【推荐1】The Long Goodbye to Saturn’s Rings

Of all the planets in our solar system, Saturn might be the prettiest. Those rings gleam in soft pinks, grays, and browns, shimmering in the darkness. But Saturn’s rings aren’t a permanent feature. In fact, they’re ________.

The rings are losing material every year. Incoming micrometeorites (微陨石) and the sun’s radiation disturb the small, dusty pieces of ring matter. The particles(微粒), suddenly transformed, start moving along those invisible paths. When the particles get too ________ to the top of Saturn’s atmosphere, gravity pulls them in, and they vaporize in the planet’s clouds.

Astronomers call this “ring rain,” and over time this and other phenomena will destroy the ________ element that, to us, makes Saturn, until nothing is left. Right now? “This is us looking at Saturn’s rings in their heyday (鼎盛时期),” James O’Donoghue, a planetary scientist at JAXA, Japan’s space agency, told me. A magnificent sight that, from our perspective, seems ________, but, on the grand scale of things, is momentary.

Saturn’s rings have impressed observers for centuries, ________ we got truly close to them for the first time in the early 1980s, when NASA’s Voyager spacecraft sped past during a grand tour of the outer planets. At the time, scientists ________ that the rings probably formed alongside Saturn about 4.6 billion years ago, when the solar system was young, noisy and full of life. Back then, with rocky objects flying around everywhere, a new planet could easily have ________ some, hung them around its middle, and let gravity flatten them.

But Voyager’s flyby suggested a ________ story. The observations captured the rings in greater detail than ever before, revealing that the system didn’t have as much ________ as researchers had predicted, which meant that they couldn’t be billions of years old.

Saturn’s ring system had seemed as ________ as the solar system itself; now it seemed that the rings didn’t exist along with dinosaurs. The solar system had ________ by then, so where would Saturn have gotten the raw material? Then in 2017, a NASA spacecraft called Cassini skimmed past Saturn’s rings, sending home as much information as possible, which ________ what the Voyager missions had observed, that the rings weren’t massive enough to be ancient.

The science community hasn’t come to a(n) ________ about the origin story of Saturn’s rings. But, if the rings are indeed cosmically young, scientists say that they probably formed when one of Saturn’s moons, itself quite old, drew too close and was smashed to bits. The moon was likely a small one; our own moon, O’Donoghue said, could be used to ________ thousands of ring systems like Saturn’s.

The story of Saturn’s rings is a reminder that the worlds of our solar system, however still and ________ they might look from here, are dynamic places, with dramatic histories of their own.

【推荐2】With billions of stars in our galaxy (银河系), many circled by planets, the chances are there should be advanced life capable of reaching out to us. Yet after decades of looking and listening, we have found ___________.

This apparent conflict is known as Fermi’s paradox- Some have used it to argue that the search for extraterrestrial(外星球的)intelligence (SETI) is sure to ___________ .

But a mathematical analysis of SETI searches done so far claims that the usual explanation for the paradox— that there is nobody out there—is ___________. Instead, it suggests the best explanation is simply that we have barely scratched the surface in our ___________ for extraterrestrial intelligence.

Jason Wright at Pennsylvania State University and his colleagues analysed the many variables involved in SETI, which involves searching for radio signals from other ___________ . These include what to look for, where to look, how often and for how long. They then devised an equation that computes the ___________ of the galaxy checked so far. The team says that the volume of the galaxy that has been checked by SETI so far is roughly___________ to just a single bathtub of water in the world’s oceans.

“You don’t have to do a calculation to say we’ve only just ___________ ,” says Duncan Forgan at the University of St Andrews, UK, who is a member of the UK SETI research network. ”But they’ve done a nice job of showing the huge scale of the problem___________.“

As well as putting SETI in context, the equation can help researchers see which search techniques have been used less than others. ____________ , we only developed the technology to listen for higher radio frequencies quite recently. ”But we’re getting better at that, so that variable will now shrink,“ says Forgan.

However, advances in ____________ will only take us so far. Certain variables, such as how often a message from space might be repeated, cannot be____________. A signal sent once a year can only be listened out for once a year. ”There are things we can do better and things we can’t,” says Forgan. “We just have to ____________ and wait for the universe to do its thing.”

Forgan has a book coming out that discusses 66 potential ____________ for Fermi’s paradox. They include the possibility that Earth is somehow unusual in its ability to harbour intelligent life or that technological civilisations are rare. Or perhaps they are ____________ but short-lived. “Genetic or nuclear disasters might wipe you out,” says Forgan.

【推荐3】COVID-19 lockdowns had strange effects on air pollution across the globe

Ever since the covid-19 spread, many changes have come with the _____________ unstoppable virus. China has shown the first sign. Rightly after a strict nationwide lockdown was _____________ in late January, most people were restricted from leaving their homes at all for as long as 3 weeks. As a result, the authority ___________ a sharp decline in the direct emissions of air pollution on a scale never observed before. “Changes in emissions would be significant and ___________ studying for it may bring us new solutions to greenhouse effect,” says Jiset Deew, a chemist at the Harvard University, “The pandemic has caused lots of tragedies, but the lesson we can learn is important.”

Researchers found it a strange but ___________ chance to capture how human economic activity—particularly car traffic—dropped rapidly and thus to seek for the answer to the influence of ___________ traffic on air quality. “Running atmospheric chemistry experiments is often a ___________ task based on the lack of experimental conditions, so we have to _________ really complex reaction chambers and computer models,” says Tg, who now works on the project _____________ organic aerosols at MIT. “But in this unprecedented year, we finally get the chance to __________ our ideas and we hope the new findings will further our understanding of the mechanisms that rule atmospheric chemistry but also offer guidance for policy makers who seek to improve air quality and ____________ climate change.”

During the lockdown, passenger traffic plumbed, and traffic-related emissions—particularly CO₂ and NO₂—__________ accordingly. Vehicles powered by gas directly release huge amounts of CO₂ and NO₂. CO₂, a greenhouse gas, plays a major role in global warming. Besides, NO₂ plays a __________ part in atmospheric reactions that produce ozone which helps __________ UV light (紫外线). Now, experts are still working to __________ how the two gases changed during pandemic.