We have seen lots of science fiction movies about aliens. 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, thought it could be dangerous to connect aliens. He said that the main purpose of aliens’ visiting 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.”

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.

Thousands of years ago, Chinese poet Qu Yuan wrote the poem Tianwen, meaning Quest for Heavenly Truth. He came up with a series of questions about the sky, stars, nature and the world around us. The poem showed his spirit of finding the truth.

Inspired (激励) by the great poet, China named its latest series of planetary exploration missions (行星探测任务) after the poem in 2020. The first one in the series — a Mars exploration mission — has been named Tianwen 1, the China National Space Administration (CNSA) said on April 24^th, 2020, China’s Space Day. This shows China’s wish to explore the universe.

China has made great progress in space exploration. In 1970, China sent its first man-made Earth satellite (卫星), becoming the fifth country in the world to send a man-made satellite independently. Since 2003, China has carried out six Shenzhou manned missions. China’s moon exploration missions — the Chang’e series — started in 2007. In December 2018, China became the first country to send the probe (探测器) Chang’e 4 to the moon’s far side.

The Tianwen series will follow the Shenzhou and Chang’e series and move further into space. The first step is to send a Mars probe this year, which will mean the start of China’s exploration of the red planet. The probe is planned to circle around, land on and explore Mars in one mission. If it succeeds, it will be the first to finish all of these tasks in one mission. The Long March 5 rocket will send the probe to Mars.

After this mission, China plans to visit Mars again in 2028, aiming to collect soil from the ground of the planet and bring it to Earth. Around 2030, China will explore Jupiter and several small planets.