(intense music) - [Narrator] Billions of years ago, our nearest planetary neighbor, Venus, may have had oceans and rivers, life-giving habitats, like the ones that graced the early Earth. (dramatic music) (thunder rumbling) Today, it's burned-out surface is a global fossil of
volcanic destruction. (lava sloshing) Concealed beneath a
dense toxic atmosphere. (wind whooshing)
(soft dramatic music) Scientists are now unveiling
daring new strategies to explore its tortured landscapes, to search for clues from a
time when the planet was alive. How did Venus descend
into this hellish state? And how did our planet,
Earth, manage to survive? (mysterious music) (thunder rumbling)
(lightning clapping) (slow music) At the surface, the air
is 95% carbon dioxide. So dense, it's more like an
ocean than an atmosphere. And it's hot enough to melt lead. Overhead, thick clouds of sulfuric acid. (eerie music)
(thunder rumbling) No spacecraft has lasted
longer than two hours on Venus. (lightning clapping) All we have seen close up, a few images transmitted by
the Soviet Venera landers back in the 1970s. (mystical music) Radar images from the
Magellan Mission in the '90s have stoked our desire for more. - We think of it as this sort of ugly,
forbidding, scary place, because we've seen these
few Russian lander images of these sort of eroded rocks
and crushing atmosphere. But when you look at the Magellan imagery and you see this bewildering array of volcanic forms and flows and bizarre and interesting
canyons and valleys and channels that have been carved by liquid lava and volcanoes of different
sizes and shapes, I think the surface of Venus
is probably really beautiful. (mystical music)
(thunder rumbling) (dramatic music) - [Narrator] Thousands of years ago, Asian skywatchers saw Venus
as two separate stars. (speaking in foreign language), the Beginner of Brightness in the morning. And (speaking in foreign language), the Exalted Western One in the evening. - It's always sort of flirting
with the edges of night. You'll never see Venus at
midnight up high in the sky. It's always just in the
edges of dawn and dusk. - [Narrator] Sumerian priests
saw it as one, Inanna, goddess of sex, fertility,
physical beauty, and attraction. (woman singing in foreign language) Inanna became Aphrodite to the Greeks. Born from the foam of the sea, protector of those who sail, the Hellenic goddess of love beckoned us to venture into the unknown. (dramatic music) Roman leaders declared
April the month of Venus throughout the empire. During the festival of Veneralia, Romans honored purity and
piety and affairs of the heart. Across the Atlantic, Venus was seen as the
little brother of the sun. - In a way, the most
astute Venus observers were the Mesoamericans, the
Aztecs, the Maya, the Toltecs. For those cultures, Venus
was this male macho warrior with a spear going down
into the underworld and doing battle against
the enemies of humanity. (light music) We think of Venus as Botticelli's Venus, the feminine figure in our culture. But, around the world, Venus has had a lot of very
different manifestations. - [Narrator] In time, the Venus of myth gave way to the scrutiny of science. (soft upbeat music) In 1610, Galileo Galilei
observed crescent Venus changing through phases like the moon. Yet another clue that
planets orbit the sun. But even through his telescope, Galileo could not discern its features. Finally, in May 1761,
thanks to a rare alignment, the Russian astronomer, Mikhail Lomonosov, glimpsed its distinctive character. (shimmering music) - About once every 100 years or so, Venus actually passes in
between the sun and the Earth, and you can see that little dot of Venus moving across the face of the sun. (dramatic music) At the moment when the dot of Venus starts to cross the disk of the sun, the very first moment
and the very last moment when the dot of Venus moves
off the disk of the sun, something weird happens. There's a distortion, what
is called the black drop. (mystical music) It's almost like the edge of the sun kinda leaps off towards it, and then is distorted inwards. And Lomonosov realized
that that would make sense if Venus had an atmosphere. Once you know that, then you can deduce the diameter of Venus. And they said, "Oh, wow! "It's basically the same size as Earth. "It's the size of Earth,
and yet it's so bright. "Why is it so bright? "Oh, because it must
be covered in clouds." And they were right about that, as well. And the assumption at that
time, which was reasonable, was that the clouds are made out of water. (intense music) - [Narrator] The idea
that Venus was like Earth sparked the imaginations of fantasy and science fiction writers. (dramatic music) (singers vocalizing) - I remember seeing a
book when I was a kid that said that Venus might
have prehistoric jungles and dinosaur-type animals. I thought that would be really exciting, but turned out to be nothing like that. (engines roaring) - [Astronaut] (indistinct)
be advised, three. - [Dispatcher] 30 seconds,
this is programming, over. - [Narrator] At the dawn of the Space Age, Mariner 2 was the first successful mission to another planet. - Way back in 1962, Mariner
2 became the first spacecraft to explore Venus on a flyby. And it made a fantastic discovery that the Venus surface was very hot. Unfortunately, that was not
very good for Venus exploration because all the classical ideas
about Venus being habitable with people and forests
living on the surface just went out the door. (intense music) - [Narrator] Stranger still, NASA's Mariner 2 found that
the planet rotates very slowly and backwards compared to Earth. Americans celebrated the triumph. (soft music) Not to be out done, the Soviet Union attempted
at least 16 missions to Venus between 1961 and 1984. (air whooshing) December 1970, Venera 7 made
the first successful landing and the first transmission
of data from its surface. Nearly five years later, Venera 9 and Venera 10
captured the first images of Venus's tormented landscape. In December 1978, the American Pioneer Venus Orbiter began a 13-year radar mapping mission. It was followed by a
separate Pioneer MultiProbe dropped into the atmosphere. - [Dispatcher] Atlantis, Houston. Sunnyvale had a good direct check and their command is complete. - [Narrator] And a decade later, NASA's flagship, Magellan, was deployed from the Space Shuttle on an unusually long 15-month
journey inward to Venus. - [Command Control] Okay,
Peter, we copy checkout. (intense music) - [Narrator] Looping pole to
pole more than 4,000 times, Magellan's imaging radar mapped more than 97% of Venus's landforms. Among Magellan's findings,
the volcanic surface of Venus overlies a surprisingly thick crust. (mystical music) Remarkably, about three billion years ago, Venus was probably much more like Earth. (gas hissing) Each one nurtured the promise of life. (water bubbling) - They're the same size. They formed in roughly the same place. There's a lot of circumstantial evidence that Venus had a more
Earth-like environment when it was young. So they may have both had warm oceans and all the other conditions
necessary for an origin of life at the time when Earth
apparently had an origin of life. - Our biggest problem with Venus is that we have so little information about its ancient past. The surface of a planet, and to some extent the
atmosphere of a planet, are like a crime scene. Venus is the worst crime scene imaginable because it's been almost
completely disrupted over time. And the big question for those of us who are trying to study Venus
and understand its history is, when did Venus's
evolution really diverge from Earth's evolution? (mysterious music) - Venus and Earth are the twin planets. It's the only planet that is likely to be
still geologically active in some of the same ways as the Earth. It's really a huge laboratory
for understanding the Earth because of its many similarities, as well as some differences. (lava sloshing) - 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. (mysterious music) - [Narrator] Early on, Venus was on a path similar
to its sister planet, Earth. The radar data hold intriguing
clues to a watery past, including vast plateaus
made up of granite rocks that likely formed at
the bottom of an ocean. - There are areas on Venus
that look like continents. They're high-standing.
They're kinda wrinkly. They are also the oldest rocks on Venus because Venus has had this weird history where much of the surface is new. So these rocks are the only rocks from the first 80% of
the history of Venus. That's where we want to go. That's where I wanted
to go is to these areas, which are called tessera terrain because of their tile-like appearance. Whatever it is that spurred
the formation of life, in my mind, why wouldn't it
have happened everywhere? And that's the record
that we're looking for in the rocks of the tessera. Were there evidence of
ancient environments that would support life? (gas hissing)
(mystical music) (light music) - [Narrator] Venus is close to Earth in size, mass, and rocky composition, but that's where the similarities end. - Now, one thing we've learned in general about the formation of the planets is that the final stages
of planetary formation were characterized by a small number of really huge collisions. (planets sizzling) Those last few violent
collisions happened on Earth in just such a way as
to leave it with a moon and on Venus, through
a different combination of impact size and impact angles, it may have had been left with no moon, but with its very slow rotation. - [Narrator] Compared to our 24 hour day, it takes more than 243 Earth days for Venus to rotate just once, the longest day in the solar system. - And it rotates in
the opposite direction, so that if you were on
the surface of Venus and could see the sun, it would rise in the
west and set in the east. (light music) On Earth, the sun moves
along in the sunrise at hundreds of miles per hour. So you have to be up in a jet airplane if you wanted the sunset to last forever. On Venus though, it's four
or five miles per hour. So you could kind of
walk along at a good clip and keep the sunset going or the sunrise going
as long as you wanted. The pace of the planetary
rotation is a human walking pace. - [Narrator] Even that slow
pace may be winding down. - The very thick atmosphere of Venus is actually being pushed and pushing back from the typography and changing its rotation rate very slowly and very slightly over the decades. And that has been measured
by ground-based units and by Magellan, and
even by Venus Express, the most recent European mission. (wind whooshing) (mystical music) - [Narrator] Though the surface
creeps along without hurry, the clouds move quickly
and their speeds change. The Japanese Akatasuki probe, also known as the Venus Climate Orbiter, recently found that the
atmosphere spins much faster than the planet itself, a phenomenon called superrotation. This movement is driven by heat rising continually from the surface. (gentle music) Mysteriously, the planet
lacks a key feature that protects Earth and its atmosphere, a strong magnetic field. (intense music) Without this protective shield, intense ultraviolet rays from the sun split water molecules apart
in the high atmosphere. Then the sun's intense
stream of charged particles, the solar wind carries much of
the hydrogen away into space. - In the very early solar system, When the sun was not quite
as bright as it was now, Venus was much more habitable. But just a little bit of
increase in solar brightness kicked off a runaway greenhouse effect where the oceans evaporated, put water vapor into the atmosphere that increased the greenhouse, and it ran away to become
the very hot, very dry planet we see today. - We definitely believe that
Venus had much more water at the surface than it does today. Potentially, a shallow
ocean's worth of water. We really have no information about when that water was lost. - That water could have persisted for billions of years, billions. And, on Earth, life evolved
incredibly quickly, actually, considering the meteorites
that were hitting the Earth. So why not Venus? And if the answer is, "It
didn't happen on Venus," that tells us something, too. (eruptions rumbling) - [Narrator] As Venus lost its water, its atmosphere gave way to the noxious outpourings of volcanoes, the primary source of carbon dioxide. (soft music) But Venus lost its ability
to recapture that carbon, trapping itself in a terrifying loop. - Ultimately, the oceans boiled off partly because of the greenhouse property of water vapor itself, leading to this positive feedback where the more water that evaporates, the more the planet heats up because of the greenhouse
effect of the water vapor. And then, once the oceans boil off and Venus loses its oceans, then that destroys the carbon cycle because you still have CO2
coming out of volcanoes on Venus, but there's no way to remove that CO2. The sink disappeared when
the water disappeared and then the thermostat sorta
gets pegged in the red zone because you're just
adding more and more CO2 to the atmosphere from volcanoes. And it can't lose it anymore without that mediating effect of water, and it ends up in that
runaway greenhouse state. (eruptions rumbling) (dramatic music) - [Narrator] Why did
volcanic CO2 runaway on Venus while Earth kept it at trace levels? One reason is a basic difference in the geology of the two planets. Earth, like Venus, harbors
a core of molten iron. Over time, the radioactive
decay of uranium, thorium, and potassium generates heat. Hot liquid rock punches through where Earth's crust is thinnest,
in the middle of oceans, and floods the seafloor with lava. In a process called plate tectonics, growing undersea mountains push aside raft-like sections of
the crust, the plates. (plates rumbling) When they collide with
thicker continental crust, they can dive beneath them. As they do, grinding friction
causes rocks to melt, hasten by oceanic water,
forming reservoirs of magma. The pressure increases, until finally, a volcano erupts. (intense music)
(eruption booming) Plate tectonics generates up to 80 volcanic eruptions each year. Sometimes, this process can release energy on such a large scale that it changes the
course of Earth's history. (lava sizzling) Today, Yellowstone National
Park in North America is an open laboratory of
Earth's remarkable geology. (geyser rumbling) The rich mix of organic
chemicals and geothermal energy in places like this may have given rise to living organisms billions of years ago. The hot springs and geysers
we come here to admire are fueled by a dome of magma that is building deep below ground. (soft dramatic music) At intervals of roughly
every 600,000 years, this dome pushes the land
up into a broad plateau. Inevitably, hot gas and lave explode through the cracks in the land. The plateau suddenly
and violently collapses, triggering eruptions so large, they'd blanket the continent with ash. (eruptions booming)
(intense music) - Plate tectonics is really
what makes Earth tick. Plate tectonics is the sort of
overall organizing principle, almost, of Earth's behavior. Not just the obvious continental drift and the movement of the continents, but even the carbon cycle
and the climate cycle and all of these other aspects of Earth that have to do with the way things cycle between the interior and the surface come down to plate tectonics. And Venus doesn't have plate tectonics. (slow music) - [Narrator] You can see why by cutting into the crust
of these sister planets. Earth has only about eight kilometers of hard crust under the oceans and no more than 30 kilometers under land. But the skin of Venus
is about twice as thick, acting as a rigid lid,
locking the surface in place. - If Earth did not have volatile cycling throughout most of its history, and we had a stagnant plate mode, like we have on Venus today, then all of the nitrogen
and all the carbon dioxide that we see in Venus's atmosphere would be in our atmosphere
in the same way. (soft dramatic music) - [Narrator] The dense shell of Venus may never have separated
into continental plates, but the heat must still find a way out. (foreboding music) - Venus is a really volcanic planet. Most of the surface of
Venus is actually covered by volcanoes and several
different types of volcanoes. - From the smallest
things that we can measure in the radar data, which is about a hundred meters per pixel, to huge lava flows, just lava flows that stretch
for thousands of kilometers. (slow music) (mystical music) - [Narrator] The Magellan Mission documented a zoo of volcano types. - Venus has some shield volcanoes. Shield volcanoes have low slopes, and they look like warrior
shields laid on the ground. That's where the name came from. In fact, it came from Iceland. Venus also has several
other types of volcanoes that we don't see in other
places in the solar system. For example, one very unusual type are some domes that we call pancake domes, and that's because they
really look like pancakes. They are flat on top. They have steep sides. Some of these domes have some
fractured and jagged edges, and they are known as ticks because they look like squashed bugs. Arachnoids because they
have a fracture pattern similar to a spider's web, with some concentric fractures
and some radial fractures. - [Narrator] The enormous
volcanic features called coronae hint that Venus may be subducting rocks back into its interior, after all. - [Rosaly] Corona on
Venus are in a way similar to calderas on Earth, where you have a pattern
of concentric fractures. There is a collapse or
successive collapses. - A plume of hot stuff comes up, pushes up the surface, breaks the surface, and a bunch of vulcanism
forms at the surface, much like what we see at Hawaii. - [Narrator] The two volcanoes
that built the Big Island are, together, about
150 kilometers across. But a few of the coronae on
Venus have grown much larger. - [Sue] There are a couple
of very big features. One is 2,600 kilometers across. - On Venus, where we don't see evidence of plate tectonics, volcanoes are really the primary way that we believe Venus is
trying to lose its heat or has lost its heat. And so that record that we see
of volcanism on the surface is essentially telling us how
Venus is trying to cool off, how its interior is losing heat and moving that hot magma and
hot lava onto the surface. (eruption rumbling)
(sinister music) - [Tony] About 500 million years to a billion years or so ago, something catastrophic happened. When you look at Venus's
surface from satellites and you count the craters
that you see on the surface, we find out that the vast
majority of Venus's surface is geologically very young. (lava sloshing) - Half a billion years ago, Venus had cause to erupt
volcanoes over its entire surface, its entire Earth-sized surface. And we're still trying to figure out how that happened and why. (lava sloshing)
(mysterious music) - [Narrator] With its steadily
declining stores of water, lack of magnetic field, no plate tectonics to drag
carbon down into its crust, but hordes of volcanoes
blasting CO2 into its skies, Venus sentenced its
surface to climatic death. A planet turned inside out. (dramatic music) (light music) Meanwhile, its sister planet,
Earth, managed to survive, to nurture a complex
and evolving biosphere. The contrasting stories of Earth and Venus are central to one of the
greatest quests in science today. The search for solar systems and life-bearing worlds out in the galaxy. That search, conducted by a growing array of ground and space-based observatories, has so far turned up over 4,000 planets with thousands more detected,
but not yet confirmed. (mystical music) Increasing numbers of these exoplanets are close in size to Earth and Venus. With orbits within the habitable zones of their solar systems, where water can exist in all three states, liquid, ice, and steam, statistical studies indicate
there could be billions of them tucked into the nooks and
crannies of our galaxy. (gentle music) Is life, even intelligent life, a natural product of the laws of nature? Or is it a fluke? Its chances mostly killed off by all that can go wrong
with planetary evolution. So far, Venus has not told us all it can about these questions. - For years and years, after we began to really understand Venus, all of the scientists
and the space advocates were saying, "Oh, no,
Venus is the one place "we don't want to go to because
it's so hot on the surface. "It's hot enough to melt land." But it turns out that, like Earth, as you get higher in the atmosphere, the temperature gets cooler. And there's a region where Venus is very, very much like the conditions at the sea level on Earth. (wind whooshing)
(gentle music) - [Narrator] The presence
of hospitable conditions in Venus's upper atmosphere led to one of the most
innovative mission ideas on the books. Imagine an entry vehicle penetrating the outer most layers
of Venus's atmosphere. Instead of continuing to the surface, it deploys an inflating envelope. (balloon flapping) An airship up to 130 meters in length. (soft dramatic music) This platform, called the High-Altitude Venus
Operational Concept, HAVOC, would host a series of
experiments and sensors. (low intense music) And its most far-ranging. It's the start of a
permanent human outpost. A science city built
in the clouds of Venus. (light music) The concept takes advantage of the unique profile
of Venus's atmosphere. At ground level, the pressure
is like being 900 meters deep in Earth's oceans. It's hotter than anywhere
else in the solar system, except the sun. But 50 kilometers up, among the clouds, the pressure has dropped to
that of sea level on Earth. It's no warmer than a day in
June in Europe or the U.S. (propellers clicking) That's where balloon-born
habitats could perpetually float. (gentle music) Consider a crew of scientist
astronauts aboard an airship. (thunder rumbling) Making their way through
the sulfuric acid clouds, their ships' electric
motors powered by the sun, on their way home from a survey mission. - [Geoff] The nice
thing about the balloons in the atmosphere of Venus,
if they're very, very large, is that they'd be riding
with the inside pressure about the same as the outside pressure. It wouldn't burst like a balloon
in a catastrophic failure. - [Narrator] These sequences
show a well-developed version of a Venus cloud city. The construction of stations
this large and complex depends on our ability
to harvest materials, like carbon fiber, directly
from the atmosphere. (propellers clicking) Its core mission to
serve as a field station for deploying research
probes around the planet and down to its hostile terrain. From their floating platforms, these experimenters would investigate the deep history of Venus's surface and how land and atmosphere connect. (lava sloshing) They would check for
signatures of live volcanoes and the interaction of the
atmosphere's physical, chemical, and possibly biological components. (lava sloshing)
(light music) (air whooshing) All in a quest to discover what went so terribly wrong on Venus. (soft dramatic music) Soviet researchers first
demonstrated balloon science with the 1985 Vega 2 probe, riding turbulent
hurricane-force thermal currents at 240 kilometers per hour. Vega 2's three and a half
meter diameter balloon found a stable altitude
at about 54 kilometers. (lightning clapping) In the most active of the
planet's three cloud layers, it traveled more than 7,400 kilometers around to the day side of Venus. (thunder rumbling) (propellers clicking)
(gentle music) Vega 2's descendants
may deploy from airships to sample specific altitudes. Triangulating their positions, they could form a global sensor network to pick up signs of seismic activity. (ground rumbling) - So our balloon can
listen for earthquakes as it floats around Venus, taking advantage of the fact that the Venus atmosphere is so thick that sound waves from
earthquakes will propagate up through the atmosphere and can be measured from
balloon or from orbit. It's astounding. (ground rumbling) (dramatic music) - [Narrator] Though it may appear as a featureless planet-wide cloud bank, Venus's atmosphere has its
own complex stories to tell. - One of the most important things in the atmosphere of Venus that we need is to understand some
of the molecular fossils that are left in Venus's atmosphere. The noble gases of argon,
neon, xenon, krypton, those gases that don't
react with anything else. They've been in the
atmosphere since Venus formed, since the atmosphere formed. And if we can measure those, they provide us these fossil evidence of what that original
atmosphere on Venus looked like. (gases hissing) - [Narrator] A profile
of the early atmosphere would tell us whether Venus
once held lakes and rivers on its surface. (propellers ticking)
(intense music) If humans do someday visit
the acidic clouds of Venus, they may find, strictly
speaking, that they're not alone. For more than 100 years, astronomers on Earth have
noticed enigmatic dark patches that appear only at
ultraviolet wavelengths. - My Venus atmosphere friends talk about the fact that there is a
signature in the atmosphere that they can't explain. And there is something in the clouds that absorbs UV radiation and
they don't know what it is. That signature may be due
to absorption by biota, by cloud creatures. - There are nutrients. There's liquid. There are a lot of the elements that we think of being
requirements for life. The one impediment to life may be the strong acid in the clouds, but we've learned more recently of all these extremophile
organisms on Earth, including what we call
acidophilic organisms or organisms that love
living in strong acid. (dramatic music) - There are bacteria on Earth, Thiobacillus ferroxidans, for example, which have an absorption spectrum which is very similar
to what we see on Venus. - [Narrator] Could life have
developed and migrated upward as the surface became lethal? In Earth's atmosphere, microbes have been found at
altitudes up to 40 kilometers. (air whooshing)
(light music) - [Mike] Earth has had 4 billion years for life to fill every
ecological niche possible. And we find life everywhere we go. We dig deep wells, we
find life down there. We find life in the clouds. - If we have the
opportunity to go to Venus and float in the Venus clouds, we should at least think about if we can measure the conditions that might be reasonable for life today and also any signature of life
in the clouds of Venus today. (soft dramatic music) (intense music) - [Narrator] Though the
cloud tops may be temperate, the hot surface is merciless. Venus engineers must take
a mechanical approach because even the most robust electronics developed for the military stop working at about 125 degrees Celsius. - Let me show you something. So this it's a clock that is fully made out of stainless steel. It's been baked out at 460 degrees Celsius and has been operated in an oven. And our goal with this was
to start to understand, what are the challenges
when you build mechanisms to operate in Venus conditions? First of all, the spring
material was really important. We have a clock spring here, as well as also a balance
spring right here, that is built out of Inconel. Even when you're going
to extreme temperatures, like Venus, 462 degrees Celsius, the entire assembly would just
expand and contract together and you wouldn't get jamming. And we were able to
demonstrate and show that by operating this clock. (clock clicking) (dramatic music) - [Narrator] As on Mars, exploring the surface of
Venus will require mobility. But strategies that work for other worlds don't work on Venus. Not even solar power. - Venus does have some
solar power on the surface. Although, it's a fraction of
what is available here on Earth is actually available
on the surface of Venus due to the thick cloud layers, due to also the red shifting of the light, and that solar panels
don't work as efficiently. The other big challenge
with using solar on Venus is that Venus has a very
long night, about 60 days. Therefore, one of the places
we're looking to get energy is from the wind. The idea is you have
low-speed, high-density wind coming at you, collect
that with a wind turbine, and then directly transfer
that to the wheels to drive you at low speed, high torque. You want to directly use that wind energy to move yourself mechanically
around the surface of Venus. - We have the sensors on the surface. We have the radio on the surface. But most of the processing
power, most of the computers, most of the things that run the mission would be high overhead. We could either put them
perhaps in an airplane flying 50 kilometers above,
or maybe in a satellite. (propellers clicking) The winds of Venus are pretty ferocious. The winds of Venus are
going 100 meters per second. Well, one thing we could
do is just fly around and let the wind take us
where the wind takes us, as long as we can fly
faster than that wind so we can stay in the sunlight. (dramatic music)
(singers vocalizing) - [Narrator] Venus's extreme surface heat drives a blustery atmosphere
of toxic acid rain. (lightning clapping)
(thunder rumbling) But the planet lies within what astronomers would think
of as the habitable zone. - Venus is a really interesting case because it forces us to think
of where is the inner edge of the habitable zone. Presumably now, in our solar system, it's somewhere between Earth and Venus. And yet, there was a time earlier in the life of our solar system when Venus was within the habitable zone, when there probably was an ocean on Venus. (dramatic music)
(singer vocalizing) - [Lori] Mars, we think at some point, used to have more atmosphere and was potentially warmer and wetter. And Venus probably had less atmosphere, at some point in the past, and had significantly more
water than we see today, which today it seems very, very dry. And so it's possible, when
Venus did have less atmosphere, it was habitable when it
had more water available and less atmosphere. We very definitely think that
it has changed over time. (soft dramatic music)
(lava crackling) - [Narrator] Looking out
in our Milky Way galaxy, astronomers are seeking
a broader understanding of how planets form and
what conditions can nurture an Earth-like world. All other exoplanets lie too far away for us to know much about them. But Venus is giving scientists a chance to understand the alien planet next door. (gentle music)
(singer vocalizing) (water sloshing) - There's probably millions,
likely billions, of planets that are like Earth and like Venus. And we'd like to understand what made the one turn into a hot desert. And Earth, on the other hand, turn into a planet with liquid
water and habitable for life. (soft dramatic music) - Different aspects of
Venus's evolutionary history would put it into the habitable zone. Then that tells the exoplanet astronomers that they should not
just discard these worlds as hot inhospitable planets, and that they should
go take a look at them. And that would expand the
idea of the habitable zone to much closer reaches to the star than we would otherwise think. (gentle music)
(water sloshing) - When we look out in the galaxy and we see all these Earth-like planets, we're looking for another Earth, right? We're looking for another
place that is like our own. We're looking at Earth-sized planets and the closest Earth-sized planet happens to be the closest planet to Earth. (laughs) It's Venus. It's right there. So it tells us about how
Earth-sized planets form and whether or not they're habitable. (gentle music)
(singer vocalizing) (soft dramatic music) - [Narrator] Two planets born together, nearly the same size and mass. (lava crackling) Built of the same stuff. At the start of their
lives, each harbored oceans, and atmospheres laden with water vapor. Over time, one increasingly draped itself in the greens and blues of life. While the other became
enshrouded in a toxic haze. Its surface paved over
with volcanic outpourings. Which type of world is
most common in the cosmos? - We know a lot about Mars. We've sent a dozen probes to Mars. We've sent rovers across the surface. But Venus, we have very
little knowledge of, so we need to start
learning how to go to Venus. Learn about the circulation of Venus, learn about the climate,
learn about the weather. Venus needs to be not the forgotten planet in the solar system. If we understand Venus,
we learn about the Earth. (soft dramatic music) - I imagine, imaged with the
right kind of whatever drone or spacecraft or even humans
ultimately going there in very well-protected suits, when we get to see it in the right way, we're gonna be like, "Wow, nobody told us. "This place is beautiful
and it's massive." Remember, there's much
more land area on Venus than there is on Earth since
Earth is two-thirds ocean, and it's going to be just a
thrilling place to explore fully when we get the opportunity. (soft dramatic music) (light music)
