고등학교 영어Ⅰ (YBM 박준언) 연계 글

Tardigrades, also known as water bears, are tiny animals that live in damp moss, in soil, and in the drops of water that cling to moist plants. Most are shorter than a millimeter, and under a microscope one moves on eight stubby legs as if it were a bear cub in slow motion. Their homes often dry out, and most living things die once they lose half of their body water, but tardigrades do not.

Open space, however, is far harsher than any dry pond. Its vacuum draws water out of cells almost completely, and radiation from the Sun strikes them without the protection that Earth's air provides. Knowing how well tardigrades endure drying, a team of Swedish and German scientists wondered whether the animals could survive in space as well. In September 2007, the team sent about three thousand dried tardigrades of two species into orbit for an experiment called TARDIS, short for "Tardigrades in Space." The animals flew on a twelve-day mission of the European Space Agency and spent ten of those days exposed to open space about 270 kilometers above Earth. Some faced the vacuum alone, while others also received different ranges of solar ultraviolet light.

After the mission, the researchers added water to the dried animals to see which of them would revive. Those that had faced only the vacuum recovered just as well as the tardigrades kept on the ground did. Would the animals that received sunlight recover too? Well over half of those given only part of the solar ultraviolet range did. Some of them died later, but the rest fed and laid eggs that hatched into normal young. Of the animals left under the Sun's full ultraviolet light, by contrast, most died, and just a handful from one species revived. Even so, those few made tardigrades the first animals known to survive both the vacuum and the radiation of open space.

Their secret is a skill they also use on Earth. When a tardigrade's home dries out, the animal tucks in its legs, shrinks into a barrel-shaped form called a tun, and gives up nearly all of its water. Its metabolism then almost stops, so the animal looks as if it were dead, yet a little water can bring it back to active life. It would be an exaggeration, however, to speak of tardigrades as if they were unbreakable: a dried body resists the vacuum far better than it resists strong ultraviolet light.