Space's Deepest Secrets

We're living in a new golden age of exploration.

Planet hunters are searching

far beyond our solar system for exoplanets.

We're not only finding different continents...

We're actually finding new worlds orbiting other suns.

Thousands of these alien worlds

have already been found,

but this is the story of perhaps the greatest discovery yet,

a star 40 light-years away with seven Earth-sized planets...

Trappist-1.

When we saw this, that was...

It was a very happy morning when we made this plot.

Really like winning the lottery, sort of cosmic lottery.

Now these modern-day explorers

are racing to learn more about these extraordinary worlds.

They want to know

what the planet's surfaces and climates are like

and could any of them win the ultimate battle...

To host life itself?

You'd see this planet light up with a glow,

then that gives us a strong indication

that something is living there on that planet.

Finding life on an alien world

is the ultimate prize for planet hunters,

and it may soon be within reach.

captions paid for by discovery communications

The story begins high in the Atacama desert in Chile.

With some of the clearest skies on Earth,

it's arguably the best place

to spot alien worlds orbiting distant stars.

And sure enough, the aptly named very large telescope

is hunting for exoplanets.

It's actually made up of four massive telescopes,

each of which is one of the biggest ever built.

Together, they form the most advanced

visible light observatory in the world.

So, already, with individual telescopes,

we can see very sharp details,

but when we combine the light of the four of them,

we can actually distinguish the two lights of a car,

of the headlight of a car, on the surface of the moon.

So that's pretty impressive.

The telescopes are used to study everything

from near-Earth asteroids to faraway galaxies.

Dr. Julien Milli is one of their top planet hunters.

We have here the primary mirror,

secondary mirror, tertiary mirror,

and then it sends the light to high-contrast imagery,

so the goal is to make images of planets around the star.

With four 26-foot-wide mirrors,

this is one of the only places in the world

where astronomers can actually see exoplanets.

But even in ideal conditions,

Julien and his colleague face a huge challenge.

Planet hunting can be like finding a needle in a haystack

because the image is full of other spots

that can look like planets,

such as bad pixels and light speckles.

All these elongated features

here or in the center...

You have some little dots close to the star...

These are speckles.

So, this is residual starlight that are created

because of the imperfect optics within the system.

Their task is to rule out

all the dots that are bad pixels in the hope

that they will be left with what's called a companion,

a real planet or other object orbiting the star.

Tonight, they've captured a rare direct image

of an alien world orbiting a distant star

almost 100 light-years away.

But this so-called "companion" is nothing like Earth.

In fact, it's not even strictly a planet...

It's a brown dwarf, an object slightly bigger than a planet.

This one is about 50 Jupiter masses.

We think that the lightest subject

that we're able to see is 1 to 2 Jupiter mass.

We can't go below that, unfortunately,

so we wouldn't be able to detect an Earth, for instance.

Even with the most advanced optical telescope

ever built,

viewing these remote worlds directly

is incredibly challenging.

And seeing exoplanets the size of Earth remains impossible.

Luckily, there's a clever way to find exoplanets

without ever actually seeing them.

The most successful planet-hunting technique so far

has bagged thousands of discoveries.

But as NASA astronomer Natasha Batalha knows well,

you need Patience.

Finding planets is a lot like a stakeout.

You're sitting around, waiting for a very long time

before something actually happens.

It can take months or even years

for a planet to orbit its star.

During most of this time,

they're virtually impossible to detect,

unless they happen to pass in front of their star.

So, if you can imagine a moth flying in front

of a car's head lamp, the head lamp would be so bright

that the moth might be washed out,

but if you looked hard enough,

you get a very, very small dip in brightness,

and so we can detect that brightness,

and so that's how we find planets.

It's very hard to see a distant planet directly,

but if you see the light from its star dim a little,

you know a planet must be passing in front of it,

an event known as a transit.

But this transit technique doesn't work as well

for small planets as big ones.

Now imagine a small fly in front of a car's head lamp.

That fly would be so small

compared to the big light of the head lamp

that the dip in brightness that you see

is very difficult to detect.

An Earth-sized planet blocks 100 times

less light from its star than a Jupiter-sized planet.

So, although hundreds of gas giants have been found

this way, smaller worlds have proved more elusive...

Until one astronomer had the idea of

looking in a different place... Small red dwarf stars.

And that changed everything.

Red dwarfs are many times smaller than stars like our sun,

so Earth-sized planets

will cause a bigger dip in their light,

allowing astronomers to spot small,

rocky worlds like our own.

So, if you're looking for a true Earth-like planet,

it's actually easier around smaller stars.

This simple but revolutionary approach meant

planet hunters didn't need a giant telescope

to search for Earth-sized alien worlds.

And just 500 miles south of the very large telescope

sits a pioneering device that's over 10 times smaller,

the brainchild of Belgian planet hunter Michael Gillon.

My goal was to detect new planets,

with a special focus on small planets

that would be potentially habitable,

so that could have all liquid water on the surface,

possibly, maybe life... Who knows?

To search for these new worlds,

Michael began stalking out red dwarf stars in 2011,

using his small telescope,

which he named "Trappist," after the beer,

which is famously brewed by hand in Belgium.

But unlike Trappist beer,

this robotic telescope can be operated

from anywhere in the world with an Internet connection.

The telescope itself is a remote-controlled device,

so we just press a button and launch a telescope,

and it starts observing.

And during the whole night, it will observe

without any human intervention.

For four years, the Trappist telescope

steadily recorded the brightness of individual stars,

one by one,

waiting for the characteristic dip that reveals a planet,

and it was remarkably successful.

So, in 2015, we had around 100 giant exoplanets

that we contributed to the discovery.

And so it was very encouraging,

but, of course, the dream was still Earth-sized planets.

The Trappist telescope was working perfectly,

but 7,000 miles away,

Michael was still hoping for an historic breakthrough.

Then, on September 16, 2015,

a dramatic sequence of events ended in a huge discovery.

On September 16, 2015,

Trappist was scheduled to watch a very faint red dwarf star

just 40 light-years away, but that night,

a powerful Earthquake struck northern Chile.

The Trappist telescope

was in one of the worst affected areas,

but it was built to withstand seismic events.

When there is a certain level of Earthquake,

the first thing that happens

is that the telescope is going to stop functioning.

The observation stopped,

and the dome was closed in safe mode.

And then, in the morning,

my student noticed the situation,

and she relaunched the observation of the star.

The telescope wasn't damaged,

but by the time it was working again,

the night was nearly over and there were only three hours

left to observe the target star before dawn.

Back in Europe, Michael was analyzing the data

when something caught his eye.

I was at home on my sofa with my laptop,

and I saw a very clear transitlike signal,

and so I was super, super excited, and furthermore,

I knew that the star was small.

So the planet should have been

more or less the size of the Earth.

40 light-years away, an Earth-sized planet

had passed in front of its dwarf star,

and the Earthquake almost caused Michael and his team to miss it.

The Trappist telescope had made its first discovery

of an Earth-sized planet... A huge achievement.