Original subtitles

(bright music)

I've always been really fascinated by Venus.

because it's kind of an alternate Earth.

Some people consider Venus

to be a sister planet to the Earth.

or perhaps a twin, but if it is,

it's really an evil twin.

I don't think it's evil,

but it's a remarkably different twin.

Earth's nearest planetary neighbor

is an enigma.

Venus has these incredibly thick clouds

that you can't really see through.

This is what makes it shine like a beacon in the sky.

Actually, sometimes people think it's a UFO

because it's so bright in the sky.

Humans have looked at Venus

and been drawn to it for millennia.

To me, it's very haunting, very rich with lessons,

and creates this desire to really understand that planet.

But to begin to understand Venus,

we have to go there.

(dramatic music)

It's definitely mysterious,

and it's, of course, important for science.

(people chatting)

But it became clear that Venus is a little bit easier

for the Soviet Union to explore for propaganda success.

(man speaks in foreign language)

And understanding Venus,

could be key to our very survival.

It's about the same radius as Earth.

It was formed, more or less, the same place

in the solar system than Earth.

Perhaps our evolution is going

to look like Venus in the future.

We can't claim to understand Earth really

if we don't understand Venus.

(bright theatrical music)

(gentle music)

For centuries people wondered if this

was what the surface of Venus looked like.

Once we realized that the other planets

were, in fact, planets, the natural assumption

was that, well, they're probably similar,

(gentle music)

Venus was one of the first objects

of scientific exploration for Russian science.

Lomonosov, who is kind of father of Russian science,

was the first astronomer

who actually studied the atmosphere of Venus.

We figured out the reason why Venus is so bright,

and, apparently, featureless,

is because it's completely covered in clouds.

Naturally, we assume these are clouds of water

like on the Earth, in which case,

Venus would be a great swampy paradise,

lots of water on the surface,

and water in the atmosphere,

totally covered by clouds.

People imagine great lizards

and dinosaurs living and swimming in the lakes

and oceans the tropical forests of Venus.

(dramatic music)

Svante Arrhenius who was a brilliant Swedish chemist,

was one of the first people to actually model

scientifically what the climate of Venus was like.

But he also had ideas about the life on Venus

and the vegetation.

He made observations that he thought confirmed this,

so he actually had a kind of scientific view,

but with a lot of imagination filling in the blanks

that promoted this idea of Venus

as a planet with a lot of vegetation

and a lot of life that was similar to Earth.

But maybe also Earth sort of stuck in the past,

in an earlier age when Earth was sort of a swamp planet.

(dramatic music)

(birds chirping)

The only way to tell actually whether Venus was

a sort of living world with jungles on the surface

was to actually go there with spacecraft.

(dramatic music)

(thunder roaring)

But before 1975,

no human had ever seen an image

from the surface of another planet, let alone Venus.

However, a Russian mission called Venera 9 was on its way.

On 20th of October of 1975,

this joint stock of spacecraft,

of Lander and the Orbiter approached Venus

and separated from each other.

Immediately they started their separate missions,

which were culminating at the same time.

The Orbiter approached Venus

and started a breaking maneuver

with its entrance to slow down at speeds just enough

that the gravity field of Venus would capture it

and leave it in a highly-stretched elliptical orbit

around the planet.

This components of the Venera 9 spacecraft

had become the first manmade object

to enter orbit around Venus.

(bright theatrical music)

But the mission was far from over.

And at the same time,

the Lander started going into the atmosphere

of Venus on the side of the planet,

which was not visible from Earth,

but sensed to the Orbiter,

which was so high in the sky over Venus,

it would later act as a lay station for the Lander

to send pictures back to mission control on Earth.

The Lander was a bowl-shaped capsule

covered with a special ablative surface,

and once it entered the atmosphere of Venus

and started breaking, layer by layer,

burning ablative surface,

and at the same time slowing down

tremendously from its initial entry speed.

The searing heat shield decelerated the Lander

from 10.7 kilometers per second

to around 250 meters per second.

(bright theatrical music)

Then once it's slowed down enough,

it was safe enough to open small opening

at the top of the capsule

and release two small breaking parachutes.

One of those two parachutes was then used

to release the top part of the capsule

and reveal the top of the Lander,

which was inside of that cocoon.

(bright theatrical music)

The speed dropped from 250 meters per second

to 150 meters per second

before a third parachute was deployed.

And once that happened, there was an antenna,

a transmission antenna exposed,

and that allowed it to immediately start transmitting

data to the Orbiter, which in turn,

relayed back to the ground control.

The third parachute brought the velocity

of the Lander down to just 50 meters per second.

And then that parachute was separated,

and it pulls out three canopy main parachute system,

which allows the Lander really slow and gentle descent.

After all the drama of it's journey so far,

the Lander would then spend 20 minutes

calmly taking measurements of the atmosphere,

but its brutal voyage was not over yet.

When the probe is around 50 kilometers over the surface,

the command is sent to cut the main lines of the parachute.

(gentle dramatic music)

Venus has always been a special object of fascination

as long as we've been observing the sky,

which is probably longer than we've been people,

and there's a reason for that.

It's so bright.

It's the brightest object

other than the full moon at night.

For much of human history,

we've mistaken Venus for a star or two stars to be precise,

the morning star and the evening star.

It appears as an evening star

for a little while near the horizon

and then disappears and then reappears

as a morning star near the horizon.

Does this intricate little dance in the sky

and then disappears again.

So it bounces from evening to morning.

It's never up in the middle of the night.

It's always at the dusk and dawn,

which are the most evocative times.

That has led it to be an object of mythology,

and folklore, and with gods and goddesses.

The association of Venus with femininity

really comes out of the fact

that we're still very dominated

by Greek and Roman Western traditions.

But, in fact, that's just one tradition,

and if you look around the world,

for instance, the Meso Americans

who were probably the greatest Venus observers

in terms of what they figured out

about how to predict the motions and everything,

for those civilizations,

Venus was this macho warrior dude,

and it was very much a male character.

So why assign a gender to a planet?

Planet's are at least as complex as people.

So, I think, it maybe does do it a bit of a disservice

just to say Venus is the female planet.

(gentle music)

After the II World War,

it wasn't long before the Soviet Union stunned the world

with the launch of Sputnik in 1957.

A year later the U.S. launched its first spacecraft.

The space race had begun.

(dramatic music)

The space race was driven by several major factors.

First of all, it was a military competition

of two superpowers which emerged after World War II,

the United States and the Soviet Union,

and the second is this ideological competition

between two systems, socialism in the Soviet Union,

and capitalism, as at least Soviet Union saw it.

That competition included scientific pursuit.

In the world of science probably the best way

to prove that superiority would be with victories in space,

and the Soviet government understood this.

Space exploration has a dark side.

We can't deny that we rode to the moon

and to the other planets on the wings of war.

That the reason we have these rockets

that can launch payloads into orbit and beyond

is because they were developed to destroy cities.

(bomb explodes)

The emergence of rocket technology immediately gives

scientists this idea that you can put

scientific instruments on the rocket

and fly them first to the upper atmospheres, then to space,

and then into deep space all across the solar system.

But within the Soviet Union,

it was in the framework of testing

intercontinental ballistic missiles and weapons systems.

It was absolutely under the same level of secrecy.

There was absolutely no public.

This was absolutely top secret.

We didn't use the term spacecraft in those days.

We called the payloads because

everything went on top of a launch vehicle.

Main thing you put on top of the launch vehicle

was the warhead, which was the payload.

The idea was we're really

trying to develop a launch vehicle.

The payload was sort of insignificant addition

back in those days.

What happened early on in

the space race is we began to say,

"Hey, the solar system let's explore it,"

and our competitors, the former Soviet Union,

was doing the same thing.

Now they happened to have set their sights on Venus

really, really hard.

(dramatic music)

The initial motivation for the

Soviet space program was propaganda success.

The ideas about Venus as a tropical paradise

were not at play in a process of decision

to fly spacecraft to Venus.

Its definitely mysterious,

and it's, of course, important for science.

But the most important factor was

that it's easier to reach than Mars.

The rocket scientists in the early space race

concluded that in order to get to Venus there's a window

of time in which the planets are closest.

This occurs every 19 months.

From the moment the race to Venus began in 1961,

only three opportunities were missed until 1986.

First off the mark was the Soviets'

Tyazhely Sputnik in February 1961.

It failed to leave low-Earth orbit.

Venera 1 became the first spacecraft to fly past Venus.

But due to a communications failure, no data were received.

(dramatic music)

The early history of trying to get to Venus

is full of failure.

There were a lot more failures than successes.

Within weeks of the first two attempts

to send a spacecraft to Venus,

a discovery from an Earth-based radio telescope

increased the intrigue about our mysterious twin.

(dramatic music)

Venus was found to have a very odd rotation.

The planets seemed to be rotating backwards very slowly.

A day on Venus is longer than its year.

You could say why does Venus rotate backwards?

But you can also say why do all

the other planets rotate forwards?

I mean, it's a mystery.

We don't really understand Venus' rotation rate,

but we don't really understand the rotation rates

of the planets in general.

(dramatic music)

Eighteen months after the discovery

of Venus' peculiar rotation,

the next opportunity to get to Venus was approaching.

(gentle dramatic music)

In the second half of summer of 1962,

all these forces finally came together.

Both sides finally had the rockets necessary to launch.

They had the spacecraft,

which was sophisticated enough to go to Venus,

and they had this motivation, money,

and all the political rationale to do this.

So within this short period of time,

from July to beginning of September,

there were five missions launched, two Mariner probes

and three Russian MV probes as they were called.

Mariners 1 and 2 were identical,

and they were both modified Ranger spacecraft

taken off the product line

and converted for a mission to Venus

rather than a Ranger mission to the moon.

(gentle dramatic music)

They were hexagonal in the shape

about six boxes bolted onto a frame.

There was a high-gain antenna,

and there was a tower structure

bolted on top of this hexagonal.

We called it a bus.

It wasn't at all unusual to be working 56 hours a week,

and if that meant everybody had to work weekends

or something like that or 16-hour days,

we did it for the time that it took

to get back on that schedule.

(dramatic music)

On the 22nd of July 1962,

Mariner 1 launched,

buts the spacecraft malfunctioned,

and flight control had to manually destroy it.

A month later, the first Soviet spacecraft called

2MV-1 Number One succeeded in getting into orbit.

But it's upper stage rocket booster failed,

and it never left low Earth orbit.

(dramatic music)

Two days later, Mariner 2

blasted off successfully from Cape Canaveral,

(dramatic music)

followed by the final two Soviet spacecraft

on the 1st and 12th of September.

Both failed to leave Earth's orbit.

(dramatic music)

Three months later on the 14th of December 1962,

(bright music)

Mariner 2 arrived safely at Venus.

Mariner 2 became the first spacecraft

to explore another planet in the solar system

and actually return useful scientific data

from the vicinity of another planet.

(bright music)

(gentle music)

The measurement that Mariner 2 made

suggested that the upper atmosphere of Venus was very hot

in the region of 500 degrees celsius.

Perhaps Venus wasn't quite

the paradise everyone had hoped for.

There was an editorial in the New York Times

when the Mariner 2 results were reported,

and it was titled "Venus Says No",

and it talks about the grand romantic dreams

of mankind being dashed.

Mariner 2 also made

another startling discovery.

It could be a hint that all was not well with Earth's twin.

Unlike our planet,

with its North and South magnetic poles,

Venus doesn't have any significant magnetic field.

It's about the same radius as Earth.

It's roughly the same rotation, right?

Maybe it's a hundred times slower,

but that's not that different, fluid dynamics wise.

These are still rapidly rotating bodies.

It's got a big core we believe.

We believe it's molten.

Something's funny that Venus has no dynamo.

Mariner 2 took measurements of high temperatures on Venus,

and there was a dispute about those temperatures,

perhaps being only high in the atmosphere

or the temperatures really showing an unbearably

hot environment everywhere around the planet.

So, of course, the immediate challenge was after this,

both for the Soviet Union and for the American scientists

was to launch more probes, more sophisticated ones,

but design them based on all of the available information

and continue this pursuit of what Venus is all about.

(dramatic music)

Mariner 2s distant flyby

hadn't settled the score for supremacy over Venus,

but the USA and the USSR were about to begin

an even more intense battle for Earth's twin.

From now on once Mariner 2 did the job,

it was absolutely paramount for the Soviet Union

to land on the surface of Venus first

and preferably to do imagery

and science on the surface of Venus.

Over the next 11 years,

there was a frenzy of missions to Venus

(dramatic theatrical music)

(bright lighthearted music)

Venera 9 is plangently increasingly

dense atmosphere of Venus.

(bright theatrical music)

About 50 kilometers up from the surface of Venus,

you pass through a region that is about

the surface temperature and pressure of Earth,

so there's a region in the upper atmosphere of Venus

that would feel pretty much like it feels in this room.

I think to any individual

who reads the description of the landing sequence,

thinks that it's really irrational

and a really bizarre way to get

equipment to the surface of Venus,

But after a little bit close examination,

we understand that each steps of the sequence

there's actually logic and behind it.

And, in fact, it's counterintuitive,

but part of the problem with a lot of designs

when you're designing an entry probe for Venus

is that you fall too slowly,

Meaning that, it takes too long,

and you're gonna heat up too much

before you get to the surface.

Then you keep falling,

and the atmosphere gets hotter and hotter

and more and more dense to the point where

it's a hundred times as dense as the atmosphere on Earth.

That means that you're falling through.

It's not quite a liquid, but it's a gas

that is approaching the properties of a liquid,

and that would slow your fall.

(voice chattering on radio)

Then when you get to the surface,

it's almost like going through the ocean.

(gentle music)

Venera 9 wasn't the first Lander

to get to the surface of Venus,

but it was the first to send back pictures.

It was a colossal achievement.

(gentle dramatic music)

Venera 9 returned the first pictures

from the surface of another planet,

and the fact that, that was done first for Venus

before the Americans did it with a Viking in 1976 at Mars

is really remarkable because it's much harder to land

on Venus and photograph it than it is on Mars.

Not that Mars is a picnic,

but just to get something to survive

in those conditions and take a photograph

and send the results back is really challenging.

That achievement in 1975 by the Soviet Union

that was a real triumph of exploration.

(gentle music)

What we have from the Russian is just unbelievable

because it was really a challenge to land there.

So even if the images are not perfect,

it's still wonderful.

But the ideas of Venus as a verdant lovely environment,

possibly with jungles on the surface

and a water rich environment, were immediately taken away.

It wasn't really until Venera 9

operated at the surface for some time

and returned data that we were sure that we had

solid data that told us, yes, this is how hot

and this is what the pressure.

Wow, that's really pretty intense.

(dramatic music)

(thunder roaring)

After Venera 9, we had a sense

of what some individual places on Venus were like.

If you send a probe in one place

and you measure the temperature

and pressure on the way down,

it gives you one slice from space to the surface.

But the more we learned about Venus,

the more we realize that

like Earth it's a complex changing planet

with different things going on in the day side

and the night side and this latitude and that latitude,

and that to really understand what's going on,

you have to measure multiple places at once.

If you have this probe on the night side,

and this probe on the day side,

and this probe at high latitude,

and this probe at low latitude

and you're able to do them all at once,

then you can put together more of a 3D picture

of the way the atmosphere is behaving

and changing over time.

In 1974, NASA approved

a double mission to explore Venus,

both from orbit and from multiple places around the planet.

This ambitious mission was called Pioneer Venus,

The Pioneer Venus mission included an Orbiter

and four probes, three small probes

and one large probe to look

at different parts of the global Venus

and to make measurements as they descended to the surface.

The Pioneer Venus Orbiter

launched in May in 1978,

and the spacecraft carrying the probes

followed it in August.

The Orbiter had arrived at Venus a few days earlier

and inserted itself into orbit in preparation

to relay data back from atmospheric probes.

The probes were not designed to survive the landing,

but fortunately one did

and continued to send back information

until the heat of the surface destroyed its electronics.

The results from the

Pioneer Venus mission were clear.

No matter where you went on Venus,

the night side, the day side,

the equator, or the higher latitudes,

its surface was uniformly hot and at high pressure.

So Venus is all bad.

The temperature only varies by a degree

or two over the whole globe,

day to night, pole to equator,

and the thick atmosphere acts like a blanket,

which keeps the entire surface of Venus very hot,

and so there's no place,

no hospitable place on the surface of Venus,

where we might imagine humans living.

It's not just the temperature.

The atmospheric pressure on the surface

is so high that it would crush almost

every military submarine ever built.

Now we see Venus is just awful environment.

I mean the atmosphere is only

CO2 is 90 bars on the surface and 500 degrees.

By the end of the '70s,

we really understood how Venus looked.

I mean, it was not gonna be habitable.

And to me that had sort of a lingering effect

that Venus was like not as exciting

as it was supposed to be,

and, therefore, it was sort of not as cool

and maybe not as worthy of our attention.

I think that was really unfortunate

because it was an outcome of those

false expectations that we had for it.

So instead of Venus being a sort of tropical paradise,

it's hell things have gone terribly bad.

Temperature on the surface is hot enough to melt lead

and the atmosphere is full of poisonous gases

and carbon dioxide.

(gentle music)

It sets up this huge mystery.

Why do you have these twin planets so nearby,

and one of them ends up like this,

this paradise for Earthly life.

This other one right here ends up in such a different state.

What happened there,

and can that happen here?

If we don't know the answer to that,

how much do we really know about our planet?

(gentle music)

In order to answer these questions,

we must go back to the formation of Venus and Earth.

(dramatic music)

Earth and Venus form this set of twins

that, as far as we can tell, started out more similar,

and then diverged.

Understanding that divergence

is an important scientific puzzle,

but it's also just sort of compelling

because Earth is our home,

and here's this other planet

that could have been like Earth, that should have been,

and yet it's so different.

(dramatic music)

The formation of Venus and Earth

was probably pretty similar.

It's made of the same type of stuff.

It seems as though the original rocky stuff

that fell together and made Earth

probably had a lot of water bound up in it,

and Venus because it seems to have been made out of

the same stuff in the same process at the same time,

then likely got a similar admixture of water

just chemically bound up in that rocky material

that made the original planet.

About 600 million years

after the beginning of the solar system,

there was a very large period of collisions

when the collision rate was very high,

and that's what we call the late heavy bombardment.

So during that time,

there were both comets and asteroids moving around

both bringing even more water to the Earth and Venus.

(gentle music)

After all the brutal drama

of the initial formation

and the violence of the late heavy bombardment,

things would have settled down for Earth and Venus.

(gentle music)

Venus might've been much more hospitable,

very similar to the Earth.

Maybe there were oceans and even life on Venus.

(gentle music)

So why is it that Earth today is an oceanic planet

and Venus is not if they both started out similar?

The one obvious difference is that Venus

is significantly closer to the Sun.

It's about three quarters

of the distance from the Sun to Earth,

which means it gets about twice the amount of sunlight.

When the planets were young,

the Sun was much less bright than it is now.

So there was a time when the ocean of Venus

was probably stable.

What happened we think was that as the Sun heated up,

it triggered something we call the runaway greenhouse,

and the way that works has to do with evaporation.

So if you're evaporating the oceans of a planet,

you're getting more water vapor in the atmosphere.

But water vapor itself is a strong greenhouse gas,

really as strong as CO2,

meaning that it's a gas that absorbs infrared radiation.

It lets the visible through.

It absorbs infrared.

So you get more water vapor,

you're absorbing more infrared.

You have a stronger greenhouse that heats up the surface.

so you get more evaporation and more evaporation,

gives you more water vapor in the atmosphere

a stronger greenhouse, hotter surface, more evaporation.

So you can see it's what we call positive feedback

because the hotter the surface is,

the more water vapor you're getting in the atmosphere.

The more water vapor, the hotter the surface is,

so that each part of the cycle reinforces the other.

That's a positive feedback and that's unstable.

It runs away.

(gentle music)

So water in the oceans evaporated

to make a blanket around the planet,

which made the planet hotter, but worse than that,

carbon dioxide was baked out of rocks.

(dramatic music)

The idea that carbon dioxide

could create a powerful greenhouse effect goes all

the way back to the Swedish pioneer Svante Arrhenius.

Svante Arrhenius correctly deduced

that there was a lot of carbon dioxide in the atmosphere.

So it was probably hot.

In fact, he was also one of the first people

that considered greenhouse warming on Earth.

Interestingly, and that partly came out of his work

on thinking about what Venus was like.

So this is one of the ways, in which,

our knowledge of Earth climate

and global warming is actually connected to thought

about Venus because Arrhenius put this together.

He said a planet with a lot of CO2 has to be warm.

(bright music)

So how did Earth escape the same fate

as Venus with a runaway greenhouse effect?

The answer begins with rain.

So on Earth the CO2 gets pulled out of the atmosphere

by what we call weathering reactions,

where water is raining out

and makes a sort of carbonic acid,

which when it runs over rocks, leaches the ions out

and it ends up in the ocean as carbonate ions

and forms carbonate rocks.

When you see the White Cliffs of Dover

or any massive deposit of carbonates,

you're seeing carbon that has been

pulled out of the atmosphere.

Those carbonate rocks get pulled

into the interior by plate tectonics,

and when you have subduction of oceanic crust

down deep into the interior where they're melted

and ultimately then the CO2 is released under pressure

and becomes a dissolved gas,

which then comes back out those volcanoes

and that completes the cycle.

But that is facilitated by water in rain

and in these chemical reactions.

If you don't have water,

you sort of break that part of the carbon cycle.

(gentle dramatic music)

But if the process that removes

carbon dioxide from the atmosphere is rain,

what happened to Venus' water.

The answer is due to a complex interaction

of the planet's atmosphere and the stream of particles

that constantly come off the Sun called the solar wind.

When the water on a planet evaporates

and is in the atmosphere as water vapor

as opposed to condensed on the surface in liquid water,

then it's much more vulnerable being lost to space,

and the main way that happens

is the water gets broken up by ultraviolet light

in what we call photo dissociation,

which is that these energetic photons of sunlight

breaks hydrogens off from the oxygen.

Then when you have a free floating hydrogen,

it's easy for that to escape into space.

In fact, all planets are losing hydrogen

all the time into space,

and when you have a steam atmosphere

and a lot of water photo dissociating,

then you're gonna have a stream of hydrogen

escaping off into space.

Then after a period of time,

you're left with less hydrogen,

and, therefore, less water on the planet.

The solar wind is a stream

of charged particles coming out of the Sun.

That is what is stripping away

the atmospheres of the planets.

All this means that you're sort of losing water,

and so Venus is becoming drier and drier.

So Earth has a magnetic field which protects it

to some extent from the onslaught of the solar wind.

Whereas, Venus we have no magnetic field

to protect the planet.

A decade or so ago people used to think

that the big difference between Earth and Venus

was that the Earth had a magnetic field,

and then we looked at Venus and we said

it's lost all its water

because solar wind strips it away.

We are finding it's more subtle now.

Pretty much all of the planets

lose their atmosphere right now at about the same rate,

so everything's scrambled.

We're back to the drawing board

to really try to understand how atmospheric escape what,

and what role, if any,

the magnetic field plays in that process.

Whether or not the lack of a magnetic field

had accelerated the loss of Venus' water.

The planet became dry

and had no chance to mop up all the CO2.

(gentle music)

But where did all this gas come from?

(gentle music)

Why was the atmosphere of Venus

so much thicker than our own?

To find out, scientists would need

to find a way to see what was going on.

One of the fantastic things

about Venus is its cloud layer.

This is what makes it shine like a beacon in the sky.

At the same time, it's one of the most frustrating things

because it stops us seeing the surface.

So what we need to do is not look with our eyes

but look with different wavelengths

that can peer through these clouds

and get down to the surface, such as radar wave lengths,

and then we can certainly see what's going on.

After the success of Venera 9 and 10 in 1975,

the Soviets continued to send

a variety of missions to Venus.

(gentle music)

But NASA was determined to try and find out

what much of the surface of Venus actually looked like,

and in the early '80s,

they started to develop a mission to do that,

called the Venus Orbiting Imaging Radar.

(gentle music)

It had multiple instruments and multiple antennas

and NASA said there's no money.

And so, this great thing narrowed down to one instrument,

and we were a spare parts mission.

We used a Voyager spare antenna,

and a Voyager spare bus, and Galileo computers,

but the radar itself was a new design.

It had this parabolic antenna,

so the signal would ping off Venus and come back,

and you'd have to capture it.

You synthesize an image from that.

You do it over, and over, and over again,

and you gradually build up radar images of the surface.

The budget version of the mission

made from old spare parts was renamed Magellan,

and on the 4th of May 1989,

it was delivered to low Earth orbit.

12, 11. (funky music)

By space shuttle Atlantis.

Zero, and lift off.

(funky electric music)

There's the Orbiter going by the launch tower.

The last one seems to be throttle down.

So the design of Magellan was to get into an orbit.

If Venus is here, it would go by really close

for an hour and radar image,

and then it would turn back to the Earth

and relay back its data for another hour.

And then it would correct its wheels and get a star scan,

and then turn back and then radar image again,

and we did this 24 seven for a Venus day.

(gentle music)

This is 1989, 1990, 1991.

We're dealing with reel to reel tapes,

and they're running these tapes

back and forth from Goldstone.

And then the data from Canberra and from Madrid

would actually be flown in in overseas packages.

The extreme efforts that the scientists

and engineers made to acquire this data was worth it.

Magellan provided an unprecedented view

of the Venusian surface.

They mapped near to the entire surface of Venus

and that was a huge revelation

because that was our first global look at

what the geology of Venus is really like.

The Magellan data was indisputable.

Venus is or was a world of volcanoes of all kinds.

It told us, yes, this is a world that's dominated

by vulcanism has been through much of its history.

(dramatic music)

It's a world that has been

resurfaced by volcanism over time.

(dramatic music)

There's a huge abundance

and variety of volcanism on Venus.

There are these huge areas of flood basalts

where this running lava has come out from the interior,

and a lot of Venus is covered with that.

(suspenseful music)

But then there are other volcanic features,

these things nicknamed pancake domes,

which are much smaller.

They're about 10 kilometers across

because they're much more sticky,

less runny, more viscous magma.

(suspenseful music)

So it's been a volcanically active planet massively

with all different kinds of volcanism

going through many different phases.

Now it doesn't mean that it's current.

It could be ancient.

All of this activity means that Venus

has been belching carbon dioxide into its atmosphere

for billions of years,

and with no rain to absorb the CO2,

the atmosphere has become thicker and thicker.

(gentle music)

(thunder roars)

The atmosphere on Venus today is almost all CO2

and here on Earth we're concerned

about 300, 400 parts per million CO2.

It's a trace gas.

It's a minor gas.

(gentle music)

If we assume that Venus and Earth started out similar,

which I think is likely,

although we still wanna gather the data to prove it,

that Venus had early oceans more like Earth

and had some kind of a tectonic cycle

and probably a carbon cycle with carbonates

and volcanoes like Earth has today, then what happened?

(dramatic music) (thunder rumbling)

Why is the solid part of the planet

the geology apparently so different from Earth's?

And in my view, it probably has to do

with the losing of the water.

That if you lose the water from the surface of the planet,

then over time you're going to also dry out the crust

and the interior of the planet

because you are also out gassing water.

You're losing water through that cycle,

and on Earth you're in gassing water too,

in the sense that, you're pulling water into the interior

all the time through that tectonic cycle.

If you lose that ability to do that

because you don't have any water on the surface,

you're not going to right away

dry out the interior of the planet.

But after a billion, two billion years,

you're going to ultimately end up with

a dried out interior and a dried out crust,

and that's going to have different material properties.

And, in fact, if you take an Earth model of plate tectonics

and mantle convection and you dry it out,

you change the properties of the rocks and say,

"Well, what if these were dry rocks

"instead of hydrated rocks,"

these models will start behaving more like Venus.

The rocks get harder.

It gets harder to subduct.

Plate tectonics gets sort of choked off,

and it's like the engine runs out of lubrication

and it gets stuck and then starts going in spurts

rather than running smoothly.

(gentle dramatic music)

And this drying up of the crust

could be responsible for the lack of

what's known as an internal dynamo,

which is what produces a magnetic field.

(gentle music)

I think the easiest explanation

for why Venus doesn't have a dynamo

is probably that heat is trapped within the core.

It appears right now

that there's no plate tectonics on Venus.

There's probably convection occurring within the mantle,

but it's not very efficient at getting heat out,

and so that probably traps heat within the core.

If heat can't get out,

then I can't cool that fluid at the surface.

I can't release those dense blobs

into the interior falling and convecting.

If it's not convecting and there's none of that

turbulent convection to stir up a magnetic field,

I think you should then see what you do see.

(gentle music)

Magellan orbited Venus

from August 1990 until October 1994.

The mission mapped 98% of the surface

and greatly increased our understanding

of the geological processes

that have shaped the planet's history.

(gentle music)

And by that time, it was done.

The computers were resetting.

We were out of fuel,

and then you gotta update

because now your timing's off

because you've got slightly out of orbit

because of your thrusters.

It was always an engineering challenge

because I was just scrambling every day

just to keep it going.

But it was a great spacecraft to be your first spacecraft

because it was a hell of a learning experience for me.

(gentle music)

The last communication with

Magellan was on the 13th of October 1994,

before the spacecraft disintegrated

deep in Venus's thick atmosphere.

In the aftermath of Magellan,

there was a lot of desire for more Venus missions,

and a lot of frustration in the community of the inability

to get NASA to send another mission to Venus,

which is a effort that continues.

But the European sort of came

to our rescue with Venus Express.

It's called Venus Express because

it was a mission that was put together very quickly.

There was a spare spacecraft from another mission,

and they had a couple of years to propose

and fly a spacecraft, and the Venus Express Mission

was the one that won.

What Venus Express really is, I think of it

as our first weather satellite at another planet.

(gentle dramatic music)

And as the first Venusian weather satellites

Venus express gave us a much greater insight

into what was really going on with Venus's atmosphere.

(dramatic music)

So Venus Express made these movies of the motions

of the atmosphere at different depths,

and indeed it's quite dynamic.

The atmosphere of Venus does this,

what we call four days super rotation,

where the atmosphere is whipping around.

These high altitude zonal winds

can zip around the equator of Venus

at 360 kilometers per hour.

But above the poles,

the rotational speeds drop almost to zero.

(dramatic music)

The intense heat on the surface of Venus

creates powerful convection currents

that drive a separate lower altitude circulation

of heat from the equator to the poles.

(dramatic music)

With Venus Express we saw these vortices near the poles,

in particular the South Pole of Venus,

which had not been seen before.

There's a little bit of like water down a bath plug,

so seeing that for the first time was very exciting.

Venus is entirely covered by clouds.

These clouds are made up of droplets of sulfuric acid,

so it's arguably the case that Venus

has the worst case of acid rain in the whole solar system.

The acid rain of Venus is created by the

vast amounts of sulfur released through the vulcanism

that has dominated the planet's evolution.

Acid rain is in an extreme state on Venus.

Acid rain has been a problem on Earth downwind of factories,

and by studying it in an extreme case on another planet,

it helps us understand more of the

interaction of acid with water clouds.

But down at the surface of Venus,

things are altogether much calmer and deeply weird.

(gentle music)

Here the wind speeds are very low.

The acid rain has evaporated

long before it gets this far down.

(gentle music)

If you could go to the surface of Venus,

not that we can right now,

I think it would be an incredibly strange experience.

The first thing you would notice is that

the quality of light would be very different

from the quality of light on Earth,

and that's mostly because the light is being filtered

through that incredibly thick atmosphere

and also through the globally extensive clouds.

So it would be kind of a red murky light.

When you look at things,

you're looking through this massively convective medium

where because of the temperature you're looking at,

and the swells and stuff, you see the refraction of light.

(dramatic music)

You probably would see that sort of shimmery

kind of effect that you get in desert areas on Earth

just because there is a lot of infrared radiation

coming up out of the surface,

and that is going to be affecting

the stability of the atmosphere near the surface.

You're in this really, really strange environment.

Any movement you feel resistance,

and it becomes this viscous fluid-like thing

that you're having to move through.

It wouldn't be quite like running through water,

but you'd be approaching that.

You'd be somewhere in between

what we feel running through the air

and that resistance of trying to run

through something really viscous.

It'd be a good workout that's for sure.

(dramatic music)

So in the future,

will there ever be a time when Venus

might've cleared its dense atmosphere

and cold enough for humans to live on its surface?

Some have proposed that Venus might

once again be hospitable, and potentially

after volcanic eruptions cease on the surface of Venus.

I don't buy that.

I think, the escape rate of the Venus atmosphere

over time is infinitesimally slow

compared to the magnitude of the atmosphere.

The time it might take for the Venus atmosphere

to be cured in that way,

would probably match the time that the Sun

would take to see out the rest of its lifetime,

swelling into a red giant and engulfing the whole planet.

So there's really no future time that I can imagine

where the atmosphere would be lost enough

so the greenhouse effect would be small enough

so the surface temperature of Venus would be cool enough

that life could exist there.

(thunder rumbles)

So if Venus is never destined to become

the paradise we once imagined through natural processes,

(gentle music)

what about through deliberate manipulation?

Can we terraform Venus?

Terraforming is an interesting concept.

It's certainly a valuable thought experiment.

I don't necessarily condone trying this,

but that's okay cause we're not gonna

have the ability for a long time.

We have millennia to sort that out,

whether we think it's a good idea.

So maybe the way to do it would be

to throw a lot of comets at Venus

where you would both raise up the dust

from the comet impact to cool it off,

and then you'd also be sort of

sprinkling it back with water.

If you start to have liquid water on the surface,

then that's gonna restart the cycle

where you're gonna then be removing

CO2 out of the atmosphere by weathering.

It would take awhile it'd build longterm renovation project,

but there's nothing physically impossible about it.

The problem with terraforming ideas is that

right now we're in a situation

where we're rapidly Venura-forming Earth,

that is turning it to be more Venus like,

and so we can't even imagine any of these futures

unless we get to the point where we're doing a much

better job of controlling our own actions on Earth.

(gentle music)

People talk about us colonizing the solar system,

escaping from the problems that we have on the planet Earth.

Maybe there's an asteroid heading towards us,

which one day will hit the surface

of the planet and cause extinction,

and, I think, these are things which are important.

We're studying them, and we really need to understand

what the possible longterm dangers are.

But there's a short-term danger,

which is climate change,

and it's happening today.

What worries me sometimes is this idea

that we can take human beings away

from all of the mess that we've created here.

Sociologically, it seems unlikely that we're just going to

become the perfect citizen once we crossed

the 100 kilometer line and go into space.

But also there's nowhere in the solar system

that's any better to live than the very worst

that we could ever do to the planet Earth.

Whatever we do here,

it won't be as bad as living on Mars or on Venus

or anywhere else in the solar system.

So at the same time as we're looking outwards and exploring,

we should never forget that this is where we come from,

and there is no planet B.

This place has to be looked after as well

as much as we're looking outwards and beyond.

(gentle music)

So perhaps one day, far in the future,

humankind will not only have the scientific ability

to make Venus into a paradise,

but the wisdom to realize

that we already have a paradise of our own

(gentle lighthearted music)

(bright music)