Unbelievable new worlds,
planets made of diamond,
planets of raining glass,
worlds in collision...
some plunging into stars...
and others that just might harbor life.
But had ancient astronomers
as far back as the days of Greece and Rome
already guessed what modern science
is about to learn?
We are the generation of human beings
that are going to know whether or not we're alone
in the universe.
Ancient mysteries
shrouded in the shadows of time.
Now can they finally be solved
by looking to the heavens?
The truth is up there,
hidden among the stars...
in a place we call...
Ancient Greece...
The greatest minds look up in wonder
at the strangest objects in the night sky...
Five brilliant points of light that look like stars
but move in mysterious ways.
They noticed that some objects
didn't behave like the stars
and that they called them "the wanderers,"
and they mapped them out in incredible detail.
The ancient Greek word for "wanderers"
is "planets."
2,000 years later,
the invention of the telescope
added three more planets,
bringing the accepted total to eight,
but if anyone thought
that these were the only planets in the universe,
they were dead wrong.
The problem was, for years,
there was simply no way to find any additional planets
that theoretically might exist around alien stars.
They didn't know how to find them
because looking at them with a telescope...
They're just invisible to us.
They're too small.
Scientists compared the challenge
of finding such planets
to placing a firefly next to a Hollywood spotlight.
Now, imagine flying to New York City
and taking your best camera,
attaching it to your best telescope,
and trying to take an image
of that spotlight and that firefly
all the way out here in Los Angeles,
where you can see the firefly
separate from the spotlight,
and that's about the scale of how difficult it is
to actually take a picture where you can see the planet
next to the star.
Yet, in just the past few years,
we've discovered hundreds of new planets
whirling around alien suns.
It's a collection of worlds that range from the bizarre
to the eerily familiar...
A planet about to be swallowed by a dying star...
Giant water worlds awash in global oceans...
A planet in a death plunge into its star...
Two planets in the fiery aftermath
of a gigantic collision...
And the holy grail... Earthlike planets
that just might harbor life.
Could this be one of the first places
in the universe we find alien life...
A newly discovered planet
called Gliese 667Cc?
It orbits what's known as an M dwarf...
A star that's 1/3 less massive than our Sun
and gives off a tiny fraction
of the visible light,
but for astronomers seeking both new worlds
and life in the universe,
it looms large,
because planet Gliese 667Cc
might actually be inhabited,
even though it's eight times closer
to its dim star than Earth is to the Sun.
If we on Earth were orbiting the Sun
at that distance, we would get fried,
but because Gliese 667 is a low-luminosity M dwarf,
a dim star, the planet, 667Cc,
that orbits it actually gets an amount of starlight
that should make its temperatures
somewhat comparable to those that we have on Earth.
So what would it be like to stand on the surface
of this world and look up into the sky?
Here we are on Earth.
That's our Sun up there.
It's so small, I can take my little finger
and block it out, but on Gliese 667C,
come on, the Sun is ten times larger.
The energy pouring onto the planet
is not visible light like on Earth
but infrared light,
otherwise known as heat.
Because the planet orbits so closely,
it's locked in the tidal grasp of its star.
It's the same side always that faces the star.
It's like the Moon... The same side of the Moon
continually faces the Earth.
Well, so, too, the same side of this planet
continually faces Gliese 667C.
Scientists once thought that such planets
would be too hot for life on one side
and too cold on the other,
but simulations now suggest that heat from the hot side
would flow to the dark side and vice versa,
evening out the temperature.
If life exists in this bath of infrared light,
it must have evolved far differently
from life on Earth,
with eyes adapted to the infrared spectrum.
If you imagine taking night vision goggles
or something which lets you see infrared light,
you would see that, in fact, everything around you is glowing
and that the amount which it glowed
varied depending on the temperature.
Things which are hot will be brighter.
Things which are cold will be fainter.
Plants, too, would have evolved
in ways hard to imagine.
On Earth, everything is green
because that's the wavelength of light
plants don't like.
They take in the red,
they take in the blue for energy,
and they reject the green,
so we live in a green world.
But on one of these worlds,
as the infrared wavelengths are brought into the plants,
everything to us would look black.
Could you imagine rolling fields of black grass,
If life can survive the turbulence
of an M dwarf star like Gliese 667C,
that would have profound implications
for one of humanity's greatest questions...
How common is life in the universe?
The reason for that is that M dwarfs
are the most common kinds of star.
It might surprise you to learn that when you look up
at the night sky, even if you're in a very dark place
and you can see lots of stars,
you can't see any of the stars
that are the most common kinds of stars in the entire universe.
70% of the stars in our galaxy
are what we call M dwarfs,
very cool, small red stars
that are half the size of the Sun
or even smaller than that.
Yet these dim suns, invisible to the naked eye,
may be humming with life.
We've learned that these are the most likely stars
to host planets that are roughly the size of Earth.
At roughly the right distance away from their star,
they receive similar amounts of light
from their star that we receive here on Earth.
One thing seems sure...
If life exists on Gliese 667Cc,
it would have far more time to evolve
than life does on Earth.
Our Sun will only last a few billion more years
before swelling into a red giant
and sterilizing the planet.
But M dwarfs are practically immortal.
We think that there are some of these stars
which live basically the age of the universe,
so that's an advantage, because we know that our Sun
isn't going to live forever.
Gliese 667Cc is just one
of dozens of Earthlike planets
that researchers have recently discovered...
planets that finally confirm the beliefs
of ancient philosophers
who taught that there were countless alien worlds.
But as we look at these new alien planets,
an even bigger question emerges...
Is anyone looking back at us?
We finally have the technology to find out.
As we search deep space for alien worlds,
the ancient understanding of what it takes
for a planet to support life
is encoded much closer to home.
When the Apollo mission
landed on the Moon's Sea of Tranquility in 1969...
many people wondered about the name.
Tranquility Base here.
The Eagle has landed.
Why Sea of Tranquility?
The answer goes back to an ancient belief
about life on other worlds.
In the first century AD,
the Greek philosopher Plutarch wrote that the Moon
was a planet like Earth
and that it might even be inhabited.
If so, he argued it would need oceans of water.
Even back to the days of Plutarch,
we realized that water was necessary for life.
Some people think wine is the elixir of life,
but in the scientific world, we realize it's water.
Ancients like Plutarch looked for lunar oceans
and thought they saw them in the dark splotches
scattered across the Moon,
so they named them "mares,"
the Latin word for "seas."
So we have the Sea of Storms, the Sea of Tranquility,
all these different seas.
The idea that water was very critical to life
goes way back in our historical records.
Today we know that the Moon's seas
are simply large basins of dark volcanic rock,
but Plutarch's original idea...
That to find life on other planets,
look for liquid water...
Has survived the test of time.
All known life on Earth appears to require
the presence of liquid water.
Molecules can get bigger and can form complex structures.
If life elsewhere is like life on Earth,
then the mantra should be "follow the water."
Water is common in the universe,
but liquid water is rare.
On the surface of planets,
it only exists in the so-called Goldilocks,
or habitable zone near a star,
where things are not too hot and not too cold.
The size of this habitable zone
depends on the size and temperature of the star
that the planets are circling.
Our Sun is a fairly ordinary mid-size star,
so our habitable zone, where Earth resides,
is one astronomical unit away, way out here...
Millions of miles.
Now, in the case of low-mass stars,
they're much smaller,
and they have much less luminosity,
or light output.
So that means that the habitable zone goes
from being way out here to being much closer in
to the central star.
So life could exist on planets
much closer to dim stars,
and as we've seen, the universe is teeming
with planets like that.
Another key thing that affects the possibility
of liquid water and life is the planet's size.
If a planet is too small,
we think it will lose its atmosphere
because it does not have enough gravity to hold on
to its atmosphere.
That's what happened to Mercury
and to some extent Mars.
If the planet's too big, it becomes a gas giant,
which, actually, are very hot planets
as one would travel down into the atmosphere.
So the planet has to be just the right size.
So the habitable zone is actually the sum of two parts.
One is being the right distance from the star,
and the other is having the right kind of planet.
These, then, are the two requirements for life,
but how often do they exist?
It turns out they're everywhere,
including here
on this incredible, newly discovered planet
called Kepler-22b.
Kepler-22b is what we call a Super Earth.
These are planets that are larger than Earth,
but smaller than the planet Neptune.
We don't have anything like that in our own solar system,
yet these planets appear everywhere
when we look at other stars.
As the list of planets
that fit these precise requirements grows,
the surprises keep coming.
Consider an alien star
only slightly smaller than our Sun
that has not one but two planets
that might be in the right spot and be the right size
to harbor life.
Kepler-62e and "f" are both Super Earths.
They've got about 1 1/2 times the diameter of the Earth,
and both of them are in, broadly speaking,
the habitable zone.
They're so close to each other
that if technological beings evolved on one,
they could easily visit the other.
If you could travel on a rocket ship,
it would take about 12 days to go between these two worlds.
That could only happen if these planets
have dry continents,
but some suspect that they're water worlds
covered in a deep global ocean.
These would be planets with a small, rocky core
and then a very massive water envelope surrounding that,
so that would certainly be an example
of a kind of planet which is fundamentally different
than anything we see in our own solar system.
A water world might be great for life,
even intelligent life,
but technological civilization is probably impossible
for a simple reason.
You can't light a match under water.
You can't have electricity.
Probably intelligent life that is capable
of making and building things
wouldn't exist there because they can't use fire.
Still, this does not rule out life in the atmosphere.
After all, some fish on Earth have evolved flight
to escape predators,
so scientists speculate that the skies of Kepler-62e
could swarm with alien birds.
Planets like Kepler-22b
and surprising twins like Kepler-62e and "f"
are revolutionizing our understanding
of what kinds of worlds might harbor life,
but how does this strange class of planet
make our solar system look like the freak of the universe?
As we search the heavens for new worlds,
we expected to find solar systems
that look like our own,
but instead, we're discovering that our solar system
might be a freak of nature,
challenging a view of the cosmos
that developed over thousands of years.
Some astronomers in the ancient world
correctly guessed that Earth was a globe
that revolved around the Sun,
but the most famous of all ancient philosophers
strongly disagreed.
In the 300s BC,
Aristotle argued that the Earth
was at the center of the universe,
and his ideas were accepted for centuries.
The Catholic Church adopted this
because it worked so well in their theology
of how the universe worked.
God had created man. Man was special.
The Earth was special, and because of this,
this was what everybody believed.
It wasn't until the 1600s that Copernicus
proposed that we inhabit a solar system
with the Sun at the center
and all the planets revolving around it,
including Earth.
By the late 20th century,
scientists believed that they fully understood
the mechanics of how solar systems evolve.
For many years, the only example of a solar system that we had
was our solar system
and the eight planets that orbit here around our Sun.
We based our entire view of how solar systems are born
on our own solar system...
but the sudden discovery of thousands of exoplanets
has shown that apparently we were wrong.
Now we have a plethora of different systems,
all of which are totally different
and some very similar to ours and then some very alien.
The way our solar system formed
produced essentially two kinds of planets.
One type is the rocky planets.
We call them terrestrial planets.
The other would be giant planets
like Jupiter and Saturn.
This made sense
because of how we thought solar systems evolve.
When solar systems form, they collapse
from a large cloud of gas,
and the central mass of them becomes the star,
whereas the disk of material that's left over
around that central star becomes the planets.
Close to the star's warmth,
the most common elements, hydrogen and helium,
are heated into gases and blown away by solar winds.
So, near the star, the only materials left
for making planets are heavier, rocky elements.
This is where its warm enough
that you can really only condense out
rock and metal to form these little planets.
However, further out in the solar system,
beyond what we call the snow line,
temperatures are cool enough
where you can condense gases
and form these very large envelopes
that eventually become planets like Jupiter and Saturn.
We thought, "This is the plan
for all solar systems."
Boy, were we wrong.
The tip-off for how wrong we were
was the discovery of a class of exoplanets
that theoretically can't exist,
except they do,
the so-called "hot Jupiters."
A lot of the first exoplanets found
are what are called "hot Jupiters"...
Big, massive planets that actually orbit
very close to a star,
having a orbital period of a day or only a few days
or ten days.
HD 209458b
zips around its Sun-like star in 3 1/2 days...
While our Sun's closest planet, Mercury,
takes 88 days.
HD 209458b is an iconic planet.
We also think that the atmosphere's being blown off
by interacting with the star and heating up
and by wind from the star hitting the planet,
and its atmosphere will be slowly whittled away.
Losing about 10,000 tons of gas every second,
this planet is, in effect, evaporating.
It looks like a comet with a huge tail
stretched out behind it.
Eventually that atmosphere's going to be gone,
and all that's going to be left
is a little molten core of what this planet used to be,
orbiting nearby this bright star.
But these hot Jupiters are far too close to their stars
to have formed there originally,
so what happened?
Scientists now believe these hot Jupiter solar systems
began like ours,
with the gas giants forming out past the snow line,
but then the gravitational pull of the disk
or of various planets or even passing stars
caused the orbits of the gas giants to go haywire.
They migrated inwards, spiraling toward their suns,
and that process spelled doom for the smaller,
Earthlike planets closer to the star.
Well, you'd have the star over here.
You'd have a Jupiter-size planet here,
and as it moved in, the little, rocky planets
would either be thrown into the star
or thrown out of the solar system,
or they could be captured by that big Jupiter
and orbit around it like a moon.
The planets tossed out of the solar system
are doomed to wander forever in deep space.
Some researchers now believe that the galaxy holds billions
of these dark, lost worlds.
So it turns out that our orderly solar system,
with the rocky planets close to the sun
and the gas giants further out,
may be a lucky exception.
Earth has achieved a stability
that allowed life to develop and evolve
in a relatively un-hassled way for billions of years,
and in many other planetary systems,
that may not be the case.
But while the discovery of new planets
has challenged some ideas of how solar systems evolve,
it's confirming others,
including the catastrophic idea
of colliding worlds
and even how the Earth will one day die.
Many ancient ideas about planets
seem simplistic...
but around 400 BC, the Greek philosopher Democritus
proposed ideas that seemed
straight out of a modern science textbook,
including ideas about fiery cataclysms
in the Earth's past...
and a terrifying idea
about how the Earth will one day die.
He was the first to come up with the idea
that things were made of smaller things.
He called them atoms,
and they came together and grew and grew
into stars, into planets,
into everything that is around us.
When it comes to planets,
Democritus wrote that
"there are innumerable worlds of different sizes.
"In some," he wrote, "there is neither sun nor moon.
"In others, their sun is larger than ours,
and others have more than one sun"...
all of which, amazingly, is true.
The interesting philosophical question is,
how did he come up with this idea?
It shows the uniqueness of the human mind
to be able to project and ask, "What if?"
And then, using logic, put together
a philosophy of how everything works.
Today, as we discover planets around alien suns,
many of Democritus' ancient ideas
have been confirmed by modern science.
For example, he wrote that some planets
are destroyed by collision...
and now we're actually watching that happen.
This is the hot Jupiter called WASP-18b,
a planet caught in the act of plunging into its star.
It's been orbiting for possibly 2 billion years,
but within the next million years,
it's going into its star,
and the whole shape of this round world
will be stretched like an egg.
While WASP-18b confirms Democritus' idea
of how planets can die,
another new discovery confirms his ancient prediction
that planets can crash head-on.
The planet HD 172555
is a world in the aftermath of a collision.
What we think we're seeing is two large rocky planets
which had just crashed into each other,
thrown up a bunch of dust,
melted rock kind of accreted together.
Scientists have long speculated that a collision like this
happened to the early Earth,
tossing up debris that created our moon.
For decades, that was just a theory.
Now they can actually watch it happen.
Gases were given off. Glass was created.
And now they're fusing back into this remain
of this world that will be cooling down,
but right before our very eyes.
There's a space wreck right in front of us.
Democritus' ancient theories about the death of planets
are bolstered by another major discovery:
a dying planet called Kepler-91b.
Scientists have long believed that in the distant future
the Sun will swell up,
engulfing the dying Earth in an inferno.
And this isn't just a theory now
because we think we see this with Kepler-91b.
Kepler-91b's star, about the same mass as the Sun,
has already swollen into a red giant.
It's now about six times our Sun's radius
and growing rapidly.
If there were oceans here...
they're already evaporated.
If there is life,
it's in trouble.
On this world, if you wanted to see life,
you'd be there at night.
Everything would come out when it's cooler,
and then in the day, it would disappear once again,
and the most precious commodity on this world would be water.
Everybody, everything would be looking for water,
and yet this is our future.
We're seeing it now.
Like Earth, Kepler-91b
is doomed to be swallowed by its sun.
Unlike Earth, its time is almost up,
but could a planet survive that fate?
Apparently we found one that did.
V391 Pegasi is an example of an exoplanet
that has physically survived the red giant stage
of the star that it orbits.
It's sun turned into a red giant and grew larger
and larger and larger
until it actually consumed this world.
And then as its sun has shrunken back down,
the world remains.
Since V391 Pegasi is still there,
it's the first known planet to survive a close encounter
with the kind of red giant that will one day threaten
to destroy Earth...
if you can call that survival.
That world now is one burnt, rocky planet.
Anything that was living is gone.
It's disappeared.
Newly discovered planets like these
give us a glimpse into Earth's future,
but there are other planets out there so strange,
they seem ripped from an alternate universe.
What is mankind's secret weapon
for unmasking these mysterious worlds?
Less than 20 years ago,
scientists were still struggling to discover
a single planet outside our solar system.
Today we've discovered thousands.
How did we do all this and do it so quickly?
The revolution begins in the 1990s.
Scientists knew that planets cause their host stars to wobble
and finally developed a way to detect this.
We now have instruments with microelectronics,
a spectrograph,
that could act like a policeman's radar gun.
We could take a look at a star,
and we could see if it was moving towards us
or away from us.
Using that technique,
scientists discovered something that had eluded
not only the ancients, but even modern astronomers...
The very first planets outside our solar system.
But were there even better ways to search?
Once we knew there were planets around other stars,
people suggested that there might be another way
in which you could find planets.
That way was to look for little eclipses
caused when the planets passed between their host stars
and our vantage point on Earth.
These tiny eclipses are called transits...
like the transit of Venus we saw from Earth
in 2012.
This creates a tiny dip in the brightness of the star,
which we can measure as it happens again and again
as the exoplanet goes around in its orbit.
But from Earth's surface,
the transit technique had serious limitations.
You really need to monitor the star all the time
without interruption in order to have
a good chance of not missing any transits.
That's where NASA's Kepler space telescope comes in.
Launched high above Earth's distorting atmosphere,
it pointed at just one spot in the sky...
A field of 150,000 stars,
taking continuous pictures of that region
over and over again for four years,
with space-age precision.
Would it find a sky brimming with planets
or a dark and empty void?
Lo and behold, planets started moving across their stars,
and we started seeing their orbits.
And we waited and waited...
Another year, another crossing,
another year, another crossing.
But scientists quickly turned to a larger question.
Could any of these planets be similar to Earth?
The majority of the stars in the Kepler field
seemed to have planets,
and Kepler was actually sensitive enough
to detect a planet the same size
or even smaller than the size of the Earth,
and it found enough of those that we now know
that small planets are much more common than large ones.
That, in fact, was Kepler's revolutionary purpose...
To find Earthlike planets that could harbor life.
In this mission, we found them,
but we found a lot of other surprises too.
But as scientists struggled to discover
the total number of planets that exist in the galaxy,
they ran up against Kepler's major limitation...
It can only spot planets that transit their star
as seen from Earth,
and most planets do not.
If we have a transiting planet system,
then we need the alignment to be perfect
for that planet to go around its star
and to block just a little bit of that light
from getting to us from our point of view.
However, if we took this system
and we tilted it up such that that alignment
no longer happened,
then the planet would still be going around its star,
but it would never block any of the star's light
from getting to us,
and we wouldn't see a transit at all.
Scientists realized that the chances
that an Earthlike planet will transit
are 1 in 210.
Using that ratio gives us a staggering estimate
of how many planets actually exist.
What this tells us is that in our Milky Way galaxy,
which has between 200 billion and 400 billion stars,
there may be almost 230 million
other planet Earths out there.
Once Kepler detects a possible planet,
scientists across the globe race into action.
Another group of astronomers takes over
with telescopes here on the Earth
with huge spectrographs,
and they take a look at this world
and look for the star to wobble.
We need both these processes now
to determine what the planet is
and how far away it is and what it looks like
and even what it's made out of.
Kepler roared into space in March 2009
on a Delta II rocket.
In the first six weeks,
it discovered five previously unknown worlds.
Today it has discovered thousands.
It's nearly impossible to describe how revolutionary
Kepler was for exoplanets.
Kepler made so many discoveries we never even expected.
So far, some of the newly discovered planets
have challenged and others have confirmed
ancient theories of how worlds
are born and die,
but even the ancients never dreamed
of the kinds of wondrous worlds we're discovering today.
How does the universe
make a planet of solid diamond?
Ancient philosophers like Democritus
believed in a universe aglow with amazing planets.
But today's planet hunters have discovered worlds
far stranger than the ancients ever suspected.
You are orbiting 55 Cancri e.
It's mostly made of carbon,
and due to extreme pressure
and a surface temperature of 4,892 degrees Fahrenheit,
it just might be a jeweler's dream.
Now, think about this.
What happens if you take a piece of carbon
and you have the strength of Superman
and you crush it like this?
What do you get?
A diamond.
If a diamond planet isn't strange enough,
let's descend to another new discovery...
HD 189773b.
Its blue color makes it look surprisingly like Earth,
but in this case, looks can be deceiving.
This is a glass planet.
It has mostly silicon,
and the silicon with the sunlight
passing through it appears to be blue,
and it's very hot.
In fact, the temperatures near the surface are such
that the silicate can condense
into fine little particles of glass,
so it might actually rain glass
on this exoplanet.
But that rain would move largely sideways
because there are huge winds in the atmosphere,
up to 4,000 miles an hour.
And the ancients never predicted a planet
covered with a seeming impossibility...
Burning ice...
Yet that's what we find on Gliese 436b.
If you touched it, you would be burned.
This is a world made of hot ice...
Something we never imagined on Earth.
Diamond planets, planets of raining glass,
worlds of burning hot ice...
Thanks to projects like Kepler,
the universe is proving far stranger
than either the ancients or modern astronomers
ever imagined,
but more is soon to come.
Scientists are bracing for the discoveries of TESS,
the Transiting Exoplanet Survey Satellite,
due to launch in 2017.
Unlike Kepler, which looks at one patch of sky,
TESS will scan only the stars that are so close,
we might actually visit them someday.
We're mapping the nearby stars for planets
that we hope, eventually in the future,
our descendents will actually be able to travel to.
So we have a huge interest in trying to find planets
orbiting stars that are very close to Earth.
Other new projects have actually begun searching
not just for life
but for intelligence and technology.
One surprising key is to look for stars
that twinkle and pulse in bizarre ways
that could only be caused
by advanced alien civilizations.
I used large databases of observations of stars
to try and understand whether any of those stars
could be varying
in a way that was caused by something artificial.
But can we ever visit the planets
we are now discovering in such abundance?
I'm hopeful that at one point, we'll eventually be able to send
robotic probes to some of these nearby solar systems.
Not everyone believes that it'll happen,
but we're born explorers.
We'll want to go.
We have to have hope that, in the future,
if there's a will, there's a way.
Whether such a thing will happen is anyone's guess,
but one thing is certain...
thanks to today's planet hunters,
our views of the universe and of our place in it
are undergoing one of the greatest revolutions
in scientific history.