[meteorite-list] Lightning Balls Created In The Lab

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 11 Jan 2007 09:49:42 -0800 (PST)
Message-ID: <200701111749.JAA18481_at_zagami.jpl.nasa.gov>

http://www.newscientist.com/channel/fundamentals/mg19325863.500

Lightning balls created in the lab
Hazel Muir
New Scientist
10 January 2007

Ball lightning could soon lose its status as a mystery, now that a team
in Brazil has cooked up a simple recipe for making similar eerie orbs of
light in the lab, even getting them to bounce around for several
seconds. Watch a movie of the boucing balls here.
<http://www.espacociencia.pe.gov.br/multimidia.php>

Thousands of people have reported seeing ball lightning, a luminous
sphere that sometimes appears during thunderstorms. It is typically the
size of a grapefruit and lasts for a few seconds or minutes, sometimes
hovering, even bouncing along the ground.

One eyewitness saw a glowing ball burn through the screen door of a
house in Oregon, navigate down to the basement and wreck an old mangle,
while in another report, a similar orb bounced on a Russian teacher's
head more than 20 times before vanishing.

One theory suggests that ball lightning is a highly ionised blob of
plasma held together by its own magnetic fields, while an exotic
explanation claims the cause is mini black holes created in the big bang.

A more down-to-earth theory, proposed by John Abrahamson and James
Dinniss at the University of Canterbury in Christchurch, New Zealand, is
that ball lightning forms when lightning strikes soil, turning any
silica in the soil into pure silicon vapour. As the vapour cools, the
silicon condenses into a floating aerosol bound into a ball by charges
that gather on its surface, and it glows with the heat of silicon
recombining with oxygen.

To test this idea, a team led by Antonio Pavao and Gerson Paiva from the
Federal University of Pernambuco in Brazil took wafers of silicon just
350 micrometres thick, placed them between two electrodes and zapped
them with currents of up to 140 amps. Then over a couple of seconds,
they moved the electrodes slightly apart, creating an electrical arc
that vaporised the silicon.

The arc spat out glowing fragments of silicon but also, sometimes,
luminous orbs the size of ping-pong balls that persisted for up to 8
seconds. "The luminous balls seem to be alive," says Pavao. He says
their fuzzy surfaces emitted little jets that seemed to jerk them
forward or sideways, as well as smoke trails that formed spiral shapes,
suggesting the balls were spinning. From their blue-white or
orange-white colour, Pavao's team estimates that they have a temperature
of roughly 2000 kelvin. The balls were able to melt plastic, and one
even burned a hole in Paiva's jeans.

These are by far the longest-lived glowing balls ever made in the lab.
Earlier experiments using microwaves created luminous balls
but they disappeared milliseconds after the microwaves were switched off.

"The lifetimes of our fireballs are about a hundred or more times higher
than that obtained by microwaves," says Pavao, whose findings will
appear in Physical Review Letters. Abrahamson is thrilled. "It made my
year when I heard about it," he says. "The balls, although still small,
lasted long enough to come into the mainstream of observed natural ball
lightning."

Pavao's team is currently working out the chemical reactions involved in
the balls' formation, and experimenting with other materials that might
work too, including pure metals, alloys and sulphur compounds.

>From issue 2586 of New Scientist magazine, 10 January 2007, page 12
Received on Thu 11 Jan 2007 12:49:42 PM PST