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Viewers like you make
this program possible.

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Support your local PBS station.

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NARRATOR:
When we look beyond Earth,

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we discover dynamic worlds.

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KATHERINE DE KLEER:
As we're exploring
the solar system,

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we are finding

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remarkably diverse

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and ferociously active worlds.

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CLARA SOUSA-SILVA:
Where lava flows,
where volcanoes erupt,

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where rumblings beneath
crack the surface.

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NARRATOR:
From giant, dead volcanoes

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on the planet next door...

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JAMES DOTTIN:
It's absolutely mind-boggling

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that there are volcanoes
that can get that big

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that it can tip a planet.
That's absolutely crazy.

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NARRATOR:
...to active ice-cold eruptions

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on frozen moons.

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PAUL BYRNE:
Where everything's frozen over,

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we see volcanic eruptions
blasting out into space,

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and that's a real surprise.

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NARRATOR:
These explosive worlds

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could even provide a clue

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to one of the biggest questions
of them all.

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JEN GUPTA:
Studying volcanoes
in the solar system

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is incredibly important.

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It can help answer that question
of where you and I came from

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and even how life first began.

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NARRATOR:
But ultimately,
volcanoes, fiery or frozen,

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reveal the incredible activity
that lies within.

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When I think of a volcano,

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I think of awesomeness and...

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how can I get a ticket
to go there?

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NARRATOR:
How can there be so many

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different kinds of eruptions
across our solar system?

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And what might
Earth's volcanoes tell us

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about the possibilities
of life elsewhere?

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"Solar System: Volcano Worlds."

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Right now, on "NOVA."

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♪

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NARRATOR:
Humans have only set foot

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on one world beyond our own.

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On the moon,
we found a barren landscape,

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appearing unchanged
for more than a billion years.

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Its surface, scarred
with craters and dark patches.

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This was activity that occurred
early on in the moon's history.

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The moon now, there isn't much
going on there.

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NARRATOR:
Our moon is an inactive world,

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frozen in time.

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In stark contrast with Earth.

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Which seethes with activity
beneath the surface.

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Who doesn't love a volcano?
I mean, hot stuff

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jumping out
of the ground at you.

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It would be really exciting.

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OLUSEYI:
I've seen erupting volcanoes,

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and I just love active geology.

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It just tells me
that the planet is alive,

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not literally, but figuratively.

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NARRATOR:
And when we look beyond
Earth and its moon,

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out into our solar system,

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other dynamic worlds like ours
do exist.

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As we're exploring
the solar system,

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both with telescopes
and with spacecraft,

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we are finding
remarkably diverse

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and ferociously active worlds
throughout the solar system.

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NARRATOR:
Many hold clues
to our own planet's story.

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JASON HOFGARTNER:
Looking at volcanoes
elsewhere in the solar system,

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we see that Earth has a special
type of volcanic activity,

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and so, by understanding
other volcanoes,

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we might understand how Earth

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had eruptions in the past
or in the future.

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NARRATOR:
And since many scientists
think volcanic activity

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might have played a major role

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in the origins of life
on Earth...

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...other active worlds
in our solar system

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are especially intriguing.

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SOUSA-SILVA:
We know that
there's a relationship

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between volcanism and life,

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but we don't know where it ends
and where it begins,

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and that's why
we need to keep exploring.

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♪

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NARRATOR:
The largest volcanoes

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discovered
in the solar system so far

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are right next door.

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Mars is one of the most
explored and photographed

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of all the planets beyond Earth.

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We've captured its stark beauty.

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From ice frosted dunes

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to canyons
just over six miles deep.

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And many of the most
detailed images

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have come from
the Mars Reconnaissance Orbiter.

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Launched in 2005,

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it is still orbiting
the planet today.

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JORGE NUÚÑEZ:
It carries instruments,
high-resolution instruments,

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that allows us
to view and explore

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the surface of Mars
in such detail

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that we could map out

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things the size of a desk
on the surface.

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OLUSEYI:
It's the length of a school bus

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with these two big solar panels
to power it,

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and as it's going
about its business,

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it's sent back
more data to Earth

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than any mission ever.

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NARRATOR:
These images show in
greater detail than ever before

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giant volcanoes

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that dwarf anything
seen on Earth.

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One so wide...

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...it would cover
the length of Nevada.

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And one so tall...

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...it reaches over twice
the height of Mount Everest.

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It's the largest volcano
in the solar system.

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Lava once flowed
from these giants,

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spilling across the land
in all directions.

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So much molten rock

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that the combined mass

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tipped the planet over
on its axis

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by about 20 degrees.

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How did these monsters
get so big?

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A hint comes from studying
active volcanoes

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here on Earth.

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OLUSEYI:
If you want to understand
volcanism on Earth,

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or if you just want

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to understand Earth at all,

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you need to start with
plate tectonics.

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NARRATOR:
Earth's crust is made up
of seven large plates

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and several smaller ones,

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which interact with each other
at their boundaries.

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AISHA MORRIS:
And they interact
in multiple different ways.

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They can be smashing
into each other,

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pulling apart from each other,

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or grinding against each other
as they move around.

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DOTTIN:
So at plate boundaries,

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what happens is that

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you end up with
rock instabilities

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and, ultimately,
the rock melts.

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NARRATOR:
Creating the conditions

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that have formed the majority
of volcanoes on Earth.

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But it's the volcanoes that
don't form at plate boundaries

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that tell us the most
about Martian volcanoes.

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GUPTA:
On Earth, we also have volcanoes

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in the middle of a plate,
not just the boundary.

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These are called
hotspot volcanoes,

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and Hawaii is a
great example of this.

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DOTTIN:
Hotspot volcanoes

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are typically created
by a plume,

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like a bubble of hot magma

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welling up directly
from the interior,

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hitting the bottom of the plate
and bursting through.

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NARRATOR:
Hawaii is a chain
of hotspot volcanoes,

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created by a tectonic plate

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moving across
a single plume of magma,

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erupting onto the surface

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forming a line of islands.

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Like on Earth,

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Mars has hotspot volcanoes,

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but with one major difference,

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no plate tectonics.

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On Mars, instead of the plate
moving over the plume

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and making a chain of volcanoes,

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you get the plume stationary,
with respect to the ground,

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and that means,

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over millions or even
billions of years,

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Mars has been able
to build up volcanoes

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that dwarf anything
that we see on Earth.

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NARRATOR:
But all of those
monster volcanoes have quieted.

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Still and cold
for millions of years.

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Why?

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To find the answer,

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scientists look deep within,

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tracing the source of heat
that drives volcanism

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on rocky planets like ours.

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Four and a half
billion years ago,

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with the rest
of the solar system,

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the Earth formed
from the collapse

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of a cloud of gas and dust

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being smashed together

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under the force
of its own gravity.

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NARRATOR:
Much of the energy
that went into these collisions

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turned into heat,
trapped inside Earth.

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Added to that is heat
from radioactive elements

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inside the planet, like uranium.

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So over time,

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these elements actually decay

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into lighter elements

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and as they do so,

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they are constantly warming
and heating our planet

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from the inside.

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When you stop
and think about it,

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it really just is incredible
that all of this heat

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that is powering volcanoes
here on Earth

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can be traced back four
and a half billion years ago

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to the formation of the Earth.

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♪

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NARRATOR:
Mars shares
Earth's origin story.

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It formed in the same way...

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...at the same time...

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...capturing enough heat
to drive volcanism

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on a staggering scale.

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But now the volcanoes are
cold and silent.

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Where did all that heat go?

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A clue exists
within this volcanic landscape.

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In Mars's northern hemisphere
lies the Marte Vallis area...

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...where cliffs are built

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from an intricate array
of pillars.

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Arranged in uniform patterns,

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these structures are made
of solidified lava.

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Similar structures also exist
here on Earth...

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...and they can help
unravel the mystery

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behind why Mars's volcanoes
are now silent.

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PAUL BYRNE:
We see columnar jointing

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in lots of places on Earth.

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There's a particularly
beautiful example

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in the Studlagil Canyon
in Iceland.

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NARRATOR:
Hot lava once flowed here.

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As it cooled,
it did something extraordinary.

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PAUL BYRNE:
As that lava's cooling down,

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it's shrinking,
it's contracting.

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And as the lava pulls apart
from itself, as it contracts,

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it makes these fractures

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and these fractures form
this very regular,

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even pattern.

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NARRATOR:
Exactly what conditions cause

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these unusual structures
to form is complex.

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But they do reveal

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one of the most fundamental
laws of nature.

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DOTTIN:
The simplest explanation

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for the second law
of thermodynamics

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is that heat flows
from hot to cold.

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So if you were to go outside
on a cold day

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with a hot cup of coffee,
eventually,

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that hot cup of coffee will be
the same temperature

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as your outdoor surroundings.

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NARRATOR:
More than 65 feet tall,

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these columns show
this very principle in action.

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BYRNE:
So we can think of how, say,
columnar joints form

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through that lens of energy
flowing from hot to cold.

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When the lava flow is
flowing over the surface,

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in the case of Earth, at least,

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it's much hotter than both
the ground and the air.

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NARRATOR:
As the lava cools,

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its heat rises
into the atmosphere

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and then out into space,

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slowly cooling
the entire planet.

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♪

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TRIPATHI:
The beautiful truth
about physics

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is that the laws are the same
everywhere.

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So the laws of thermodynamics
work on Earth,

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they work on Mars,
they work beyond.

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NARRATOR:
The physics may be the same:

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volcanoes driven
by ancient internal heat

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moving towards equilibrium

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with the coldness
of outer space.

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But one key difference

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caused a big change
in how quickly

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00:14:59,484 --> 00:15:01,210
Mars lost its heat.

255
00:15:03,799 --> 00:15:05,352
OLUSEYI:
If we look at these two balls

256
00:15:05,352 --> 00:15:09,115
as an example for Earth--
the baseball--

257
00:15:09,115 --> 00:15:11,945
and Mars-- the golf ball--

258
00:15:11,945 --> 00:15:13,498
then they're different sizes.

259
00:15:13,498 --> 00:15:16,053
So as the object gets bigger,

260
00:15:16,053 --> 00:15:19,746
the volume grows faster
than the surface area grows.

261
00:15:19,746 --> 00:15:24,889
In spite of having a volume
that's only 15% of the Earth,

262
00:15:24,889 --> 00:15:27,857
Mars's surface area is,
actually, bigger proportionally.

263
00:15:27,857 --> 00:15:29,480
It's got about 28%

264
00:15:29,480 --> 00:15:31,931
of the surface area
of the Earth.

265
00:15:31,931 --> 00:15:33,518
You can think of it this way.

266
00:15:33,518 --> 00:15:36,970
If I make a big pot of coffee,
it's gonna stay warm for hours.

267
00:15:36,970 --> 00:15:39,662
If I pour some of that coffee
into a mug,

268
00:15:39,662 --> 00:15:42,182
it'll cool down much faster
because there's less of it,

269
00:15:42,182 --> 00:15:43,701
but there's more surface area.

270
00:15:43,701 --> 00:15:45,875
And these differences
have resulted

271
00:15:45,875 --> 00:15:48,430
in so much of what we see today,

272
00:15:48,430 --> 00:15:51,502
including the geologic
and volcanic history

273
00:15:51,502 --> 00:15:52,917
on the two worlds.

274
00:15:52,917 --> 00:15:54,954
♪

275
00:15:58,888 --> 00:16:00,752
NARRATOR:
Earth and Mars started out

276
00:16:00,752 --> 00:16:06,620
with similar materials:
heat and volcanic activity.

277
00:16:08,381 --> 00:16:12,557
But while Mars's heat
and its volcanism ebbed away,

278
00:16:12,557 --> 00:16:16,182
Earth's volcanoes continue
erupting to this day.

279
00:16:18,287 --> 00:16:21,187
And many scientists believe
that on Earth,

280
00:16:21,187 --> 00:16:24,776
volcanism on the ocean floor
played a role

281
00:16:24,776 --> 00:16:26,675
in life's beginnings.

282
00:16:28,918 --> 00:16:31,680
So with such similar
origin stories...

283
00:16:32,681 --> 00:16:35,684
...could there once have been
life on Mars?

284
00:16:37,203 --> 00:16:39,274
NUÚÑEZ:
Mars is like Earth's cousin.

285
00:16:39,274 --> 00:16:41,931
And so very early
in their history as they formed,

286
00:16:41,931 --> 00:16:44,175
they had this volcanic activity,
and we found evidence

287
00:16:44,175 --> 00:16:47,868
that Mars had liquid water
on its surface.

288
00:16:47,868 --> 00:16:50,561
It had a thicker atmosphere.

289
00:16:50,561 --> 00:16:52,287
And around the same time

290
00:16:52,287 --> 00:16:55,186
that we know that life emerged
here on Earth,

291
00:16:55,186 --> 00:16:59,156
there was liquid water
on the surface of Mars

292
00:16:59,156 --> 00:17:04,195
and it had conditions
very similar to early Earth.

293
00:17:05,852 --> 00:17:10,408
NARRATOR:
Today the Perseverance rover,
on Mars since 2021,

294
00:17:10,408 --> 00:17:15,068
is creating packages of rock
samples with the intention

295
00:17:15,068 --> 00:17:18,796
that a later mission will
one day return them to Earth.

296
00:17:20,453 --> 00:17:24,112
Could they contain evidence
of Martian life?

297
00:17:25,906 --> 00:17:28,944
DOTTIN:
So generally, in these rock
samples from Mars,

298
00:17:28,944 --> 00:17:30,497
we're looking for signatures

299
00:17:30,497 --> 00:17:32,982
that there was life
on the planet.

300
00:17:32,982 --> 00:17:35,675
But it would be
absolutely amazing

301
00:17:35,675 --> 00:17:39,575
if we actually found cells
or something similar

302
00:17:39,575 --> 00:17:41,198
in these rocks that indicated

303
00:17:41,198 --> 00:17:43,579
that there is life
on Mars today.

304
00:17:45,029 --> 00:17:49,827
NARRATOR:
For now, any secrets of life
on Mars remain a mystery.

305
00:17:51,104 --> 00:17:53,831
But what Mars does demonstrate

306
00:17:53,831 --> 00:17:58,698
is the smaller the planet,
the more quickly it loses heat.

307
00:18:02,909 --> 00:18:06,257
Still, there is a rule breaker:

308
00:18:06,257 --> 00:18:08,811
a world even smaller than Mars

309
00:18:08,811 --> 00:18:12,263
that is somehow the most
ferociously active body

310
00:18:12,263 --> 00:18:13,920
in the solar system.

311
00:18:19,753 --> 00:18:23,481
Leaving the quiet
volcanoes of Mars behind...

312
00:18:24,517 --> 00:18:27,244
...passing through
the asteroid belt,

313
00:18:27,244 --> 00:18:29,004
the cold rubble left over

314
00:18:29,004 --> 00:18:30,902
from the formation
of the planets...

315
00:18:32,939 --> 00:18:36,322
...we reach the first
of the gas giants.

316
00:18:39,739 --> 00:18:43,087
Twice the mass of all
the other planets combined,

317
00:18:43,087 --> 00:18:47,540
Jupiter is circled
by more than 80 moons.

318
00:18:49,714 --> 00:18:51,440
Some are icy.

319
00:18:52,717 --> 00:18:55,513
Like the frozen expanses
of Ganymede.

320
00:18:56,549 --> 00:18:58,102
And Europa.

321
00:18:59,931 --> 00:19:03,142
But then, there is Io.

322
00:19:09,113 --> 00:19:11,288
About the size of our moon,

323
00:19:11,288 --> 00:19:15,671
Io orbits closer to Jupiter
than any other moon of its size.

324
00:19:19,192 --> 00:19:21,194
Since 2016,

325
00:19:21,194 --> 00:19:23,783
the space probe Juno
has been our eyes

326
00:19:23,783 --> 00:19:25,681
on Jupiter and its moons.

327
00:19:26,682 --> 00:19:29,098
With an elongated orbit,

328
00:19:29,098 --> 00:19:32,205
it has made regular
flybys past Io...

329
00:19:36,175 --> 00:19:39,074
...witnessing violent eruptions,

330
00:19:39,074 --> 00:19:42,767
which shoot out
columns of gas and dust

331
00:19:42,767 --> 00:19:45,632
that reach far out into space...

332
00:19:49,429 --> 00:19:54,607
...and send rivers of lava
pouring across the landscape...

333
00:19:55,953 --> 00:19:59,991
...creating a surface
dotted with lakes of lava.

334
00:20:01,407 --> 00:20:04,858
Io is a volcanic powerhouse,

335
00:20:04,858 --> 00:20:07,861
defying all expectations.

336
00:20:09,069 --> 00:20:12,107
DE KLEER:
Considering how small Io is,

337
00:20:12,107 --> 00:20:15,248
the heat sources
like we have on Earth,

338
00:20:15,248 --> 00:20:18,009
the heat of formation
and the radioactive decay,

339
00:20:18,009 --> 00:20:21,081
those should be, essentially,
completely gone on Io by now.

340
00:20:22,117 --> 00:20:25,362
OLUSEYI:
This little, tiny,
small world of Io,

341
00:20:25,362 --> 00:20:28,192
you'd expect it to be
geologically inactive.

342
00:20:28,192 --> 00:20:29,607
Instead, it's the most

343
00:20:29,607 --> 00:20:30,850
volcanically active body

344
00:20:30,850 --> 00:20:33,128
in our solar system.

345
00:20:33,128 --> 00:20:34,888
That's a surprise.

346
00:20:37,650 --> 00:20:42,102
NARRATOR:
Eruptions continue
day in, day out,

347
00:20:42,102 --> 00:20:45,347
across the entire surface.

348
00:20:47,522 --> 00:20:51,008
A world like no other
in our solar system.

349
00:20:52,251 --> 00:20:54,253
♪

350
00:20:55,944 --> 00:20:59,154
But similarities can be found

351
00:20:59,154 --> 00:21:02,157
by taking a closer look
beneath the surface

352
00:21:02,157 --> 00:21:05,609
inside volcanoes here on Earth.

353
00:21:13,202 --> 00:21:17,172
Astrophysicist Jen Gupta
is entering a chamber

354
00:21:17,172 --> 00:21:19,623
created by a volcanic eruption

355
00:21:19,623 --> 00:21:22,729
over 4,000 years ago.

356
00:21:25,663 --> 00:21:28,114
GUPTA:
The incredible thing
about this place

357
00:21:28,114 --> 00:21:30,012
is that
as the magma drained away,

358
00:21:30,012 --> 00:21:32,221
it left behind these colors

359
00:21:32,221 --> 00:21:35,155
that we can see here
on the walls,

360
00:21:35,155 --> 00:21:36,812
from elements and minerals

361
00:21:36,812 --> 00:21:39,298
that were dragged up
from the interior of the Earth

362
00:21:39,298 --> 00:21:41,230
during that volcanic eruption.

363
00:21:42,680 --> 00:21:45,821
The one that immediately grabbed
my attention is the yellow.

364
00:21:45,821 --> 00:21:48,928
This is from sulphates
and sulphur,

365
00:21:48,928 --> 00:21:50,205
and these are
the exact same colors

366
00:21:50,205 --> 00:21:53,173
that we see covering
the entire surface of Io.

367
00:21:59,870 --> 00:22:01,837
NARRATOR:
Images of Io are dominated

368
00:22:01,837 --> 00:22:04,115
by its yellow surface,

369
00:22:04,115 --> 00:22:08,396
created by the same sulphates
and sulphur

370
00:22:08,396 --> 00:22:12,054
that line the chamber walls
here in Iceland.

371
00:22:15,748 --> 00:22:18,302
GUPTA:
The scale of this place
is just astonishing,

372
00:22:18,302 --> 00:22:21,650
and to think that
there are chambers like this

373
00:22:21,650 --> 00:22:23,514
under the surface of Io,

374
00:22:23,514 --> 00:22:27,829
filled with molten magma
ready to erupt out.

375
00:22:27,829 --> 00:22:30,521
It's easy to think that Earth,
our home planet,

376
00:22:30,521 --> 00:22:32,627
is completely unique,

377
00:22:32,627 --> 00:22:34,905
but the more we discover
about the solar system,

378
00:22:34,905 --> 00:22:37,770
the more we see
these remarkable similarities,

379
00:22:37,770 --> 00:22:39,496
like having volcanoes on Io.

380
00:22:42,533 --> 00:22:45,950
NARRATOR:
And unlike Mars's
ancient dead volcanoes,

381
00:22:45,950 --> 00:22:51,991
Io's are continually erupting,

382
00:22:51,991 --> 00:22:55,408
creating a thin atmosphere
of volcanic gases.

383
00:23:02,035 --> 00:23:05,211
As Jupiter blocks the sun,

384
00:23:05,211 --> 00:23:07,834
Io passes into its shadow.

385
00:23:10,941 --> 00:23:14,254
Even
with such constant activity,

386
00:23:14,254 --> 00:23:16,395
temperatures plummet,

387
00:23:18,086 --> 00:23:23,263
so low that the thin atmosphere
begins to freeze,

388
00:23:23,263 --> 00:23:25,783
creating an incredible frost.

389
00:23:31,064 --> 00:23:32,687
Made not of water,

390
00:23:32,687 --> 00:23:37,519
but of delicate crystals
of sulphur dioxide.

391
00:23:43,283 --> 00:23:46,045
A few hours later,

392
00:23:46,045 --> 00:23:49,255
they are gone,

393
00:23:49,255 --> 00:23:52,327
evaporating away

394
00:23:52,327 --> 00:23:54,433
as the sun returns.

395
00:23:56,469 --> 00:23:58,333
DOTTIN:
Sulphur is a major component

396
00:23:58,333 --> 00:24:00,266
of volcanic eruptions.

397
00:24:00,266 --> 00:24:02,337
And so it's not surprising

398
00:24:02,337 --> 00:24:06,065
that the surface of Io is

399
00:24:06,065 --> 00:24:07,307
covered with sulphur crystals

400
00:24:07,307 --> 00:24:09,620
because there's so much
volcanic activity

401
00:24:09,620 --> 00:24:11,622
going on there.

402
00:24:16,938 --> 00:24:18,422
NARRATOR:
Io isn't big enough

403
00:24:18,422 --> 00:24:20,804
to have retained heat
from its formation.

404
00:24:22,012 --> 00:24:24,083
So the heat
that drives this much sulphur

405
00:24:24,083 --> 00:24:26,913
to the surface

406
00:24:26,913 --> 00:24:29,468
must be coming
from somewhere else.

407
00:24:31,470 --> 00:24:32,919
DE KLEER:
So, the question is,

408
00:24:32,919 --> 00:24:35,439
why is an object this small

409
00:24:35,439 --> 00:24:37,130
still volcanically active?

410
00:24:37,130 --> 00:24:39,788
Why hasn't it run out
of heat yet?

411
00:24:44,552 --> 00:24:46,070
GUPTA:
The thing about Io

412
00:24:46,070 --> 00:24:49,971
is it doesn't orbit Jupiter
in a circular orbit.

413
00:24:49,971 --> 00:24:51,766
What it does instead is
travel round

414
00:24:51,766 --> 00:24:55,390
in an elliptical orbit
like this.

415
00:24:55,390 --> 00:24:57,185
And it's that elliptical orbit

416
00:24:57,185 --> 00:24:59,014
that's one of the driving forces

417
00:24:59,014 --> 00:25:01,292
behind the level
of volcanic activity

418
00:25:01,292 --> 00:25:03,847
on the moon.

419
00:25:03,847 --> 00:25:05,883
NARRATOR:
Jupiter is the largest planet

420
00:25:05,883 --> 00:25:07,333
in our solar system,

421
00:25:07,333 --> 00:25:11,544
and its gravitational pull
on Io is enormous.

422
00:25:13,235 --> 00:25:16,169
GUPTA:
As Io comes in
towards the planet,

423
00:25:16,169 --> 00:25:18,344
the gravitational pull
of Jupiter is stronger,

424
00:25:18,344 --> 00:25:20,864
causing the very rock on Io

425
00:25:20,864 --> 00:25:23,556
to bulge out
towards its host planet.

426
00:25:23,556 --> 00:25:26,490
Then as Io moves further away,

427
00:25:26,490 --> 00:25:28,768
the bulge shrinks and moves,

428
00:25:28,768 --> 00:25:32,289
causing a tide of rock on Io

429
00:25:32,289 --> 00:25:35,464
that's over 300 feet tall.

430
00:25:35,464 --> 00:25:39,123
That's rock the height
of this chamber

431
00:25:39,123 --> 00:25:42,817
bulging and moving
on that rocky moon.

432
00:25:42,817 --> 00:25:45,889
This is rock
rubbing against rock

433
00:25:45,889 --> 00:25:48,477
in a similar way to
when we rub our hands together,

434
00:25:48,477 --> 00:25:49,789
and they warm up.

435
00:25:49,789 --> 00:25:51,584
It's generating huge amounts

436
00:25:51,584 --> 00:25:54,173
of heat
underneath the surface of Io.

437
00:25:56,831 --> 00:25:59,558
NARRATOR:
A process known as
"tidal heating."

438
00:26:00,973 --> 00:26:04,735
But this bulging movement
generates only some of the heat

439
00:26:04,735 --> 00:26:07,462
that drives
Io's violent volcanoes.

440
00:26:09,568 --> 00:26:12,260
So where is the rest
of the heat coming from?

441
00:26:13,399 --> 00:26:15,643
DOTTIN:
When we think about our moon,

442
00:26:15,643 --> 00:26:19,129
we understand that we only see
one side of the moon,

443
00:26:19,129 --> 00:26:20,440
and this is because

444
00:26:20,440 --> 00:26:22,546
the Earth and the moon
are tidally locked.

445
00:26:22,546 --> 00:26:24,790
NARRATOR:
But as the moon travels

446
00:26:24,790 --> 00:26:27,413
its elliptical path
around Earth,

447
00:26:27,413 --> 00:26:30,002
we actually see it
at slightly different angles.

448
00:26:31,382 --> 00:26:32,591
OLUSEYI:
It's sort of like

449
00:26:32,591 --> 00:26:34,593
if I was to shake my head
and say "no."

450
00:26:36,180 --> 00:26:38,458
Right? You see my face
the entire time,

451
00:26:38,458 --> 00:26:40,495
but because it rocks
back and forth,

452
00:26:40,495 --> 00:26:42,911
you see slightly more of my head

453
00:26:42,911 --> 00:26:46,052
than if I just kept it
pointing right at it.

454
00:26:46,052 --> 00:26:48,848
So, it's like the moon is
looking down on the Earth

455
00:26:48,848 --> 00:26:51,575
and going, "Mm, mm, mm.

456
00:26:51,575 --> 00:26:53,612
Look at those humans."

457
00:26:55,061 --> 00:26:56,753
NARRATOR:
Just like our moon,

458
00:26:56,753 --> 00:26:59,963
Io is tidally locked
to its planet

459
00:26:59,963 --> 00:27:01,861
and has an elliptical orbit.

460
00:27:03,552 --> 00:27:06,348
Which means
that as Io orbits Jupiter,

461
00:27:06,348 --> 00:27:10,111
it appears to rock back
and forth by around one degree.

462
00:27:11,560 --> 00:27:14,840
But there's one big difference
between our moon and Io.

463
00:27:16,358 --> 00:27:19,016
OLUSEYI:
Jupiter is way more massive
than the Earth,

464
00:27:19,016 --> 00:27:21,605
and Io is similar to the moon,

465
00:27:21,605 --> 00:27:24,539
so the tidal effects
are more extreme.

466
00:27:25,713 --> 00:27:27,128
NARRATOR:
Io's tidal bulge

467
00:27:27,128 --> 00:27:30,614
is continuously pulled
towards Jupiter.

468
00:27:30,614 --> 00:27:33,686
So as Io faces the planet
at slightly different angles

469
00:27:33,686 --> 00:27:35,619
throughout its orbit,

470
00:27:35,619 --> 00:27:40,210
Jupiter not only raises the
rock tide 300 feet up and down,

471
00:27:40,210 --> 00:27:44,904
but also drags that tidal bulge
back and forth

472
00:27:44,904 --> 00:27:47,251
40 miles across Io's surface.

473
00:27:48,494 --> 00:27:51,635
Earth's heat was captured
billions of years ago,

474
00:27:51,635 --> 00:27:54,569
locked inside the planet
at the time of formation.

475
00:27:55,570 --> 00:27:59,332
But on Io, its heat
is constantly replenished

476
00:27:59,332 --> 00:28:01,576
by its elliptical orbit.

477
00:28:04,752 --> 00:28:07,064
NARRATOR:
As Io deforms,

478
00:28:07,064 --> 00:28:08,963
the intense friction generated

479
00:28:08,963 --> 00:28:12,794
by these tidal forces
produces enough heat

480
00:28:12,794 --> 00:28:17,626
to drive Io's spectacularly
violent volcanism.

481
00:28:19,836 --> 00:28:21,803
But could all that heat
have driven out

482
00:28:21,803 --> 00:28:25,496
some common planetary
ingredients, like water?

483
00:28:28,534 --> 00:28:30,156
Io doesn't seem
to have any water today,

484
00:28:30,156 --> 00:28:33,366
and we actually don't
entirely know why that is.

485
00:28:33,366 --> 00:28:37,094
Maybe it was never able
to form with any water,

486
00:28:37,094 --> 00:28:39,752
but maybe it just lost
all of its water over time

487
00:28:39,752 --> 00:28:41,547
because of
this tremendous amount of heat

488
00:28:41,547 --> 00:28:44,343
that's produced in it.

489
00:28:47,380 --> 00:28:49,693
FRANCK MARCHIS:
So, there is no water on Io.

490
00:28:49,693 --> 00:28:52,109
Is there life?
We don't know.

491
00:28:52,109 --> 00:28:53,455
If there is life,
it would be a life

492
00:28:53,455 --> 00:28:54,905
which is very different

493
00:28:54,905 --> 00:28:57,839
to the life
we have on our own planet,

494
00:28:57,839 --> 00:28:59,772
and the only way
for us to find it will be

495
00:28:59,772 --> 00:29:02,119
to go there
and to explore directly.

496
00:29:03,120 --> 00:29:05,226
DE KLEER:
Every time
I point a telescope at Io,

497
00:29:05,226 --> 00:29:07,159
I still have that new excitement

498
00:29:07,159 --> 00:29:08,712
because you don't know
what's going to be happening.

499
00:29:08,712 --> 00:29:10,576
You take an image of Io,

500
00:29:10,576 --> 00:29:12,923
and you're saying,
"Which volcanoes are active?"

501
00:29:12,923 --> 00:29:15,374
And you look at it,
and you can just immediately see

502
00:29:15,374 --> 00:29:17,100
from the picture and identify

503
00:29:17,100 --> 00:29:20,517
which volcanoes are going off
at that time.

504
00:29:22,795 --> 00:29:24,624
NARRATOR:
As scientists learn more,

505
00:29:24,624 --> 00:29:26,488
they are finding the effects

506
00:29:26,488 --> 00:29:30,596
of tidal heating
on an even stranger world.

507
00:29:31,562 --> 00:29:34,186
That same source of heat,

508
00:29:34,186 --> 00:29:36,395
caused by an elliptical orbit,

509
00:29:36,395 --> 00:29:40,779
drives volcanic eruptions
that aren't even hot.

510
00:29:43,022 --> 00:29:45,853
Even farther
from Earth than Jupiter,

511
00:29:45,853 --> 00:29:49,546
across a great gulf of space,

512
00:29:49,546 --> 00:29:51,962
lies the next planet.

513
00:29:57,692 --> 00:30:02,179
Saturn's rings loop for hundreds
of thousands of miles.

514
00:30:06,528 --> 00:30:08,082
And just beyond them,

515
00:30:08,082 --> 00:30:10,878
one of its largest moons
changed everything

516
00:30:10,878 --> 00:30:13,846
we thought we knew
about volcanic activity

517
00:30:13,846 --> 00:30:16,124
this far out
in the solar system.

518
00:30:22,096 --> 00:30:26,238
♪

519
00:30:26,238 --> 00:30:29,310
With a hard, frozen exterior,

520
00:30:29,310 --> 00:30:32,623
Enceladus' surface
averages a chilly

521
00:30:32,623 --> 00:30:36,110
330 degrees Fahrenheit.

522
00:30:37,801 --> 00:30:42,047
It's one of the coldest places
in the Saturn system.

523
00:30:42,047 --> 00:30:44,981
An ice world,

524
00:30:44,981 --> 00:30:48,777
where we'd expect everything
to be completely still,

525
00:30:48,777 --> 00:30:51,297
frozen and unchanging.

526
00:30:55,819 --> 00:30:57,752
But in 2005,

527
00:30:57,752 --> 00:31:01,860
NASA's Cassini spacecraft
travelled to the South Pole

528
00:31:01,860 --> 00:31:04,793
and discovered
that stillness shattered.

529
00:31:07,072 --> 00:31:10,247
It captured explosive jets

530
00:31:10,247 --> 00:31:12,836
constantly erupting
from the surface.

531
00:31:12,836 --> 00:31:14,873
♪

532
00:31:17,289 --> 00:31:19,325
NUÚÑEZ:
So, when we first saw
those plumes

533
00:31:19,325 --> 00:31:20,948
coming out of Enceladus,

534
00:31:20,948 --> 00:31:24,744
it was just... mind-boggling

535
00:31:24,744 --> 00:31:27,299
that to see this tiny world

536
00:31:27,299 --> 00:31:29,473
spewing material out,

537
00:31:29,473 --> 00:31:32,407
indicating
that it was geologically active.

538
00:31:34,996 --> 00:31:36,895
Discovering the jets
at Enceladus's south pole

539
00:31:36,895 --> 00:31:39,242
completely changed the way
that we see icy worlds.

540
00:31:39,242 --> 00:31:42,521
It changed the way that we see
small, icy worlds in particular.

541
00:31:45,869 --> 00:31:49,908
NARRATOR:
Giant plumes far bigger
than the moon they erupt from

542
00:31:49,908 --> 00:31:51,910
are an incredible sight.

543
00:31:53,808 --> 00:31:57,916
But how is it possible
to have such powerful eruptions

544
00:31:57,916 --> 00:31:59,987
on a frozen moon?

545
00:32:06,062 --> 00:32:08,616
Our usual experience
of volcanic eruptions

546
00:32:08,616 --> 00:32:10,342
is of molten rock

547
00:32:10,342 --> 00:32:12,861
bursting onto the surface.

548
00:32:16,037 --> 00:32:19,765
But eruptions on Enceladus
are different,

549
00:32:19,765 --> 00:32:21,905
more like what's happening here.

550
00:32:24,011 --> 00:32:26,461
At a geothermal power plant
in Iceland.

551
00:32:28,187 --> 00:32:30,810
A mile below the surface

552
00:32:30,810 --> 00:32:34,124
lies a reservoir
of superheated water.

553
00:32:35,298 --> 00:32:38,577
Drilling down into it
allows steam and water

554
00:32:38,577 --> 00:32:42,753
to erupt out
and generate electricity.

555
00:32:44,893 --> 00:32:47,034
HOWETT:
To be here is amazing!

556
00:32:47,034 --> 00:32:50,451
I spent most of my entire
adult life studying Enceladus,

557
00:32:50,451 --> 00:32:53,074
but I've never heard it,
I've never seen it,

558
00:32:53,074 --> 00:32:55,387
I've never felt it,
and this is one-tenth

559
00:32:55,387 --> 00:32:58,700
of what one of the jets
on Enceladus would be like.

560
00:32:58,700 --> 00:33:01,117
It's astounding.

561
00:33:03,567 --> 00:33:06,570
NARRATOR:
Over 660 pounds of water

562
00:33:06,570 --> 00:33:11,058
erupt from the surface
of Enceladus every second,

563
00:33:11,058 --> 00:33:13,060
creating visible eruptions

564
00:33:13,060 --> 00:33:16,442
that can thrust up to
6,000 miles into space.

565
00:33:19,066 --> 00:33:22,069
It's called cryovolcanism.

566
00:33:22,069 --> 00:33:24,761
"Cryo" from the Greek for cold.

567
00:33:26,728 --> 00:33:29,766
Cryovolcanism
is absolutely volcanism.

568
00:33:29,766 --> 00:33:32,010
When we study the planets,
we learned that,

569
00:33:32,010 --> 00:33:35,013
even though they have different
chemistry or slight differences,

570
00:33:35,013 --> 00:33:38,326
that these processes are common
throughout the planets,

571
00:33:38,326 --> 00:33:40,328
and volcanism is one of them.

572
00:33:43,538 --> 00:33:44,608
MARCHIS:
What is surprising

573
00:33:44,608 --> 00:33:46,990
is not only the presence
of the jets,

574
00:33:46,990 --> 00:33:49,648
but their size,
the fact that this is

575
00:33:49,648 --> 00:33:51,650
an extreme cryovolcanism

576
00:33:51,650 --> 00:33:54,101
coming from such a small body.

577
00:33:57,000 --> 00:33:59,865
NARRATOR:
But where does such
an enormous amount of water

578
00:33:59,865 --> 00:34:02,488
come from on a frigid ice moon?

579
00:34:05,871 --> 00:34:08,598
There is a hint.

580
00:34:08,598 --> 00:34:11,497
As Enceladus orbits Saturn,

581
00:34:11,497 --> 00:34:16,054
it wobbles by about 0.12 degrees
on its axis.

582
00:34:19,712 --> 00:34:22,370
A tiny but significant
movement...

583
00:34:23,751 --> 00:34:26,857
...that tells us something
about the moon's interior.

584
00:34:27,893 --> 00:34:29,308
HOWETT:
A simple way to think about

585
00:34:29,308 --> 00:34:31,276
what's happening
inside Enceladus

586
00:34:31,276 --> 00:34:34,934
is to consider what happens
when we rotate two eggs,

587
00:34:34,934 --> 00:34:37,972
one of which is hard-boiled
and the other one isn't.

588
00:34:37,972 --> 00:34:41,148
So, we'll start with this one.

589
00:34:41,148 --> 00:34:42,563
If we spin the egg...

590
00:34:46,187 --> 00:34:48,500
[laughs] Just with eggs,

591
00:34:48,500 --> 00:34:49,949
doesn't seem like
the most obvious solution.

592
00:34:49,949 --> 00:34:52,020
You can see that it...

593
00:34:52,020 --> 00:34:54,057
As it rotates, it's got
a bit of a wobble to it,

594
00:34:54,057 --> 00:34:56,404
and if we rotate it a bit faster
and then stop it,

595
00:34:56,404 --> 00:34:58,372
it'll continue to rotate.

596
00:34:59,683 --> 00:35:01,029
Whereas this one,

597
00:35:01,029 --> 00:35:02,307
we do the same thing.

598
00:35:02,307 --> 00:35:05,033
It rotates more smoothly,

599
00:35:05,033 --> 00:35:07,105
and if we rotate it and stop it,

600
00:35:07,105 --> 00:35:09,348
you can see it stops.

601
00:35:10,694 --> 00:35:12,593
NARRATOR:
The reason the first one wobbles

602
00:35:12,593 --> 00:35:15,147
is because it is raw.

603
00:35:15,147 --> 00:35:17,391
Whereas this one...

604
00:35:20,670 --> 00:35:22,568
...is hard-boiled.

605
00:35:24,881 --> 00:35:27,055
The raw one, of course,
has a liquid in the middle,

606
00:35:27,055 --> 00:35:29,161
and so, even after
you stop the shell,

607
00:35:29,161 --> 00:35:31,059
the liquid continues to rotate,

608
00:35:31,059 --> 00:35:33,061
and that causes
the shell to rotate.

609
00:35:33,061 --> 00:35:35,271
It also caused
that wobbly rotation

610
00:35:35,271 --> 00:35:36,824
that we see all the way along.

611
00:35:36,824 --> 00:35:39,585
Whereas the hard-boiled one
is solid all the way through.

612
00:35:39,585 --> 00:35:41,691
When you stop the shell,
you stop all of it.

613
00:35:41,691 --> 00:35:44,521
It also causes it
to rotate very nicely.

614
00:35:44,521 --> 00:35:46,282
But it's the liquid one,
the raw one,

615
00:35:46,282 --> 00:35:47,524
that's like Enceladus.

616
00:35:49,733 --> 00:35:53,289
NARRATOR:
Enceladus is unlikely
to crack like a raw egg.

617
00:35:54,255 --> 00:35:56,533
But it does wobble like one.

618
00:35:59,433 --> 00:36:03,747
And that tells us that
there is an outer shell of ice,

619
00:36:03,747 --> 00:36:07,751
sitting on top
of a global ocean of water.

620
00:36:11,238 --> 00:36:14,965
But how does that water
manage to erupt

621
00:36:14,965 --> 00:36:19,177
through a shell of around
three miles of solid ice?

622
00:36:20,661 --> 00:36:23,008
QUICK:
When the liquid ocean
is heated from below

623
00:36:23,008 --> 00:36:25,976
by energy from tidal heating,
it expands,

624
00:36:25,976 --> 00:36:28,393
so the liquid wants
to take up more space.

625
00:36:28,393 --> 00:36:30,671
As it seeks
to take up more space,

626
00:36:30,671 --> 00:36:33,018
it pushes up against
the bottom of the ice shell.

627
00:36:34,468 --> 00:36:37,954
NARRATOR:
Once there, another force
comes into action.

628
00:36:39,266 --> 00:36:41,440
Once that water goes
through a crack

629
00:36:41,440 --> 00:36:44,340
and then is exposed to the
vacuum of space,

630
00:36:44,340 --> 00:36:45,824
it's like a suction.

631
00:36:45,824 --> 00:36:47,757
That's what vacuum does.

632
00:36:47,757 --> 00:36:49,655
BYRNE:
The reason water
behaves this way

633
00:36:49,655 --> 00:36:51,657
when it's exposed
to zero pressure

634
00:36:51,657 --> 00:36:53,521
is because
there's nothing acting

635
00:36:53,521 --> 00:36:54,867
to keep
the water together.

636
00:36:54,867 --> 00:36:57,145
So, the water will try
its best to expand

637
00:36:57,145 --> 00:36:59,078
as much as it possibly can.

638
00:37:01,046 --> 00:37:02,392
One force pushes the water up,

639
00:37:02,392 --> 00:37:04,981
and the other force
pulls it out onto the surface,

640
00:37:04,981 --> 00:37:07,225
and that's why we have
these magnificent jets.

641
00:37:09,019 --> 00:37:11,090
NARRATOR:
And they carry with them
the secrets

642
00:37:11,090 --> 00:37:14,439
of what lies beneath the ice.

643
00:37:16,372 --> 00:37:19,409
These plumes contain
traces of silica

644
00:37:19,409 --> 00:37:21,480
and molecular hydrogen

645
00:37:21,480 --> 00:37:23,689
that could've come
from the ocean water

646
00:37:23,689 --> 00:37:26,451
interacting
with hot volcanic rocks.

647
00:37:28,832 --> 00:37:32,491
Suggesting that, in the depths
of Enceladus's ocean,

648
00:37:32,491 --> 00:37:35,563
there may be hydrothermal vents,

649
00:37:35,563 --> 00:37:38,670
towering structures
created by water flowing

650
00:37:38,670 --> 00:37:41,569
into the volcanic rocks
on the seabed.

651
00:37:43,744 --> 00:37:44,814
I think the chances
are pretty high

652
00:37:44,814 --> 00:37:45,953
that there are
hydrothermal vents

653
00:37:45,953 --> 00:37:47,886
at the bottom
of Enceladus' ocean.

654
00:37:47,886 --> 00:37:49,370
Just like Earth's ocean,

655
00:37:49,370 --> 00:37:52,131
Enceladus's ocean sits right
on top of its rocky mantle.

656
00:37:53,167 --> 00:37:56,101
NARRATOR:
And with probable
hydrothermal vents,

657
00:37:56,101 --> 00:37:59,380
an exciting possibility
for life.

658
00:37:59,380 --> 00:38:03,729
NUÚÑEZ:
We think that life
could've originated on Earth

659
00:38:03,729 --> 00:38:05,524
in hydrothermal vents.

660
00:38:05,524 --> 00:38:07,423
And these hydrothermal vents

661
00:38:07,423 --> 00:38:08,907
have those ingredients

662
00:38:08,907 --> 00:38:11,427
that are essential for life.

663
00:38:14,222 --> 00:38:17,053
NARRATOR:
And it isn't just
the possibility of heat

664
00:38:17,053 --> 00:38:20,781
that makes Enceladus
a compelling incubator for life.

665
00:38:22,334 --> 00:38:23,680
HOFGARTNER:
There are three key ingredients

666
00:38:23,680 --> 00:38:25,372
to a habitable environment:

667
00:38:25,372 --> 00:38:28,271
liquid water,
chemical nutrients,

668
00:38:28,271 --> 00:38:30,031
and an energy source to use,

669
00:38:30,031 --> 00:38:34,104
and now we know that Enceladus
has all three within its ocean.

670
00:38:37,176 --> 00:38:40,283
QUICK:
A 2023 study showed
that Enceladus's jets

671
00:38:40,283 --> 00:38:41,940
have phosphates in it,

672
00:38:41,940 --> 00:38:45,219
anywhere from 100 to 1,000 times
the amount of phosphates

673
00:38:45,219 --> 00:38:46,669
that we find in Earth's oceans.

674
00:38:46,669 --> 00:38:50,914
Phosphates, we know,
are a key component of DNA,

675
00:38:50,914 --> 00:38:52,502
which is the
building block of life.

676
00:38:55,574 --> 00:38:57,921
NUÚÑEZ:
Does that mean
that we found life?

677
00:38:57,921 --> 00:38:59,371
Well, we don't know.

678
00:38:59,371 --> 00:39:00,752
Just because
we found phosphates,

679
00:39:00,752 --> 00:39:03,755
it's-it's a potential
ingredient,

680
00:39:03,755 --> 00:39:05,066
but it's not a slam dunk,

681
00:39:05,066 --> 00:39:08,380
and so, we need to go back
and really explore

682
00:39:08,380 --> 00:39:10,175
in more detail to see

683
00:39:10,175 --> 00:39:12,833
what is the origin
of this phosphate.

684
00:39:15,698 --> 00:39:19,149
NARRATOR:
Any mission to Enceladus
is a ways off.

685
00:39:20,634 --> 00:39:24,154
But there is another world
much closer to home

686
00:39:24,154 --> 00:39:27,537
that has more volcanoes
strewn across its surface

687
00:39:27,537 --> 00:39:29,677
than any other planet.

688
00:39:38,997 --> 00:39:40,999
To find it, we have to return

689
00:39:40,999 --> 00:39:44,382
all the way back
into the inner solar system.

690
00:39:46,418 --> 00:39:48,386
Past Mars's ancient peaks...

691
00:39:50,526 --> 00:39:52,182
...and beyond Earth.

692
00:39:53,252 --> 00:39:56,532
...to a mysterious,
cloud-covered planet.

693
00:40:06,990 --> 00:40:10,131
Venus's dense atmosphere
of carbon dioxide

694
00:40:10,131 --> 00:40:13,445
and clouds of sulfuric acid

695
00:40:13,445 --> 00:40:15,620
obscure the surface.

696
00:40:19,727 --> 00:40:23,006
For decades, orbiting probes
have used radar

697
00:40:23,006 --> 00:40:25,353
to peer through the clouds.

698
00:40:28,356 --> 00:40:30,669
Revealing a landscape dominated

699
00:40:30,669 --> 00:40:33,603
by more than 85,000 volcanoes.

700
00:40:36,572 --> 00:40:38,677
But it was hard to see
in the images

701
00:40:38,677 --> 00:40:40,886
if any were recently active,

702
00:40:40,886 --> 00:40:43,579
or if, like Mars,

703
00:40:43,579 --> 00:40:45,857
they were relics of the past.

704
00:40:47,410 --> 00:40:51,276
So why does Venus
have so many volcanoes?

705
00:40:53,520 --> 00:40:55,970
And are they still
erupting today?

706
00:40:59,526 --> 00:41:03,322
To find out, scientists
are studying Iceland,

707
00:41:03,322 --> 00:41:06,878
one of the most volcanically
active places on Earth.

708
00:41:16,301 --> 00:41:20,823
Here they are investigating
recent lava flow activity

709
00:41:20,823 --> 00:41:23,653
to help prepare
for future missions to Venus.

710
00:41:26,794 --> 00:41:28,934
SUE SMREKAR:
I have remained
fascinated by Venus

711
00:41:28,934 --> 00:41:32,282
because it tells us so much
about the Earth.

712
00:41:32,282 --> 00:41:33,283
They really are twin planets

713
00:41:33,283 --> 00:41:36,390
evolving down different paths.

714
00:41:39,151 --> 00:41:41,913
NARRATOR:
Sue Smrekar is leading
the Veritas mission

715
00:41:41,913 --> 00:41:45,330
preparing to launch to Venus
in the next decade.

716
00:41:46,952 --> 00:41:48,816
She uses radar data,

717
00:41:48,816 --> 00:41:50,853
which creates
black-and-white images

718
00:41:50,853 --> 00:41:53,407
that reveal the texture
of the surface.

719
00:41:56,375 --> 00:41:59,517
♪

720
00:42:01,208 --> 00:42:03,555
SMREKAR:
I try to see things
with my radar eyes,

721
00:42:03,555 --> 00:42:05,212
just imagining
what they look like.

722
00:42:06,593 --> 00:42:09,941
When it's a nice smooth surface,
the radar wave comes down,

723
00:42:09,941 --> 00:42:11,390
and it looks dark.

724
00:42:11,390 --> 00:42:14,290
But these areas
that are super rough,

725
00:42:14,290 --> 00:42:16,085
you'll get
a lot more reflection, so,

726
00:42:16,085 --> 00:42:19,985
in radar, these areas
will be much brighter.

727
00:42:23,264 --> 00:42:25,543
NARRATOR:
Whether new lava flows
like we see on Earth

728
00:42:25,543 --> 00:42:30,582
exist on Venus
was a much debated subject,

729
00:42:30,582 --> 00:42:32,757
as scientists
had no direct evidence

730
00:42:32,757 --> 00:42:35,104
of recent volcanic activity
on Venus.

731
00:42:37,589 --> 00:42:39,591
Until now.

732
00:42:40,592 --> 00:42:41,800
ROBERT HERRICK:
It's really

733
00:42:41,800 --> 00:42:44,423
only been
in the last decade or so

734
00:42:44,423 --> 00:42:46,805
that technology
has made it possible

735
00:42:46,805 --> 00:42:48,462
to be able to zoom in and out

736
00:42:48,462 --> 00:42:51,638
and flip back and forth
between data.

737
00:42:53,329 --> 00:42:55,607
NARRATOR:
Using today's faster computers,

738
00:42:55,607 --> 00:42:59,404
Robert Herrick and his team
reanalyzed images taken

739
00:42:59,404 --> 00:43:01,924
by the Magellan orbiter...

740
00:43:01,924 --> 00:43:04,720
over 30 years ago,

741
00:43:04,720 --> 00:43:06,998
and spotted a volcanic crater

742
00:43:06,998 --> 00:43:09,897
that had doubled in size
over eight months.

743
00:43:10,864 --> 00:43:13,521
Proving that a volcano,

744
00:43:13,521 --> 00:43:16,870
about the size of Mount Everest,

745
00:43:16,870 --> 00:43:19,527
was erupting
from its northern flank.

746
00:43:20,839 --> 00:43:22,979
HERRICK:
When an investigation
actually works out,

747
00:43:22,979 --> 00:43:25,326
and you learn something
important, and you're like,

748
00:43:25,326 --> 00:43:26,776
"Oh, this is... this is cool."

749
00:43:28,847 --> 00:43:31,229
So, yes,
it's a thrill to, you know,

750
00:43:31,229 --> 00:43:34,094
"Wow, I've-I've made my mark
on the field."

751
00:43:34,094 --> 00:43:36,475
I was so excited
when we saw those images

752
00:43:36,475 --> 00:43:38,339
because what that tells us
is that everything

753
00:43:38,339 --> 00:43:40,721
we've been thinking
about Venus is right,

754
00:43:40,721 --> 00:43:43,172
that this world probably
is volcanically active,

755
00:43:43,172 --> 00:43:46,037
and that just makes us hungry
for more.

756
00:43:47,935 --> 00:43:51,387
NARRATOR:
But evidence of one
probable eruption can't reveal

757
00:43:51,387 --> 00:43:54,597
if the rest of Venus's volcanoes
are still active.

758
00:43:55,840 --> 00:43:58,774
And another mystery remains.

759
00:43:59,809 --> 00:44:01,984
Venus could have been
Earth's twin.

760
00:44:02,985 --> 00:44:06,505
It is roughly the same size
and built of the same stuff.

761
00:44:09,612 --> 00:44:12,546
So why are the two planets
so different today?

762
00:44:15,307 --> 00:44:19,139
Understanding where volcanoes
are found may solve this puzzle

763
00:44:19,139 --> 00:44:23,039
and explain
why Venus is now a planet

764
00:44:23,039 --> 00:44:25,939
with such extreme conditions.

765
00:44:30,668 --> 00:44:32,255
SMREKAR:
So, this map shows
the distribution

766
00:44:32,255 --> 00:44:33,878
of volcanoes on the Earth.

767
00:44:33,878 --> 00:44:35,880
And you can see
there's a big line of them

768
00:44:35,880 --> 00:44:38,261
that goes down the coast
of North America

769
00:44:38,261 --> 00:44:40,747
on down to South America,

770
00:44:40,747 --> 00:44:43,750
and their location
is really controlled

771
00:44:43,750 --> 00:44:47,546
to a large degree by the
location of plate boundaries.

772
00:44:48,616 --> 00:44:50,826
NARRATOR:
Most volcanoes
on Earth are found

773
00:44:50,826 --> 00:44:54,553
where two plates meet,
or are pulling apart,

774
00:44:54,553 --> 00:44:57,349
creating lines of volcanoes
along their edges.

775
00:44:58,454 --> 00:45:01,871
But on Venus,
the pattern is very different.

776
00:45:01,871 --> 00:45:04,840
SMREKAR:
So, this is a map
of the volcanism on Venus,

777
00:45:04,840 --> 00:45:06,876
the volcanoes, and you can see

778
00:45:06,876 --> 00:45:08,602
that they are
all over the place.

779
00:45:08,602 --> 00:45:09,810
They don't follow any nice,

780
00:45:09,810 --> 00:45:12,399
uh, tight line of volcanism

781
00:45:12,399 --> 00:45:14,332
the way we saw for Earth.

782
00:45:14,332 --> 00:45:15,920
And, you know, the difference is

783
00:45:15,920 --> 00:45:18,681
that, uh, on Venus,
we don't have plate tectonics.

784
00:45:18,681 --> 00:45:21,132
Venus has
some entirely different system.

785
00:45:24,894 --> 00:45:27,310
NARRATOR:
Not only are
there numerous volcanoes

786
00:45:27,310 --> 00:45:29,899
scattered
across Venus' landscape,

787
00:45:29,899 --> 00:45:32,522
they take on odd forms.

788
00:45:34,973 --> 00:45:38,597
From lines
of flattened volcanic domes

789
00:45:38,597 --> 00:45:40,979
that look like chains
of pancakes...

790
00:45:43,499 --> 00:45:45,225
...to strange volcanoes

791
00:45:45,225 --> 00:45:48,676
whose rutted sides make them
look almost like insects,

792
00:45:48,676 --> 00:45:51,679
clamped to the surface.

793
00:45:52,680 --> 00:45:55,718
Venus is a volcanic zoo,

794
00:45:55,718 --> 00:45:58,445
with a variety of volcanoes,

795
00:45:58,445 --> 00:46:01,655
including some that are unique
in the solar system.

796
00:46:04,037 --> 00:46:05,659
Venus doesn't have
plate tectonics,

797
00:46:05,659 --> 00:46:09,456
but its crust has
uneven thickness,

798
00:46:09,456 --> 00:46:12,390
and so, magma from within

799
00:46:12,390 --> 00:46:15,013
can climb and poke into
the crust and then cool.

800
00:46:16,739 --> 00:46:19,811
NARRATOR:
The inner heat drives
vast lava flows

801
00:46:19,811 --> 00:46:23,781
that can run
for thousands of miles,

802
00:46:23,781 --> 00:46:26,024
and creates far more blemishes
and bubbles

803
00:46:26,024 --> 00:46:28,613
on the surface
than here on Earth.

804
00:46:31,202 --> 00:46:33,480
But the lack of plate tectonics

805
00:46:33,480 --> 00:46:36,828
points to a far more
profound difference

806
00:46:36,828 --> 00:46:39,072
between Earth and Venus.

807
00:46:41,522 --> 00:46:42,834
DOTTIN:
So on Earth,

808
00:46:42,834 --> 00:46:43,835
there have
been times where

809
00:46:43,835 --> 00:46:47,114
there were
volcanic eruptions

810
00:46:47,114 --> 00:46:49,530
that were so large
and so constant

811
00:46:49,530 --> 00:46:52,223
that it was filling
the atmosphere

812
00:46:52,223 --> 00:46:55,640
with tons of toxic gases
and greenhouse gases.

813
00:46:57,262 --> 00:46:59,540
NARRATOR:
Venus's greenhouse gases
trapped heat,

814
00:46:59,540 --> 00:47:02,198
increasing the temperature,

815
00:47:02,198 --> 00:47:05,201
but thanks to plate tectonics,

816
00:47:05,201 --> 00:47:07,859
Earth had a way
to balance this effect.

817
00:47:08,895 --> 00:47:10,241
MORRIS:
On Earth,

818
00:47:10,241 --> 00:47:11,276
carbon dioxide is actually

819
00:47:11,276 --> 00:47:13,071
pulled out of the atmosphere

820
00:47:13,071 --> 00:47:14,866
when it rains,

821
00:47:14,866 --> 00:47:17,662
and those molecules interact
with the rocks

822
00:47:17,662 --> 00:47:20,699
and the carbon dioxide gets
deposited in the rocks,

823
00:47:20,699 --> 00:47:23,633
and as the plate tectonics
cycle occurs,

824
00:47:23,633 --> 00:47:27,672
that material gets then
pulled into the subsurface

825
00:47:27,672 --> 00:47:29,812
and removed from the atmosphere.

826
00:47:29,812 --> 00:47:31,124
BYRNE:
When we have

827
00:47:31,124 --> 00:47:33,126
these huge volcanic eruptions

828
00:47:33,126 --> 00:47:34,955
injecting all this CO2

829
00:47:34,955 --> 00:47:36,267
into the atmosphere,

830
00:47:36,267 --> 00:47:39,891
we see substantial
and severe climate change,

831
00:47:39,891 --> 00:47:41,168
at least for a while,

832
00:47:41,168 --> 00:47:43,136
until plate tectonics is able

833
00:47:43,136 --> 00:47:46,898
to regulate things
and get them back under control.

834
00:47:46,898 --> 00:47:48,072
DOTTIN:
So, plate tectonics

835
00:47:48,072 --> 00:47:51,178
is probably one
of the main reasons

836
00:47:51,178 --> 00:47:54,388
why we've been able
to maintain the climate

837
00:47:54,388 --> 00:47:56,149
that we have on our planet.

838
00:47:58,530 --> 00:48:01,085
NARRATOR:
As Venus's volcanoes erupted,

839
00:48:01,085 --> 00:48:03,156
it seems there was no mechanism

840
00:48:03,156 --> 00:48:05,675
to remove those gases
from the atmosphere

841
00:48:05,675 --> 00:48:07,539
back to the interior.

842
00:48:10,957 --> 00:48:15,444
So the planet got hotter
and hotter,

843
00:48:15,444 --> 00:48:19,517
turning it into the hellish
landscape we see today.

844
00:48:21,070 --> 00:48:24,487
Venus shows the importance
of plate tectonics

845
00:48:24,487 --> 00:48:27,697
in helping to control
not just volcanoes,

846
00:48:27,697 --> 00:48:29,872
but the climate, too.

847
00:48:31,425 --> 00:48:33,669
MORRIS:
So, the lesson
that we can learn from Venus

848
00:48:33,669 --> 00:48:35,602
is that on Earth,

849
00:48:35,602 --> 00:48:38,674
the planet is actually able
to stabilize itself

850
00:48:38,674 --> 00:48:40,641
through the process
of plate tectonics,

851
00:48:40,641 --> 00:48:42,954
and we see on Venus what happens

852
00:48:42,954 --> 00:48:44,438
when the planet's not able

853
00:48:44,438 --> 00:48:46,682
to maintain that stability
in the atmosphere.

854
00:48:50,444 --> 00:48:52,136
NARRATOR:
But human activity emits

855
00:48:52,136 --> 00:48:55,035
at least 60 times
more carbon dioxide

856
00:48:55,035 --> 00:48:58,245
than all the volcanoes
on Earth each year,

857
00:48:58,245 --> 00:49:02,594
and plate tectonics
is a slow process.

858
00:49:03,975 --> 00:49:06,564
OLUSEYI:
What we see in Venus's
atmosphere is a cautionary tale

859
00:49:06,564 --> 00:49:10,223
for the situation that Earth
is in at this very moment.

860
00:49:10,223 --> 00:49:12,501
We have a greenhouse effect
taking place

861
00:49:12,501 --> 00:49:14,641
that's warming
our planet.

862
00:49:15,676 --> 00:49:18,610
Venus is a runaway
greenhouse effect

863
00:49:18,610 --> 00:49:20,405
just gone rampant,

864
00:49:20,405 --> 00:49:23,546
and the whole planet is now
a hotbox of it.

865
00:49:28,379 --> 00:49:29,725
NARRATOR:
Scientists don't think

866
00:49:29,725 --> 00:49:32,279
human emissions alone
can send us

867
00:49:32,279 --> 00:49:34,350
to those extremes.

868
00:49:35,834 --> 00:49:38,009
But with Venus,
we have another planet

869
00:49:38,009 --> 00:49:40,736
that's identical in many ways.

870
00:49:40,736 --> 00:49:45,016
And by understanding
why it's so different today,

871
00:49:45,016 --> 00:49:49,676
we can appreciate the unique
habitability of our own planet.

872
00:49:49,676 --> 00:49:52,713
[explosive pop]

873
00:49:52,713 --> 00:49:55,993
SMREKAR:
Venus is kind of a...
like a teenager.

874
00:49:55,993 --> 00:49:59,375
We go back in time to the
early part of Earth's geology

875
00:49:59,375 --> 00:50:00,894
when we study Venus.

876
00:50:00,894 --> 00:50:03,586
So, it's a... it's a really
a fascinating, you know,

877
00:50:03,586 --> 00:50:06,313
look at our...
the evolution of our own planet.

878
00:50:08,108 --> 00:50:11,249
NARRATOR:
Future missions
like the Veritas orbiter

879
00:50:11,249 --> 00:50:13,700
will help explain
the different processes

880
00:50:13,700 --> 00:50:16,116
behind volcanism on Venus.

881
00:50:17,531 --> 00:50:18,877
SMREKAR:
With Veritas, we have just

882
00:50:18,877 --> 00:50:22,329
all kinds of ways
to look for new volcanism.

883
00:50:23,744 --> 00:50:27,162
We can actually see the surface
deforming at the scale of,

884
00:50:27,162 --> 00:50:28,784
you know, an inch or so.

885
00:50:28,784 --> 00:50:31,959
And I think we're just going
to see vastly more flows

886
00:50:31,959 --> 00:50:33,823
that are young and even,

887
00:50:33,823 --> 00:50:35,377
I predict,
happening during our mission.

888
00:50:37,379 --> 00:50:39,829
NARRATOR:
With new insights into Venus,

889
00:50:39,829 --> 00:50:41,624
we can better understand
the role

890
00:50:41,624 --> 00:50:46,250
plate tectonics plays in
balancing our own environment,

891
00:50:46,250 --> 00:50:49,977
creating the conditions
for life to thrive.

892
00:50:54,361 --> 00:50:56,881
One of the revelations
in our exploration

893
00:50:56,881 --> 00:51:00,195
of the solar system is
what we are finding

894
00:51:00,195 --> 00:51:02,818
isn't a collection
of inactive worlds.

895
00:51:05,096 --> 00:51:06,511
HOFGARTNER:
There is a great diversity

896
00:51:06,511 --> 00:51:09,135
of geological activity in
the solar system,

897
00:51:09,135 --> 00:51:10,860
and sometimes nature

898
00:51:10,860 --> 00:51:14,071
makes it occur
in surprising places.

899
00:51:15,969 --> 00:51:20,353
NARRATOR:
From the tiny,
explosive moon of Io...

900
00:51:20,353 --> 00:51:24,184
to the stunning cryovolcanoes
on Enceladus,

901
00:51:24,184 --> 00:51:28,913
they are telling us
so much about Earth.

902
00:51:28,913 --> 00:51:31,088
SOUSA-SILVA:
When we look
at other planets and moons,

903
00:51:31,088 --> 00:51:34,367
we see snippets
of Earth's past and future.

904
00:51:34,367 --> 00:51:38,025
We were once covered
in volcanoes like Io is now,

905
00:51:38,025 --> 00:51:40,131
and in Venus,
we see what happens

906
00:51:40,131 --> 00:51:43,445
when greenhouse gases
get out of control.

907
00:51:45,136 --> 00:51:46,896
NARRATOR:
But they also tell us

908
00:51:46,896 --> 00:51:50,176
just how remarkable Earth is,

909
00:51:50,176 --> 00:51:52,971
for one very special reason.

910
00:51:55,871 --> 00:51:57,873
Amongst all these geologically
active worlds,

911
00:51:57,873 --> 00:52:00,841
it's still pretty amazing
that the only place

912
00:52:00,841 --> 00:52:04,259
where we saw these
active geology become biology

913
00:52:04,259 --> 00:52:08,293
is here on Earth.