All language subtitles for The universe S06E02 Nemesis The Suns Evil Twin

Male narrator: In the beginning,
there was darkness,

and then, bang,

giving birth to an endless
expanding existence

of time, space, and matter.

Every day, new discoveries
are unlocking the mysterious,

the mind-blowing,
the deadly secrets

of a place we call
The Universe.

Could our Sun
have an evil companion,

an undiscovered death star

rotating at the furthest edges
of the solar system?

Does this mysterious star

scatter destruction
through the solar system

at regular intervals,

accounting
for the greatest extinctions

in Earth's history?

Sifting through a realm
populated by giant worlds

and mysterious planetoids,

scientists are on the hunt
for Nemesis,

the Sun's evil twin.

Of the billions of stars
twinkling overhead,

one may be a scourge
to life on Earth,

an evil twin to the Sun
named Nemesis.

Some scientists suspect
that Nemesis is a dark,

still-undiscovered star
orbiting our Sun.

And every 26 million years,
it triggers a disaster.

- We know that the solar system
is surrounded

by this enormous cloud
of comets,

and so these successive passages
of the Sun's companion

would send comets
into the inner solar system.

Some of them would hit Earth.

Narrator: What follows is death
on a colossal scale.

It is now widely accepted
that a rock from space

caused the end
of the age of dinosaurs

65 million years ago.

- So we now are pretty convinced
that the reason

that a huge fraction
of life on the Earth

went extinct
65 million years ago

was because a comet slammed
into the Earth.

Narrator:
But astronomer Richard Muller

has proposed
a revolutionary theory

to explain why that space rock
crashed to Earth

at that particular moment.

- The Nemesis theory postulates
that there's a star

orbiting the Sun
at a 26-million-year period.

That's about it.

Almost no other assumptions
need to be made.

Narrator: Muller believes
that as Nemesis nears the Sun,

its gravitational disturbance

sends comets flying
through the solar system.

The resulting impacts
have been the source

of many major extinction events
in Earth's history.

Muller explains
how the theory came about.

- Two paleontologists,

when looking at patterns
of extinctions,

came across something
that seemed utterly insane.

They said
that similar extinctions

were taking place
every 26 million years

on a regular schedule.

Narrator: The discovery
of a 26-million-year pattern

of extinctions
seemed impossible to explain

by any process
native to the Earth itself.

- This is the sort of thing
you dream about in science.

It means there's something
we don't understand.

It means there's
a discovery waiting.

So I set about trying
to figure out what that was.

Narrator: Muller made
an astonishing proposal.

The only logical cause
of these periodic extinctions

is a cosmic stalker

that orbits our Sun
every 26 million years,

disturbing the comets
on each approach;

in short, a death star companion
to our Sun.

- If this star is discovered,
it is so important.

It was a major player

in the evolution
of life on Earth.

Without this,

perhaps the dinosaurs
would still be here.

Narrator:
If Muller is right,

humanity itself
could owe its existence

to the Nemesis death star.

After all,
each mass extinction

wiped out vast numbers
of species,

but each also cleared the way
for new species to arise,

including,
ultimately, humans.

We can witness the way Nemesis

would have altered evolution
on Earth

by looking at a controlled burn

on the Santa Rosa Plateau
in California.

- So every now and again,
some cataclysmic event happens

that wipes out a huge number
of species here on Earth.

And this is just like happens
with these controlled burns,

where the burn wipes out
a number of species,

which then makes room
for new things to take hold.

[fire crackling]

So I'm seeing
the fire raging behind us.

What's going on there?

Why do you light fires?

- We're out here
setting this fire

to clear part
of this vegetation away,

to get rid
of the nonnative species

of plants
that are growing here

so the native can grow back.

We come here and burn annually
in different plots of land

so that it can be studied,

and we can also see the impact
it's having on that environment.

Narrator:
A prescribed fire

mimics the kinds
of mass extinctions

that Nemesis may have caused.

Many species are swept away,

but the destruction leaves room
for the survivors to flourish

and evolve...

just as mammals survived
and thrived

after the fiery death
of the dinosaurs,

setting the stage
for human evolution.

These prescribed fires return
to Santa Rosa every year

and imitate
the driving motivation

behind the creation
of the Nemesis hypothesis

that extinctions occur
over and over.

- There are really
only two viable explanations

for the regularity
of the extinctions.

One of them is
the Nemesis theory.

The other is that,
by the throw of the dice,

they just accidentally
happen to line up

every 26 million years.

Narrator: But how exactly would
Nemesis trigger extinctions

with the regularity
of a prescribed burn?

The possible answer lies
in a region of the solar system

known as the Oort cloud.

- The Oort cloud is the place

where comets are kept
in cold storage

until they come screaming in
towards the Sun.

So these things are sitting
in deep freeze,

sort of at the distance
halfway between us

and the nearest stars.

Narrator. The vast majority
of Oort cloud comets

orbit at the safe distance

of up to one light-year
from the Sun...

that is, unless something
disturbs their orbits.

- Occasionally,
a star will come by,

and they get
a little bit jostled.

And a little jostling
can do a lot of things.

It can make them go away
and leave the Sun entirely.

It can put them
on a slightly different orbit.

But one of the things it can do
is put them on an orbit

that slowly falls in
toward the Sun.

Narrator: By following
the motions of a juggler,

astronomer Greg Laughlin
can help visualize

why cometary orbits are
so vulnerable

to the effects of a passing star
like Nemesis.

- Hey, Greg.

- So this is Josh Horton,

and we've enlisted Josh
to kind of help us understand

how the Oort cloud really works.

How many balls
are you actually able

to keep up in the air
at one time?

- That was seven.

I can do a little bit
of eight and nine,

but seven is what
I practice the most.

- The arc of something
that a juggler is tossing up

is very much like the arc
that a comet makes

on its centric orbit,

especially because it's going
slow near the top,

and it's going very quickly
near the bottom.

If we want to simulate
the whole Oort cloud,

then we've gotta keep
a lot of balls in motion.

So I'm wondering if you
can maybe give me a quick—

- Yeah.
Yeah, I can try.

Okay, well,
let's start with two.

- Two balls.

- And so what
you're gonna do here is,

you're gonna cross both balls
in the air.

So it's gonna be throw—no.

The throws are exactly the same,

just like the path of a comet.

So...cross, cross.

And they are making an X
in the air.

- Do they leave
at the same time or—

- No, it's right, left,
catch, catch.

- Right, left—

- Yeah, that was it.

Just throw your left hand
a little bit higher.

- Right, left, catch, catch.

- Good, you're kind of
catching 'em at the same time.

- Right, left, catch, catch.
- That was better.

- So I'm a little bit
like a solar system

where there's some serious

gravitational instability
in the mix.

So Josh is keeping seven balls
in the air at the same time,

and that's not unlike
the Sun's job,

which is to keep
trillions of comets

all orbiting
in the Oort cloud.

Narrator: But according
to the Nemesis hypothesis,

the Sun's delicate juggling act

is disrupted
by its evil stellar twin

every 26 million years.

And like something
out of a horror movie,

this evil twin
could be nearly invisible.

Does our Sun
have an evil twin,

a star named "Nemesis"

orbiting the distant reaches
of our solar system?

And every 26 million years,

does it fling comets from
the Oort cloud toward Earth?

- Sometimes they get tossed out;

other times,
they orbit harmlessly

until they evaporate
and go away.

If you have comets rattling
through the inner solar system,

then, in a sense,
all bets are off.

Narrator:
Scientist Richard Muller

not only theorizes
that this periodic mayhem

is caused by a deadly
companion star to the Sun,

he believes he knows precisely
what kind of star it is:

a red dwarf.

- That there is a star
orbiting the Sun

in a 26-million-year period,
that was my idea.

Let's assume the star is
a red dwarf star.

Why a red dwarf?

Because that's the most populous
star in the galaxy.

Narrator:
A red dwarf is a tiny star

that weighs in with a mass
less than 1/10 of our Sun.

But as astronomer Greg Laughlin
demonstrates,

it can have the effect
of a nine-pound bowling ball

tossed into the arms
of a juggler playing with fire.

- All by itself, the Oort cloud
is a pretty boring place,

and so we're gonna have to
up the ante a little bit.

These are gonna represent
the comets in the Oort cloud.

- Are you ready?

- I think I'm gonna step back
a little bit.

So Josh has got 'em all
going nicely,

just like the comets orbiting
in the Oort cloud.

So let's see what would happen
if I took this red dwarf

and tossed it
into the solar system.

Josh, are you ready
for the red dwarf?

- Yeah.

- Here we go.

- Oh!

- So as you can see,
the red dwarf

coming through the solar system

has really changed the orbits
of the comets.

Notice that two of these comets
actually crashed onto the Earth.

That's not unlike what happens
when a giant impact occurs

and we get one of these
mass extinctions.

Narrator:
For many people,

the idea that Earth
has been the victim

of a series of impacts caused
by an orbiting death star

seems unlikely.

After all,
when we look at the sky,

we only see one Sun.

But in fact, the majority
of stars come in pairs.

- Probably something
like 60%, 70% of stars

may indeed be binary

or have even higher numbers
of stars in the system.

Narrator: According
to Richard Muller's

Nemesis hypothesis,

our Sun is part of such
a binary star system.

- It all works.

All you have to do is
hypothesize that the Sun,

like 2/3 of all the other stars
in the galaxy,

has a companion—

This one
with a 26-million-year period—

And there you have it.

Narrator: But if so,
why don't we see

the Sun's twin in the sky?

According to Muller,
the reason is simple.

Nemesis is an extremely dim
red dwarf.

- When I first came up with
the Nemesis theory,

the issue was,
"Well, wait a minute.

How come nobody found it?"

And that was pretty obvious.

It has to be hard to find.

Narrator: By definition,
a red dwarf barely glows at all.

- It would be the closest star
to our Sun,

and we wouldn't even know it.

Now, why is that?

The way we discover
nearby stars

is either because
they're very bright—

And a red dwarf star
is not very bright—

Or because the Sun
is moving past it.

This star is moving with us.

Yes, it's orbiting us,
but that orbit is very slow:

26 million years.

So it'd be moving with us.

It would just be at
a fixed position in the sky

and wouldn't move.

Narrator: In other words,
when viewed from Earth,

most nearby objects
are shifting over time.

But Nemesis is sitting still.

So as the search for Nemesis
enters high gear,

one key question is
where to look.

Luckily,
scientists understand

how binary stars
orbit each other,

and they can apply
this knowledge

to the search for Nemesis.

If both the Sun and Nemesis
were of equal mass,

they would orbit each other
in a vast but equal circle,

and the search for Nemesis
would be relatively easy.

But binary stars are rarely
equally sized.

- 10% or 20% of binary stars
have two components

where the stars are really
on an equal footing.

And then there are also
a large number of stars

where one star is considerably
more massive than the other.

Narrator: When binary stars
are of different sizes,

the smaller star—
in this case, Nemesis—

Swings in a wide orbit
around its larger companion—

In this case, the Sun—

Which barely seems
to orbit at all.

Why does the smaller one move
in a much wider circle?

The answer has to do
with a concept called

the center of mass.

A pair of gymnasts
on a balance beam

can help us visualize
how it works.

- Stars in a binary pair

orbit around their common
center of mass.

If two stars are
about the same mass,

they orbit around
an invisible spot in the middle,

right in between
the two of them,

just like Tami and Carly
are balanced on this seesaw.

Wow, are you guys balanced?

Narrator:
But unlike these gymnasts,

Nemesis and the Sun
are not equal.

Astronomer Richard Muller
estimates

that the Sun has
ten times more mass

than its undiscovered twin.

And when one binary star
is larger than its sibling,

the center of mass between them

shifts closer
to the larger star.

- So Tami's going to help
illustrate that.

Tami, how much do you weigh?

- About 130.
- About 1307

And we have weights at this end
that are about 35 pounds.

So you're just a little bit less
than four times that weight.

So climb on up.

Let's see where you have to be
to balance the balance beam.

Narrator: Since Tami weighs
about four times as much

as the metal weights,

she must move far closer
to the center of mass

to maintain balance.

If Tami and the weights
represented binary stars,

the weights would orbit
far out in the distance,

while Tami would barely move.

In fact, both would be orbiting
each other.

- It's kind of a misconception
to think

that the more massive star
doesn't move

and the less massive star
just goes around it.

In fact, they're still
both orbiting

the common center of mass.

The more massive star
moves less,

and the less massive star
moves more.

Narrator: This insight
is key to calculating

where Nemesis might lie
in relation to the Sun.

- We know it's
a 26-million-year period.

That tells us how far out it is.

It has a radius of about
a little over a light-year.

So we know the orbital size.

Narrator: Now that scientists
know roughly where to look,

the search for Nemesis is
in full swing.

And so far, that search has led
to an astounding new theory.

Not only might the Sun have
an undiscovered twin,

the solar system
may be harboring

a massive undiscovered planet.

In the hunt for an evil twin
to our Sun

that shakes comets loose

and rains death
across the Earth,

all of the pieces are in place
except one.

- The Nemesis theory really
needs the smoking gun

of actually finding
direct evidence

for the object itself

in order for the whole thing
to hold together.

- Now, why haven't we
found it yet?

Actually, there are
quite a few astronomers

who don't pay
very much attention to this

and simply assume
that if it existed,

it would have been found by now.

We believe this thing can be
found within the next few years.

What it takes is a survey
of dim stars.

Narrator:
Enter W.I.S.E.,

the orbiting Wide-field
Infrared Survey Explorer,

a powerful new tool
that just might crack

the Nemesis mystery.

- The reason that W.I.S.E. is
gonna be so good is because

it operates in the infrared.

It sees heat, basically.

Narrator: By measuring heat
instead of light,

infrared scanners can make warm
but dark objects easy to spot.

- The nice thing about looking
in the infrared

at the heat of it is,

you don't care how far away
you are from the Sun.

Narrator:
Jupiter provides an example.

The temperature
on the surface of Jupiter

measures 230 degrees
below zero Fahrenheit.

But that's blazing hot
when contrasted with

the 450-degree-below-zero
temperature of space.

So even in the absence
of sunlight,

a distant, Jupiter-like planet

would glow brightly
in the infrared.

[engines revving]

By visiting a motor speedway,

we can see
how the W.I.S.E. survey

might help find Nemesis

by exploiting
the infrared contrast

between objects
of different temperatures.

Here, the roar of the engine
only tells half the story.

- I came out here today
to the Drive Tech Racing School

to be in a race car
that would go zooming

around this track
a bunch of times.

And the idea was to film the car
with an infrared camera

and show us things
that are hot—

Hotter than
the outside surroundings—

And glowing
at infrared wavelengths.

So hey, Ted.
- How you doing?

- Good to meet you.
- Likewise.

- Yeah.
You're the driver?

- Yes, sir.

- Now, how fast are we
gonna be going?

- Approximately
170 miles an hour.

- Now, that's about three times
normal highway driving speed,

so, whoa, things are
really gonna heat up.

- Oh, yeah.

- All right, let's go, then.

Blair Dupree of Drive Tech
helped me get into the car.

- Good protection.
- This is a nice, thick helmet.

And it's not so easy,
'cause there's no doors, okay?

You have to kind of climb in
through a window.

- Bring your left foot
up in there.

- Okay.

- Bring your right foot on up.

- I feel like I'm breaking
into a car.

And then kind of slither
your way in.

[engine revving]

Being in that race car was
really exciting.

When I was going
around the turns,

I could really feel
the G-forces.

- Ted give you a good ride,
did he?

- Yeah, well, I'm glad
Ted was the driver.

I couldn't do this, you know?

I was scared out of my seat,

and I wasn't even
the driver, okay?

Narrator:
With the car nicely warmed,

a FLIR infrared camera,

set up by thermal-imaging expert
Ross Over street,

sees everything,
literally, in a new light.

- Hello, Alex.
- Hey, Ross, how you doing?

- Doing good.
How are you doing?

- Good, good, let's look
at these infrared images.

- Right now we're pointed
at the back of the car.

The best way
to think about it is,

it's more of a measurement
device than a camera.

It's like having a million
different thermometers spread

across the image.

We're actually getting
temperature measurements

on each of those pixels.

Things that are
supposed to be hot

look like they're glowing.

They're red and orange
and white.

And things that are cold
are colored blue and black

and, you know, colors you
associate with cool objects.

- Right.

- And you'll notice there's

several different hot areas
of the vehicle.

- Now, I see some variations
across the tires.

- Yeah, and you'll notice
that the one tire

is a little bit warmer
than the other.

- The right-hand tire
was indeed hotter

than the left-hand tire

because there was more pressure
on it during the turns.

So how hot is
that hotter tire there?

- We made a measurement earlier
of about 190 degrees Fahrenheit.

Almost the temperature
of boiling water on the tires.

- Wow.

When we just look by eye,

we can't tell whether something
is hotter than something else.

But here you can tell,
and that's really cool.

- Right, and this camera
would work just as well

if it was pitch black
or in the middle of the day.

It doesn't care
about solar light at all.

Narrator: The infrared camera
sees the racetrack

the way the W.I.S.E. survey

scans the dark
and faraway realms

of our solar system.

If Nemesis is out there,
infrared should reveal it.

- The hot spots on the race car

are sort of like
warm, glowing objects

out in the cold depths of space,
far from the Sun.

This is a whole new way
of discovering objects,

objects too faint to be seen

through a normal
optical telescope

but bright enough to be
detected in the infrared.

Narrator: The W.I.S.E. telescope
completed its sky survey

in early 2011,

but in the search for Nemesis,

the results are still
inconclusive.

- The W.I.S.E. survey is going
to take a long time to analyze

simply because
there's a huge amount of data

that had been gathered
by this craft.

- About half
of the Nemesis candidates

have not yet been studied.

But in the next few years,

we expect the theory will be
either proven right or wrong.

Until that time, it is
and should be controversial.

Narrator. That something
so relatively near to Earth

can be so obscure

is what Frank Jankowski
of Mobile, Alabama,

wants to ask the universe.

- That's an interesting
question, Frank.

The objects that are millions
of light-years away

that astronomers can see
are powerful and luminous.

They produce a lot of energy
on their own,

like an exploding star.

But an object near the edge of
our solar system might be small,

and it reflects only
a little bit of sunlight,

so we can't see it
at visible wavelengths.

Narrator: But as scientists
analyze the data

for signs of Nemesis,

they have made
a disturbing discovery.

Although calculations indicate

that Nemesis isn't due back
for millions of years,

something appears to be
shaking up the comets

in the Oort cloud right now.

Could Nemesis already be
upon us?

Since the birth
of the Nemesis hypothesis,

astronomers have been
on the lookout

for a faint red star

that periodically disturbs
the gravitation

of the Oort cloud comets.

This sends them
on a catastrophic rendezvous

with the inner solar system,
including Earth,

every 26 million years.

But as scientists study
the Oort cloud,

they have uncovered
unsettling evidence

that something is disturbing
comet orbits right now.

Has Nemesis already returned?

- If the Sun was all by itself
and there was no Nemesis,

then the comets
in the Oort cloud

would all have very predictable
and regular orbits.

They would be very regular
in their arrival times

and departure times.

Narrator: Without
gravitational interference

from anything other
than the Sun,

Oort cloud comets,
like juggled objects,

could spread out evenly
across the sky.

However, that's not what
some scientists report.

- When we look out into the sky

and look at where the comets
are coming from,

their directions tend
to concentrate

in a certain region of the sky.

And one possible explanation
for that

is that that skew
is being directed

by the gravitational
perturbations

from an unseen object
that is out there.

Narrator:
Based on these observations,

scientists infer
that a huge object

is disturbing the Oort cloud.

They do this the same way

that California
transit officials infer

that an accident is disturbing
traffic patterns in Los Angeles.

- So, Marco, where are we?
What is this room?

- Well, the map we have here
on the wall,

that's our freeway system map.

And as you can see, it shows
the major freeway routes

in Los Angeles.

Narrator. The green dots
represent normal traffic flow,

while the red dots indicate

that something is causing
traffic to back up.

- So the speed here
is just one indicator

that something's going on,

but to really know
what's going on,

you either have to have
a camera or a report

from somebody
who's actually there

and able to tell you what it is.

- That's correct.

- Astronomers have this problem
all the time.

They're trying to understand
what they can't actually see.

In astronomy,
we frequently infer

the existence of something

not because
we can actually see it

but because we can see
the influence it has

on the objects around it.

Narrator. Whether too many cars
are crowding too few lanes

during rush hour

or an accident is slowing
traffic flow,

something causes congestion.

Since scientists see similar
congestion in the Oort cloud,

could Nemesis be
the perpetrator?

- This place is
very impressive.

It's got all the cameras,
all the sensor data,

all the California
Highway Patrol incident reports.

This is far more data than
astronomers have to work with.

If we only had remote cameras

all throughout the outskirts
of the solar system,

we might know
a lot more about it.

Narrator:
Even without remote cameras,

scientists have proposed
a remarkable theory

to explain the congestion
in the Oort cloud.

According to this theory,

the culprit disturbing
the Oort cloud isn't Nemesis.

Instead, it's something
equally astounding:

a giant, undiscovered planet
four times the mass of Jupiter;

in short, the largest planet
in the solar system.

Scientists have proposed
naming it Tyche.

- In a nutshell, Tyche is
"Nemesis light."

Nemesis,
in the original hypothesis,

was literally a red dwarf star,

something that was 100 times
more massive than Jupiter.

Narrator:
Unlike Nemesis,

Tyche would not glow
like a star.

Instead, it would look like
a strange version of Jupiter.

- If you put on
night-vision goggles,

then it would be quite
a bit more impressive sight.

You would see breaks
in the clouds,

and there would be lightning.

You would see the clouds
light up from the lightning

down beneath the cloud tops.

Narrator: Tyche may disturb
the orbits

of comets in the Oort cloud,

but it can't be the source
of Earth's periodic extinctions.

First, its proposed position

puts it
on a 1-million-year orbit,

not 26 million,
like Nemesis.

Second, it's too small.

- Tyche doesn't really have
the gravitational mojo

to dislodge comets,

send them crashing in
in these periodic extinctions,

really rearrange the Oort cloud.

And so its effects
would be visible

only in these small skews

and not in the form
of huge pulses of comets

coming out of seemingly nowhere.

Narrator:
Just as with Nemesis,

NASA's W.I.S.E. survey
should be able to detect Tyche,

if it exists.

While it's surprising
that our solar system

might harbor a giant,
undiscovered planet,

it doesn't support
or refute the idea

that it also harbors
the undiscovered star Nemesis.

But a recent finding
in the outer solar system

may shed more light on whether
Nemesis really exists

and the kind of threat
it may pose to life on Earth.

In 2003, astronomer Mike Brown
made an historic discovery

when he found something floating
around the night sky

he couldn't explain.

- I remember the day
that I discovered Sedna.

Looking at it
on my computer screen,

looking at these pictures,
my first reaction was,

"That can't be real.

"It's too far away.

Nothing like that exists
in the solar system."

Narrator: What he stumbled upon
turned out to be a planetoid

just smaller than our Moon,
now named Sedna.

But Sedna presents
a scientific quandary.

At its nearest point,
Sedna lies about three times

farther away from the Sun
than Pluto

in a region where astronomers
never expected to find

planetary bodies.

- It's the coldest,
most distant place

that we know
in the whole solar system.

If you were sitting
on the surface of Sedna,

you could take a straight pin
and hold it out at arm's length,

and with the head of that pin,
you could cover up the Sun.

Narrator:
In addition to being

in an unexpectedly
distant region,

Sedna also takes
a wildly elliptical orbit

through the solar system.

The mystery is, there's nothing
anywhere near Sedna

that could account for an orbit
that distant and that extreme.

- The place where it is now,
nothing ever affects it.

It doesn't come close
to any planets.

There are no stars that
ever come close to it.

Narrator: So what forced Sedna
into its unique orbit?

And in theory,
could the death star Nemesis

have played a role?

For Brown,
the bounce of a trampoline

offers a way to understand
how Sedna ended up in an orbit

that remains a head-scratcher
for astronomers.

- I have behind me
a measuring stick

that gives how high
I'm gonna bounce

in two-foot intervals
you see here.

And what that bounce
is supposed to represent is

how far away from the Sun
I am in my orbit.

In a normal planetary orbit,
in a circular planetary orbit,

the planet circles
around the Sun,

always staying the same distance
from the Sun.

And that's sort of like me
staying on a trampoline.

I'm always the same distance
from the floor.

Other sorts of orbits can be,

instead of going
in a circular orbit,

you can go
in an elliptical orbit

around the Sun.

You move away from the Sun.

You come back towards the Sun.

And so you'll be moving
further away and getting closer.

And that would be starting
to jump up and down

on the trampoline.

Narrator: Like gravity
keeping us in orbit,

when we reach the apex
on the trampoline,

gravity will pull us back down.

- So as long as nothing
happens to me,

I stay in this orbit forever,
jumping up and down,

always to the same height.

Narrator. But something unusual
afflicted Sedna.

It brushed up against
a mysterious force

that shoved it into a region

where no planetary body
should exist.

Some suspect that force
was Nemesis.

And if the Sun's evil twin
is out there,

scientists can tell exactly
when we'll see

the terrifying signs
of its return.

As astronomers search
for a death star named Nemesis

that might periodically cause
mass extinctions on Earth,

the recent discovery
of a tiny world named Sedna

could prove key.

Billions of years ago,
Sedna revolved around our Sun,

like other planets,
in a nearly circular orbit.

But then two strange things
happened.

First, something forced Sedna

into an extremely
elliptical orbit.

And then something else
pushed that orbit out so far

that it seems to defy
any visible explanation.

The first question—

What caused
its elliptical orbit—

Is fairly easily explained.

It could simply have been
gravitational tugs

from the outer gas giants
Jupiter and Saturn.

A trampoline
can help illustrate.

- To really understand how
orbits in the solar system work

and we get these
very elliptical orbits,

we need to get more height
on the trampoline.

And I can't do it, so, Ken,
I'm gonna need your help.

- Awesome.
I'm ready to help.

- Let me get out of your way.

Narrator: Just as extra people
on a trampoline

create extra bounce,

the large gas giants
in the solar system

can create
enough gravitational bounce

to stretch
a smaller body's orbit

into a wide ellipse.

- So here's Sedna
on a nice elliptical orbit.

But then Sedna got a little bit
close to one of the planets.

As soon as it does that,
the extra gravity of the planet

gives it a little boost into
an even more elliptical orbit.

But then it gets close
to another planet—

let's say Jupiter.

Here comes Jupiter.

It bounces even higher.

With enough bouncing
from Jupiter,

we could bounce Sedna

all of the way out
of the solar system.

Narrator: The orbital bounce
provided by Jupiter and Saturn

can explain how Sedna's orbit
got its elliptical shape

but not how it ended up being
forced into a distant region

of the solar system,

where scientists never expected
to find a planetary body.

- Sedna was on
an elliptical orbit,

getting further and further
and further.

And then something happened
to it when it was out here.

Some other gravitational force

pushed it off
into a different orbit,

and so it didn't come back
to the same place it was before.

Narrator: It's as if
some second gravitational force

was passing by and shoved Sedna
onto a different trampoline

so that it bounces
in an unexpected region.

- The most likely answer is that
there was another star

very, very close to the Sun

at the time when Sedna was going
through this process.

- The solar system probably
formed in a cluster of stars,

and so close encounters
with nearby stars,

nearby rogue planets even,

were much more common
during the very earliest days

of the solar system's formation.

Narrator: Most of these solar
brothers and sisters

have long since dispersed.

But according
to the Nemesis hypothesis,

one of them is still out there,
still circling the Sun,

still causing periodic chaos
amongst the comets,

and still waiting to rain death
on the Earth once more.

If that is correct,
future generations will be faced

with a monumental threat
when Nemesis returns...

in 10 million years.

- The Moon, Mars, the planets
would basically be unaltered

from their current condition.

On Earth,
cities might not be there,

but the continents
would still be almost

in exactly the same places
that they are now.

Narrator: But according
to the Nemesis hypothesis,

a major change is under way
one light-year from the Sun.

A dark reddish star has entered
the Oort cloud.

Nemesis has returned.

If humans still exist on Earth,

they'll face a slow-building
but imminent cosmic threat.

- The Oort cloud contains
perhaps 10 trillion comets,

maybe even more.

But remember, it's really big.

So if you were
in the Oort cloud,

it's not like you would be
pelted by comets all the time.

The spaces between them
would be pretty big.

Narrator: Like a bowling ball
in a juggler's hands,

Nemesis simply shuffles
some comets out of its way.

- The Oort cloud has an empty
region in the middle.

It's been cleaned out by Jupiter
and by the Sun.

We live in that region.

Narrator:
But as Nemesis approaches,

the inner solar system becomes
a shooting gallery.

- And so there would start to be
a few more comets than usual,

and then, suddenly,
there are just comets, comets

coming all the time.

- And at the peak,
there might be

1,000 to 10,000 comets
per year in the sky.

Narrator:
According to the projections,

Earth would be in the crosshairs
of this comet storm

for a million years.

- Over a period
of a million years,

there would be visits
by about a billion comets.

Actually,
you do the calculation,

it turns out one of them
will hit the Earth,

one or two.

- It would be difficult
to predict

exactly when the impact
would happen,

but there would be this phase,
this sort of danger zone,

in which the chances
for a catastrophic impact

with something
of a comet's size

would be much, much higher
than they are now.

Narrator:
Will the impact spark

another catastrophic extinction
on Earth?

Perhaps.

But only if we let it happen.

- I like to joke that Nemesis
planned this one poorly.

In between the last extinction
and the next one,

there's plenty of time
for intelligent life

to get its act together
to make sure

that next time Nemesis
comes back

and the sky is filled
with comets

to make sure
that none of them hit us.

Narrator:
Is this future inevitable?

Until scientists
either discover Nemesis

or definitively rule it out,

no one can know for sure.

- It's important to realize

this is not just
an abstract discussion.

Clearly, these objects colliding
with Earth happen very rarely.

But on the other hand,
when they do collide,

they're extremely cataclysmic.

So what we need to be able to do

is get better understanding
of our solar system

and keep an eye on the sky,

because it may be crucial
for our survival.

Narrator: If the future sky
one day does fill with comets,

perhaps humanity will have found
a way to save itself

rather than end up
one more victim

of the Sun's evil twin.