PBS NOVA - Alien Planets Revealed (Alien Planets Revealed)

Hundreds of billions of stars in our galaxy.

And yet we know of only one that shines

on a life-filled planet.

Is Earth unique?

Or are there other solar systems and planets like ours...

out there?

Now, scientists are finding the answer.

Thanks to this:

The Kepler Space Telescope.

The most powerful planet hunter ever built.

It's making astonishing discoveries.

The sheer numbers of planets out there

is really quite stupendous.

From enormous gas giants...

to a land where the sun never sets...

to worlds that may be entirely covered in water.

Kepler is even finding planets like our own.

This might be the first Earth analogue

around a sun-like star that's ever been found.

Scientists are beginning to wonder if those planets

could be inhabited.

And if so, by what?

It's fun to speculate about life,

but any life is going to be subject to the laws

of chemistry and physics.

Even on another planet

we can work out how biology is likely to adapt.

This is the story of how one spectacular spacecraft

has brought us closer than ever

to answering mankind's ultimate question:

Are we alone?

"Alien Planets Revealed," right now on NOVA.

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The most ambitious planet-hunter ever built sits on a launch pad

at Cape Canaveral, Florida.

T minus five, four, three, two,

engines start, one, zero.

Over two decades in the making,

it is about to radically alter what we know about our galaxy.

MAN (on radio): Running out of the solids.

Ready for separation.

Meet the Kepler Space Telescope.

Its mission: to detect alien worlds orbiting distant stars.

And to discover if any of them could be a suitable home

for life as we know it.

Project scientist Natalie Batalha

has lived with the Kepler mission

from the very first moment.

To watch it launch was really quite something.

This feeling that after decades of planning

it was finally happening, it was going up there.

That was a tremendous moment.

Launched in 2009, this incredible optical telescope

has revealed that planets are far more common

than we ever imagined.

What's amazing is not just the number of planets

that Kepler has found, but the types of planets.

Of the 3,500 potential planets that Kepler has spotted,

some seem familiar.

Huge gas giants similar to Jupiter or Saturn,

or smaller, rocky worlds that could be like Earth,

Venus, Mars or Mercury.

But others are straight out of science fiction.

Like Kepler-16b, which orbits a double star.

Just like Luke Skywalker's home planet in Star Wars.

Even more bizarre is Kepler-10b.

It orbits so closely to its sun that the surface

is a vision of hell.

Kepler-10b is a scorched world.

It's got an ocean

bigger than the Pacific Ocean,

but it's an ocean not of water but of molten lava.

That star-facing side as it orbits

has surface temperatures in excess of that required

to melt iron.

So this is a blow-torched world.

But for Kepler, these oddities are just a sideshow,

because its primary mission is to find a planet

that might have the right conditions for alien life--

a planet like Earth.

Now, Kepler might be closing in on just such a world.

The Kepler data suggests that potentially habitable planets

are out there.

And applying the principles of biology and evolution,

scientists are even beginning to guess how ETs

could have adapted to their environments.

The best speculation recognizes that there are rules

to the game.

Any life that we can contemplate is going to be subject

to the laws of chemistry and physics.

Kepler is finding worlds

that, as far as we can tell, have the right environment,

the correct temperatures

suitable for life as we know it.

Kepler is unique among space telescopes.

Unlike the Hubble, which turned its gaze far and wide

and sent back stunning images of the cosmos,

Kepler is designed to stare fixedly

at one small patch of sky, taking the same snapshot

day in and day out for years on end.

It began-- as with any new telescope--

with what astronomers call "First Light."

Kepler's first light image came down to us at NASA Ames

about 24 hours after we ejected the disc cover.

As it filled my computer screen, the image that came to my mind

was like champagne filling a glass

with all of these stars being the little bubbles.

It was very exciting.

Every single tiny dot that you see is a star

that is in the field of view of Kepler.

Kepler is focused on a small patch of sky

near the constellation of Cygnus the swan.

In that area of sky are four and a half million stars

in our galaxy alone.

But Kepler isn't looking for stars.

It's looking for planets that orbit the stars.

But that's a problem,

because Kepler can't directly see planets.

Planets are much smaller and dimmer than stars.

They get lost in the glare.

So Kepler is looking for something called a transit,

which occurs when a planet passes in front of the star.

As it does so, it dims the light by a fraction.

That dimming is what Kepler is designed to detect.

It's a principle that can be illustrated

with a distant tower and a spotlight.

Okay, let's imagine that there's a moth flying

around that spotlight.

Could we ever hope to see the moth?

No way.

The moth-- although it does reflect a tiny bit

of the spotlight's light-- it's far too feeble

for us to see that.

Since the light reflected

off a planet is typically ten billion times fainter

than the light emitted by its star,

detecting a planet might seem impossible.

But Kepler has a way around that problem.

If the moth passes in front of the bright light,

a little bit of the light that was going to reach us

obviously gets blocked by the moth.

Then we are able to detect the moth

by measuring very carefully that very subtle change

in the total brightness of the spotlight.

The bigger the moth, the more light it blocks,

and the more the light dims.

In exactly the same fashion, that's how we can detect

small planets orbiting other stars

and even measure their sizes.

That's Kepler's primary mission:

to watch thousands of stars for signs of a transit.

Scientists plot the brightness of each star in Kepler's view

on a graph to see how it changes over time.

This is an actual plot of one star over two weeks.

Sure enough, every three days

there's a tiny dip in brightness,

revealing a planet orbiting this star once every three days.

Just like the moth, the bigger the planet,

the more light it blocks.

In this plot, a huge planet transits in front of its star

causing a much larger dip.

Right from the start, Kepler saw stars dimming.

By June 2010, 15 months after launch,

Kepler had found over 700 potential planets.

The sheer numbers of planets out there

is really quite stupendous.

Here you see just a small sample of them.

And the planets range in size

from, you know, a half radius of the Earth,

up to things that are several times larger than Jupiter.

Already, Kepler's discoveries are changing what we know

about alien planets.

Kepler has revolutionized our view of planets

and planetary systems in our galaxy.

It turns out that any kind of planet is possible,

within the laws of physics and chemistry.

Any planet you can conceive of can exist in any location

in a planetary system.

Extrapolating from the Kepler data,

some estimates put the number of planets in the universe

in the trillions.

But what everyone really wants to know

is do any of these planets have life?

To answer that, we have to go back to the basics

and ask, is the universe full of the same stuff everywhere?

Are the elements needed for life as we know it

commonplace?

The lightest elements-- hydrogen and helium--

were made in the moments after the Big Bang.

Other elements are made in stars--

a product of nuclear fusion during the star's

normal life cycle--

or produced when some stars explode as supernovas,

scattering these essential building blocks into space.

Every molecule in your body, every element in your body,

was generated some time in the distant past,