中央大学
理工学部

In February 2021, three new spacecraft arrived independently at Mars. For two of them, it was the first time their countries had sent craft so deeply into space, while the third opened a new period of Mars exploration. The first was the UAE's Mars Mission, also known as Hope, which entered *orbit on 9 February. Shortly after, China's Tianwen-1 spacecraft reached the planet with a plan to send a *rover down to its surface.

Both of these missions were extraordinary achievements for their countries, allowing their makers to join the U.S., Russia, Europe, and India in having successfully sent spacecraft to Mars. However, it was the third mission that captured the most headlines.

On 18 February, NASA landed the car-sized rover Perseverance onto the surface of Mars. It had a long list of scientific objectives to work through. "We want to get a fuller understanding of how Mars formed as a planet," says Sanjeev Gupta, a member of the Perseverance science team. On Earth, the constant movement of the *crust has mostly destroyed the very first surface rocks to form, but on Mars the oldest rocks are [ 1 ], so there is an unbroken record stretching back more than four billion years. As well as telling us about the history of the planet's formation, those ancient rocks could also contain clues as to whether life ever started on the red planet.

Yet what makes the Perseverance mission unique is that it is also the first part of an ambitious 10-year plan between NASA and the European Space Agency to bring *Martian rocks to Earth in around 2031. "Scientists really want rocks from Mars back on Earth," says Gupta. Samples can be analyzed much more carefully on Earth than using even the most advanced Mars vehicle. And because laboratory techniques improve constantly, (ア)they can continue to be examined year after year for new discoveries.

The [ 2 ] of returning samples to Earth was demonstrated in the 1970s when the analysis of moon rocks brought back by the Apollo astronauts changed our understanding of the solar system's history and formation.

To repeat this success for Mars, Perseverance is equipped with more than 30 containers into which interesting-looking rocks will be loaded. In accordance with the joint project between NASA and the European Space Agency, a European rover will arrive on Mars in 2028 to collect the containers. It will load them into a NASA spacecraft known as the Mars Ascent Vehicle, which will carry them to a European craft called the Earth Return Orbiter that will bring the samples to Earth.

[ 3 ] the moon samples of the 1970s were from a lifeless world, Mars could once have been a *habitable planet. So key investigations will involve looking for evidence of past — or possibly present — life, and that produces a whole new problem. "If you discover signs of life on Mars, you want to know that it's Martian life, right? You don't want to discover bacteria that accidentally came with you on your spacecraft," says Casey Dreier, a space policy adviser.

To keep the scientific results as pure as possible, spacecraft and equipment are cleaned with chemicals or by heating. Such measures are known as planetary protection, which is split into two parts. Forward *contamination is the introduction of Earth life on to other worlds; backwards contamination is concerned with the possibility, however unlikely, of alien life being brought back to Earth and escaping into the open.

The issue of planetary protection was originally discussed in the 1950s when the first satellites were launched into orbit around Earth. But the story changed in 1971 when Mariner 9 became the first spacecraft to enter orbit around Mars. The pictures (イ)it sent back disappointed many people. There was no vegetation and no visible signs of life. Indeed, there was not even an indication of past life. "People were surprised at just how dead Mars actually turned out to look," says space lecturer Thomas Cheney.

Closer investigation in more recent decades, however, has swung opinions back again. It is now thought that Mars could have been habitable and that tiny bacteria may still be surviving in parts of the planet where liquid water is present. Planetary protection means spacecraft cannot go into (ウ)these areas. So life-detection experiments cannot investigate the areas most likely to support life and must concentrate, therefore, on looking for evidence of past life on Mars.

There is also concern about repeating the mistakes people made in terms of exploration on Earth in the past. The European colonization of Hawaii, for example, introduced various bacteria to the island that had not existed there previously, killing a large number of the native people with diseases (エ)they had no natural protection against. While there is no real chance of animal life on Mars, some scientists think that the same concerns should apply to bacteria. "If there's life there, we don't want to accidentally introduce an organism that destroys it," argues Cheney. This is particularly significant with NASA's plan to send people to Mars and eventually set up a human colony.

Not everyone agrees, however, that planetary protection rules should be [ 4 ]. Robert Zubrin, a strong supporter of sending humans to Mars, points out that *meteorites regularly crash into Earth from outer space. One Martian meteorite in particular, ALH84001, attracted great interest in 1996 when a group of scientists claimed to have found fossils of Martian bacteria inside. Although that conclusion is still hotly debated, the analysis showed that the meteorite had never been exposed to temperatures above 40 degrees Celsius. "If there had been bacteria in it, they could have survived the trip," says Zubrin, "and billions of tons of such material have transferred from Mars to Earth in the last four billion years." In other words, if nature does not respect planetary protection rules, why should we?

It feels good to recycle. When you sort soda bottles and plastic bags from the rest of your garbage, it seems like you're helping the planet. The more plastic you put in the unburnable bin, the more you're keeping out of landfills, right? Wrong. [ 1 ] how much plastic you try to recycle, most ends up in the trash. Take food packages. Those packages contain several layers, each constructed of a different type of plastic. Because each type is different, these packages are not recyclable. Even some items made from only one kind of plastic are not recyclable. Yogurt cups, for instance, contain a plastic called polypropylene. When this gets recycled, it turns into a dark and smelly material. [ 2 ], most recycling plants don't do anything with it.

Only two kinds of plastic are commonly recycled. One is the type used in soda bottles, known as PET, and [ 3 ] is the plastic in soap containers. Together, those plastics [ 4 ] only a small fraction of plastic trash. What this means is that only 9 percent of all the world's plastic trash is recycled. Almost 12 percent is burned, while the remaining 79 percent piles up on land or sea. [ 5 ].

To: Richard Landon, Hinkerton Retail Ltd
From: Peter Girton
Subject: Retail Times advertisement

Dear Mr. Landon,

I am writing to apply for the position of marketing manager that was advertised in Retail Times magazine on October 14th.

I have over twenty years' experience in the supermarket industry, having worked for Kallmart Holdings, Fresco Supermarkets and, most recently, the Balmoral Group. At the Balmoral Group, I served as the assistant manager of the marketing department, where I was jointly [ 1 ] organizing the launch of all new products and services within the group. In 2018, I took charge of Balmoral's move into banking services, [ 2 ] a national advertising campaign that helped to beat predicted sales by over forty percent. The following year, I managed a project to gather data about the [ 3 ] new store layouts on customer behavior. The project made several recommendations that were put into operation in Balmoral stores nationwide.

I believe that with my strong professional background and hard work, I can make a positive contribution to your marketing team at Hinkerton Retail. Please find [ 4 ] my resumé, which provides further details of my qualifications and experience.

[ 5 ]. I look forward to hearing from you in due course.

Yours sincerely,
Peter Girton

In 1697 a man in France wrote to his cousin in the Netherlands to request an important certificate. He folded and sealed his letter so it would hold together without an envelope and mailed it off to his cousin. For some reason, it [ 1 ] and remains sealed today. Yet a team of historians and scientists have still read it — thanks to high-resolution imaging and a "virtual unfolding" algorithm.

The scanning-and-unfolding technique [ 2 ] of applications, from revealing text on historical documents too delicate to touch to understanding historical origami procedures. But the researchers behind the new study, published in Nature Communications, are most excited about using it to examine the art of "letterlocking." Letterlocking is a technique to carefully fold, cut, and seal letters so that they cannot be opened easily. This technique was used widely in the period before the invention of modern envelopes, which are also used to keep letters "locked" inside. Almost two decades ago it [ 3 ] of Jana Dambrogio, a researcher at Massachusetts Institute of Technology Libraries and a co-author of the new paper.

Dambrogio had noticed tiny cuts and folds, apparently done on purpose, in a number of historical documents and eventually guessed their purpose. "They [ 4 ], and security was my guess — that it was built in on purpose," she says. "The reaction for me was, 'Oh my gosh, we need to let people know not to remove this evidence, because the little tiny cuts and folds [ 5 ] of this security tradition that has not been deeply studied.'"

For the past seven years, she has collaborated in this quest with Daniel Starza Smith, a lecturer in early modern English literature at King's College London and a co-author of the paper. The two researchers and their team [ 6 ] more than 60 letterlocking methods. "Before 1850 there weren't really any such things as modern envelopes," Smith says. Paper [ 7 ] not to be wasted on a separate envelope. "So if you wanted to send a letter, you had to use letterlocking — the letter had to become its own envelope or sending device."