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The Earth, home to millions of species.

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But what might live... beyond?

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Astronomers have
discovered thousands of planets

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outside our solar system.

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They believe there are trillions more.

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If life exists on only
a fraction of them,

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then the universe must be... alive.

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All living things have the same needs.

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To feed...

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reproduce...

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and evolve.

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By applying the laws of life on Earth

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to the rest of the universe...

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it's possible to imagine

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what could live...

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on alien worlds.

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Most planets we know of are so hellish,

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it seems impossible
that anything could live.

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But it's amazing
where life can take hold.

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For as long as I can remember, my
mom always told me I was an alien,

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because I just had my mind on
outer space from the beginning.

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I just had always known that I wanted to
get out there and explore the universe.

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Oh, my God.

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This is the most incredible
place I think I've ever seen.

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This is what I dream
other planets looking like.

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It's... it's incredible.

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So, yeah.

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The Danakil Depression is known
locally as "The Gateway to Hell."

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120 meters below
sea level and volcanic...

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it's the hottest place on Earth.

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We're at 79C. 82C.

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This one's topping out at 87.

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If life can exist here...

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it could exist on any number
of worlds in the universe.

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Life on other planets, they're
gonna have, uh, chemistry.

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Whether it looks exactly
like ours, we don't know,

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but they're gonna have
chemistry that helps them live.

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And that chemistry is
going to be subject to limits.

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For example, all life
is made up of cells.

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Inside these cells
they have biomolecules

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that allow the cells to
function and live and work.

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That's our machinery that runs
and makes this chemistry happen,

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that keeps life living.

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And so we really wanna
understand how that machinery works

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and what's gonna make
that machinery break down.

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Until recently, it was assumed

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that Danakil was too
extreme to support life.

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But astrobiologists come here to
look for simple single-celled microbes...

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known as extremophiles.

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Microbes are too small
to see with the naked eye,

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so it's not going to be as simple as
taking a little bit of water out of a lake

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and putting it under a microscope
and seeing lots of teeming bugs.

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The only way to detect the
presence of extremophiles

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is to find traces of their DNA,

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using a portable genetic sequencer.

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This is a very small device and
it's very sensitive to temperature,

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and we're in one of the hottest
places on the planet Earth.

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So, here in the field right
now, we do... a cool block,

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to kind of keep it cool, and
we have our channels running.

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And we have...

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We have sequencing!

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We actually have sequencing happening.

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We have DNA in here.

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Excellent.

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Sequencing of DNA is proof

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that extremophiles can survive
in the acidic waters of Danakil.

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These guys are like the superheroes
of microbes, and it's just amazing,

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as we learn more and more about
the different strategies and mechanisms

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that they come up with to survive
these kinds of environments.

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Finding things alive here
opens up an intriguing possibility.

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But some life forms are tough
enough to survive anywhere...

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even in the deepest reaches of space.

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A red dwarf star.

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The most common
type of star in our galaxy.

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Imagine a planet in such a close orbit,

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its rotation is locked
by the star's gravity,

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so it always shows
the same face to its sun.

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This is Janus.

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How would life adapt on
such an extreme world?

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On one side of the
planet, it's always daytime,

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a searing desert.

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On the other side, it's forever night,

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a frozen shadowland.

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Squeezed between the two,
a sliver of perpetual twilight.

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Freezing meltwater
flows from the cold side,

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carving canyons through the landscape.

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Even here, where the
planet's most hospitable,

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there's little vegetation.

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But deep in these canyons

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lives an extraordinary
five-legged creature...

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a pentapod.

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No bigger than a cat,

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it's the dominant life form on Janus,

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capable of adapting to any conditions.

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On the cold side,

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it's stocky and hairy.

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On the hot side, it's
shiny, slender and skittish.

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Pentapods can become
whatever they need to be

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in order to survive.

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On Earth, all animals
adapt to fit their environment.

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But some are more adaptable than others.

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This trail that I just came across here,

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it's a beautifully manicured trail,

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and you would think it was made by
some bigger animal or maybe even a human.

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But it's actually made by ants.

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The leaf-cutter ant, in particular.

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All looks quiet right now,

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but if we come back at night, this will
actually turn into an ant super-highway,

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with leaves just streaming
up, like, towards their nest.

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Oh, wow.

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Look at that.

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This is the ant nest.

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You can really see into
the heart of this colony.

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There's a lot going on.

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There's actually, for leaf-cutter
ants, there's different castes.

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There is the soldiers,
there are different workers.

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There's also the queen.

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She's the only one who's laying
eggs, and there's only a single queen.

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Without her, none of this would be here.

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An ant colony depends
on the division of labor.

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Different castes have different jobs,
and they come in all shapes and sizes.

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I just grabbed one of the soldiers,

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and I also grabbed the
really, really small worker.

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And it's not the smallest
worker in this colony,

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but it's... it's pretty close.

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And I mean, the soldiers,
I barely can hold her.

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It's really hard. I can feel her power.

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I can feel she's trying to get
out. Her jaws are wide open.

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But, I mean, the
difference is incredible.

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And to think that they all started
from the same... the same larva.

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All ants in a colony
are closely related.

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They share most of the same genes.

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But as they grow up, some genes
are switched on, others switched off,

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depending on the food they are fed.

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Any of them can become
workers, foragers or soldiers.

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So, this ability to create such different
shapes and forms from the same blueprint,

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this is actually called polyphenism.

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And "poly" just means "many,"
and "phenism" would be "shapes."

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Oh, the spider just did exactly
what I was trying to avoid all night.

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She walked exactly into one of
these trails of these leaf-cutters here.

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And that's not good news.

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So here, you really see the power
of these soldiers and their jaws.

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If something disturbs the colony,

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it's their job to come in and get
it, and that's exactly what they did.

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But wow.

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Aaah!

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All right, I'm already being attacked.

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Ooh, that's gonna hurt.

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They are now coming for me.

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So, any creature that
has this ability to morph

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and react to changes in its
environment as quickly as ants can do,

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has an amazing
advantage to not just survive,

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but actually dominate its world.

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On Janus, pentapods are
masters of polyphenism.

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Like ants, they're able to
develop into different forms.

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But they all begin life
in the same place...

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the Twilight Zone.

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A pair of adults is ready to breed.

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They're both male and female.

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Hermaphrodites.

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Each can produce offspring,

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doubling their chances of success.

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Having mated, a pentapod
leaves the shelter of the canyon.

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It climbs to high ground,

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ready to spawn.

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At the top, a constant wind blows between
the cold and hot sides of the planet.

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But the wind provides an
opportunity to scatter their larvae.

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This way, they can colonize the planet.

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On the hot side, water is scarce...

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condensing only in shaded areas.

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If there's nothing to eat, they move on.

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With five legs, they can
skitter in any direction.

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And with ten eyes,

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not much escapes their attention.

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If they sense a meal,

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they use feelers to root it out.

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They need to make the
most of every opportunity.

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Life in any desert is an ordeal.

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Only the tough survive.

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And in the natural world,

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there's nothing much tougher...

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than a scorpion.

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- Oh. Anything?
- Here?

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I don't think so.

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My first childhood
memory of the scorpion,

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I was, uh, ten years old
and I see this big scorpion.

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I screamed "Mom!"

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Uh, so she came to my aid

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and she was like, "What? What happened?"

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And I point to the
scorpion, uh, on the ceiling,

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I said, "That's gonna eat me."

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And she was just like, "No, come
on. Be cool. This is just a scorpion."

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So, as a cute Mexican mother,

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she took, uh... her sandal

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and just smashed the, uh,
little bastard on the ceiling.

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Carlos Santibáñez-López is
now an expert on scorpions,

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specializing in the
study of their venom.

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I go at night and I use the UV light,

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because UV light makes scorpions glow.

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They have a special
protein in their shell.

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Yeah, let's... Let's
take a look at this one.

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- Oh, look at this!
- There's a lot of them.

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Yeah, this is great.

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Scorpions have barely
changed in 400 million years.

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Perfectly adapted
for life in the desert.

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Scorpions have a very slow metabolism.

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They can spend long
periods without food or water.

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We have records of some
species lasting one year

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without eating anything.

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And they have just enough energy

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to sustain essential
functions to keep them alive.

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They need to ensure that
the next time food is available,

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they catch it.

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So, scorpions have developed a lot of
weapons that they can use to hunt prey,

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including the most important weapon...

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venom.

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To study scorpion venom,

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Carlos needs to extract
it from glands in the tail.

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00:22:18,720 --> 00:22:25,240
Venom is a powerful cocktail
that contains minerals, salts

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00:22:25,320 --> 00:22:29,120
and hundreds of proteins
with a different function.

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00:22:30,240 --> 00:22:32,400
Try to be as fast as you can.

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There you go.

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We use electricity to
stimulate the muscles.

224
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We're only gonna get
small... very small amounts,

225
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a teeny, tiny drop of it.

226
00:22:46,240 --> 00:22:50,040
But this drop is so valuable
that we don't wanna lose it.

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Give him a nice massage.

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Yeah. There's a tiny droplet.

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- There.
- Oh, yes, it's... Okay, so it's working.

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Uh, we have venom.

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It is right there, but
it's a teeny, tiny drop.

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- Uh... do you see it?
- That's right. Yeah.

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I mean, it's... it's like
a... a drop of water.

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Venom is such an effective weapon,

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it's used by reptiles, insects and fish.

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00:23:30,320 --> 00:23:34,600
It has evolved, separately,
at least 30 times.

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The more often a trait like
venom has evolved on Earth,

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the more likely it is to
exist on other planets.

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On the hot side of Janus,

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pentapods use venom to catch their prey.

241
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But hunting alone is risky.

242
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Even a venomous predator is powerless

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against a swarm.

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On the cold side of the
planet, things are just as tough.

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In perpetual darkness and
with no energy from the sun...

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00:25:09,920 --> 00:25:12,000
how can anything survive?

247
00:25:22,320 --> 00:25:26,520
On Earth, nearly all
life depends on sunlight.

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00:25:29,680 --> 00:25:32,760
Plants convert solar energy into food,

249
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which feeds other life forms.

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But there are some
extraordinary places on Earth

251
00:25:42,480 --> 00:25:46,120
where life has evolved
without any light.

252
00:25:57,040 --> 00:25:59,760
When I contemplate
going in a cave like this,

253
00:25:59,840 --> 00:26:03,200
one of the things I know
is it's an alien environment.

254
00:26:03,280 --> 00:26:05,360
- It's fogging up a little bit.
- Yeah.

255
00:26:05,440 --> 00:26:08,000
It is full of good ways to die.

256
00:26:09,160 --> 00:26:14,760
One of the big risks in this cave
is there is a lot of hydrogen sulfide.

257
00:26:15,960 --> 00:26:17,920
Hydrogen sulfide can kill you.

258
00:26:18,000 --> 00:26:19,640
- Okay. You ready?
- Yeah.

259
00:26:19,720 --> 00:26:24,080
And so my husband comes
along to act as a safety officer.

260
00:26:26,080 --> 00:26:30,760
He's not afraid to pull us out and
say, "Time to go, you've had enough."

261
00:26:49,040 --> 00:26:53,400
Cueva de Villa Luz is a
maze of limestone chambers.

262
00:26:57,680 --> 00:27:01,920
Hydrogen sulfide bubbles
up from the Earth's crust.

263
00:27:04,160 --> 00:27:10,400
Mixing with oxygen, it forms sulfuric
acid and turns the water milky white.

264
00:27:13,720 --> 00:27:16,960
And yet, some life forms survive,

265
00:27:17,520 --> 00:27:20,080
and even thrive in these conditions.

266
00:27:25,600 --> 00:27:26,840
Snottites...

267
00:27:30,280 --> 00:27:32,800
dripping colonies of bacteria.

268
00:27:38,040 --> 00:27:42,040
There are a lot of
organisms in one snottite.

269
00:27:44,080 --> 00:27:46,880
Instead of relying on photosynthesis,

270
00:27:47,520 --> 00:27:50,960
they are eating hydrogen sulfide

271
00:27:52,160 --> 00:27:55,680
and are using it as their energy source.

272
00:28:01,000 --> 00:28:03,280
- Okay, ready to flame?
- Yep.

273
00:28:04,280 --> 00:28:06,200
So, make it nice and sterile.

274
00:28:07,480 --> 00:28:09,560
Okay, cap that, please.

275
00:28:13,800 --> 00:28:15,640
Okay, let's go for this one.

276
00:28:16,400 --> 00:28:17,360
Okay.

277
00:28:18,400 --> 00:28:20,680
Okay. One snottite.

278
00:28:23,520 --> 00:28:26,240
These are some of the
best snottites in the world.

279
00:28:27,200 --> 00:28:28,280
So acidic.

280
00:28:29,080 --> 00:28:31,720
More acidic than car battery acid.

281
00:28:36,400 --> 00:28:39,280
An entire ecosystem has evolved

282
00:28:40,040 --> 00:28:42,200
to feed off the snottites.

283
00:28:44,440 --> 00:28:47,240
Creatures that have never seen daylight.

284
00:28:55,160 --> 00:28:56,160
Can you see those?

285
00:28:58,120 --> 00:28:59,360
Yes, I do.

286
00:29:00,360 --> 00:29:03,560
So, there's some really big
ones over here to the right.

287
00:29:05,040 --> 00:29:09,600
So, whenever you see one of
those white streamers of bacteria,

288
00:29:10,320 --> 00:29:12,200
you'll see a fish go after it.

289
00:29:13,840 --> 00:29:17,680
Okay, here comes some more over
there. See? Here comes a big one, see?

290
00:29:18,360 --> 00:29:20,920
It's coming. There, it got it!

291
00:29:24,960 --> 00:29:28,080
Studying life in total darkness

292
00:29:28,160 --> 00:29:33,920
has expanded how we look for
life in other places in the universe.

293
00:29:34,440 --> 00:29:36,600
It's made us think about the fact

294
00:29:36,680 --> 00:29:40,640
that we could find life in
places we never considered.

295
00:29:42,680 --> 00:29:44,320
- Yep, there we go.
- 25.

296
00:29:44,400 --> 00:29:47,200
25. It's getting pretty high.

297
00:29:47,280 --> 00:29:48,240
All right.

298
00:29:48,320 --> 00:29:50,240
You think we ought to get out of here?

299
00:29:50,320 --> 00:29:51,280
Yeah.

300
00:30:04,880 --> 00:30:07,800
All life needs some form of energy.

301
00:30:10,040 --> 00:30:13,920
On the hot face of Janus,
it comes from starlight.

302
00:30:17,680 --> 00:30:21,920
On the cold face, it
comes from deep within.

303
00:30:29,000 --> 00:30:31,320
Geothermal activity.

304
00:30:35,720 --> 00:30:39,560
When volcanic pressure
forces water to the surface,

305
00:30:40,520 --> 00:30:42,760
there's a flurry of new life...

306
00:30:45,120 --> 00:30:47,800
which stirs pentapods into action.

307
00:31:01,560 --> 00:31:05,800
They're after grubs that
emerge around geothermal pools.

308
00:31:10,240 --> 00:31:11,640
But it's not so easy.

309
00:31:17,800 --> 00:31:20,200
The grubs have evolved a defense.

310
00:31:21,240 --> 00:31:24,640
They jump and flash a
warning signal to others...

311
00:31:27,320 --> 00:31:29,880
acting as one to stay alive.

312
00:31:46,120 --> 00:31:50,360
On Earth, some animals
use light in the same way...

313
00:31:51,120 --> 00:31:53,040
to send signals.

314
00:32:01,520 --> 00:32:05,080
Every single point of light that
you see out there is a firefly.

315
00:32:07,160 --> 00:32:10,080
Right as the sun sets, you'll
start to see them come up,

316
00:32:11,240 --> 00:32:13,120
like little sparks rising from a fire.

317
00:32:13,200 --> 00:32:16,760
It's just spectacular, and it only
gets better as the night gets darker.

318
00:32:26,080 --> 00:32:28,680
Fireflies flash as a
form of communication.

319
00:32:29,720 --> 00:32:32,760
They are among the only land animals

320
00:32:32,840 --> 00:32:35,440
that communicate with
light of their own making.

321
00:32:39,280 --> 00:32:42,760
Bioluminescence evolved among fireflies

322
00:32:42,840 --> 00:32:44,600
as a warning to predators

323
00:32:45,320 --> 00:32:50,240
that they're packed with toxins
and should be given a wide berth.

324
00:32:53,840 --> 00:32:55,200
Now the same mechanism

325
00:32:55,840 --> 00:32:58,000
is used for finding a mate.

326
00:33:01,720 --> 00:33:07,480
So, the firefly produces light from an
organ on its abdomen called the lantern.

327
00:33:08,280 --> 00:33:11,000
And this organ has an enzyme

328
00:33:11,080 --> 00:33:13,160
that produces one photon of light.

329
00:33:13,240 --> 00:33:15,000
This chemical reaction involves oxygen.

330
00:33:15,080 --> 00:33:18,400
So, by controlling the flow
of oxygen to their lantern,

331
00:33:18,480 --> 00:33:20,760
they can produce, uh, flashes.

332
00:33:20,840 --> 00:33:22,920
They can turn the
chemical reaction on and off,

333
00:33:23,000 --> 00:33:27,000
and use these flashes to
communicate with each other.

334
00:33:35,520 --> 00:33:39,720
The males are flying around, and
they're doing little advertisements,

335
00:33:39,800 --> 00:33:43,160
little flashes that say, "Here I
am. This is me, check me out."

336
00:33:46,040 --> 00:33:49,360
And then the females are waiting on
the ground below and they're looking up.

337
00:33:51,520 --> 00:33:54,720
And when they see a guy
that they like, they flash back.

338
00:33:57,840 --> 00:34:00,400
And then the male will
come over, he'll flash again.

339
00:34:00,480 --> 00:34:03,080
She flashes back and they
come together and mate.

340
00:34:04,160 --> 00:34:08,400
So, this is actually
one big flirtatious dance

341
00:34:08,480 --> 00:34:10,600
that we're seeing right here behind us.

342
00:34:13,440 --> 00:34:16,000
Each species creates
its own little language

343
00:34:16,080 --> 00:34:18,080
that they can use to find
each other in the dark.

344
00:34:20,320 --> 00:34:24,440
But using light to
communicate is inherently risky.

345
00:34:26,440 --> 00:34:31,200
Some species have
evolved to emit fake signals.

346
00:34:34,920 --> 00:34:39,720
What we have here is a
predatory Photuris female,

347
00:34:39,800 --> 00:34:43,040
also called femmes fatales,
because they have a reputation

348
00:34:43,120 --> 00:34:46,800
for luring in males of
other species to eat them.

349
00:34:47,720 --> 00:34:52,560
They can hack in to the communication
between a male and a female

350
00:34:52,640 --> 00:34:54,600
and use that to her advantage.

351
00:34:56,320 --> 00:34:59,120
So, you can tell this
is a predatory firefly

352
00:34:59,200 --> 00:35:02,600
because her lantern
has a different shape to it.

353
00:35:03,640 --> 00:35:07,800
Only two... two little lines light
up, almost like an equals sign.

354
00:35:08,520 --> 00:35:12,160
So, basically, a male will be
flying around looking for a mate

355
00:35:12,240 --> 00:35:15,120
and then when the males
flash, they flash back,

356
00:35:15,200 --> 00:35:17,920
just as if they were a
female of that species.

357
00:35:18,000 --> 00:35:20,520
So, they're imitating the
females of that other species

358
00:35:20,600 --> 00:35:22,240
to get the male to come over,

359
00:35:22,320 --> 00:35:24,280
but they don't wanna
mate with that male...

360
00:35:25,400 --> 00:35:27,800
she wants to eat that male.

361
00:35:30,400 --> 00:35:34,480
And she proceeds to do so
in an extremely violent way.

362
00:35:39,360 --> 00:35:43,880
This is a classic example
of a predator using mimicry.

363
00:35:48,120 --> 00:35:51,480
One species copying
the behavior of another...

364
00:35:52,840 --> 00:35:54,720
in order to kill it.

365
00:35:58,960 --> 00:36:00,480
Lying and deceit is...

366
00:36:00,560 --> 00:36:03,520
is pretty widespread in the
animal kingdom, I would say.

367
00:36:04,720 --> 00:36:07,720
And I think it would be on any planet.

368
00:36:23,080 --> 00:36:27,000
On Janus, the grubs
use light to stay alive.

369
00:36:32,040 --> 00:36:35,240
But their system is about to be hacked.

370
00:36:47,040 --> 00:36:52,600
By catching a few grubs, the
pentapods absorb their bioluminescence...

371
00:36:56,120 --> 00:36:58,400
and mimic their warning signals.

372
00:37:04,640 --> 00:37:08,680
The grubs instinctively jump
away from flashing lights.

373
00:37:10,520 --> 00:37:12,600
But this time, it's a trap.

374
00:37:15,840 --> 00:37:19,000
The pentapods have
them where they want them.

375
00:37:24,120 --> 00:37:29,200
Again, adaptability is
the secret to their survival.

376
00:37:42,440 --> 00:37:44,600
But for all creatures on Janus,

377
00:37:45,400 --> 00:37:49,200
existence depends
on one key ingredient...

378
00:37:53,000 --> 00:37:56,840
whether in the hot,
cold or twilight worlds.

379
00:37:59,920 --> 00:38:01,080
Water.

380
00:38:20,240 --> 00:38:23,640
Everybody knows the story of
Goldilocks and the Three Bears.

381
00:38:26,440 --> 00:38:29,880
She sneaks into their house
and tries to eat their porridge.

382
00:38:33,640 --> 00:38:35,480
The first bowl is too hot.

383
00:38:39,680 --> 00:38:41,840
The second bowl is freezing cold.

384
00:38:46,440 --> 00:38:49,720
It's only when she tries the
third bowl that she's happy.

385
00:38:54,840 --> 00:38:58,480
"This one," Goldilocks
says, "is just right."

386
00:39:01,160 --> 00:39:04,120
When we look around the
universe in the search for life,

387
00:39:04,200 --> 00:39:07,360
we are looking for
conditions that are "just right."

388
00:39:13,640 --> 00:39:15,760
And "just right," in this case,

389
00:39:16,600 --> 00:39:19,080
is defined by the
presence of this stuff.

390
00:39:20,280 --> 00:39:21,400
Water.

391
00:39:27,680 --> 00:39:32,120
Water transports the essentials
for life around the planet

392
00:39:34,760 --> 00:39:37,000
and around every living body.

393
00:39:41,440 --> 00:39:45,120
It's the most important
substance in the universe.

394
00:39:52,960 --> 00:39:54,800
Because water is so familiar to us,

395
00:39:54,880 --> 00:40:00,360
it's not until you really stop and think
about it that you realize how weird it is.

396
00:40:00,440 --> 00:40:03,320
Water is made up by one oxygen atom...

397
00:40:05,440 --> 00:40:07,320
and two hydrogen atoms.

398
00:40:08,160 --> 00:40:11,600
And because of the nature of the
elements and the way they're bound,

399
00:40:11,680 --> 00:40:15,000
we have a net negative
charge at the oxygen side

400
00:40:15,080 --> 00:40:16,960
and positive on the two hydrogens.

401
00:40:17,040 --> 00:40:19,440
This means that every
hydrogen in a molecule

402
00:40:19,520 --> 00:40:22,880
can interact with the oxygen on
the other molecules neighboring.

403
00:40:23,680 --> 00:40:27,400
Replicate this attraction for
billions of neighboring molecules

404
00:40:27,480 --> 00:40:29,400
and you get a substance
that is very sticky.

405
00:40:31,800 --> 00:40:34,640
And water molecules
don't just attract each other,

406
00:40:34,720 --> 00:40:38,200
they attract almost any other
molecule they come in contact with.

407
00:40:41,040 --> 00:40:43,280
They pull other substances apart,

408
00:40:43,960 --> 00:40:46,480
break them down, and dissolve them.

409
00:40:59,520 --> 00:41:02,320
Water is the universal solvent

410
00:41:03,440 --> 00:41:07,600
because of its unique ability to
dissolve nutrients and chemicals.

411
00:41:15,840 --> 00:41:21,680
It seems certain the first spark of
life on Earth happened not on land...

412
00:41:24,040 --> 00:41:25,560
but in water.

413
00:41:31,640 --> 00:41:34,200
Deep underwater, in
the primordial oceans,

414
00:41:34,280 --> 00:41:37,560
the chemical ingredients
for life were swirling around.

415
00:41:40,400 --> 00:41:43,840
What was needed was a place
to concentrate these ingredients...

416
00:41:45,920 --> 00:41:49,560
to allow the chemical reaction
that would eventually lead to life.

417
00:41:52,440 --> 00:41:55,880
That place could have
been a hydrothermal vent.

418
00:41:59,800 --> 00:42:03,120
Water interacts with hot
rocks deep underground.

419
00:42:04,120 --> 00:42:07,200
It comes gushing back up
into the freezing seawater

420
00:42:07,280 --> 00:42:09,280
carrying nutrients and chemicals...

421
00:42:11,360 --> 00:42:13,320
little bubbles of life.

422
00:42:17,440 --> 00:42:21,000
The link between water
and life is so strong,

423
00:42:21,920 --> 00:42:26,320
it's hard to imagine any
life anywhere in the universe

424
00:42:26,400 --> 00:42:28,400
existing without it.

425
00:42:37,520 --> 00:42:39,040
It's mind-boggling to think,

426
00:42:39,120 --> 00:42:42,520
you know, how life can find
a way in very extreme places.

427
00:42:42,600 --> 00:42:43,800
Very hot, very cold.

428
00:42:44,200 --> 00:42:46,480
And at the end, it's
all about the water.

429
00:42:46,560 --> 00:42:49,000
If there's liquid
water, you'll find life.

430
00:43:00,120 --> 00:43:02,880
Water on Janus is scarce.

431
00:43:05,840 --> 00:43:08,160
It either freezes as ice...

432
00:43:11,240 --> 00:43:13,480
or evaporates into the wind.

433
00:43:18,240 --> 00:43:20,760
But there's just enough liquid water

434
00:43:21,320 --> 00:43:23,120
for life to take hold...

435
00:43:26,320 --> 00:43:28,840
and for the toughest of creatures

436
00:43:29,440 --> 00:43:31,760
to adapt and survive.

437
00:43:42,640 --> 00:43:44,920
At NASA, they have a saying.

438
00:43:46,240 --> 00:43:48,240
"If you want to find life...

439
00:43:48,880 --> 00:43:50,600
follow the water."

440
00:43:59,760 --> 00:44:03,080
How might life adapt
on a different world?

441
00:44:04,520 --> 00:44:06,440
One with two stars,

442
00:44:09,480 --> 00:44:12,200
where there's more energy than on Earth.

443
00:44:15,800 --> 00:44:19,400
A planet perfect for life.