Original subtitles

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- [Sue] Venus and Earth are the twin planets.

We've seen thousands of exoplanets around other stars

but Venus is still the planet most like Earth.

- [Tony] The surface of Venus is hot enough to melt lead.

- [Jonathan] Venus is incredibly hot,

it has what we call a runaway greenhouse,

where it's sort of the extreme state of what happens

if you let a greenhouse go completely crazy

on an Earth-like planet.

- [Rosaly] Venus is kind of a warning

that we have to pay attention to what's happening

to the atmosphere of the Earth.

We don't want the Earth to become evil like Venus.

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- Venus and Earth are actually really similar

in many, many ways.

They are almost exactly the same size,

and they have similar gravity.

Venus has about 90% of Earth's gravity.

And we think that they both formed in a similar part

of the solar system at about the same time

from more or less the same materials.

So they, they really should have a lot of similarities,

we see they both have atmospheres,

they both show the same types of geologic processes

on their surfaces with volcanoes

and tectonic regions,

which is where the crust is moving around.

- It's the only planet

that is likely to be still geologically active

in some of the same ways as, as the Earth.

It has a similar bulk composition.

It has an atmosphere, a huge atmosphere,

one of the very few plants in our atmosphere

to have a huge atmosphere.

- [Lori] That thick carbon dioxide atmosphere acts

as a greenhouse,

warming the surface to hundreds of degrees Fahrenheit,

and pressures that are like being about mile deep

in the ocean.

At Venus, there's no magnetic field,

whereas at Earth, there is.

- [Rosaly] So Venus is kind of the Earth's evil twin sister.

It shows how two worlds of similar size, similar density,

not that far apart in terms of distance to the sun,

evolved very differently.

- So the real core question it comes down to

is what was it in Venus's and Earth's history

that made these two similar planets

take very different paths.

And then how do we apply that

to planets beyond our solar system

and look at how understanding Venus could help us

better understand what exoplanets are like,

and which ones are the ones

that could potentially harbor life like Earth?

And which ones are those that are like Venus

and are very hostile to life?

- [Mike] We believe that Earth and Venus formed

around the same time in our original circumstellar disc.

They are probably geo-chemically very similar

because they formed very close to each other in the disc,

much closer than Earth did to Mars and from what we know

about the geo-chemical similarities between Venus and Earth

and Earth and Mars,

certainly we believe that Earth is more similar to Venus

than it is to Mars.

We don't know that much about Venus

because we haven't sent enough missions there

as we have for Mars.

It does have similar amounts of carbon dioxide

in its surface and in its atmosphere compared to Earth.

- Venus is, in some sense, the poster child

for the greenhouse effect of carbon dioxide.

It's a planet that has much more carbon dioxide

than the Earth has in its atmosphere.

And even though it is covered

by this bright sulfuric acid haze,

Venus reflects 70-something percent of the sunlight

that reaches it, so even though it's very close,

it actually doesn't get nearly as much sunlight

as you imagine because of that haze.

Yet it's got this crushingly hot surface.

And the only way to explain that

is because of the greenhouse effect of the carbon dioxide.

Venus tells us

that the greenhouse effect is a real phenomenon.

- [David] Venus, in many ways,

is an extreme case of some of Earth's environmental issues.

I mean, the most obvious one being global warming

and the greenhouse effect,

which is something we're all obviously aware of

here on Earth because the amount of CO2 has risen

above 400 parts per million,

and that is causing global warming

because of the infrared absorption of CO2.

And yet here's Venus, the Earth-sized planet next door

with an atmosphere that is almost 100% CO2.

Venus, as far we can tell, was a habitable planet

for some time

before it went through this runaway greenhouse transition.

- Imagine a graph where we have,

you know, temperature versus CO2.

And so Earth is in this section over here,

right, 'cause we have this much CO2.

So if we want to understand this process,

Venus offers data up here, right?

Another set of data points that we can use

to sort of link how much CO2 do we need before this happens?

When do we get into a position where we're really in trouble

and there's nothing we can do about it

except move to Mars?

- [Tony] We don't expect the Earth

to turn into Venus anytime soon.

Humankind is putting more and more carbon dioxide

into the atmosphere

as humankind has been doing now for a few centuries,

since the Industrial Revolution began.

We know that the climate is going to get warmer.

How warm it will get depends

on how much carbon dioxide we put into the atmosphere.

Humans are not going to be able

to put enough carbon dioxide into the atmosphere

to turn the Earth into Venus.

- So there's this whole long-term cycle

where the carbon comes out of volcanoes

and ends up in the atmosphere

and then gets pulled out by chemistry

and made into carbonate rocks,

which get deposited on the ocean floor

and then subducted by plate tectonics

into the interior of the planet

and ultimately sort of heated and squished

to the point where the carbon dioxide is, is released

and then comes out again in a volcano.

That's a cycle that takes millions of years

and it ultimately regulates the carbon

in Earth's atmosphere, of course,

recently, we've been perturbing it with our automobiles

and smoke stacks and things,

but that's all probably a temporary sharp perturbation

in what is a multi-million-year cycle

that's been operating for billions of years.

Now, compare that to Venus.

We think that early on Venus probably had a similar cycle

because it has volcanoes, it had volcanoes,

it's probably been volcanically active its whole life.

And it used to, we believe, have an ocean

which facilitated those weathering reactions

that pull carbon dioxide out of the atmosphere.

- Part of the issue is that Venus no longer has an ocean.

We think it had an ocean earlier in its history,

we don't really know when water was lost.

Having an ocean is an important part

of pulling carbon dioxide out of the atmosphere.

We think that Earth and Venus have similar amounts

of carbon dioxide.

But, on Earth, those are locked up in carbonate rocks.

And those carbonate rocks often are subducted

back into the interior,

sequestered, in effect, by geologic processes.

- [Martha] So you need an ocean.

And we hope that we can find evidence

in early Venus history of sequestering

of carbon in rocks.

That's what we look for on Mars,

that's, a lot of Mars work has been to look

for those carbonate rocks on Mars.

What Venus shows us, without a doubt,

is that there is a relationship

between the amount of CO2 you have in an atmosphere

and the temperature.

- [Sue] Will the Earth become 500 degrees Celsius,

900 degrees Fahrenheit?

That's really not likely to happen.

But understanding chemical reactions

in this very active atmosphere that Venus has

is so important for being able to understand

how climate change comes about.

What are the important chemicals,

what are the important processes?

So we really have a lot to learn

from the atmosphere of Venus.

- [David] For example, acid rain is a problem here on Earth

because of sulfur dioxide from our smoke stacks

getting into the clouds and mixing with water

and making strong acid.

Well, Venus, again, is sort of the poster child for,

for that condition with clouds

that are basically made out of purer sulfuric acid,

and so it's, it's a place

where we can study this environmental problem, acid rain,

in its most extreme manifestation.

And to give one more example,

another problem of our own making

is the problem with the ozone hole

and the ozone layer being eroded

by these chemicals, these chlorofluorocarbons

that we released into the atmosphere

where the chlorine gets loose

because of ultraviolet light in the stratosphere

and destroys ozone, which then becomes a threat

to life here on the surface of the planet.

Well, one of the ways we discovered the ozone layer

was being eroded on Earth came about

because we were studying the upper atmosphere of Venus.

- [Sue] Venus's atmosphere is so intriguing.

We actually found the ozone hole on the Earth

because people were studying chemistry

of what was going on in the atmosphere,

upper atmosphere of Venus.

- Some scientists were trying to understand why,

why isn't there more ozone on Venus,

why aren't there more oxygen compounds

in the high atmosphere of Venus?

And some other scientists said, well, you know,

we've seen these experiments with chlorine

and chlorine can, can destroy oxygen compounds.

And then they came out with a paper

saying we think it's chlorine that is destroying ozone

on Venus.

Some other scientists saw that paper.

- And it made them ask this question, well,

what's going on in the upper atmosphere of Earth,

are there similar types of chemical reactions going on?

- And they said, oh, that's interesting,

what about these, these chlorine compounds

that we're putting up into the atmosphere on Earth,

that, couldn't that, and they said, uh oh, wait a minute.

And that helped them realize what was happening

and help them sort of sound the alarm.

- Look at that huge difference that that made

in terms of discovering the ozone hole on the Earth

and, you know, since people have taken action

to actually stop putting those chemicals into the atmosphere

that was creating such a destructive process.

- And, indeed, that's an example where we've responded

in a healthy way to this knowledge

that we were doing something to our planet

and have taken measures to fix it.

And it came about

partly because we were studying this neighboring planet

out of pure curiosity,

trying to understand the chemistry there.

- The link between innovation and expanding our thinking

is not linear.

In science and technology,

you don't plan for that necessarily,

you don't say, okay, I'm gonna discover this great thing,

and I'm gonna start here,

and I'm gonna, at the end will be this great discovery.

That comes from a lot of tries and a lot of failure.

And if we don't push at the limits

of what we can do as a society, we won't succeed.

That's the way it works.

That's what we do as scientists.

That's why we sail across the ocean.

That's why we climb the mountain.

And that's why we should go to Venus.

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