102 lines
5.3 KiB
Plaintext
102 lines
5.3 KiB
Plaintext
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SUBJECT: GREAT BALLS OF STEAM FILE: UFO3118
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** Courtesy of David Bloomberg **
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========================================================================
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GREAT BALLS OF STEAM
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by Carl Zimmer
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Source: Discover Magazine, July 1993
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David Turner does mostly bread-and-butter chemistry. The University of
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Bristol researcher is an expert on steam turbines, and he can, among other
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things, describe the conditions inside nuclear reactor turbines and the
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possible hazards of an explosion. But recently Turner realized that his
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work could help solve a more exotic puzzle. The peculiar chemistry of steam
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could help explain a strange weather phenomenon known as ball lightning.
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Over the past 200 years there have been thousands of reports of people
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seeing these globes of light. The glowing grapefruit-size spheres seem
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almost alive, floating down the aisles of passenger planes, gliding down
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chimneys, dodging objects in their path. When ball lightning passes close
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to people, they claim not to feel any heat, and yet apparently it can
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melt a hole in a glass window. It lives for a few seconds or minutes and
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then either fades away or explodes.
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Many explanations have been advanced for ball lightning, including some
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from the esoteric frontiers of science. Perhaps a nugget of antimatter
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lies at the heart of ball lightning, some researchers have suggested, or a
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magnetic monopole-a particle predicted by theoretical physics but never
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seen. Or perhaps a lightning ball is a natural nuclear fusion reactor whose
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energy we could somehow harness. But the most popular theory of late has
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been the tamest one; it holds that ball lightning arises from unusual con-
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ditions in the same thunderstorms that create ordinary lightning bolts.
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In a thunderstorm, an intense electric field between the positively charged
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ground and the negatively charged cloud excites air molecules, causing them
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to lose eIectrons and become charged ions. A bolt of lightning further
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energizes the molecules until they become a plasma- a soup of hot, charged
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molecules and electrons. Perhaps, researchers have suggested, the
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electric or magnetic field created by a small lump of plasma could trap
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it in the shape of a ball. Short-lived plasma fireballs have even been
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created in laboratory experiments, giving the idea some support.
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Yet the plasma model has its drawbacks. A hot ball of gas shouldn't keep
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close to the ground the way ball lightning does; it should rise like a he-
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lium balloon, quickly dissipating its heat until it vanishes.
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What's more, the reports that ball lightning has a cool surface make no
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sense at all if it is a fireball.
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But those reports, Turner says-indeed, all the commonly reported traits
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of ball lightning-fit nicely into the new model he has proposed. In
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Turner's model, ball lightning is a reactor, but not a fusion reactor. It
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is a floating, self-sustaining chemical reactor, in which certain
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chemical reactions between the plasma and the surrounding air release heat
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and others absorb it. As a result, instead of simply dissipating into the
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air, the initial heat of the plasma gets recycled back into the blazing
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interior of the ball, while the outside of the ball becomes a cool, wa-
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tery skin.
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The ions making up the plasma, Turner says, fly around crazily, moving away
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from the core of the the ball. Certain reactive ions, such as oxygen or
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hydroxide (OH), combine almost immediately, forming stable compounds like
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water or ozone and shedding their energy as heat and light. But three
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kinds of ions are much more stable and don't combine so quickly. They are
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positively charged hydrogen and negatively charged nitrites (NO2) and
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nitrates (NO3). Their chemistry, in Turner's view, explains most of ball
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lightning's properties.
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Traveling farther from the hot core into cooler air, these three types of
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ions start attracting water molecuIes. (A water molecule has electric
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poles; the side of the molecule that has the two hydrogens attached is
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slightly positive, while the other side is negative.) As the water mole-
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cules huddle around the ions, they condense to form liquid droplets. They
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thereby surrender heat. Some of the nitrites-the least stable of the
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three ions-react with some of the hydrogen to form nitrous acid and
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release even more heat. These two reactions, condensation and combination,
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keep the interior of the ball lightning hot.
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But the formation of nitrous acid is also what gives the ball its cold
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skin. As nitrites travel farther from the core, the ones that still haven't
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turned into nitrous acid keep gathering more water. From his previous
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research into steam, Turner knew that swarms of water molecules can have
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strange effects. If a nitrite is surrounded by six or more water
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molecules, he calculates, it actually has to absorb energy from its sur-
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roundings in order to combine with a hydrogen ion and create nitrous acid;
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basically it needs the energy to push the water out of its way. Sucking in
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heat, the nitrites now chill their surroundings instead of heating them.
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Hence the cool skin.
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