How the Universe Works

Comets... messengers from

the dawn of the solar system.

For the first time, we sent a spacecraft

to orbit and land on one.

To go outside of the inner solar system

and catch a speeding comet

and then send a lander down to land on its surface...

That is nuts.

The Rosetta mission answers

our most fundamental questions.

Rosetta is really teaching us

how comets live in real time.

This is a game changer.

Rosetta changes our understanding

of the cosmos forever.

The secrets of life itself may be wrapped up on Comet 67P.

530 million miles from the sun,

a tiny lump of ice and rock

starts its journey towards the inner solar system.

Scientifically, comets are more precious

than pure gold... They're actual time capsules.

They're preservations of what the chemistry, the environment

was like when our solar system formed,

and they hold clues as to how our chemistry arrived

here on Earth... Comets are some of

the most valuable scientific treasures that exist.

Finding a comet we can study is not an easy task.

Finding the right comet for a mission...

It's kind of like you're auditioning them, right?

One comes in, and it's like, oh, the other orbit's okay,

but it's not exactly what we're looking for.

And, oh, this one is too big.

This one's too little. This one's too active.

What we really want to see is that comet come from

outer parts of the solar system and get heated up as it

gets close to the sun,

pass around the sun and head back out to the outer part of

the solar system, so you need to get way out in

the solar system and catch a comet on its way in.

Comet 67P fits the bill.

The special thing about Comet 67P

is how accessible it is here on Earth.

It actually orbits around the sun once every 6.5 years,

and its orbit doesn't take it all that far out,

only about this far out of the planet Jupiter.

That gives us many chances to actually

reach the comet and successfully rendezvous with it.

67P's moment in the spotlight arrived.

The European Space Agency launched the groundbreaking

Rosetta probe.

For years, we've studied comets from afar.

We had never seen one up close

with cutting-edge technology to

learn about how comets behave as they orbit the sun.

Missions to large, planet-sized objects are hard.

The Hubble space telescope's blurry images revealed

Rosetta's target is just two miles wide,

and not just a small target, a moving one.

Comet 67P races through the solar system

at over 33,000 miles an hour.

The precision involved is pretty incredible.

It's like making that hole-in-one

golf shot from New York to San Francisco.

But catching Comet 67P wasn't just a straight shot.

The spacecraft had to actually get the same velocity

as the comet, and with current propulsion systems,

we can't achieve that by flying directly to the comet.

Instead, Rosetta performed a slingshot

maneuver that would take 10 years.

So what it's doing, it's actually taking

some energy away from the planet,

so it's slowing the planet down a little bit and then

imparting that energy into the probe.

Rosetta flew past Jupiter

nearly 100 million miles from the warmth of

the sun and entered the most dangerous part of its journey,

hibernation.

Even though Rosetta had solar panels on it,

it still had to be put to sleep, and the reason for that

is that it had to track 67P a ways away from the sun,

and there just was not enough collection area

and solar power to be able to power the instruments.

It's normal to put spacecraft into hibernation,

but the worrying thing at the back of your mind is that it

had never been done for this long before.

31 months of hibernation gave Rosetta's team plenty

of time to worry about what could go wrong.

It's dark and cold out there in space.

There's a lot of things going on.

There's a lot of little micro-meteorites out there,

and without the constant communication with

that spacecraft,

just is a little nerve-racking when the day comes

and it's time to flip the switch and turn it back on.

January 20th, 2014.

After almost 10 years in space, it was finally time for

Rosetta to wake up,

reactivate its communication system, and phone home.

I mean, the tension was just palpable.

It was just, I mean, how long do we have to wait

before we're gonna get the signal?

It's got to work. It has to work.

Oh, gosh, maybe it's just not gonna turn on it all.

Have we lost the spacecraft?

And then the peak appeared on the graph.

It's like, yes, we've got contact with the spacecraft.

Rosetta began to send back images of its target,

and after months of seeing a small dot in the distance,

the comet slowly came into focus.

When I saw this comet, crystal clear,

this mountain floating in space of ice and rock,

my heart just dropped... they are some of the most dramatic,

beautiful images I have ever seen.

Then, as it got closer, and we got to see more

and more details on it, yeah,

that's when things started getting really strange.

Quite simply, arrival at 67P,

we expected to see something shaped like a potato,

and we found something shaped like a rubber duck.

67P is no ugly duckling,

but its strange shape created a problem for Rosetta.

Orbiting the comet was going to be

far more difficult than anyone had imagined.

A planet has a lot of gravity,

so you can send the spacecraft out there and then just slow it

down a little bit with a rocket burn,

and it will drop into orbit.

In the case of Comet 67P,

you're dealing with a very small little rock.

The spacecraft cannot feel the gravity of that rock,

at least not until it's right up against it.

Well, the engineers had to actually plot

triangular orbits.

It was a very complicated set of maneuvers.

Once in orbit, Rosetta could start work.

Its first task...

Figure out how 67P formed.

So how did this comet get this weird shape?

There's two main ideas.

One is just that it was eroded somehow in the center.

And so it started off as a more spherical thing

and became the shape it is today through some

unknown process.

The other idea is that it started

as two separate objects.

Space rocks normally hit each other hard.

They collide with an average impact speed

of more than 11,000 miles an hour.

That's five times faster than a rifle bullet.

Was 67P involved in a pile-up?

A clue came from the distinct layers on the comet's surface.

The layers in Comet 67P

are a little like the layers in an onion.

If you see them aligned, that's a clue that perhaps

the object formed as a single entity

and only eroded later into its present form.

But if you see those layers misaligned like we actually do

in the comet, that's a big clue

that it started out as two separate

objects formed independently,

sticking together to form the comet we see today.

The layers prove that 67P was

originally two separate objects that fused together.

The process of potentially putting Comet 67P

together from two different pieces

is important, because it can teach us about what was

happening in the early solar system.

So as far as we can tell,

these two separate bodies must have

been formed in the same area.

They're very similar in composition,

but they are so light and fluffy that they would have

destroyed each other if they had hit fast.

They had a low speed collision

and basically stuck together like two wet snowballs.

With one mystery solved, Rosetta began to

investigate the chemical makeup of 67P.

The little comet could answer one

of the biggest questions in planetary science.

From where did our blue planet get its water?

The Rosetta Mission, a four billion mile journey

to Comet 67P and a 4.5 billion-year

trip back in time to the birth of the solar system.

This comet is a remnant of

the formation of the solar system itself.

So this is an opportunity to open that time capsule

and get a view into the ancient solar system.

Comet 67P could help us answer one

of the most important questions about our planet.

One of the big mysteries that we have

about Earth is where did the water come from?

Today, water covers over two-thirds

of the Earth's surface.

But it wasn't always that way.

4.6 billion years ago,

the inner solar system formed from a maelstrom

of rocky debris.

Temperatures were so hot,

any water on the early Earth boiled away.

What the evidence suggests to us is that Earth's water arrived