Nowadays, many astronomers (天文学家) are looking for new planets and new places for humans to live in the future. But where do astronomers start exploring (探索)?

First of all, astronomers look for a star. That’s because our own Earth moves around a star—the Sun. More importantly, it is neither too far from nor too near to the Sun for heat and light. So when astronomers have found the star, they look at the planets around it. In recent years, astronomers have found nearly 400 new planets with stars. Many of these planets are either too near to the star or too far away.

However, if the planet is in a good place, astronomers look for three key things: water, air and rock (岩石). Water is the most important because all life needs water. Humans can drink it and they can also grow plants with water. And plants produce air for humans to breathe (呼吸) and food to eat. Rock on a planet is also important. That’s because there is often water under the rock.

After many years of exploring, astronomers have found a planet like the Earth. It’s Gliese 581 g and it’s near a star. The astronomers think it has water and rock and the temperature is between -31℃ and -12℃. That’s cold, but not colder than Antarctica or the Arctic Circle. A year on Gliese 581 g is only 37 Earth days, not 365 Earth days. But astronomers do not think these are big differences and some of them think Gliese 581 g will be a new Earth.

Do you know anything about the Moon? How much do you know about it?

【小题1】 Scientists have told us so much about the Moon. So it’s easy for us to have the idea of going to the Moon. But what would it be like to really go there?

The Moon is an unfriendly place. There is no air or water. There are only lots of dust and mountains around on it. 【小题2】 The temperature of the Moon is different from day to night. 【小题3】 However, it’s very cold at night.

【小题4】 As we know, sound can only travel in the air but there is no air on the Moon. So people can’t hear any sounds on it.

But from the Moon, you can see our beautiful Earth. It is shining more brightly than the other stars in the dark. 【小题5】 The photos would be wonderful.

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.