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<div class="rich-text">(This video is no longer available for streaming.) What causes lightning? The mystery has confounded scientists for centuries, but researchers like Joe Dwyer are hot on the pursuit of an answer. At the International Center for Lightning Research and Testing in Florida, Dwyer and colleagues use rockets to lure down lightning bolts, the better to study them. And to test a hypothesis—that they're triggered by cosmic rays from outer space.
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Experts still aren't sure what triggers lightning, but they suspect cosmic rays from outer space.

<div class="rich-text">Experts still aren't sure what triggers lightning, but they suspect cosmic rays from outer space.</div>

Experts aren't sure what triggers lightning, but suspect cosmic rays from outer space.

Lightning

Planet Earth

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 Lightning
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 PBS air date: October 18, 2005



 ROBERT KRULWICH:
 
 By the way, maybe you've noticed, in the old
movies, when it's time to zap the monster on the table and bring it to life,
they always use lightning. I mean always. And why? Well, because lightning is
electrical. It turns things on. Though exactly what lightning does is left to
your imagination, because, in the end, what makes life, that's still a
mystery.


 But interestingly—and I didn't know this—it turns out that what
makes lightning is also still a mystery. In fact, it's kind of a big mystery.
Here's correspondent Chad Cohen



 CHAD COHEN
 
 (Correspondent): It's an elemental force of
nature and still one of the most mysterious.



 JOSEPH DWYER
 
 (Florida Institute of Technology): Lightning is very
difficult to study, and I think we probably understand better how a star
explodes halfway across the galaxy than how lightning propagates from six miles
up.



 CHAD COHEN:
 
 Lightning strikes the Earth 4,000,000 times a day.
And after hundreds of years of scientific scrutiny, we still do not understand
the essential secret of how it begins inside a storm. That's why Professors Ken
Eack and Richard Sonnenfeld and their team from New Mexico Tech are on a
10,000-foot mountain, waiting for lightning to strike.



 KENNETH EACK
 
 (New Mexico Institute of Mining and Technology):
We're trying to find out something new about thunderstorms and lightning. That
discovery I think is, is worth the risk.



 CHAD COHEN:
 
 Whatever causes lightning to start has always been
hidden inside the clouds, so unlocking that process requires waiting for the
weather to reach maximum force, then launching sensitive instruments into the
heart of the storm. It's hazardous and frustrating.



 RICHARD SONNENFELD:
 
 Come on out. Let's go. Go, go, keep going. Hey,
don't drop it. Don't drop it. Okay, let's go, let's go. Go ahead, you get in
position, you get in position. Oh! Let's go in, in, in. It hit the ground.



 DR. MARTIN UMAN
 
 (University of Florida): A thunderstorm has got
the energy of an atomic bomb.



 CHAD COHEN:
 
 Dr. Martin Uman is the director of the
International Center for Lightning Testing and Research in Camp Blanding,
Florida.



 MARTIN UMAN:
 
 It's the brightest light that we see; it's the loudest
noise that we hear. The only thing hotter than lightning on Earth would be a
nuclear weapon explosion.



 CHAD COHEN:
 
 But what triggers the release of all that power?
We know that lightning is a huge electric spark, and sparks happen when
positive and negative charges build up so much energy they leap through the air
to get at each other. It can only happen when the negative charge in that ball
on the right and the positive charge in that metal rod on the left get so
overwhelmingly strong, they cut a path through the air in the middle.



 DR. MARTIN UMAN:
 
 It's like a hose full of pressure and it can't hold on
anymore.



 CHAD COHEN:
 
 That's what most scientists thought was happening
inside thunderstorms, as ice and water particles collide with each other,
moving electric charges to opposite ends of a cloud. When the charge above and
the charge below get strong enough, they leap through the air as a bolt of
lightning. Except for one thing, when you actually examine the storm cloud, the
strength of the positive and negative charges and the electric field around
them isn't nearly enough to create that big spark.



 JOSEPH DWYER:
 
 Well, the problem is, after decades and decades of
measurements up in thunderstorms, nobody has ever managed to find an electric
field anywhere near that big.



 CHAD COHEN:
 
 Dr. Joe Dwyer is a professor at Florida Tech.



 JOSEPH DWYER:
 
 Well, maybe we're looking for something that doesn't
exist. Maybe there's something wrong with our understanding about how
electrical discharges get started in places like thunderstorms.



 CHAD COHEN:
 
 So if thunderclouds, even great big thunderclouds,
don't have electric fields big enough to generate the giant spark that
lightning actually is, where's all that energy coming from? Well, here in
Florida they have a pretty dramatic way of trying to figure that out. They
launch rockets with really long wires attached to try to create that express
lane to ground that lightning likes so much.


 To get lightning from these clouds to strike where scientists can measure
it requires a simple trigger.



 MARTIN UMAN:
 
 First of all, you need to have a propellant that can get
this thing up there in a hurry. It has to be able to go 700 yards or so in
about two seconds.



 CHAD COHEN:
 
 What is this, actually? This is...is it just
copper wire?



 MARTIN UMAN:
 
 It's Kevlar®-covered copper wire.



 CHAD COHEN:
 
 Kevlar, okay.



 MARTIN UMAN:
 
 So, we load it, connect it electrically. When we're about
to fire, switches are turned on here, manually. After that, everything is done
with air pressure from downstairs.



 JASON JERAULD
 
 :	Okay, Casey, Tube 2 is armed. Three, two, one, fire!



 CHAD COHEN:
 
 From 2,000 feet up, the wire triggers lightning
with a path to ground higher than the Empire State building. And when it
strikes, over a hundred million volts zap the array of test equipment on the
ground.



 CASEY RODRIGUEZ:
 
 Okay, Tube 4 is good. Go ahead and fire 11 when ready.



 JASON JERAULD:
 
 Tube 11 is armed. Three, two, one, fire!



 CHAD COHEN:
 
 The rockets are, for the first time, allowing
physicists to experiment with lightning under repeatable and controllable
conditions, so that now Joe Dwyer and other researchers can test an alternate
theory of how lightning starts. That theory is called "Runaway Breakdown."
Using this model, the energy field inside the storm cloud, that force between
positive and negative, too weak to form a bolt of lightning, is struck by
outside particles, bursts of electrons, which carry their own energy, very high
energy. And with that added energy, you can now get that big spark.



 JOSEPH DWYER:
 
 You end up with an avalanche of electrons moving near the
speed of light. Now this model will work, as long as you have one fast electron
to start it off, sort of the first...the finger that pushes the first domino to
get the whole thing started.



 CHAD COHEN:
 
 And here's where things get really interesting.
Joe Dwyer and many other scientists believe that this outside energy force
comes, not from the clouds, or anywhere else on Earth for that matter, but from
cosmic rays: tiny, subatomic particles ejected from dying stars millions of
years ago and billions of miles away. But how do you test this theory?



 JOSEPH DWYER:
 
 We have 10 of these detectors spread out over the facility
right now.



 CHAD COHEN:
 
 Well, it turns out, when cosmic particles hit the
Earth's atmosphere, they leave a unique signature in the form of gamma and
x-rays. If scientists can detect these x-rays, they'll have the proof they
need.





 JOSEPH DWYER:
 
 This is what's called a sodium iodide detector. There's a
piece of crystal in here that will absorb x-rays and gamma rays, and these
things are not difficult to measure.



 CHAD COHEN:
 
 That's where triggered lightning comes in. For the
first time, the Florida Research Center's rockets allow Dwyer to place his
x-ray detectors in lightning's path. He made his first series of measurements
in 2002.



 JOSEPH DWYER:
 
 A big negative voltage pulse would mean that we got a
burst of x-rays in the detector. I actually didn't think we were going to see
x-rays. The first plot we brought up, there was a nice little pulse that looked
just like an x-ray right at the time that the lightning occurred. "Now, that's,
that's interesting; that's probably a coincidence, you know? What's the chance
of that?" So, we looked at the next lightning stroke—and there was an
even bigger pulse—and the next one and the next one. And every one had
these pulses that looked exactly like x-rays. I think I just about fell out of
my chair at that point.



 CHAD COHEN:
 
 Every single lightning strike Dwyer measured
showed the presence of x-rays. But ground measurements can't reach high enough
to where lightning actually starts. For that, you need to get instruments right
up into the heart of the storm.



 KENNETH EACK:
 
 We finally have the technology to build these instruments
that are small enough and rugged enough to handle a thunderstorm
environment.



 CHAD COHEN:
 
 Lightning is striking all around them. It's time
to launch.



 KENNETH EACK:
 
 One event won't be enough. If we see an x-ray burst, and
we call it quits on one event, well, that's, that's not good enough. And it's
just going to take a lot of measurements to get in the right spot at the right
time.



 RICHARD SONNENFELD:
 
 Three, two, one...go!



 CHAD COHEN:
 
 The balloon is sucked into the storm, trailing its
cargo of instruments. Launches like these have finally traced x-rays all the
way up to where lightning begins and have given scientists the strongest
evidence yet that lightning's spark comes from forces outside the Earth itself.



 JOSEPH DWYER:
 
 These cosmic rays may be the link which will connect a
dying star halfway across the galaxy with lightning.



 ROBERT KRULWICH:
 
 Thank you Chad Cohen. And now for our regular
segment, "Don't Ask the Expert."


 Astrophysicist Neil deGrasse Tyson said, "Whatever you do, please do not
ask me about Hollywood space aliens." But we did.



 NEIL deGRASSE TYSON:
 
 Hollywood? Don't get me started. Every time they
put out an alien, it's for all intents and purposes identically human. If you
were a jellyfish and saw the Hollywood aliens, you'd say they looked exactly
like human beings. Two arms, two legs, a head, a neck, maybe they'll give it
three eyes, instead of two, or antennae. They always have a face which is a
very vertebrate kind of thing to have. So many other life forms on our planet,
with whom we have DNA in common, do not have faces. Trees don't have faces;
worms don't have faces; jellyfish don't have faces. The list is long.


 You could draw from our own planet, finding creatures that look so unlike us
that you'll do better tapping them as alien life forms than anything Hollywood
comes up with in all of their movies. And I'm very disappointed. You know what
the best Hollywood alien movie has been in my list?
 
 The Blob
 
 , the old
Steve McQueen movie from the '50s,
 
 The Blob
 
 . That didn't have a face,
did it? It was just this creature. And you didn't know what made it work, but
it loved your blood. Even though it was a B-movie they did well
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