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The Carletonian

Water, Water Everywhere

<aphene may be my favorite molecule, but for sheer pervasiveness, you can’t beat H2O. Water makes up 70 percent of our planet and up to 78 percent of our bodies, it makes life possible and sustains it—everyone has heard these platitudes dozens of times. This week, a lot of science stories dealt with one of the most essential molecules in our lives.

Let’s start with water in its solid form: ice. Though its form may be familiar, this H2O lives far from its expected environment—over 200,000 miles away, in fact. About a year ago, NASA sent a spent rocket plowing into the lunar crater Cabeus. When the rocket hit, it sent debris spraying into the air, debris that contained ice.

ecause the plume of moon-dirt did not produce any images in the visible spectrum (viewers who trained their telescopes on the moon in the hopes of seeing the impact were disappointed), scientists had to analyze it based on other factors. A spaceship followed the rocket, and collecting data as it fell through the churned-up debris to the moon’s surface. Meanwhile, a lunar orbiter recorded more information. This data allowed scientists to analyze the plume based on its ultraviolet and infrared spectra.

Long after the dust had settled to the lunar surface, scientists are finally publishing their findings. The lunar soil in Cabeus Crater contained about 5.6 percent water. One of the reasons that scientists sought ice here in the first place is that craters, with their high walls blocking out sunlight, can be significantly colder than the surface of their planet (temperatures in shadowed areas of the moon are closer to those on Pluto than on Earth), allowing ice to hide away from the sun.

Water’s not the only substance found in Cabeus. The measured spectra suggest that materials such as carbon dioxide and monoxide, nitrogen and sulfur, sodium and silver, and, unexpectedly, mercury. Although these materials don’t fire the imagination the way water’s presence does, they nonetheless allow us to understand lunar cold sinks much better.

As long as the ice and its chemical companions remain hidden from the sun, they manage to defy the moon’s typical dry composition. When water does go from solid to liquid, a fate the plume’s ice probably underwent when it reached the light of day, it can be as harmless as ice cubes melting in a glass of soda—or it can have significant consequences.

Back at the beginning of term, I wrote about the Arctic Sea ice shrinking. In addition, the ice was calving—when chunks break off of the larger mass of frozen ocean and drift away as floes or icebergs—with an unusually high frequency this summer. It turns out that these changes to the Arctic landscape may be permanent.

A total of 69 researchers contributed to a grim report: the Arctic is “unlikely” to return to its pre-warming state. They predict that the ice will continue to melt, triggering a trend in global weather. For example, the “snowpocalypse” that hit the Atlantic states during winter break last year owed part of its power to warming in the Arctic, which freed up cold air to drift south.

But depressing science news was the topic of last week’s column! To avoid repeating myself, let’s turn to a less grim topic. We’ve melted our ice, now let’s look at liquid water in a very particular situation, specifically, in a dog’s coat of fur.

This past summer, my family took our two dogs with us to the beach. Although the animals looked adorable running into the water (and dashing out as soon as a wave threatened), I quickly learned to avoid them when they emerged because otherwise, I would find myself covered with the salty spray they shook from their fur.

Researchers at the Georgia Institute of Technology decided to investigate this phenomenon. Mammals of all shapes and sizes, from mice to grizzly bears, shake their pelts with an oscillatory motion to dry off. If these warm-blooded animals couldn’t shake water out of their coats, they would have to dry it with body heat, which wastes precious caloric energy.

The efficiency with which they do so depends not only on the rate of shaking, but also on skin looseness and body size. Loose skin allows fur to wobble more and shake off more water than it could if the skin stuck tight to the body.

In order for the water to defy the surface tension that holds it to each hair, the animal must shake from side to side to generate sufficient centripetal force. Because centripetal force is greater for an animal with a larger “radius” (bigger body), the large beasts don’t have to shake as quickly as the small ones in order to fling the water free.

Scientists managed to mathematically model the motion of an animal shaking its fur dry, using physical principles like surface tension and centripetal force. It may not be the noblest application of physics, but it’s certainly cool and, if you’ve watched the video made by the scientists, utterly adorable.
Water is everywhere and, because of its power to support life, vital. Its presence is awe (and hope) inducing when we see it far out in space, threatening when we fear it will irrevocably change our world, and sometimes just plain fun. Now go watch a high-speed video of animals shaking themselves dry. Cute, huh?

-Sophie Bushwick is a Carletonian columnist.

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