6 . A study confirmed that the cracks (裂缝) found on the surface of Mars last year by the Curiosity Rover are evidence of ancient lakes that likely dried up about 3.5 billion years ago. The new study provides further evidence of what the climate on the Red Planet may have been like in its ancient past.

The study, published online in Geology, proved that cracks on Mars’s surface previously photographed by Curiosity are dry mud cracks which could have only been formed when wet ground was exposed to the air. This conclusion was based on an analysis of a single area of rock known as “Old Soaker.”

Researchers used the Curiosity Rover and information from its many tools including the Mars Hand Lens Imager, ChemCam Laser-Induced Breakdown Spectrometer (LIBS) and the Alpha Particle X-Ray Spectrometer (APXS) to study both the physical appearance and the chemistry of the rock, which is described as no bigger than a coffee table.

The analysis showed that cracks on the rock were formed by exposure to air, rather than heat or the flow of water. In addition, the shape of the cracks suggests it experienced a single drying event on the planet, rather than getting wet and drying over repeatedly. The position of the cracks, closer to the center of the ancient lake rather than alongside it, also suggests that the lake levels changed often, rising and falling over time.

“The mud cracks are exciting because they help us to understand this ancient lake system,” lead study author Nathaniel Stein, a geologist at the California Institute of Technology in Pasadena, said, referring to the ancient lake system on the planet.

Scientists have known of the existence of ancient water on Mars for years. A 2015 NASA study that measured water in Mars’s atmosphere suggested that ancient oceans may once have had more water than our own Arctic Ocean. However, because the planet has less gravity and a thinner atmosphere than Earth, this water evaporated into space over the course of several billion years.

7 . 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.

8 . The company SpaceX has already launched hundreds of its Star-link satellites, with plans to put as many as 42,000 of them in Earth orbit. Its goal is to provide high-speed Internet to billions of people. Moving toward that kind of access is important, but it comes at a cost. Glittering with reflected sunlight, these first orbiters, sent up in the past year, are brighter than 99 percent of the 5,000 or so other satellites now circling Earth, and obviously there are going to be a lot more. This sudden increase is bad for astronomy: the probability of a Star-link satellite crossing a telescope’s field of view and ruining an observation will be quite high near sunset. For that reason, my fellow astronomers have signed a petition (请愿书) calling for governments to protect the night sky from this invasion.

In response to protests, SpaceX has promised to address the visibility problem by, for example, applying experimental coatings — essentially painting the satellites black — but the company’s aggressive launch schedule remains unchanged. And the satellites’ illuminated (被照亮) surfaces are mostly their solar panels — exactly the part that cannot be painted over.

Unfortunately, at present no regulations govern how bright a single satellite can be, let alone thousands of them together. Even if there were such regulations, one nation’s laws can not hinder (阻碍) another country’s launches. Space literally has no borders, and the sky will need to be protected at an international level. As a consequence, we hope that the United Nations will find a way to think outside of the box to save the sky for everyone.

When I was growing up in Montana, it was a game to be the first to find a moving satellite among the host of stars in the night sky. Soon it could be a game to recognize the constellations (星座) behind a swarm of moving points of light.

9 . 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.

China has become only the third country in the world to    1    (successful) collect rocks from the moon.

In the early hours of Thursday morning Beijing time, the country's unmanned Chang’e-5 mission returned to Earth     2    (carry) the country's first moon samples, according to Chinese state media outlet Xinhua.

The samples were brought back to earth from a previously unvisited area of the moon,    3    they are also the first samples    4    (collect) by any country since the 1790s.

The returning capsule landed in Siziwang Banner,    5    lies north of China's Inner Mongolia Autonomous Region, just before 2:00 a.m. Thursday Beijing time (1:00 p.m. ET Wednesday), according to China's National Space Administration (CNSA).

The probe,    6    (name) after the ancient Chinese goddess of the moon, first took off from the Wenchang Spacecraft Launch Site in Hainan on November 24.

It    7    (land) on the near side of the moon on December 1, on a massive lava plain known as Oceanus Procellarum, or “Ocean of Storms." According to NASA, this large dark spot could be a scar from a giant cosmic    8    (collide) that created an ancient sea of magma (岩浆).

The samples from this region could help scientists understand more about the moon's    9    (origin) and foundations — and set the foundation for more complex sample retrieval missions in the future, potentially    10    other planets.