maybe they are much smarter than us, but why do they want to hurt us? I think we can try to connect them.”

4 . The 2022 Winter Olympics were held successfully. Athletes across the world came to Beijing and Zhangjiakou. Winter sports need to be in cold places. So, is it possible to hold the Winter Olympics on other planets?

It’s the closest planet to the Sun. In the daytime, the temperature can be 430℃. At night it cools down to -200℃. There’s one area that the Sun can never reach. There’s lots of ice there. Maybe we could go speed skating there!

The temperature on Mars is between -140℃ and 30℃. At the north and south poles of Mars, there are areas covered by ice and snow. Some of the ice is made of carbon dioxide, not water. There is also a big mountain called Mount Olympus. So maybe we can ski on Mars!

Pluto is a dwarf planet(矮行星) far away from the Sun. It’s very cold there, about -229℃. There’s lots of ice. It’s even harder than steel(钢铁). So maybe we could go sledding(滑雪橇) on Pluto.

Is there intelligent (有智力的) life on other planets? For years, scientists said “no.” or “we don’t know.” But today this is changing. Seth Shostakovitch and Alexandra Barnett are astronomers (天文学家). They believe intelligent life exists (存在)     1     in the universe. They also think we sill soon contact these beings(人；生物).

Why do Shostakovitch and Barnett think intelligent life exists on other planets? The first     2     is time. Scientists believe the universe is about 12 billion years old. “This is     3     enough for other planets to have intelligent life,” says Shostakovitch and Barnett. The second reason is size—the universe is huge. “Tools like the Hubble Telescope (哈勃望远镜) have     4     that there are at least 100 billion galaxies,” says Shostakovitch. “And our galaxy, the Milky Way, has at least 100 billion stars. Some planets going around these stars might be     5     to Earth.”

In the past, it was hard to look for     6     of intelligent life in the universe. But now, powerful telescopes (高倍望远镜) allow scientists to     7     smaller planets—the size of Mars or Earth—in     8     solar systems. These planets might have intelligent life.

Have beings from space already visited Earth? “Probably not,” says Shostakovitch. “It’s a long way away. However, intelligent beings may contact us in other way, such as radio signals (信号). In fact, they may be trying to communicate with us now, but we don’t have the right tools to     9     their messages. However, this is changing. By 2025, we could make contact with other life     10     in our universe and we might help each other.”

6 . In the universe, there is the earth, the moon, the sun, the stars and all other things too far away ________. The earth is one of the sun’s planets（行星）, and the moon is our satellite. The moon is about three hundred and eighty thousand kilometers away ________ the earth, but it’s our ________ neighbour in space. It ________ more than three days to get there by spaceship. No man ________ farther than the moon, but spaceships ________ people have reached other planets.

Of ________ the stars, the sun is the nearest to the earth. ________ other stars are even bigger and brighter than the sun. They look small only ________ they are much farther away. You ________ see them in the daytime. But if you go out at night, you’ll be able to see many of them.

9 . Many people know that rubbish is a big problem on the planet Earth. What many people don’t know is that junk（垃圾）has become a problem in outer space too.

According to BBC News, there are more than 22, 000 pieces of space junk floating around the earth. And these are just the things that we can see from the surface of the earth by telescopes （望远镜）. There are also millions of smaller pieces of junk that we can’t see.

Objects, like bits of old space rockets（火箭）or satellites（卫星）, move around the planet at very high speed so fast that even a very small piece can break important satellites or become dangerous to astronauts. If the tiniest piece of junk crashed into a spaceship, it could damage （损害）the space tool.

To make things worse, when two objects in space crash, they break into many smaller pieces. For example, when a U.S. satellite hit an old Russian rocket in 2009, it broke into more than 2,000 pieces, increasing the amount of space junk.

To reduce additional （额外的）space junk, countries have agreed that all new space tools can only stay in space for 25 years at most. Each tool must be built to fall safely into the earth’s atmosphere （大气层）after that time. In the upper parts of the atmosphere, it will burn up.

Many scientists also suggest different ways to clean up space junk. In England, scientists are testing a special net that can be sent into space junk. The net catches the junk and then pulls it into the earth's atmosphere to burn up. The Germans are building robots that can collect pieces of space junk and bring them back to Earth to be safely dealt with.

“The problem is becoming more challenging because we’re sending more objects into space to help people use their mobile phones and computers,” says Marco Castronuovo, an Italian space researcher.

10 . As space science develops, man has learned more and more about space. Space is not only amazing but also dangerous. While working in space, spacemen are facing danger.

Scientists have found out that radiation (辐射) is the greatest danger to spacemen in space. When spacemen are working in space, they are in danger of radiation from the sun and other stars, which is bad for their health. The damage done by radiation won’t be discovered until their children or even grandchildren are born. Some special medicine may work a little, but no really helpful medicine has been found.

Space junk is also thought to be a great danger to spacemen. It’s reported that there are 9,000 man-made things flying in space. About 30% of these are man-made satellites (卫星), 10% are spaceships, and the rest are space junk. An explosion (爆炸) in 1999 made a cloud of 300,000 fragments , each at least 4mm in size, and even a small piece of these knocked against a spaceship window and did some damage. Scientists are watching and reporting any possible danger all the time. They are working on helpful ways to deal with space junk.

Although space is really dangerous, it interests everyone on the earth. In the near future, it may become usual for people to spend a few days in a space hotel. We may even choose to leave the earth and live in space in a few years. So we should care for space and do something to help improve the space environment.