All language subtitles for The Universe S02EP01 Alien Planet

In the beginning,
there was darkness...

and then, bang...

giving birth to an endless
expanding existence...

of time, space, and matter.

Now, see further
than we've ever imagined...

beyond the limits of our existence...

in a place we call "The Universe. "

Are there planets
beyond our solar system?

It's a question few have dared to probe.

The origin of hunting
for planets started, really...

from the lunatic fringe of science.

Now, hundreds of these
exotic worlds have been found.

Could any of them
be home to alien life?

Right now, the sort of planets
we're discovering are kind of monsters.

You would be incinerated immediately
before you had a chance...

to really sort of groove
on your surroundings.

But some planets
hold more promise.

I'm so excited
about Gliese 436...

I'm almost jumping out
of my clothes.

Could we be on the verge
of finding another Earth?

We still don't know
whether our Earth...

is a commonly occurring planet
or a one-in-a-billion freak.

Cutting-edge science,
strange worlds, and wild weather...

as we travel the universe
in search of "Alien Planets. "

Lurking in
the constellation Pegasus...

fifty light-years from Earth,
is a monstrous planet...

a superheated gas giant
almost as massive as Jupiter...

whipping around its star
in a little over four days.

It's called 51 Pegasi b...

and in 1995...

it became the first planet
detected orbiting an alien sun.

It was a landmark discovery...

but just a stepping stone
on an even greater quest...

to find a planet
that looks more like our own.

The ultimate
but elusive goal for astronomers...

is to find another Earth.

What we're after is the appreciation
of where our Earth fits in...

in the grand context of our universe...

and we'd love to be able
to find other Earths.

But Earths are so undetectable...

little chunks of rock
that don't emit much light.

How common might Earthlike
planets be in the universe?

Even if only
one percent of all stars...

were circled
by a planet like our own...

that would still mean there are
billions of other Earths...

waiting to be discovered.

We are almost sure
that rocky, Earthlike planets...

exist in abundance out there,
but how Earthlike?

There are still open questions
about the uniqueness of our Earth...

and we don't know whether
our Earth is unusual or not.

It's an extremely profound
and, I think, disturbing question.

In the realm of alien planets...

there's a wide range
of imaginable worlds.

We might find ocean worlds,
completely covered in water...

frigid ice planets...

Mars-like worlds...

but perhaps with thick atmospheres,
fed by massive active volcanoes...

and even planets
with two suns in their skies.

There may be planets that humans
would find hospitable...

and others on which humans
wouldn't dare tread...

that could still be home
to other types of creatures.

Perhaps the major lesson
we've learned so far...

from looking for planets
around other stars...

is that nature can make a lot more
planets than we can dream of.

Finding just one other
truly Earthlike planet...

would hint that Earths
are common in the universe.

And if Earths are common,
then, perhaps, life, too, is widespread.

But of the over two hundred
alien planets detected so far...

most of them seem utterly
hostile to life as we know it.

So far, we found
sort of three kinds of worlds.

One kind are the planets...

that are really close
to the star that they orbit...

and they're totally baked to death.

Then there are the ones
that are quite far away...

and they're pretty cold.

And then there are the ones
in the highly eccentric orbits...

which sometimes
get close to the star...

and sometimes far away.

So they're alternately
very hot and cold.

So far, we definitely
haven't found any worlds...

with jungles and forests.

Indeed, we haven't found any worlds...

that are square smack
in the habitable zone...

where there's liquid water
on the surface...

and other nice conditions.

Our frame of reference...

for what we consider to be
a nice planet is this one.

We like it quite a bit.

We've got breathable air,
it's a pleasant temperature...

and there's water.

And even in our own solar system,
we don't see a lot of planets like that.

And right now, the sort
of planets we're discovering...

are kind of monsters.

In other words, they're extremes.

So is the Earth, with its rocky surface,
oceans, and abundant life...

just a planetary wonder
with no close kin in the cosmos?

The early discoveries of alien planets
have yet to answer that question...

but they have brought legitimacy
to what once seemed like a futile quest.

While many believed there had
to be other worlds out there...

in the vastness of the universe...

locating them was widely considered
beyond the reach of modern science.

Only a few decades ago...

an astronomer hunting for
these so-called "extrasolar planets"...

was taken about as seriously
as someone searching for UFOs.

The search for planets,
as it started in the 1980s and 1990s...

was considered off
of the beaten track of standard science.

In the early eighties...

astronomer Geoff Marcy's career
was going nowhere.

His research into the magnetic fields
of stars had reached a dead end...

and he was beginning to question
his own abilities as a scientist.

When I first began thinking
about looking for planets...

it was in a time in my career
when I thought it was over.

I thought there's
no hope for me as a scientist...

and I thought the best shot I had...

going out in flames,
was to try an experiment...

that everybody thought
would never work...

namely, looking for planets
around other stars.

And most people thought
we would never find any planets.

Before Geoff Marcy,
his collaborator, Paul Butler...

and a handful of pioneering
astronomers around the globe...

could begin the search
for alien planets...

they had to first perfect methods
for finding them.

Stars are easy to locate
using conventional telescopes...

but to find a planet takes
some ingenuity and patience.

Unlike the stars they orbit...

planets are small
and emit very little light.

Even the giant
of our solar system, Jupiter...

is a thousand times
less massive than the Sun...

and ten billion times fainter.

A huge difficulty in taking a picture
of a planet around a star...

is that the planet is extremely,
extremely faint compared to the star.

The star is so bright...

it almost completely obscures
the much, much dimmer planet.

Blinded by starlight,
planet hunters realized...

that even if they couldn't
see a planet directly...

they should still be able to detect its
gravitational effect on the star it orbits.

A star with no planets should
drift smoothly through the sky...

while one with planets should exhibit
a telltale gravitational wobble.

We often say that planets
orbit the Sun or other stars...

but that's not exactly true.

The planets and the stars orbit
their common center of mass...

or center of gravity.

And this center of mass
isn't halfway between them.

Just like on a seesaw,
the more massive object...

must be closer to the center of mass
to bring balance to the system.

So consider the Sun and Jupiter.

The Sun is about a thousand
times more massive than Jupiter.

So the Sun is here,
the fulcrum or balancing point is there...

and Jupiter is way out here
a thousand times farther away.

In space, this means that planets
trace out large orbits...

around the center of mass...

while stars make much smaller,
but still detectable orbits.

Here's a hypothetical planet
orbiting a star.

In fact, they're orbiting
their common center of mass.

So the planet moves
in a relatively large orbit...

but the star also moves,
but in a much smaller orbit.

So the star moves only a little bit,
and the planet moves a lot.

I have a somewhat unusual
hobby for an astronomer.

I'm a belly dancer and fire performer.

But it turns out that spinning fire...

is a great way of simulating
the motion of a planet.

The centrifugal motion
of your fire on the chain...

is very similar to the motion
of a planet under gravity.

The light on my wrist
represents the star...

and the spinning ball of fire
around that is a planet.

And as you can see, the ball of fire
draws out a large circle...

and my wrist is drawing out
a smaller circle inside it.

It's this tiny wobble of starlight...

that scientists use to find
extrasolar planets.

But even this wobble
would be undetectable...

if it wasn't for the Doppler effect...

the fact that wavelengths get shorter...

as the object emitting them moves toward
you...

and longer as it moves away from you.

The Doppler effect is very familiar...

if you've ever heard a train going by,
blowing its whistle.

So when the train
is coming toward you...

you hear a high-pitched whistle...

and as the train recedes
into the distance away from you...

you hear the pitch of the whistle
get lower and lower in frequency.

Just like sound waves, light waves
appear to shift in frequency...

as the object emitting them
comes toward or away from you.

Light from an object
moving toward you...

will look slightly bluer.

Light from an object
moving away from you...

will look slightly redder.

When the light waves
shift their wavelength...

toward the blue
and toward the red...

and back toward the blue again
as the star wobbles around...

the shift is excruciatingly tiny...

but it's that difference
in the wavelength...

of the light waves coming at you,
that is what we measure...

and it's what allows us
to detect planets around other stars.

Using this Doppler technique...

Marcy and Butler spent
over a decade patiently studying...

one hundred twenty nearby stars
for any sign of a wobble.

I went eleven years without finding
a single planet, nothing...

and no one was surprised by that.

It seemed logical to everybody else
that it was a fruitless, frivolous...

maybe even lunatic exercise
to look for planets of any sort.

But then, in 1995,
came the surprise announcement...

from Swiss astronomers,
Michel Mayor and Diedre Queloz...

that they had discovered
a gas giant planet...

circling the star 51 Pegasi.

Marcy and Butler
rushed up to Lick Observatory...

on Northern California's
Mount Hamilton...

to aim their own telescope at the star...

and see if they could confirm
the Swiss team's results.

Yup, there it is. Looks beautiful.

Paul Butler and I were shocked
to see that the wobble of the star...

was precisely
as the Swiss had said it was.

And I remember
driving off Mount Hamilton...

from Lick Observatory
in complete silence...

Paul Butler next to me.

We knew that the first extrasolar planet
had been discovered.

It was a very moving, you know,
personally moving moment.

Despite the monumental nature
of the discovery...

this, like all future
extrasolar planets...

wouldn't get the name
of a Greek or Roman god.

It would take
the astronomical catalog name...

of its parent star, 51 Pegasi...

and add to it a lowercase b.

In this standard nomenclature...

if a second planet was found
around the same star...

it would get a lowercase c,
and so on through the alphabet.

Its name was the only thing
unassuming about 51 Pegasi b.

The discovery shook the foundations
of our understanding of planets.

In 1995, astrophysicist Alan Boss
was asked to review a paper...

announcing the discovery
by two Swiss astronomers...

of the first planet
orbiting an alien sun.

Reviewing this paper...

caused me a fair number
of sleepless nights...

because it was pretty stunning
what they had found.

Stunning because the Swiss...

claimed to have found
a Jupiter-like planet.

But where Jupiter orbits
the Sun in twelve years...

this planet zipped around
its star in only four days.

And that also meant that the planet...

had to be much, much closer
to its central star...

roughly a hundred times closer
than Jupiter is.

And that just was hard
to understand.

Jupiter orbits the Sun...

at a comfortable distance
of around half a billion miles.

51 Pegasi b is more
like five million miles from its star.

If it were dropped
into our own solar system...

this alien planet would orbit
much closer to the sun...

than Mercury,
our innermost planet.

Being so close to the star...

means that the planet
is being literally fried.

The radiation from the star
is incredible...

compared to what we experience
here on Earth...

relatively far from our sun.

So this was a completely
unexpected discovery.

It was a planet that could not
have formed there.

Astronomers knew
it didn't belong there.

In the same way that if we found...

a giant redwood
in the middle of Central Park...

we would know
that it didn't belong there.

You'd have to ask yourself,
how did it get there?

And that's what astronomers
were asking themselves...

about these giant planets
that they were finding.

51 Pegasi b wasn't
just a freak of nature.

It was the first of dozens
of so-called "roasters"...

or "hot Jupiters" to be discovered
in seemingly impossible close-in orbits.

Impossible
because the accepted theory...

for how gas planets form
suggests that rock and ice...

in a disk surrounding a young star...

coalesces into a solid core
that then accretes gas...

growing larger and larger
until it has cleared out...

all the planet-forming material
in its area.

This process can only occur...

at a distance
far enough from the star...

where it's cold enough
for ice to exist.

You can't form something
that massive, that close in to a star.

It needs to form past the snow line
where ice can form.

And in our solar system,
that's about where Jupiter is...

about five times further out
from the Sun than the Earth.

So how could a gas giant
planet like 51 Pegasi b...

form so scorchingly close
to its star?

It was one of these things...

where I woke up
in the middle of the night...

and, one night, I said to myself,
maybe what this means...

is that this object
had to have migrated inwards...

from where it originally formed.

We now, I think,
have an understanding...

that planet formation
is an almost chaotic process...

a sort of roll of the dice
with many planetesimals...

wannabe planets forming,
building up...

and a competition...

a sort of gravitational
musical chairs takes place...

in which the planets compete
for their own space.

In this competition...

some planets are flung out
of the solar system...

and some are tossed
toward the center.

It's believed some planets
crash and burn on their parent star...

while others survive
in a close but stable orbit.

These survivors
are the hot Jupiters.

The discovery of the hot Jupiter
circling 51 Pegasi...

sent planet hunters
Geoff Marcy and Paul Butler...

back to analyze the data
they had been collecting...

for the past decade.

Their team had been looking...

for the expected long-term wobbles
caused by a giant planet.

We ourselves suddenly realized...

we should analyze our data
in a slightly different way...

look for the shorter period planets...

not just planets that take a long time
to go around their star.

And that led us to discover
within existing data...

all of these planets that had
been buried there for years.

I remember the day
like it was yesterday...

December 30, 1995.

And at 8 A.M., the phone rings.

I pick it up, it's Paul Butler...

my ace collaborator
for twenty years now.

And Paul just said,
"Geoff, come over here. "

So, of course,
I immediately got in my car.

I drove right to this very office,
right here where I'm sitting now...

in Campbell Hall at UC Berkeley...

and he showed me
his computer screen.

And there on that screen
was the unmistakable graph...

of the wobble
of the star 70 Virginis...

going up and down
and up and down...

the star wobbling to and fro,
exactly as we had imagined...

a planet's signature
would look in our data.

So that was the moment,
with both of our eyes open this wide...

that we knew we had discovered
our first planet...

the second planet ever discovered.

70 Virginis b is
fifty-nine light-years from Earth...

in the constellation Virgo.

With a mass at least seven times
larger than Jupiter...

this world immediately
claimed the title...

as the planetary heavyweight
of the known universe.

Here, right before our eyes, essentially...

is a planet seven, maybe ten times
bigger than our own Jupiter...

telling us immediately that, yes...

nature does make planets
even bigger...

than the largest ones we have
here in the solar system.

Rather than a hot Jupiter...

this planet was the first
of a new class of alien worlds...

called eccentric giants...

because of their eccentric
or elongated orbits.

70 Virginis b swings out...

as far as sixty-three million miles
from its star...

and passes as close
as twenty-seven million miles.

The frightening aspect
of the planet around 70 Virginis...

is that we all grew up
in kindergarten...

learning that planets
go around the sun...

in merely circular orbits...

so what in the world is a planet doing
going around its star...

in one of these
elongated, wacky orbits?

Already the first two planets
discovered around alien suns...

were challenging our view
of how planets should behave.

Further discoveries
over the next decade...

would show that eccentric orbits
are common in the universe...

while the circular orbits
of our solar system seem to be rare.

It's embarrassing, frankly,
when you think about...

how we humans imagined planets
would orbit other stars...

how common they would be,
what properties they would have.

Guess what?

We imagined that those planets...

would look just like the planets
that orbit our Sun.

Extraordinarily nearsighted
in retrospect.

And for a scientist,
I find it embarrassing...

that I was a party to this.

But, in fact, what we've learned
is that planets around other stars...

are remarkably different
from the representatives...

we have around our Sun.

The planet-hunting revolution
that began in the 1990s...

has also obliterated any notion
that planets are rare in the universe.

With an ever-growing catalog
of alien planets...

astronomers are now trying
to learn all they can...

about the more than 200 worlds
they've already discovered.

The Doppler technique used by
Geoff Marcy and other astronomers...

tells them the mass
of the planet they found...

but it doesn't tell them the size.

To figure out just how big
an alien planet is...

requires a bit of good luck.

The orbit of the planet
has to be aligned in such a way...

that from Earth, we can see it pass
directly in front of its star.

This is called transiting.

By measuring how much
the starlight dims during this transit...

astronomers can actually
determine the size of the planet.

In the fall of 2007,
astronomers were watching...

when a hot Jupiter called
Tres-4 transited its star.

The planet was about
the same mass as Jupiter...

and, therefore, should have
been roughly the same size.

But astronomers
were in for a surprise.

Tres-4 turned out to be
almost twice as big as Jupiter.

It was, in fact,
the largest planet ever discovered...

sort of a Jupiter on steroids.

Some of these extrasolar
planets are really fluffy.

They're really expanded in size.

And we think that the reason
why that's happening...

is because they have
an internal source of heat...

which is raising the pressure
inside the planet...

causing it to expand.

That's very similar
to a steam boiler on a steam train.

In a steam boiler,
you have water...

which is being heated
by a heat source.

That water is turning to steam.

The pressure is increasing...

and that's causing
the piston of the boiler...

to move out, to expand.

If you didn't have
the gases' ability to expand...

the planets wouldn't inflate.

Steam trains wouldn't work.

We wouldn't be climbing up
this mountain.

While internal heating
is the likely cause...

of the so-called fluffy Jupiters...

something much stranger is
happening on this alien world.

In the field of extrasolar planets,
it seems each new discovery...

creates a brand-new world
of scientific intrigue.

At the University of Arizona,
planetary scientist Adam Showman...

ponders the weather
on other planets.

Recently, Showman helped
generate the first-ever forecast...

for a planet
beyond our solar system.

And what he found was weather
truly befitting an alien world.

We think that the winds
are probably...

about 6,000 miles per hour,
possibly even more.

This is huge
compared to the wind speed...

on any planet
in our solar system.

This is HD 189733 b.

It's a hot Jupiter, more
than sixty light-years from Earth...

that races around its Sunlike star
in a little over two days...

at a distance
of only three million miles.

How is it possible
to divine the weather...

on a planet 370 trillion miles away?

First, you have to take
the planet's temperature.

Scientists knew that, since
the planet orbits so close to its star...

it would be tidally locked...

a gravitational effect
that would cause it...

to show the same face
to the star at all times.

One side would always be bathed
in the burning hot light...

of the alien sun...

while the other would be cloaked
in perpetual darkness.

If there was no wind
on these planets...

then that would mean
that the day side...

would then be very, very hot...

and the night side
would be very, very cold.

In the spring of 2007...

scientists used
the Spitzer Space Telescope...

which sees in infrared wavelengths
associated with heat...

to generate a crude map
of the temperature...

on both the day
and night side of the planet.

You are actually looking
at the first map of any kind...

made of an alien world.

What the map shows...

is that the day side
of the planet is roasting...

at an otherworldly
1,500 degrees Fahrenheit.

No surprise, given how close
the planet orbits to its star.

What was surprising...

was how hot the night side
of the planet turned out to be.

Despite being in total darkness,
it swelters at around 1,000 degrees.

Clearly,
something was distributing heat...

throughout the planet's atmosphere...

carrying thermal energy
from the day side...

clear around the other side
of the planet.

From his knowledge of weather
in our own solar system...

Showman knew
what the culprit was.

He ran the numbers...

and that's when he figured out
that this alien world...

had jet streams
of unprecedented magnitude.

Their 6,000 mile-per-hour winds
dwarf anything...

in our own solar system.

Earth, actually,
has the slowest speeds...

of any planet in our solar system...

with a typical speed
of about twenty miles per hour.

The gas giants
in our solar system...

actually have somewhat
faster winds than the Earth...

simply because there's no surface...

to have friction
to slow down the winds.

On Jupiter and Saturn,
for example...

the winds are
a few hundred miles per hour.

So you're still about
almost a factor of ten lower...

than on these hot Jupiters.

The weather on hot Jupiters
may be extreme...

but the forecast for another
class of alien planets...

the eccentric giants,
is tailor-made for a disaster movie.

This is HD 80606 b,
a gas-giant planet...

located roughly two hundred
light-years from Earth...

orbiting a star
in the constellation Ursa Major.

A year on this bizarre world
lasts 111 days...

and it has the most eccentric
orbit of any known planet.

With its nearly circular orbit...

Earth's distance from the Sun changes
relatively little throughout the year...

varying by only
about four million miles.

But during its year...

HD 80606 b comes as close
as three million miles to its sun...

and as far as seventy-eight million...

a difference
of seventy-five million miles.

This crazy orbit leads
to completely crazy weather.

The planet heats up by hundreds
and hundreds of degrees...

in a matter of a few hours...

and that drives just absolutely
tremendous storms.

As the planet swings in
close to its star...

the alien sun looms
ever larger in the sky.

And so you get
a huge amount of heating...

on one side of the planet.

The other side of the planet
is in the night.

What that does is
it drives an intense storm.

It's basically a shockwave
around both sides of the planet...

that is moving roughly
at the speed of a supersonic jet.

This fiery hurricane rips
around the planet in only twelve hours.

As the shockwave
slowly dies down...

the superheated atmosphere
churns into a giant vortex...

that engulfs an entire hemisphere,
a sort of greater red spot.

As the planet moves away
from the heat of its star...

the storm gradually loses energy
and intensity.

But on this eccentric giant,
the calm never lasts for long.

Every 111 days,
the shockwave is reignited...

and the violent cycle
begins anew.

It's much stranger
than anything that we have...

in our own solar system.

If you were there, you would be
incinerated immediately...

before you had a chance
to really, sort of...

groove on your surroundings.

The universe seems adept
at creating strange worlds...

even in the most
unlikely of places.

This is a pulsar...

a rapidly spinning variety
of an exotic stellar object...

called a neutron star.

Neutron stars
are the remnants left behind...

after a massive star
explodes in a supernova.

No one expected to find
planets circling...

in such a treacherous
cosmic neighborhood.

Never in my wildest dreams...

did I think we would ever
find planets...

orbiting a neutron star, a pulsar.

I mean, after all,
neutron stars are formed...

as a result of supernova explosions,
where the starjust blows up.

So certainly any planets that
might have been there to begin with...

would have been blown away.

And yet, in the early 1990s...

astronomers discovered
two rocky planets...

around a pulsar
7,000 trillion miles from Earth.

Their discovery, in fact,
predates 51 Pegasi b...

making them, technically,
the first alien worlds ever detected.

But since they orbit
such strange stars...

many astronomers
consider pulsar planets...

to be in a category of their own.

The pulsar planets
were very interesting.

They're actually
very low in mass...

and more similar
to the Earth's mass.

They form an interesting,
exotic classification...

or family of planets...

but it's by no means
the mainstream.

While most planets
are believed to have formed...

out of the same disk of gas
and dust as their parent stars...

clearly these pulsar planets
formed a different way.

The planets
that have been found...

must have formed
after the supernova explosion.

And that's really bizarre
because we would think...

that all of the material
was blown away...

but apparently
some of that debris...

must have somehow
been in a disk...

and parts of that disk
coalesced into planets.

But that's extremely surprising.

I don't know that anyone really
understands that process yet.

Although the pulsar planets...

are believed
to have rocky surfaces...

it's unlikely they would be
a platform for life...

and any visit by humans
would be short-lived.

As the pulsar rotates...

it emits well-focused beams
of charged particles from its poles...

creating a rotating spotlight
of horrific radiation.

Standing on a pulsar planet...

would be
a very dangerous proposition.

There would be high-energy
radiation all around you...

just an onslaught
of particles and waves...

and the radiation field
would be so strong...

that it would probably destroy
your living tissue...

and it would certainly cause cancer
and mutations very quickly.

But it would probably kill you.

If you were really unlucky-
or lucky, I suppose.

If you're gonna die anyway...

you might as well die
in a spectacular way.

You would be in the beam
of the pulsar.

So, every rotation,
the beam would flash past you...

and you would see
this incredibly bright beacon...

like a lighthouse really close
to you just flashing in your face.

It would not be
a very hospitable environment.

No way.

While the pulsar planets
might not be nice places to visit...

they have taught us
something fundamental...

about planet formation
in the universe.

These planets, weird planets,
around a neutron star...

have taught us
that planetary formation...

appears to be relatively easy.

Gravity appears to like
to pull stuff together...

when there's enough stuff
in a given region.

If nature is so good
at making planets...

even under difficult circumstances...

then the odds are fairly high
that the universe is full of planets...

and that somewhere
out there in the cosmos...

other Earths are waiting
to be discovered.

But if that's the case,
then where are the Earths?

Why haven't we found them yet?

The first planets that were
found in the late 1990s...

were massive planets,
300 times the mass of our Earth.

And it's really not a surprise...

that we found
the most massive ones first.

Like the giant redwood trees
behind me...

they were the easiest to see...

from the enormous distances
that we were looking.

So when we find stars,
where we say...

"Ah, there's just
one single massive planet...

"one giant redwood,"
that's almost certain to not be true.

There's almost certainly
a forest of planets...

and asteroids and comets
also orbiting that star.

As astronomers continue
to scrutinize alien solar systems...

they are edging ever closer
to finding Earthlike planets.

This is Gliese 436 b.

It's a world roughly twenty times
the mass of Earth...

similar in mass and size
to Neptune.

It orbits a star thirty light-years away
in the constellation Leo.

I'm so excited
about Gliese 436...

I'm almost jumping out
of my clothes.

It's the most important
discovery since 51 Pegasi...

maybe even more important.

What has Geoff Marcy so excited
is that this planet...

was found to have a density
of 2. 1 grams per cubic centimeter.

What does that mean?

It's a spectacular number...

because every schoolchild knows
that the density of water...

is one gram per cubic centimeter...

and we also know that rocks
that you pick up on the street...

the density of our Earth,
for example, as a rock...

is about five grams
per cubic centimeter.

And therefore,
this planet, around 436...

is composed of a mixture
of rock and water.

A planet made of rock and water
sounds tantalizingly Earthlike...

but Gliese 436 b
has so much water...

there would be
no landmasses exposed at all.

And you wouldn't want
to take a swim...

in the oceans
of this watery alien world.

There may be a layer
of liquid water on the surface...

but below that, things begin
to get a little weird.

There's so much water
that the sheer gravitational force...

of the water molecules
pressing down toward the center...

will crush the water so tightly...

that the water molecules
are almost touching each other.

It's a very odd type of water.

In fact, we call it ice,
even though it's not cold...

because the water molecules...

will be arranged
in a structure like ice...

but only due
to its high pressure.

Clearly, Gliese 436 b isn't
quite an Earthlike planet...

but what about this alien world?

What would make
an alien planet truly Earthlike?

It should be made primarily of rock
with enough water for oceans...

but not so much water...

that the land masses
are completely submerged.

It would also have to be
in its star's habitable zone.

The typical idea
for a habitable zone...

is the range of distances
from a star...

where an Earthlike planet
could have liquid water at its surface.

The idea would be that if you took Earth
and pushed it in too far...

the oceans would all boil away,
and that's bad for life.

Or if you took the Earth
and pushed it out too far...

the oceans would all freeze,
and that's bad for life.

In our own solar system...

the habitable zone
ranges from Mars' orbit...

into as close
as to where Venus orbits.

But the habitable zone
in alien solar systems varies...

depending on how hot the star is.

Currently, our best hope for
finding habitable Earthlike planets...

is to look around cool, dim stars
called red dwarfs or M dwarfs.

The M dwarfs themselves
are very special stars.

So our Sun might be
a hundred-watt light bulb.

An M dwarf is perhaps
a ten-watt light bulb.

And so what that means is...

that to stay warm enough
so that you have liquid water...

not ice, but still not too hot...

you move the planet in much closer.

And those close planets are easier
for us to detect with our technique...

because they tug
on the star more.

One of these M dwarfs,
called Gliese 876...

has been found to have at least
three planets orbiting it.

Two of them are gas giants,
but the third, Gliese 876 d...

is one of the smallest planets
discovered so far...

at roughly six or seven times
the mass of the Earth.

It's also just on the edge
of its star's habitable zone.

The planet orbits in just 1.9 days
around its host star...

but because the host star
is so low in luminosity...

it puts it on the edge...

of what you might imagine
a habitable zone to be.

There could be some region...

a ring around the planet
towards the backside...

where the temperature's
actually just right...

for liquid water to exist.

When it was first discovered,
scientists hailed this planet...

as the first of the super Earths.

Seven times the mass of the Earth...

sounds so close
to the size of our Earth...

that you wonder whether or not
it's a rocky planet...

maybe with a thick atmosphere.

But today,
the experts are unsure...

whether this is a large,
rocky planet at all.

Like Gliese 436 b, it may be...

completely covered in an ocean
of super dense water.

To call it a super Earth
is to suggest...

that we've found a planet
that's a close cousin of our Earth.

I would now rather think of it
as a distant cousin...

not unrelated to our Earth,
but far enough away...

indeed, more like Neptune
in our own solar system...

that has a big, rocky core...

but surrounded
by a big envelope of water.

So the race continues...

to discover
the first truly Earthlike planet.

At the University of Arizona,
astronomer Laird Close...

is hoping to capture
the first picture of an alien Earth.

But to do that will take a giant leap
in telescope technology.

Here at the Steward Observatory
Mirror Lab...

in a cavernous space
underneath the bleachers...

of the university's
football stadium...

engineers are working
on the next generation...

of super telescopes.

This is the largest mirror
that's ever been made.

This mirror is 8.4 meters across...

but it's just 1/7 of the size
that's needed...

for the Giant Magellan Telescope.

And together, when combined
with seven other mirrors like it...

in the Giant
Magellan telescope...

we will be able to actually
directly image extrasolar planets...

and maybe even Earthlike
planets around alien suns.

Scheduled for completion in 2016...

this telescope will be able
to make images...

up to ten times sharper
than the Hubble space telescope.

NASA and the European Space Agency
are also developing several missions...

that will use
space-based telescopes...

to search the stars
for our planetary kin.

This will be incredibly
exciting for humankind...

to know whether or not
around those little points of light...

that we see in the night sky...

whether there's Earthlike planets tied
in...

in orbit around those stars.

As technology improves,
we're gonna be able to find planets...

that look much more
like the Earth...

planets that, perhaps,
have life on them...

and maybe even planets that have
forests and steam trains.

The astronomers who have
dedicated their lives to this quest...

all believe
it's only a matter of time...

before we find
the first truly Earthlike planet.

The most exciting thing
I can tell you...

is that we are now
routinely discovering...

commonly discovering planets...

that are a mere five or ten times
the mass of our Earth.

We're not quite to the point
where we're finding Earths...

and that's where we really
want to be.

But we're finding planets...

that are ever so close
to our home planet.

So when we actually do cross
that final threshold...

and do find evidence that there's
a habitable planet out there...

this is gonna be a quite
an epochal event for humanity.

People should not worry
too much yet...

that we haven't found
any Earthlike planets...

because, well, a lot of effort
is going into it right now...

and I think it will be done
in the next ten years.

Yeah, stay tuned.