2 . It took humans thousands of years to understand our own planet, and centuries _______ our neighboring planets. Nowadays, new worlds are being _______ every week.

Up to the present time, astronomers have _______ more than 370 “exoplanets”—planets orbiting (绕……运动) outer space stars (恒星) other than our sun. There is a “hot Saturn (土星)” 260 light-years from Earth that orbits its parent star so _______ that a year there lasts less than three days. _______ another star 150 light-years out is a burning “hot Jupiter (木星),” where upper atmosphere (大气层) is being burning to form a huge comet-like tail. Astronomers have found another three _______ orbiting a pulsar (脉冲星)—the remains of a once huge star shrinking (收缩) into a small atomic nucleus the _______ of a city. Some planets have obviously fallen into their suns. Others have been thrown out of their _______ to become “floaters” that float in the darkness of the universe.

Among all these, scientists are eager to find a clue of the _______: planets like the Earth. That is, planets orbiting their stars at just the right distance—neither too hot nor too cold—to ________ life as we know it. We have not yet found planets that are quite like our own, ________ because they’re inconspicuous (不起眼的). To see a planet as ________ and slim as ours among the brightness of its star is like trying to see a firefly in a fireworks display.   ________ by pushing technology to the ________, astronomers are rapidly approaching the day when they can find another Earth. And when they do, they can examine it for ________ of life.

4 . A new study focuses on K2-18b, an exoplanet(系外行星) discovered in 2018, which orbits a red dwarf star close enough to receive about the same amount of radiation from its star as Earth does from our sun.

Recently, scientists have discovered gas giants that have water in their atmospheres, but this is the least giant planet ever to have water detected in its atmosphere. “The water detection was quite clear to us relatively early on,” lead author Bjorn Benneke, a professor at the Institute for Research on Exoplanets at the Universite de Montreal, told Space.com in an interview.

“Studies have suggested that planets with hydrogen-rich atmospheres could host certain forms of life.” Benneke said. However, “K2-18b’s large atmosphere is extremely thick and creates high-pressure conditions, which likely prevents life as we know it from existing on the planet’s surface.” a news release reads. While these researchers found evidence for liquid water clouds on K2-18b, because of its lack of surface, rain wouldn’t pool on the planet. Without a real surface, so to speak, landing on the planet would also be nearly impossible to land on, especially because the gas is so thick and has such an incredibly high pressure that any Earth-created spacecraft sent there would be destroyed.

Benneke suggests that, possibly, this planet formed by rock absorbing large amounts of gas, “like a vacuum cleaner,” he said. The gas absorbed would have more than doubled the planet and increased its volume Warren eightfood.

To come to these conclusions, the research team analyzed data from Hubble Space Telescope observations that they made between 2019 and 2020 of the K2-18b planet passing in front of its star eight times. This type of research, Benneke said, is leading toward a final goal of “being able to study real, true earth-like planets.” We are not quite there yet, he said, but this is really exciting.”

Three Chinese astronauts recently arrived at the Country’s new space station in another step forward for the growing space power. The three-member crew will stay for three months in the station's main living space    1     (call) a module. The module is named Tianhe,     2     means “Harmony of the Heavens” in Chinese. The astronauts will carry out science experiments and perform maintenance. They also plan to complete space walks and prepare the station     3     (receive) two other modules next year.

Up to now, China     4    (send) 14 astronauts into space since its first launch in 2003. It is the     5    (three) country after the former Soviet Union and the United States to do so. As its economy experienced     6    (grow) in the 1990s, China made a plan for space exploration. Since then, it has attempted to carry out this plan carefully and     7    (steady).

China was banned from drawing the ISS. It's likely, however,     8     China would have built on its own station anyway because of its goal to become a major space power. The building and operation of the space station will raise the level of Chinese technologies and will accumulate experience for all the people. China's space program has been     9     larger part of its national pride. It represents the country's rise from a poor nation to     10    (become) the world’s second -largest economy in the last 40 years.

7 . One of the biggest barriers to a manned mission to Mars is the fuel problem. If future Mars explorers ever want to return to Earth, they’ll not only need enough fuel to get to Mars, but also enough to get back home. And fuel is heavy. If the plan is to pack it from Earth for the whole journey, then that adds a lot of weight to the aircraft. It’s a difficult problem.

Now, in a new plan outlined in an article by a NASA team leader Kurt Leucht, the dream of making fuel right on Mars itself appears to be a real possibility. And the only raw material needed to make the rocket fuel? Martian soil.

The NASA team calls the method “in situ resource utilization”, or ISRU. It involves extracting（提炼）water from Mars’ distinctive red-colored dirt and using a process called electrolysis（电解）to separate water into hydrogen and oxygen. The hydrogen can then be combined with carbon, which is plentiful in Mars’ atmosphere, to make methane, which can be used as rocket fuel.

Of course, all of this requires time and an on-site factory that’s up to the task. For that, NASA is developing a team of robots that can be set up on Mars years in advance of a return trip to Earth, which will tirelessly work to manufacture the rocket fuel.

The whole plan does have one small challenge. Namely, it depends on the water content of Martian soil. If we start digging and there’s no water, or far less of it than expected, that could be a problem. But scientists are becoming increasingly confident that Mars’ soil actually has a fair amount of water locked into it, which is also enough for the survival needs of astronauts who plan to stay a while on the Red Planet.

“This technology will one day allow humans to live and work on Mars,” wrote Leucht, “and return to Earth to tell the story.”

8 . Edmund Halley was an English scientist who lived over 200 years ago. He studied the observations of comets which other scientists had made. The orbit of one particular comet was a very difficult mathematical problem. He could not figure it out. Neither could other scientists who dealt with such problems.

However, Halley had a friend named Newton, who was a brilliant mathematician. Newton thought he had already worked out that problem, but he could not find the papers on which he had done it. He told Halley that the orbit of a comet had the shape of an ellipse.

Now Halley set to work. He figured out the orbits of some of the comets that had been observed by scientists. He made a surprising discovery. The comets that had appeared in the years 1531, 1607, and 1682 all had the same orbit. Yet their appearances had been 75 to 76 years apart.

This seemed very strange to Halley. The different comets followed the same orbit. The more Halley thought about it, the more he thought that there had not been three different comets, as people thought. He decided that they had simply seen the same comet three times. The comet had gone away and had come back again.

It was an astonishing idea! Halley felt certain enough to make a prediction of what comet would happen in the future. He decided that this comet would appear in the year 1758. There were 53 years to go before Halley’s prediction could be tested. In 1758 the comet appeared in the sky. Halley did not see it, for he had died some years before. Ever since then that comet has been called Halley’s comet, in his honor.

9 . “We are running out of space and the only places to go to are other worlds.... Spreading out may be the only thing that saves us from ourselves. I am convinced that humans need to leave Earth.” These are the words of the famous scientist Stephen Hawking, spoken at a science festival in Norway in 2017, a year before his death.

Hawking was not alone in this view. Many experts feel that the only way for humanity to last far into the future is to colonize （移民） other planets. That way, if an asteroid （小行星）, a terrible disease, nuclear war, or some other disaster strikes Earth, civilization would still have a chance. Mars is one of the ideal destinations. NASA, SpaceX, and Mars One all have plans to send humans there. “Either we spread Earth to other planets, or we risk going extinct,” SpaceX founder Elon Musk said at a conference in 2013.

But not everyone agrees that colonizing Mars or any other planet is such a great plan. The most common argument against going is that it’s just too expensive or dangerous. It will take huge amounts of money and other resources just to get people there, let alone set up a place for them to live. It’s not even clear if humans could survive on Mars.

Maybe all the time and money people would pour into a Mars mission would be better spent on more urgent projects here on Earth, like dealing with poverty or climate change. Some experts argue that handling a problem like an asteroid strike or disease outbreak while staying here on Earth would be much easier and less expensive than surviving on a new planet.

In addition, moving to a new planet could harm or destroy anything that already lives there. Human visitors change or damage the Martian environment. Some feel that’s too much of a risk to take.