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ROWE: An invisible danger
hurtles towards Earth

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at close to the speed of light.

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These are intergalactic alien
interlopers on our Milky Way.

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ROWE: Cosmic rays.

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Getting hit by
a cosmic ray is like

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getting hit by a cosmic bullet.

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Cosmic rays are billions of
times more energetic than any

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other types of particles,

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vastly more energetic
than anything

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we can even create in

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a laboratory, in a nuclear
fusion reactor, anywhere.

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ROWE: They pierce spaceships,
putting our astronauts

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in danger.

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But the source of their power
is a mystery.

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Are they coming from
other galaxies?

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Are they coming from things in
between the galaxies?

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BULLOCK: Where do cosmic rays
come from?

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Truth is,
the most powerful ones,

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we haven't got a clue.

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ROWE: The race is on
to solve the mystery

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of the fastest particles
in the universe.

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PLAIT: If I were to make a list
of the dangers of space,

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it would be a long list.

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You know, there's hard vacuum,
huge swings in temperatures,

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micro meteorites,
all kinds of things.

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But probably at the very top
of that list, cosmic rays.

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ROWE: These space invaders
are not what they seem.

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When you hear the name
cosmic rays,

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you might think
it's like a beam,

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like a laser beam of light.
No, no, no, no, no, no.

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It's a tiny little
death particle.

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ROWE: To fight them,

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we must first understand them.

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April 2019.

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NASA's Parker probe flies
closer to the sun than

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ever before.

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We know the sun produces some of

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the cosmic rays that fill
the solar system,

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but we don't know how.

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Our sun looks like
a beautiful glowing orb,

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bringing energy and light to
Earth and allowing life

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to thrive.

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But if you look at it up close,

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you'll see a tumultuous storm
of events.

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PLAIT: The amount of energy
the sun is emitting every

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second is the equivalent of
100 billion one megaton bombs.

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It's a dangerous neighborhood.

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ROWE: Suddenly,
the probe is caught head-on

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in a powerful blast.

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It's perfectly
positioned to monitor

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the outburst from the inside.

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OLUSEYI: The entire outer
third of the sun is a boiling

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cauldron, and tied up in that
plasma are magnetic fields.

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They get tied and twisted,
and energy is stored in them,

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so they rise towards
the surface, and there,

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they rearrange, they reconnect,
they twist, they spin.

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ROWE: When the magnetic
field lines snap,

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energy bursts out.

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And sometimes, that energy
release is explosive

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and that's what
results in flares,

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which are these huge
bursts of light.

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ROWE: The probe discovers
that after a solar flare,

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the sun's surface stores
electrically charged particles.

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But sometimes, there's
a second explosion called

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a coronal mass ejection,
releasing superheated,

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electrically charged gas
called plasma.

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These giant balls of plasma
go flying off the surface of

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the sun,
and in those balls of plasma

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are contained
these charged particles.

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ROWE: The charged particles move
fast, but they hit a roadblock,

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a cloud of
slower-moving particles

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that always surrounds
the sun, the solar wind.

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Well, the coronal mass ejection
is moving into the solar wind

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much faster
than the wind is moving.

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So it sort of runs into it
and creates this shockwave

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and ends up piling up
particles at the edge.

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ROWE:
The shockwave and particles

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slam together --
In the collision,

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the particles steal
energy and speed,

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like a baseball accelerating
off a bat.

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The particles transform into
something far more powerful --

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A solar cosmic ray.

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They're light,
but they're moving

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incredibly fast.

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The Earth is on average
93 million miles away from

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the sun, and these guys reach
us in about an hour.

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That's 93 million miles an hour.

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That's pretty fast.

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ROWE: The cosmic rays speed
towards Earth.

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We're under attack.

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Cosmic rays are, by far,
the most energetic

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particles that we know
to exist in the universe.

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And when things with very high
energy, no matter how small

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they are, impact something else,

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they deposit that energy, right,
and so cosmic rays

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can be very dangerous.

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ROWE: Solar cosmic rays aren't
the only threat we face.

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Other space bullets arrive
from beyond our solar system.

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There are different kinds of
cosmic rays,

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just like there are different
kinds of bullets.

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At the lowest end
of the spectrum

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are these solar cosmic rays.

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These are like the BBs,
and when a BB hits you,

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it might sting for a little
bit, but you're not gonna get

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too worried about it.

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ROWE: A bigger concern --
Galactic cosmic rays.

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They travel faster
and have more energy.

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If solar rays are like BBs,

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the galactic cosmic rays are
like rifle bullets.

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They're far more dangerous.

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They're moving a lot faster.

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But they're also more rare.

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ROWE: Faster still are
the universe's most wanted --

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Ultra-high-energy cosmic rays.

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If you thought galactic
cosmic rays were bad, it's

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because you haven't met
an ultra-high-energy cosmic ray.

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These are the biggest, baddest,

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meanest cosmic rays in
the universe.

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These ultra-high-energy
cosmic rays

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are like hypersonic missiles.

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They are screaming,
and they come from

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the most energetic events in
the universe.

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ROWE: The ultra-high-energy
cosmic missiles

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are the rarest
but also the swiftest.

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These cosmic ray particles
are moving fast.

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These mysterious particles
are moving incredibly

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close to the speed of light.

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I'm not talking about
99 percent the speed of light.

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PLAIT: They're moving through
space at

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like 99.999...

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- 9999...
- 9999...

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- 99999...
- 999999...

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99999 -- 21 nines.

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That's fast.

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That's wild. That's scary.

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ROWE:
All three types of cosmic rays

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are racing
through the solar system.

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If I were to hold up a golf
ball in the middle of space,

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almost 100 cosmic rays pass
through that golf ball every

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single second.

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ROWE: It's a deadly hail of
particle bullets,

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and out in space,

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our astronauts are caught in
the crossfire.

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Cosmic rays represent one of

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the greatest dangers for
human space flight.

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ROWE: NASA plans to send
astronauts back to the moon,

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where radiation levels
-OVER RADIO: Lift-off.

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From cosmic rays are
200 times greater than

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on Earth,
and that is just the start.

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One of NASA's big goals is to
send humans to Mars,

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and that is a long way away,

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at least a six-month journey,
and more often,

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about a nine-month journey.
That's a big problem.

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I am hoping that one day, I can
go to Mars as an astronaut,

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but I'm definitely afraid of
cosmic rays,

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and the more that I read
about it,

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the bigger of a threat it seems.

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So I think that NASA and other
space organizations

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are going to need to work on

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how to protect
their astronauts in these

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really dangerous situations.

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ROWE: Only one group
of people have been

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exposed to these high levels
of cosmic rays,

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the crew members of
the Apollo missions

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July 1969.

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NEIL ARMSTRONG: That's one
small step for man,

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one giant leap for mankind.

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ROWE: One of the astronauts,
Buzz Aldrin,

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sees something strange.

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PLAIT:
During Apollo 11,

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Buzz Aldrin reported
seeing tiny little

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flashes sometimes
when he was looking around.

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That's pretty weird.

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But what's weirder
is that he saw them

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when his eyes were closed.

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ROWE: Later missions also report
seeing odd flashes of light.

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ASTRONAUT: A streak in
the lower left side of the...

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left eye, moving down.

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ROWE: The astronauts describe
the flashes as spots,

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streaks, and clouds.

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Apollo 15 Commander David
Scott reported seeing one that

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was blue with a white cast,
like a blue diamond.

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What's happening is that
a cosmic ray is entering

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the eyeball

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and then striking molecules
and giving off

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a flash of light.

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An alternative theory is that
it triggers the layer of

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sensitive cells in your retina,

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so you perceive
a streak of light even though

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no light ever actually existed.

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ROWE: The cosmic rays
cause long-term damage.

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Inside of the eye's lens,

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there are these fiber cells
that are transparent.

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Well, when a cosmic ray
travels through them,

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it can damage those cells
and make them cloudy,

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causing cataracts.

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When NASA examines
ROWE: the astronauts' helmets,

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they find tiny tracks etched
through them,

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evidence of cosmic ray impacts.

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00:10:07,540 --> 00:10:10,642
When we say that cosmic rays
are like tiny little bullets,

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we're not joking around.

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And some of these burrowed all
the way through the helmet,

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which means it ended up
in the astronaut's brain,

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which just makes me feel weird
to think about.

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DARTNELL: What might that
long-term radiation

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do to your brain,
to your ability to reason

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00:10:30,630 --> 00:10:33,665
and problem solve in one of
the most dangerous environments

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that humanity has ever
placed itself?

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ROWE: The farther we venture
from our home planet,

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the more danger we face.

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ROWE: Cosmic rays, highly
energetic space particles,

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may be the most serious threat
to human space exploration.

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DARTNELL: The Hollywood
conception of outer space is

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00:11:02,929 --> 00:11:05,296
it's full of dangers like aliens

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00:11:05,298 --> 00:11:08,099
wielding ray guns or black holes

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00:11:08,201 --> 00:11:09,534
or asteroid showers.

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00:11:09,603 --> 00:11:11,302
But in reality, the biggest

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00:11:11,304 --> 00:11:13,938
danger facing astronauts
is invisible.

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00:11:14,007 --> 00:11:15,240
It's the cosmic radiation.

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Cosmic rays damaged
ROWE: Apollo astronauts' eyes

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00:11:19,913 --> 00:11:22,747
after just a few days' exposure.

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00:11:22,816 --> 00:11:26,651
A one-way trip to Mars takes
nine months.

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00:11:26,720 --> 00:11:28,319
Future missions are going to be

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00:11:28,321 --> 00:11:30,455
spending much longer times
in space,

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which means we really need to

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00:11:31,758 --> 00:11:34,726
consider how cosmic rays will
impact us.

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CHRISTIAN: We don't understand
all the long-term effects

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00:11:38,832 --> 00:11:42,801
from a steady rain of
cosmic rays,

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but the astronauts are gonna
have to deal with it.

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ROWE: To find out more,
scientists bombarded

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00:11:48,709 --> 00:11:52,711
human cells with manmade
cosmic ray particles.

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They discovered cosmic rays
physically cut through DNA,

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chopping it apart.

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00:12:00,721 --> 00:12:04,756
Damage to DNA in your cell is

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00:12:04,858 --> 00:12:09,260
by far the worst kind,
because your DNA

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is the cell's operating
manuals, the blueprints

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so the cell knows how it
should be functioning normally.

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You can trigger that cell to

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00:12:17,938 --> 00:12:21,306
turn tumorous,
to start producing cancer.

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In 2019, scientists
ROWE: took the experiment

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00:12:26,313 --> 00:12:29,114
further and simulated
a trip to Mars...

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00:12:30,117 --> 00:12:32,550
for mice --
For six months,

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00:12:32,619 --> 00:12:34,652
they blasted the rodents with
a steady

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00:12:34,721 --> 00:12:38,757
stream of lab-made
cosmic ray particles.

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00:12:38,858 --> 00:12:42,460
The experiment found
profound alterations

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00:12:42,529 --> 00:12:45,430
to the mice's normal behavior.

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They learned new tasks
much more slowly.

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Their memory was affected,
and they

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00:12:50,604 --> 00:12:53,638
forgot things they had
already learned.

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ROWE: They were more anxious
and prone to

251
00:12:55,542 --> 00:12:58,910
giving up on tasks
they'd normally complete.

252
00:12:58,912 --> 00:13:01,312
If you put some of these
irradiated mice into

253
00:13:01,447 --> 00:13:05,617
a swimming test, rather than
trying to swim to safety,

254
00:13:05,619 --> 00:13:07,218
many of them just simply
gave up.

255
00:13:09,055 --> 00:13:10,722
CHRISTIAN: This is important,
because we need

256
00:13:10,824 --> 00:13:13,124
our astronauts to be
fully functioning.

257
00:13:13,126 --> 00:13:16,628
The reason why you do
crewed missions is because

258
00:13:16,730 --> 00:13:20,832
the human brain is much better
than any computer.

259
00:13:20,934 --> 00:13:23,134
PLAIT: If even one of them
has a problem,

260
00:13:23,203 --> 00:13:26,204
it can even put the mission
and their lives in jeopardy.

261
00:13:27,707 --> 00:13:31,109
ROWE: Other studies discover
cosmic rays can accelerate

262
00:13:31,211 --> 00:13:35,313
aging, alter genes, and cause
cardiovascular disease.

263
00:13:37,050 --> 00:13:38,850
That sounds bad enough,

264
00:13:38,952 --> 00:13:41,953
but there's
a more immediate danger.

265
00:13:42,022 --> 00:13:44,789
When cosmic rays
penetrate spaceships,

266
00:13:44,791 --> 00:13:47,926
they can fry electronic
systems, and that's enough to

267
00:13:47,928 --> 00:13:49,561
jeopardize a mission.

268
00:13:49,629 --> 00:13:54,899
Our operations in space depend
on electronics, on computers.

269
00:13:54,901 --> 00:13:59,604
And the worst case scenario is
that the wrong cosmic ray comes

270
00:13:59,706 --> 00:14:01,639
at the wrong time and hits

271
00:14:01,741 --> 00:14:06,344
the wrong circuit, and it leads
to a cascading series of

272
00:14:06,446 --> 00:14:10,014
failures that can totally
jeopardize a mission.

273
00:14:11,051 --> 00:14:13,918
ROWE: We see evidence of this
onslaught in mission cameras.

274
00:14:15,255 --> 00:14:17,121
Even when we have
a detector in space

275
00:14:17,257 --> 00:14:18,823
like on
the Hubble Space Telescope,

276
00:14:18,925 --> 00:14:20,358
if you saw a raw image,

277
00:14:20,460 --> 00:14:23,061
it doesn't look like
the beautiful images

278
00:14:23,129 --> 00:14:24,329
that are shown to the public.

279
00:14:24,464 --> 00:14:26,865
They're just crossed with
cosmic rays, and those

280
00:14:26,966 --> 00:14:31,202
cosmic rays are destroying
that detector slowly over time.

281
00:14:33,106 --> 00:14:36,040
ROWE: So how can we protect
astronauts and their equipment?

282
00:14:37,444 --> 00:14:39,711
The obvious answer is to
add shielding.

283
00:14:41,715 --> 00:14:45,049
SUTTER: It's one thing to say
like, oh, just add more stuff.

284
00:14:45,151 --> 00:14:48,820
But have you seen rocket
launches and how hard they are,

285
00:14:48,922 --> 00:14:51,823
how expensive it is to get
stuff up into space?

286
00:14:53,226 --> 00:14:55,960
ROWE: NASA does have a plan.

287
00:14:56,062 --> 00:14:58,763
The spacecraft for the Artemis
moon landing mission

288
00:14:58,831 --> 00:15:02,033
will be packed for optimum
cosmic ray protection.

289
00:15:02,102 --> 00:15:05,036
CHRISTIAN: So one of the ways
you can get around

290
00:15:05,138 --> 00:15:08,306
the mass limit is
to basically get dual use

291
00:15:08,408 --> 00:15:10,041
out of everything --
Your supplies,

292
00:15:10,110 --> 00:15:13,811
your fuel, your water, and you
can use those as shielding.

293
00:15:13,813 --> 00:15:15,813
ROWE:
But it's not that simple.

294
00:15:15,815 --> 00:15:19,017
Just as more powerful bullets
penetrate armor,

295
00:15:19,019 --> 00:15:22,353
more energetic cosmic rays
pierce the shielding

296
00:15:22,422 --> 00:15:24,022
on spaceships.

297
00:15:24,024 --> 00:15:26,124
The solar ones --
Yeah, you can just put up some

298
00:15:26,259 --> 00:15:28,960
material, some shielding, and
it'll generally block them.

299
00:15:29,062 --> 00:15:31,863
But the higher energy ones,
they can just burrow

300
00:15:31,998 --> 00:15:33,197
on through.

301
00:15:33,233 --> 00:15:37,302
If they hit one of the atoms
in the shielding that is

302
00:15:37,404 --> 00:15:38,836
protecting our astronauts,

303
00:15:38,938 --> 00:15:42,040
it can create
a shower of particles.

304
00:15:42,141 --> 00:15:44,709
DARTNELL: That radiation
particle might have missed

305
00:15:44,811 --> 00:15:46,210
any of the cells in your body.

306
00:15:46,313 --> 00:15:47,645
But you've now turned it into

307
00:15:47,747 --> 00:15:51,549
a blast, shredding through
everything in the spacecraft.

308
00:15:51,618 --> 00:15:55,687
And so it turns out
your shielding becomes

309
00:15:55,689 --> 00:15:59,223
the weapon that the cosmic
rays use against you.

310
00:15:59,325 --> 00:16:04,529
ROWE: But NASA is recruiting
an unexpected ally -- the sun.

311
00:16:04,631 --> 00:16:09,300
Can we protect our astronauts
by fighting fire with fire?

312
00:16:17,911 --> 00:16:22,413
ROWE: Powerful cosmic rays
smash through spaceships.

313
00:16:22,515 --> 00:16:27,518
But how can objects smaller
than an atom carry enough

314
00:16:27,653 --> 00:16:30,455
energy to be
dangerous to astronauts?

315
00:16:30,556 --> 00:16:33,424
Moving objects carry energy.

316
00:16:33,526 --> 00:16:35,960
We call this kinetic energy,
and when

317
00:16:36,029 --> 00:16:39,530
they strike something,
they transform that energy.

318
00:16:40,934 --> 00:16:44,202
When I hit my hand,
the kinetic energy of

319
00:16:44,337 --> 00:16:49,640
my fist transforms into sound
and heat and vibration.

320
00:16:49,709 --> 00:16:51,743
My hand hurts a little from

321
00:16:51,811 --> 00:16:55,613
that impact, from
the transformation of energy.

322
00:16:55,715 --> 00:16:58,149
ROWE: It's the same thing
with cosmic rays.

323
00:16:58,218 --> 00:17:02,253
When they slam into a human
brain cell or a computer chip,

324
00:17:02,355 --> 00:17:04,956
they dump some energy,
causing damage.

325
00:17:06,326 --> 00:17:09,727
How much damage depends on
their kinetic energy,

326
00:17:09,729 --> 00:17:12,063
and that comes down
to two things --

327
00:17:12,132 --> 00:17:13,965
Mass and speed.

328
00:17:15,001 --> 00:17:18,936
Intuitively, things that are
moving at the same speed,

329
00:17:19,038 --> 00:17:21,406
if they're more massive,
they carry more energy.

330
00:17:21,408 --> 00:17:23,941
A bigger asteroid slamming
into Earth will

331
00:17:24,010 --> 00:17:26,711
do more damage than
a smaller asteroid.

332
00:17:26,813 --> 00:17:29,414
ROWE: If you double
the mass of an object,

333
00:17:29,516 --> 00:17:32,316
its kinetic energy also doubles.

334
00:17:32,318 --> 00:17:35,053
Although mass is important,

335
00:17:35,154 --> 00:17:36,721
it's not as important as speed.

336
00:17:39,626 --> 00:17:42,727
OLUSEYI: Speed matters
even more than mass.

337
00:17:42,729 --> 00:17:46,064
The kinetic energy depends
directly on the mass,

338
00:17:46,132 --> 00:17:48,699
but it depends on
the square of the speed.

339
00:17:48,701 --> 00:17:51,402
Here's what that means --
You double the mass,

340
00:17:51,404 --> 00:17:54,439
you have double the kinetic
energy, you double the speed,

341
00:17:54,540 --> 00:17:56,808
you have four times
the kinetic energy.

342
00:17:59,712 --> 00:18:05,650
ROWE: When it comes to speed,
cosmic rays are the elite.

343
00:18:05,751 --> 00:18:07,919
An ultra-high-energy cosmic ray

344
00:18:07,921 --> 00:18:12,523
detected in 1991 hit
the atmosphere so fast,

345
00:18:12,525 --> 00:18:15,960
scientists called it the
"Oh My God Particle."

346
00:18:19,232 --> 00:18:22,500
This particle was higher
energy than they thought

347
00:18:22,602 --> 00:18:24,335
they would ever, ever see.

348
00:18:24,437 --> 00:18:27,805
ROWE: Until this fluorescent
streak in the Utah sky,

349
00:18:27,907 --> 00:18:31,209
no one believed a particle
could reach the Earth traveling

350
00:18:31,211 --> 00:18:33,311
so close to the speed of light,

351
00:18:33,313 --> 00:18:36,614
making cosmic ray particles
far more dangerous

352
00:18:36,716 --> 00:18:37,949
than expected.

353
00:18:38,050 --> 00:18:40,218
As you approach
the speed of light,

354
00:18:40,320 --> 00:18:42,753
energy, momentum, mass,
they start

355
00:18:42,822 --> 00:18:44,722
to act a little bit differently.

356
00:18:44,857 --> 00:18:47,525
PLAIT: Einstein's equations of
relativity become important,

357
00:18:47,627 --> 00:18:50,328
because the physics changes,
and the energy it has

358
00:18:50,463 --> 00:18:53,464
becomes much, much,
much stronger.

359
00:18:53,533 --> 00:18:56,400
OLUSEYI: If a particle is moving
at close to the speed of light,

360
00:18:56,402 --> 00:19:00,505
that means that its energy is
almost at the maximum allowed

361
00:19:00,607 --> 00:19:02,607
by the laws of physics.

362
00:19:04,711 --> 00:19:06,811
THALLER: It's amazing to think
that something as tiny as

363
00:19:06,813 --> 00:19:09,814
a proton could actually be
dangerous to a human being.

364
00:19:09,949 --> 00:19:13,217
But amazingly, that proton is
moving so fast,

365
00:19:13,319 --> 00:19:15,586
it carries as much energy
as a baseball

366
00:19:15,588 --> 00:19:17,255
thrown at 100 miles an hour.

367
00:19:17,323 --> 00:19:21,159
ROWE: A baseball contains over
a trillion, trillion protons.

368
00:19:21,260 --> 00:19:25,229
Imagine all that energy
carried by just one particle.

369
00:19:25,331 --> 00:19:29,200
So now you get a sense of just
how risky these can be.

370
00:19:29,202 --> 00:19:31,602
ROWE: Ultra-high-energy
cosmic rays like

371
00:19:31,704 --> 00:19:35,706
the Oh My God Particle are
like supersonic missiles.

372
00:19:35,708 --> 00:19:38,609
They are the fastest,
but they're so rare,

373
00:19:38,711 --> 00:19:41,812
astronauts are unlikely
to be hit by one.

374
00:19:41,915 --> 00:19:46,017
Solar cosmic rays are like
BB pellets -- abundant,

375
00:19:46,019 --> 00:19:48,719
but our spacecraft can
block them.

376
00:19:48,788 --> 00:19:50,454
The biggest threat to
our astronauts,

377
00:19:50,523 --> 00:19:53,124
however, are galactic
cosmic rays.

378
00:19:53,226 --> 00:19:56,127
They come from elsewhere
in the Milky Way.

379
00:19:56,129 --> 00:19:57,862
The combination of their speed

380
00:19:57,997 --> 00:20:01,599
and frequency makes them
the most dangerous.

381
00:20:01,601 --> 00:20:05,703
These galactic cosmic rays
are much more powerful than

382
00:20:05,705 --> 00:20:07,405
the solar cosmic rays,

383
00:20:07,507 --> 00:20:10,808
and they've traveled
enormous distances

384
00:20:10,810 --> 00:20:13,544
to mess you up.

385
00:20:13,613 --> 00:20:18,015
ROWE: Luckily, our astronauts
have a surprising protector,

386
00:20:18,017 --> 00:20:21,619
a guardian of the solar system,
the sun.

387
00:20:23,156 --> 00:20:24,622
DARTNELL:
As well as spitting out these

388
00:20:24,724 --> 00:20:29,126
high-energy solar cosmic
ray particles,

389
00:20:29,128 --> 00:20:33,431
the sun is also streaming out
lots of much lower energy

390
00:20:33,499 --> 00:20:36,033
particles of the solar wind.

391
00:20:36,135 --> 00:20:38,202
That outward moving
solar wind acts

392
00:20:38,204 --> 00:20:41,772
as a force field, and
the cosmic rays have to work

393
00:20:41,774 --> 00:20:47,011
their way upstream to get to
Earth far inside this bubble.

394
00:20:47,013 --> 00:20:51,716
ROWE: The solar wind extends
11 billion miles

395
00:20:51,818 --> 00:20:53,117
around the solar system,

396
00:20:53,252 --> 00:20:57,121
generating a magnetic field
that repels incoming

397
00:20:57,123 --> 00:20:59,423
galactic cosmic rays.

398
00:20:59,525 --> 00:21:01,892
DARTNELL: It's almost like
the deflector shield

399
00:21:01,894 --> 00:21:04,128
of the Starship Enterprise.

400
00:21:04,130 --> 00:21:08,933
So the sun's magnetic field
partially helps protect

401
00:21:09,002 --> 00:21:11,335
the Earth and any astronauts

402
00:21:11,404 --> 00:21:12,803
from the incoming radiation.

403
00:21:12,905 --> 00:21:16,707
OLUSEYI: Not long ago,
our Voyager spacecraft

404
00:21:16,809 --> 00:21:19,944
made it to that boundary
between the sun's bubble

405
00:21:20,046 --> 00:21:21,445
and the galaxy and was able

406
00:21:21,547 --> 00:21:24,649
to study that region, and we
see the difference between

407
00:21:24,750 --> 00:21:27,518
inside the sun's bubble
and what's going on

408
00:21:27,520 --> 00:21:29,120
outside the sun's bubble.

409
00:21:29,122 --> 00:21:31,522
The sun has our back, billions

410
00:21:31,624 --> 00:21:34,659
of miles away,
and that's pretty cool.

411
00:21:34,760 --> 00:21:37,828
ROWE: The Voyager
space probes discovered

412
00:21:37,830 --> 00:21:40,665
a moving battlefield.

413
00:21:40,733 --> 00:21:44,602
The solar wind behaves a bit
like a storm front on Earth.

414
00:21:44,604 --> 00:21:46,504
Sometimes, it advances.

415
00:21:46,506 --> 00:21:48,739
Sometimes, it retreats.

416
00:21:49,809 --> 00:21:51,809
OLUSEYI: When the sun's
activity is the highest,

417
00:21:51,911 --> 00:21:54,812
it's spitting out more
solar energetic protons,

418
00:21:54,914 --> 00:21:58,749
but those solar cosmic rays
are much less damaging

419
00:21:58,818 --> 00:22:00,017
than the galactic ones,

420
00:22:00,019 --> 00:22:02,520
so the net is a benefit.

421
00:22:03,690 --> 00:22:06,524
DARTNELL: So actually,
ironically, you might find that,

422
00:22:06,526 --> 00:22:10,127
for astronauts, it is safer
to launch missions to Mars

423
00:22:10,129 --> 00:22:14,065
during a period of higher
solar activity, because although

424
00:22:14,133 --> 00:22:18,602
you have more of
the solar particle radiation,

425
00:22:18,604 --> 00:22:22,106
you also get a better
shielding effect

426
00:22:22,108 --> 00:22:23,808
from the solar wind.

427
00:22:23,810 --> 00:22:25,843
ROWE: The sun's activity
goes through

428
00:22:25,945 --> 00:22:28,412
an 11-year cycle
of highs and lows.

429
00:22:28,414 --> 00:22:32,116
The protective bubble follows
the same cycle,

430
00:22:32,118 --> 00:22:36,620
allowing NASA to predict
the safest times to launch.

431
00:22:36,622 --> 00:22:38,522
This is a thorny problem,
and, you know,

432
00:22:38,624 --> 00:22:41,759
we have very smart people
working on it, but we want to

433
00:22:41,861 --> 00:22:44,228
explore space as much as we can,

434
00:22:44,230 --> 00:22:45,830
but we have to lower the risk

435
00:22:45,932 --> 00:22:47,832
to the astronauts
as much as possible.

436
00:22:49,936 --> 00:22:53,437
ROWE: NASA's fight against
the cosmic invaders continues,

437
00:22:53,506 --> 00:22:56,240
but the biggest mystery remains.

438
00:22:56,309 --> 00:22:59,744
What exactly is launching
the deadliest

439
00:22:59,812 --> 00:23:02,046
galactic cosmic rays?

440
00:23:10,323 --> 00:23:12,923
ROWE: Every second,
quadrillions of bits

441
00:23:12,925 --> 00:23:15,359
of space shrapnel
race towards Earth

442
00:23:15,428 --> 00:23:17,361
at close to
the speed of light --

443
00:23:17,430 --> 00:23:20,030
Galactic cosmic rays.

444
00:23:21,100 --> 00:23:24,402
The galactic cosmic rays
are like a rifle bullet.

445
00:23:24,404 --> 00:23:27,405
You do not want to get hit
by one of these.

446
00:23:27,540 --> 00:23:31,308
ROWE: They are invaders from
outside the solar system.

447
00:23:31,411 --> 00:23:34,044
We know they're made by
something powerful

448
00:23:34,113 --> 00:23:35,413
within our galaxy,

449
00:23:35,415 --> 00:23:39,049
so the source should be
easy to detect.

450
00:23:39,151 --> 00:23:41,552
HOPKINS: You'd think
if one of them

451
00:23:41,654 --> 00:23:44,321
hits a detector on Earth,
that we'd just be able

452
00:23:44,424 --> 00:23:46,056
to point back
in a straight line and say,

453
00:23:46,125 --> 00:23:47,291
"It came from over there."

454
00:23:47,326 --> 00:23:49,126
And then look, is there
something else over there,

455
00:23:49,128 --> 00:23:51,028
like a supernova explosion that

456
00:23:51,030 --> 00:23:52,963
could explain the source
of this?

457
00:23:53,032 --> 00:23:55,599
The problem is
that cosmic rays get

458
00:23:55,601 --> 00:24:00,004
bent as they move
by magnetic fields.

459
00:24:00,006 --> 00:24:01,939
ROWE: The electric charge
on a cosmic ray

460
00:24:02,041 --> 00:24:04,108
makes it act like
a little magnet,

461
00:24:05,178 --> 00:24:08,045
and the Milky Way
is full of other magnets.

462
00:24:08,114 --> 00:24:12,249
SUTTER: If I'm a cosmic ray just
barreling through the galaxy,

463
00:24:12,351 --> 00:24:14,752
and I encounter
a magnetic field,

464
00:24:14,821 --> 00:24:17,121
I'm gonna slightly
change directions.

465
00:24:17,223 --> 00:24:20,224
Maybe here, maybe there,
maybe up there.

466
00:24:20,226 --> 00:24:23,260
My trajectory is going to
become scrambled.

467
00:24:23,329 --> 00:24:25,963
HOPKINS: And after
a few million years or so,

468
00:24:26,065 --> 00:24:28,732
basically all the information
about where it started has

469
00:24:28,801 --> 00:24:30,334
been lost --
It's going in a completely

470
00:24:30,403 --> 00:24:34,305
random direction for all
practical purposes.

471
00:24:34,407 --> 00:24:38,309
ROWE: But galactic cosmic rays
also have a sidekick,

472
00:24:38,411 --> 00:24:44,048
one that is far less elusive --
Gamma rays.

473
00:24:44,149 --> 00:24:47,351
When a galactic cosmic ray
hits a regular atom out

474
00:24:47,453 --> 00:24:50,321
in space,
it causes this big reaction.

475
00:24:51,624 --> 00:24:53,891
HOPKINS: It emits all sorts
of other particles,

476
00:24:53,893 --> 00:24:55,226
including gamma rays,

477
00:24:55,361 --> 00:24:58,729
which are basically extremely
energetic photons of light.

478
00:24:58,831 --> 00:25:02,700
Critically, gamma rays don't
get bent by magnetic fields,

479
00:25:02,835 --> 00:25:04,502
because they don't have
an electric charge,

480
00:25:04,604 --> 00:25:07,538
so they just beeline off in
a straight line along whatever

481
00:25:07,640 --> 00:25:10,841
direction the cosmic ray was
moving in the first place.

482
00:25:10,943 --> 00:25:14,945
So we can look back at where
gamma rays are coming from in

483
00:25:15,014 --> 00:25:18,415
the sky, and that tells us
where there are a lot of

484
00:25:18,417 --> 00:25:19,750
cosmic rays having collisions.

485
00:25:21,053 --> 00:25:24,855
ROWE: And they've led us
to a prime suspect...

486
00:25:26,125 --> 00:25:27,124
supernovas.

487
00:25:30,696 --> 00:25:31,962
Supernova are some of

488
00:25:32,064 --> 00:25:34,398
the most powerful explosions
in the universe,

489
00:25:34,400 --> 00:25:37,434
and so they're ripe grounds
for these highly energetic,

490
00:25:37,536 --> 00:25:41,705
extremely fast particles
to be created.

491
00:25:41,807 --> 00:25:44,041
ROWE: When a giant star
runs out of fuel,

492
00:25:44,110 --> 00:25:46,977
it can no longer support its
own weight.

493
00:25:46,979 --> 00:25:48,612
It collapses inward,

494
00:25:50,550 --> 00:25:54,051
triggering a huge explosion,
powerful enough

495
00:25:54,120 --> 00:25:57,721
to smash atoms into tiny pieces.

496
00:25:57,723 --> 00:26:01,025
The explosion pushes out
an expanding cloud

497
00:26:01,027 --> 00:26:04,828
of gas and dust,
the supernova remnant.

498
00:26:04,830 --> 00:26:06,964
HOPKINS: And that material,
as it's moving out at

499
00:26:07,066 --> 00:26:08,165
1,000 miles a second,

500
00:26:08,233 --> 00:26:11,535
generates an incredibly
powerful shockwave.

501
00:26:11,604 --> 00:26:14,038
And that shockwave
could be where

502
00:26:14,106 --> 00:26:19,443
a particle swept up in
the shock gets accelerated.

503
00:26:19,545 --> 00:26:22,012
ROWE: The magnetic fields
inside the cloud

504
00:26:22,014 --> 00:26:24,615
trap the subatomic particles.

505
00:26:24,684 --> 00:26:27,551
Cosmic rays inside of
the supernova remnant

506
00:26:27,620 --> 00:26:29,453
are a lot like being
in a pinball machine.

507
00:26:31,524 --> 00:26:35,526
So you have the shockwave as
the flipper, and then your

508
00:26:35,528 --> 00:26:37,828
magnetic fields
are these bumpers,

509
00:26:37,830 --> 00:26:40,064
prohibiting it from
actually leaving.

510
00:26:41,434 --> 00:26:42,900
They're bouncing back
and forth across

511
00:26:42,902 --> 00:26:45,903
this incredibly energetic shock,
and each time

512
00:26:45,905 --> 00:26:47,037
they bounce back and forth,

513
00:26:47,106 --> 00:26:49,607
the key is they pick up
a little more energy.

514
00:26:50,643 --> 00:26:53,944
ROWE: When a galactic cosmic ray
gains enough energy,

515
00:26:54,013 --> 00:26:57,281
the magnetic fields can no
longer hold on to it.

516
00:26:57,283 --> 00:26:58,515
It escapes.

517
00:27:01,153 --> 00:27:03,821
The supernova theory
explains the birth

518
00:27:03,823 --> 00:27:06,457
of many of these cosmic bullets.

519
00:27:06,558 --> 00:27:09,393
But then we discovered
a super gamma ray

520
00:27:09,395 --> 00:27:13,130
so powerful, it must have
a completely different

521
00:27:13,232 --> 00:27:14,565
origin story.

522
00:27:14,633 --> 00:27:17,501
So this gamma ray was
incredibly high energy,

523
00:27:17,636 --> 00:27:20,804
which means that the cosmic
ray responsible for it was

524
00:27:20,806 --> 00:27:23,540
probably also extremely
high in energy.

525
00:27:23,642 --> 00:27:25,743
If you fire a bullet into
a pinball machine,

526
00:27:25,778 --> 00:27:27,444
it's not gonna bounce back
and forth.

527
00:27:27,513 --> 00:27:29,113
[gunshot sound effect]

528
00:27:29,248 --> 00:27:30,948
I'm just gonna break
through the machinery.

529
00:27:31,050 --> 00:27:32,416
The problem is that these

530
00:27:32,418 --> 00:27:35,219
are vastly more energetic
than that.

531
00:27:35,321 --> 00:27:38,122
So there's no way they could
have been bouncing around all

532
00:27:38,124 --> 00:27:41,558
the way up to their current
energies inside of that

533
00:27:41,627 --> 00:27:45,029
particular pinball machine.

534
00:27:45,031 --> 00:27:48,065
ROWE: There must be
something else in the Milky Way

535
00:27:48,133 --> 00:27:50,434
creating galactic cosmic rays,

536
00:27:50,503 --> 00:27:54,705
something more powerful
than a supernova.

537
00:27:56,308 --> 00:27:59,510
The question is, what?

538
00:27:59,612 --> 00:28:03,047
January 2021.

539
00:28:03,148 --> 00:28:04,815
At an observatory

540
00:28:04,817 --> 00:28:07,818
high up on the side of
a Mexican volcano,

541
00:28:07,820 --> 00:28:11,321
blue light zaps through
water tanks,

542
00:28:12,425 --> 00:28:15,025
signs of incoming gamma rays.

543
00:28:16,829 --> 00:28:19,830
Their trail stretches back
across the Milky Way,

544
00:28:19,832 --> 00:28:24,101
crossing billions of miles,
but suddenly goes cold.

545
00:28:25,337 --> 00:28:28,439
Instead of originating
in a huge explosion,

546
00:28:28,507 --> 00:28:33,444
the trail ends in a cold,
sparse cloud of dust.

547
00:28:33,545 --> 00:28:36,714
SUTTER: Molecular clouds,
at first glance, seem like

548
00:28:36,816 --> 00:28:38,315
one of the most boring,

549
00:28:38,317 --> 00:28:41,118
innocuous places in
the universe.

550
00:28:41,220 --> 00:28:45,522
You can barely even see them
without an infrared telescope.

551
00:28:45,524 --> 00:28:48,258
They're not events
like supernova

552
00:28:48,360 --> 00:28:50,327
that have enormously
high energies.

553
00:28:50,429 --> 00:28:52,463
So you wouldn't expect it
to create super

554
00:28:52,531 --> 00:28:54,298
energetic particles.

555
00:28:54,300 --> 00:28:57,034
ROWE: Something must be
hidden in the cloud,

556
00:28:57,103 --> 00:29:01,405
something powerful enough to
accelerate the cosmic rays.

557
00:29:01,407 --> 00:29:03,507
We just don't know what.

558
00:29:03,509 --> 00:29:06,410
We can't see inside
the molecular clouds,

559
00:29:06,545 --> 00:29:09,747
so it could be that,
deep inside them,

560
00:29:09,848 --> 00:29:13,317
there are clusters of newborn
stars that are cranking out

561
00:29:13,419 --> 00:29:14,818
these cosmic rays,

562
00:29:14,820 --> 00:29:18,756
but we don't know if even
the crankiest of stars are

563
00:29:18,824 --> 00:29:23,527
capable of producing cosmic
rays at these energies.

564
00:29:23,529 --> 00:29:25,662
ROWE:
Just two months later,

565
00:29:25,764 --> 00:29:29,233
in March of 2021,
we get another clue.

566
00:29:29,334 --> 00:29:31,935
Scientists detect
gamma rays coming

567
00:29:32,037 --> 00:29:35,239
from the Cygnus Cocoon Nebula.

568
00:29:35,340 --> 00:29:37,941
It's a dense molecular
cloud with

569
00:29:38,043 --> 00:29:41,612
a difference --
At the center is a cavity.

570
00:29:41,714 --> 00:29:46,450
Hundreds of closely packed
stars push against the dust

571
00:29:46,552 --> 00:29:48,819
and gas, including

572
00:29:48,888 --> 00:29:52,856
huge bright stars
called spectral type O and B

573
00:29:53,926 --> 00:29:56,160
Spectral type O and B stars are

574
00:29:56,228 --> 00:29:58,362
some of the hottest stars in
our universe.

575
00:30:00,032 --> 00:30:02,599
ROWE: The massive stars
blast out solar winds far

576
00:30:02,734 --> 00:30:05,035
stronger than the wind
produced by our sun.

577
00:30:06,705 --> 00:30:09,039
When you think about all these
stars forming together,

578
00:30:09,141 --> 00:30:12,342
they are all putting off
a wind of high-energy particles

579
00:30:12,444 --> 00:30:13,644
from their surfaces.

580
00:30:13,679 --> 00:30:16,713
These winds collide
and form big shock structures

581
00:30:16,816 --> 00:30:18,649
between all of
these young stars.

582
00:30:18,750 --> 00:30:20,951
CHRISTIAN: You're getting
so much energy from

583
00:30:21,053 --> 00:30:22,753
so many different winds,
coming from so many

584
00:30:22,855 --> 00:30:27,357
different directions, that it
forms a boiling mass of

585
00:30:27,426 --> 00:30:29,493
shockwaves and magnetic fields.

586
00:30:29,495 --> 00:30:30,961
ROWE:
It's a pinball machine

587
00:30:31,030 --> 00:30:34,965
on a far bigger scale --
The magnetic fields are stronger

588
00:30:35,034 --> 00:30:36,300
than a supernova's,

589
00:30:36,302 --> 00:30:40,604
trapping and accelerating
the more energetic cosmic rays

590
00:30:40,606 --> 00:30:41,805
for longer.

591
00:30:41,807 --> 00:30:44,241
One important thing about
star clusters is that

592
00:30:44,343 --> 00:30:47,010
they are around for millions
and millions of years.

593
00:30:47,012 --> 00:30:49,947
It's not just a one-off event
like a supernova.

594
00:30:49,982 --> 00:30:52,916
CHRISTIAN: And so you've got
this magnetic field

595
00:30:52,918 --> 00:30:56,119
and these shocks happening
over a long period of time,

596
00:30:56,255 --> 00:30:58,522
and that may be what you need
to accelerate cosmic rays.

597
00:30:59,925 --> 00:31:04,428
ROWE: Molecular clouds may
shoot out galactic cosmic rays,

598
00:31:04,530 --> 00:31:07,664
but what fires the hypersonic
space missiles,

599
00:31:07,733 --> 00:31:10,801
the ultra-high-energy
cosmic rays?

600
00:31:10,936 --> 00:31:14,805
The culprit may be hiding out
in distant galaxies --

601
00:31:14,940 --> 00:31:18,108
Supermassive black holes.

602
00:31:25,217 --> 00:31:27,517
ROWE: Ultra-high-energy
cosmic rays are

603
00:31:27,620 --> 00:31:31,221
the hypersonic missiles of
the particle world.

604
00:31:31,290 --> 00:31:33,323
If a photon of light,
the fastest thing in

605
00:31:33,325 --> 00:31:37,227
the universe, had a race with
an ultra-high-energy cosmic ray,

606
00:31:37,329 --> 00:31:41,665
it would be so close,
that after 200,000 years,

607
00:31:41,700 --> 00:31:44,501
that photon would be
half an inch ahead of

608
00:31:44,636 --> 00:31:46,403
the ultra-high-energy
cosmic ray.

609
00:31:46,405 --> 00:31:50,941
ROWE: They appear to come from
beyond our Milky Way galaxy.

610
00:31:51,043 --> 00:31:55,812
OLUSEYI: Our galaxy is
100,000 light years across.

611
00:31:55,915 --> 00:31:59,616
The next nearest galaxy to us
is two million light years away.

612
00:31:59,718 --> 00:32:01,752
So these are traveling to us

613
00:32:01,853 --> 00:32:04,821
across millions and billions
of light years.

614
00:32:04,924 --> 00:32:09,326
How do you accelerate this tiny

615
00:32:09,461 --> 00:32:13,964
little particle to such
insane velocities?

616
00:32:14,066 --> 00:32:15,899
What is the power source?

617
00:32:15,901 --> 00:32:19,536
What in the universe has
that kind of capability?

618
00:32:19,605 --> 00:32:22,406
Where's the Death Star here?

619
00:32:22,541 --> 00:32:25,142
ROWE: Their speed makes
them dangerous,

620
00:32:25,210 --> 00:32:29,046
but it also makes it easier to
find their source.

621
00:32:29,114 --> 00:32:32,416
Ultra-high-energy cosmic rays
are moving so rapidly,

622
00:32:32,551 --> 00:32:34,518
that they're really not
affected that much by

623
00:32:34,620 --> 00:32:35,752
magnetic fields.

624
00:32:35,821 --> 00:32:38,021
It's like a bullet going
through a fisherman's net.

625
00:32:38,023 --> 00:32:41,825
CHRISTIAN: And so they're coming
mostly in a straight line.

626
00:32:41,827 --> 00:32:44,161
When they're coming in a
straight line, and we can point

627
00:32:44,229 --> 00:32:45,729
back to their origin,

628
00:32:45,731 --> 00:32:49,499
and that's something we can
use to figure out where

629
00:32:49,501 --> 00:32:50,934
and how they're getting
accelerated.

630
00:32:52,905 --> 00:32:54,604
ROWE:
In the Argentinian desert,

631
00:32:54,707 --> 00:32:58,241
the Pierre Auger Cosmic Ray
Detector completes

632
00:32:58,310 --> 00:33:00,410
a 12-year study of the sky.

633
00:33:02,648 --> 00:33:05,549
It confirms that most
galaxies have a supermassive

634
00:33:05,650 --> 00:33:07,351
black hole at their center,

635
00:33:07,419 --> 00:33:11,154
but only a few are active,
shooting out energy.

636
00:33:11,256 --> 00:33:15,058
These active
supermassive black holes also

637
00:33:15,127 --> 00:33:18,428
blast out ultra-high-energy
cosmic rays.

638
00:33:19,431 --> 00:33:23,300
Supermassive black holes are
already extremely powerful.

639
00:33:23,302 --> 00:33:25,035
So it makes a lot
of sense to me that

640
00:33:25,137 --> 00:33:28,238
the ultra-high-energy cosmic
rays could originate at

641
00:33:28,340 --> 00:33:30,440
supermassive black holes.

642
00:33:30,509 --> 00:33:35,712
ROWE: The M87 galaxy is
54 million light years away.

643
00:33:35,714 --> 00:33:38,315
It's famous
because we took a photo

644
00:33:38,317 --> 00:33:41,718
of the supermassive black hole
at its core.

645
00:33:41,720 --> 00:33:45,989
So the event horizon telescope
image of the swirling vortex of

646
00:33:45,991 --> 00:33:48,458
gas around
that central black hole,

647
00:33:48,527 --> 00:33:50,560
that shadow that
you can't actually see,

648
00:33:50,629 --> 00:33:55,432
that could be a site for
the unbelievably energetic

649
00:33:55,534 --> 00:33:56,933
acceleration of cosmic rays.

650
00:33:57,035 --> 00:34:00,303
ROWE: In March 2021,

651
00:34:00,305 --> 00:34:03,306
scientists analyze
the data further.

652
00:34:03,442 --> 00:34:07,310
MINGARELLI: This new image
of M87 shows very clear

653
00:34:07,446 --> 00:34:08,945
magnetic field lines,

654
00:34:09,048 --> 00:34:11,815
which is really stunning and
reminds us of how much energy

655
00:34:11,917 --> 00:34:15,052
could be contained close to
the supermassive black hole.

656
00:34:15,153 --> 00:34:17,821
ROWE: Black holes have
enormous power,

657
00:34:17,923 --> 00:34:20,924
but how do they transfer some
of that energy

658
00:34:20,926 --> 00:34:22,159
to a tiny particle?

659
00:34:22,260 --> 00:34:25,328
HOPKINS: One possibility for how
supermassive black holes

660
00:34:25,464 --> 00:34:27,631
could accelerate such
enormously energetic

661
00:34:27,733 --> 00:34:31,601
cosmic rays is that they
actually drag or capture via

662
00:34:31,736 --> 00:34:32,936
their gravity

663
00:34:33,071 --> 00:34:36,406
preexisting normal cosmic rays,
which are already

664
00:34:36,541 --> 00:34:37,841
extremely energetic,

665
00:34:37,943 --> 00:34:41,812
and then give them an extra
boost to even higher energies.

666
00:34:41,914 --> 00:34:45,048
MINGARELLI: So supermassive
black holes bend the fabric

667
00:34:45,117 --> 00:34:46,450
of spacetime around them,

668
00:34:46,551 --> 00:34:50,620
and even light particles can
get stuck, and cosmic rays are

669
00:34:50,622 --> 00:34:53,657
no different -- they can also be
attracted by the supermassive

670
00:34:53,758 --> 00:34:57,360
black holes and get drawn
into their orbit.

671
00:34:57,462 --> 00:35:00,831
ROWE: It makes sense that
the black hole captures

672
00:35:00,833 --> 00:35:02,499
passing cosmic rays,

673
00:35:02,601 --> 00:35:05,635
but how do the particles
escape its clutches

674
00:35:05,737 --> 00:35:07,104
and hurtle towards us?

675
00:35:08,474 --> 00:35:12,275
M87 has a fearsome weapon
in its arsenal.

676
00:35:12,277 --> 00:35:17,314
Enormous jets of energy
blast out of its poles.

677
00:35:17,316 --> 00:35:20,851
TREMBLAY: So M87's jets are
spectacularly large,

678
00:35:20,986 --> 00:35:23,954
larger than the entire galaxy
that houses this black hole

679
00:35:24,056 --> 00:35:25,422
that's launching those jets.

680
00:35:25,524 --> 00:35:28,158
ROWE: The powerful jets
may give the cosmic rays

681
00:35:28,193 --> 00:35:29,559
a speed injection,

682
00:35:29,661 --> 00:35:33,163
transforming them from
galactic rifle bullets into

683
00:35:33,265 --> 00:35:36,500
ultra-high-energy
hypersonic missiles.

684
00:35:36,602 --> 00:35:41,037
So imagine if you had
a regular bullet that

685
00:35:41,139 --> 00:35:43,807
you fired out of a gun
at high speed,

686
00:35:43,809 --> 00:35:47,944
and as its flying,
a little rocket motor in

687
00:35:48,079 --> 00:35:52,315
the bullet kicks in and takes
it up to even higher speeds.

688
00:35:52,317 --> 00:35:54,651
That's sort of what's
happening to

689
00:35:54,753 --> 00:35:57,120
the cosmic rays in these jets.

690
00:35:58,457 --> 00:36:00,357
ROWE: Black holes may be
the supervillains

691
00:36:00,458 --> 00:36:02,025
we've been looking for,

692
00:36:02,027 --> 00:36:04,928
firing out the fastest
cosmic bullets,

693
00:36:04,930 --> 00:36:08,899
but cosmic rays have
a superpower of their own.

694
00:36:08,901 --> 00:36:10,400
They're time travelers.

695
00:36:18,110 --> 00:36:20,710
ROWE: Cosmic rays race through
the universe at close

696
00:36:20,845 --> 00:36:24,814
to the speed of light --
Like subatomic bullets,

697
00:36:24,917 --> 00:36:28,919
they can pierce spaceships
and harm astronauts.

698
00:36:31,924 --> 00:36:34,624
But down on Earth,
we're protected.

699
00:36:36,562 --> 00:36:41,698
Out of all of the rocky inner
planets in the solar system,

700
00:36:41,700 --> 00:36:44,201
the Earth is the only one
to generate

701
00:36:44,336 --> 00:36:48,305
its own deflector shield
against this cosmic radiation.

702
00:36:48,373 --> 00:36:50,607
That's amazing.
And that's where life is.

703
00:36:50,742 --> 00:36:54,211
I don't think that's actually
all that much of a coincidence.

704
00:36:54,346 --> 00:36:58,048
ROWE: The Earth creates
its own magnetic field.

705
00:36:58,116 --> 00:37:01,218
The Earth has this wonderful
active molten core of metal.

706
00:37:01,320 --> 00:37:04,788
All of that metal is moving
around inside the Earth,

707
00:37:04,790 --> 00:37:07,557
and that moving metal generates
a strong magnetic field.

708
00:37:07,659 --> 00:37:09,926
These cosmic rays are
electrically charged.

709
00:37:09,928 --> 00:37:11,561
They follow a magnetic field.

710
00:37:11,663 --> 00:37:13,964
So our magnetic field
deflects most

711
00:37:14,065 --> 00:37:15,932
of the cosmic rays around it.

712
00:37:16,034 --> 00:37:18,201
ROWE:
The shield is not perfect.

713
00:37:18,203 --> 00:37:21,271
Some cosmic rays do get through,

714
00:37:21,273 --> 00:37:24,307
but then they hit
our second line of defense --

715
00:37:24,309 --> 00:37:25,809
The atmosphere.

716
00:37:25,811 --> 00:37:27,844
One of the things we have to
be thankful for is

717
00:37:27,979 --> 00:37:30,513
our atmosphere -- not only
does it give us air to breathe,

718
00:37:30,649 --> 00:37:32,515
but it protects us
from these space bullets.

719
00:37:32,517 --> 00:37:37,754
ROWE: The atmosphere is like
a missile defense system.

720
00:37:37,822 --> 00:37:40,624
Cosmic rays collide
with air molecules,

721
00:37:40,626 --> 00:37:44,127
shattering into
safer, smaller particles.

722
00:37:44,262 --> 00:37:48,365
The most common ones
are called muons.

723
00:37:49,701 --> 00:37:54,204
The muons are the children
of the cosmic rays.

724
00:37:54,306 --> 00:37:57,540
They're produced by
these high-energy collisions

725
00:37:57,609 --> 00:37:58,908
in our upper atmosphere that

726
00:37:58,910 --> 00:38:02,545
create these showers of
muons that then come down to

727
00:38:02,647 --> 00:38:03,779
the surface.

728
00:38:03,781 --> 00:38:06,016
There's as many as four of
these cosmic rays passing

729
00:38:06,018 --> 00:38:07,617
through my hand every second.

730
00:38:07,619 --> 00:38:09,719
They're passing through
your body right now.

731
00:38:09,788 --> 00:38:11,755
ROWE:
Muons are so abundant,

732
00:38:11,856 --> 00:38:14,824
we don't need a high-tech
observatory to detect them,

733
00:38:14,959 --> 00:38:18,762
just a few things you'd find
in a high school science lab.

734
00:38:18,830 --> 00:38:23,133
A small aquarium that I've
attached a small piece of felt

735
00:38:23,234 --> 00:38:24,801
to the bottom.

736
00:38:24,803 --> 00:38:27,804
Some frozen carbon dioxide,
some dry ice,

737
00:38:27,906 --> 00:38:33,810
hence the safety gloves,
a flat piece of metal like this,

738
00:38:33,812 --> 00:38:35,645
some isopropyl alcohol.

739
00:38:37,416 --> 00:38:40,050
Then I flip the whole thing over

740
00:38:40,151 --> 00:38:43,320
onto the bottom, and I wait.

741
00:38:45,524 --> 00:38:49,526
So what's happening is that
the alcohol in the felt is

742
00:38:49,528 --> 00:38:52,929
evaporating in sinking down,
and because

743
00:38:52,931 --> 00:38:55,732
that bottom layer is
so cold from the dry ice,

744
00:38:55,734 --> 00:39:00,136
it forms a super saturated
cloud of alcohol vapor.

745
00:39:01,506 --> 00:39:05,308
ROWE: When the charged particles
pass through the cold vapor,

746
00:39:05,310 --> 00:39:09,713
they create tiny ghostly trails.

747
00:39:09,815 --> 00:39:12,615
What we're looking for
are the muons,

748
00:39:12,617 --> 00:39:16,219
the subatomic particles
generated when a cosmic ray

749
00:39:16,354 --> 00:39:18,722
strikes the upper atmosphere.

750
00:39:18,724 --> 00:39:21,825
ROWE: Each silvery thread
in the cloud chamber

751
00:39:21,960 --> 00:39:25,028
is the sign of a cosmic ray.

752
00:39:25,030 --> 00:39:28,898
These muons should never
make it down to Earth at all.

753
00:39:28,900 --> 00:39:34,003
They only live for 2.2
microseconds before breaking up,

754
00:39:34,005 --> 00:39:35,705
not enough time to travel

755
00:39:35,807 --> 00:39:38,708
through six miles of
Earth's atmosphere.

756
00:39:38,710 --> 00:39:41,845
Naively, we would think there's
no way that a muon could make it

757
00:39:41,980 --> 00:39:44,147
from the upper atmosphere
to where we are now

758
00:39:44,249 --> 00:39:45,215
without decaying.

759
00:39:45,217 --> 00:39:47,016
It turns out they do,
and the only

760
00:39:47,018 --> 00:39:50,920
way they do this is
they effectively time travel.

761
00:39:50,922 --> 00:39:54,424
The muons move at 98 percent
the speed of light.

762
00:39:55,827 --> 00:39:57,527
They move so fast,

763
00:39:57,529 --> 00:40:01,064
they experience what Einstein
called time dilation.

764
00:40:01,132 --> 00:40:04,734
Albert Einstein taught us that
we live

765
00:40:04,803 --> 00:40:06,736
in a space time,
and so that means

766
00:40:06,805 --> 00:40:10,340
that all measurements of
lengths and durations of time

767
00:40:10,409 --> 00:40:11,941
are relative.

768
00:40:12,043 --> 00:40:13,810
ROWE: From
a muon's perspective,

769
00:40:13,912 --> 00:40:17,447
we humans move
incredibly slowly.

770
00:40:17,516 --> 00:40:20,817
They're moving so fast that,
for them,

771
00:40:20,819 --> 00:40:23,720
time is stretched out.

772
00:40:23,822 --> 00:40:27,857
What we found by measuring
the energy and the lifetime of

773
00:40:27,959 --> 00:40:33,229
muons is that as muons got
closer to the speed of light,

774
00:40:33,331 --> 00:40:37,734
their lifetime increased,
because to them, time is

775
00:40:37,803 --> 00:40:41,237
slowing down, exactly the way
Einstein predicted.

776
00:40:41,339 --> 00:40:45,408
OLUSEYI: Their lifespan is
extended by more than 20 times

777
00:40:45,410 --> 00:40:46,609
from our perspective,

778
00:40:46,711 --> 00:40:49,012
so they make it to the ground.

779
00:40:51,950 --> 00:40:55,952
ROWE: Cosmic rays are
the ultimate space travelers.

780
00:40:56,054 --> 00:40:59,722
They're awe-inspiring speed
allows us to unlock

781
00:40:59,825 --> 00:41:03,426
hidden processes and test
our theories of physics.

782
00:41:04,729 --> 00:41:06,463
They're way more energetic
than anything

783
00:41:06,531 --> 00:41:08,465
we can do in a laboratory
on Earth.

784
00:41:08,533 --> 00:41:10,400
So that means we can unlock
all kinds of

785
00:41:10,502 --> 00:41:13,036
new domains about physics
at the highest,

786
00:41:13,137 --> 00:41:15,238
most extreme energies.

787
00:41:15,307 --> 00:41:17,874
ROWE: They're our best link
to the farthest reaches of

788
00:41:17,876 --> 00:41:19,642
the cosmos.

789
00:41:19,711 --> 00:41:23,446
To me, it's really exciting
that we're actually sampling

790
00:41:23,548 --> 00:41:26,316
pieces of matter from distant

791
00:41:26,418 --> 00:41:30,220
stars, from distant galaxies,
and we're getting them here at

792
00:41:30,222 --> 00:41:31,955
Earth and studying them.

793
00:41:33,925 --> 00:41:37,427
There are so many amazingly
violent events in the universe,

794
00:41:37,429 --> 00:41:40,330
the birth of black holes,
exploding stars.

795
00:41:40,332 --> 00:41:42,365
These cosmic rays that are
going through your body

796
00:41:42,433 --> 00:41:45,602
right now are messengers
from those events.

797
00:41:45,604 --> 00:41:47,504
In some way,
you're still connected to

798
00:41:47,606 --> 00:41:49,939
those events, millions
of light years away.

799
00:41:51,843 --> 00:41:54,043
These are messengers
from the universe,

800
00:41:54,112 --> 00:41:56,012
telling us about how it works.