5 . There are nearly 2,800 working satellites in space, which we depend on for technology we use every day, such as video calls, online maps, satellite TV, and weather tracking. Scientists use them to study space and learn more about our planet.

But there are many other satellites in orbit (轨道) that are no longer working. They're among the objects cluttering (使杂乱) up space. Some of these eventually fall back toward Earth, either landing or burning up in the atmosphere. But much of this space junk (垃圾) circles Earth for years. Space junk is a problem. Debris (残骸)   floating around Earth puts technology and future space tasks at risk. Experts are working on ways to solve it.

Orbital debris, a type of space junk, is any human-made object that has slopped working but continues to float around the Earth. This includes satellites that are no longer used and pieces of spacecraft, such as rocket stages. It has been a large problem since the 1960s.

Space junk also includes broken pieces of objects. These occur when satellites hit against things. They also result from an object crashing into an old rocket stage that still contains fuel, causing an explosion (爆炸) . There have been more than 250 space explosions since the 1960s. These tiny broken pieces can damage working satellites, which can affect research in space.

Companies all over the world are working to clean up the area surrounding our planet. A company based in Japan will test the method of using magnets (磁石) to collect space debris. Another mission is led by a company based in Switzerland. It plans to carry out a debris-removal spacecraft in 2025. The craft will get hold of a piece of an old rocket, slow it down, and move it back to Earth. Eventually, the debris will burn out like a shooting star.

Governments are trying to help too. Some are updating their country's space guidelines to limit the amount of debris created. Space is so large that the problem won't be solved by a single organization or a single country. We have to work on this together.

6 . China launched a large robotic spacecraft on Nov. 24, 2020 at the Wenchang Space Launch Center in South China's Hainan province, tasking it with landing on the moon and bringing back lunar samples, 44 years after the last time such substances were brought back to Earth.

If everything proceeds smoothly, about 2 kilograms of stones and soil will be collected and packed in a vacuum metal container. The entire mission is scheduled to last about 23 days, according to the China National Space Administration. Considering these highly sophisticated operations, Chang'e 5 will be more difficult and challenging than previous Chinese lunar expeditions, designers have said.

According to a statement published by the space administration, the Chang'e 5 mission is intended to fulfill several objectives. In terms of space engineering, it will demonstrate technical plans and apparatus for autonomous lunar sampling and packing and moon-based launching, as well as lunar orbital docking. In the scientific field, it will investigate the landing site's features, and enable scientists to analyze the lunar samples' structure and physical traits so they can deepen their research into the moon's origin and evolution. It added that the mission also will help to foster the country's knowledge, technology and talent pool for its future manned missions to the moon and other deepspace expeditions.

Pei Zhaoyu, spokesman for the Chang'e 5 mission, said if the mission becomes successful, it will be a milestone in the nation's lunar exploration and will show the world China's scientific, technological and engineering capabilities.

Furthermore, Chang'e 5 will strengthen the nation's status and influence in the international space community, pave the way for the country's future lunar expeditions and boost its space science, and will offer more opportunities to lunar researchers around the world. Scientists around the world are welcome to participate in the research related to the lunar samples brought back by the mission. China will publish a set of guidelines about the use and distribution of the samples after the mission.

7 . The universe is expanding faster than it used to, meaning it’s about a billion years younger than we thought, a new study by a Nobel Prize winner says.

At issue is a number called the Hubble constant, a calculation for how fast the universe is expanding. Some scientists call it the most important number in cosmology, the study of the origin and development of the universe.

Using NASAS Hubble Space Telescope, lohns Hopkings University astronomer Adam Riess concluded in this week’s Astrophysical Journal that the figure is 9% higher than the previous calculation, which was based on studying leftovers from the Big Bang.

The trouble is， Riess and others think both calculations are correct. Confused? That’s OK, so are the experts. They find the conflict so confusing that they are talking about coming up with “new physics”, incorporating (合作) perhaps some yet-to-be-discovered particle or other cosmic (宇宙) “fudge factors” like dark energy or dark matter

“Its looking more and more like were going to need something new to explain this,” said Reiss, who won the 2011 Nobel in physics.

NASA astrophysicist John Mather, another Nobel winner, said this leaves two obvious options, “1. We’re making mistakes we can’t find yet. 2. Nature has something we can’t find yet.”

Even with the discovery, life continues on Earth the way it always has. But to astrophysicists trying to get a handle on our place in this expanding universe, this is a cosmic concern. In fact, the universe is really mystical (神秘的). Scientists have done lots of study about it but there is still much they haven’t discovered.

8 . Many scientists today are convinced that life exists elsewhere in the universe---life probably much like that on our own planet. They reason in the following way.

As far as astronomers can determine, the entire universe is built of the same matter. They have no reason to doubt that matter obeys the same laws in every part of the universe. Therefore, it is reasonable to guess that other stars, with their own planets, were born in the same way as our own solar system. What we know of life on earth suggests that life will arise wherever the proper conditions exist.

Life requires the right amount and kind of atmosphere. This eliminates(除去) all those planets in the universe that are not about the same size and weight as the earth. A smaller planet would lose its atmosphere; a larger one would hold too much of it.

Life also requires a steady supply of heat and light. This eliminates double stars, or stars that flare up suddenly. Only single stars that are steady sources of heat and light like our sun would qualify.

Finally, life could evolve(进化) only if the planet is just the right distance from its sun. With a weaker sun than our own, the planet would have to be closer to it. With a stronger sun, it would have to be farther away.

If we suppose that every star in the universe has a family of planets, then how many planets might support life? First, eliminate those stars that are not like our sun. Next eliminate most of their planets; they are either too far from or too close to their suns. Then eliminate all those planets which are not the same size and weight as the earth. Finally, remember that the proper conditions do not necessarily mean that life actually does exist on a planet. It may not have begun yet, or it may have already died out.

This process of elimination seems to leave very few planets on which earthlike life might be found. However, even if life could exist on only one planet in a million, there are so many billions of planets that this would still leave a vast number on which life could exist.

The earth, the planet on     1     we are living, is the third planet from the sun. It came from the shrinking (收缩) of a vast cloud of dust and gas in outer space. Many scientist believe that the earth,   as well as the sun and the other planets in our solar system,     2     (form)   at least five billion years ago.   The earth is slightly flattened at the North and South Poles,     3     it would look like a perfect ball if you were far out in space.