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.

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.

RICHARD MULLER: 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.

RICHARD MULLER: 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.

RICHARD MULLER: 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.

RICHARD MULLER: 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 WISE, the orbiting Wide-field Infrared

Survey Explorer, a powerful new tool that just might

crack the Nemesis mystery.

The reason that WISE is going to 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 0 Fahrenheit.

But that's blazing hot when contrasted

with the 450-degree below 0 temperature of space.

So even in the absence of sunlight,

a distant Jupiter-like planet would

glow brightly in the infrared.

The hot spots of 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 WISE telescope completed

its sky survey in early 2011.

But in the search for Nemesis, the results

are still inconclusive.

The WISE 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.

RICHARD MULLER: 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.