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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 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, then the universe must be alive.

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All living things have the same needs to feed, reproduce and evolve.

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By applying the laws of life on Earth to the rest of the universe, it's possible to imagine what could live on alien worlds.

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Most planets we know of are so hellish, 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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This is the most incredible place I've ever seen.

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This is what I dream other planets looking like. It's incredible.

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So, yeah.

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The Danakal 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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Now, what's 79C? 82C? This one's topping out at 87.

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If life can exist here, it could exist on any number of worlds in the universe.

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Life on other planets, they're going to have chemistry, whether it looks exactly like ours, we don't know.

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But they're going to have chemistry that helps them live and that chemistry is going to be subject to limits.

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For example, our life is made up of cells.

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Inside these cells, we have biomolecules 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 that keeps life living.

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And so we really want to understand how that machinery works and what's going to make that machinery break down.

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Until recently, it was assumed Danakal 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, so it's not going to be as simple as taking a little bit of water out of a lake 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 is to find traces of their DNA using a portable genetic sequencer.

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This is a very small device and it's very substantive to temperature. 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 to kind of keep it cool.

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And we have our channels running.

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And we have sequencing. We actually have sequencing happening. We have DNA in here. Excellent.

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Sequencing of DNA is proof that extremophiles can survive in the acidic waters of Danakal.

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These guys are like the superheroes of microbes and it's just amazing as we learn more and more about the different strategies and mechanisms that they come up with to survive these kinds of environments.

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Finding things alive here opens up an intriguing possibility that some life forms are tough enough to survive anywhere, 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, 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. A searing desert.

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On the other side, it's forever night. A frozen shadow land.

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Squeezed between the two, a sliver of perpetual twilight.

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Freezing meltwater flows from the cold side, carving canyons through the landscape.

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Even here, where the planet's most hospitable, there's little vegetation.

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But deep in these canyons lives an extraordinary five-legged creature. A pentapod.

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No bigger than a cat, it's the dominant life form on Janus, capable of adapting to any conditions.

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On the cold side, 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, 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, it's a beautifully manicured trail.

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And you would think it was made by some bigger animal, or maybe even the human.

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But it's actually made by ants.

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It's a leaf cutter ant in particular.

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It's a leaf cutter ant.

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It's a leaf cutter ant in particular.

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It all looks quiet right now, but if we come back at night, this will actually turn into an ant's superhighway,

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with leaves just streaming up towards their nest.

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Oh wow, 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, there's a lot going on.

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

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There's 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 labour.

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

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I just grabbed one of the soldiers, and I also grabbed the really, really small worker.

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It's not the smallest worker in this colony, but it's pretty close.

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The soldiers I barely can hold her, it's really hard.

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I can feel her power, I can feel, she's trying to get out, her jaws are wide open.

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But the difference is incredible, and to think that they all started from 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, 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, 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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It's something that disturbs the colony.

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

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But, wow.

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Ah!

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Alright, I'm already being attacked.

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Oh, that's gonna hurt.

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Yeah, now, come and find me.

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So any creature that has this ability to morph 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, but actually dominate its world.

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So, what do you think?

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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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Hermafrodites.

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Each can produce offspring, 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 be fed.

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And the rest of the animals are ready to be fed.

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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, not much escapes their attention.

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If they sense a meal, 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 nordeal.

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Only the tough survive.

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And in the natural world, there's nothing much tougher than a scorpion.

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I don't think so.

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My first childhood memory of the scorpion, I was ten years old,

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and I see this big scorpion.

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It's a little bit like a scorpion.

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It's a little bit like a scorpion.

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It's a little bit like a scorpion.

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

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I scream, Mom.

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So she came to my aid, and she was like, What? What happened?

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And I point the scorpion on the ceiling, and I said, That's gonna eat me.

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And she's like, No, come on, be cool. This is just a scorpion.

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So, as a cute Mexican mother, she took her sound to the ground.

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And she just smashed the little bastard on the ceiling.

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Carlos Santibanez Lopez 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 take a look at this one.

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Oh, look at this.

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That'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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They're 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 without eating anything.

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And they have just enough energy to sustain essential functions to keep them alive.

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They need to assure that the next time food is available, they catch it.

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

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including the most important weapon, 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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Venom is a powerful cocktail that contains minerals, salts,

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and hundreds of proteins with a different function.

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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.

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We're only going to get a small, very small amount, a teeny tiny drop of it.

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But this drop is so valuable that we don't want to lose it.

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Give him a nice massage.

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Yeah, use a tiny drop.

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Oh yes, it's working. We have a venom.

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

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You see it? It's like 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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It has evolved separately, at least 30 times as much as it used to.

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It's a very powerful weapon.

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It's a very powerful weapon.

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It's a very powerful weapon.

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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.

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But hunting alone is risky.

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Even a venomous predator is powerless 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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how can anything survive?

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On Earth, nearly all life depends on sunlight.

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Plants convert solar energy into food,

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which feeds other life forms.

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But there are some extraordinary places on Earth

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where life has evolved without any light.

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When I contemplate going in a cave like this,

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one of the things I know is that it's an alien environment.

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It is full of good ways to die.

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One of the big risks in this cave is there is a lot of hydrogen sulfide.

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Hydrogen sulfide can kill you.

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And so my husband comes along to act as a safety officer.

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He's not afraid to pull us out and say,

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time to go, you've had enough.

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Kuweva de Villaluz.

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Kuweva de Villaluz is a maze of limestone chambers.

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Hydrogen sulfide bubbles up from the Earth's crust.

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Mixing with oxygen, it forms sulfuric acid

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and turns the water milky white.

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And yet, some life forms survive and even thrive in these conditions.

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Snotite.

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Dripping colonies of bacteria.

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There are a lot of organisms in one snotite.

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Instead of relying on photosynthesis,

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they are eating hydrogen sulfide

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and are using it as their energy source.

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Okay, ready to flame?

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Yep.

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So make it nice and sterile.

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Okay, can I cap that please?

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Okay, let's go for this one.

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Okay.

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Okay.

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Okay.

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Okay.

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Okay.

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Okay.

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Okay.

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Okay.

226
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Okay.

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Okay.

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Okay.

229
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Okay.

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Okay.

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Okay.

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Okay.

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Okay.

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One snotite.

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These are some of the best snotites in the world.

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So acidic, more acidic than carb battery acid.

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An entire ecosystem has evolved to feed off the snotites.

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Creatures that have never seen daylight.

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Can you see those?

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Yes, I do.

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So there's some really big ones over here to the right.

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So whenever you see one of those white streamers of bacteria,

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you'll see a fish go after it.

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Okay, here comes some more over there.

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See?

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00:29:15,800 --> 00:29:16,800
Here comes a big one.

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00:29:16,800 --> 00:29:17,800
See?

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It's coming.

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00:29:18,800 --> 00:29:20,800
There, got it.

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Studying life in total darkness has expanded how we look for life

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in other places in the universe.

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It's made us think about the fact that we could find life in places we never considered.

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There we go.

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25.

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25.

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It's getting pretty high.

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All right.

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Do you think we ought to get out of here?

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00:29:49,800 --> 00:29:50,800
Yeah.

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

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00:30:09,800 --> 00:30:13,800
On the hot face of Janus, it comes from starlight.

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On the cold face, it comes from deep within.

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Geothermal activity.

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When volcanic pressure forces water to the surface, there's a flurry of new life,

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which stirs pentapods into action.

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There are some new life forms.

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They're after grubs that emerge around geothermal pools,

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but it's not so easy.

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The grubs have evolved a defense.

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They jump and flash a warning signal to others,

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acting as one to stay alive.

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The grubs are now in the air.

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They're in the air.

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They're in the air.

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They're in the air.

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They're in the air.

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They're in the air.

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And there's one to stay alive.

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On Earth, some animals use light in the same way.

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To send signals.

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Every single point of light that you see out there is a firefly.

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Right as the sun sets, you'll start to see them come up.

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Like little sparks rising from a fire.

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It's just spectacular.

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And then only gets better as the night gets darker.

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Fireflies flash as a form of energy.

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They're a communication.

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They are among the only land animals

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that communicate with light of their own making.

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Bioluminescence evolved among fireflies as a warning to predators

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that they're packed with toxins and should be given a wide berth.

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Now the same mechanism is used for finding a mate.

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So the firefly produces light from an organ on its abdomen called the lantern.

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And this organ has an enzyme that produces one photon of light.

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This chemical reaction involves oxygen.

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So by controlling the flow of oxygen to their lantern,

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they can produce a single photon of light.

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And by using oxygen to their lantern, they can produce flashes.

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They can turn the chemical reaction on and off

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and use these flashes to communicate with each other.

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The males are flying around and they're doing little advertisements,

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little flashes that say, here I am, this is me, check me out.

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And then the females are waiting on the ground below and they're looking up.

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And when they see a guy that they like, they flash back.

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And then the male will come over, he'll flash again, she flashes back,

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and they come together and mate.

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So this is actually one big flirtatious dance that we're seeing right here behind us.

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Each species creates its own little language that they can use to find each other in the dark.

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But using light to communicate is inherently risky.

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Some species have evolved to emit fake signals.

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What we have here is a predatory, futurist female, also called femme fatale,

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because they have a reputation for luring in males of other species to eat them.

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They can hack into the communication between a male and a female and use that to her advantage.

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So you can tell this is a predatory firefly because her lantern has a different shape to it.

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Only two little lines light up, almost like an equal sign.

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So basically a male will be flying around looking for a mate,

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00:35:11,800 --> 00:35:17,800
and then when the males flash, they flash back just as if they were a female of that species.

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00:35:17,800 --> 00:35:21,800
So they're imitating the females of that other species to get the male to come over.

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But they don't want to mate with that male.

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She wants to eat that male.

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And she proceeds to do so in an extremely violent way.

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This is a classic example of a predator using mimicry.

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One species copying the behavior of another in order to kill it.

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Lying in the sea is pretty widespread in the animal kingdom, I would say.

325
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And I think it would be on any planet.

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On Janus, the grubs use light to stay alive.

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But their system is about to be hacked.

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By catching a few grubs, the pentapods absorb their bioluminescence

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and mimic their warning signals.

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00:36:58,800 --> 00:37:03,800
The grubs instinctively jump away from flashing lights.

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00:37:04,800 --> 00:37:09,800
But this time, it's a trap.

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00:37:09,800 --> 00:37:14,800
The pentapods have them where they want them.

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00:37:15,800 --> 00:37:20,800
Again, adaptability is the secret to their survival.

334
00:37:30,800 --> 00:37:36,800
But for all creatures on Janus, the grubs are not the only ones who can do it.

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They are the ones who can do it.

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Existence depends on one key ingredient.

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Whether in the hot, cold or twilight worlds.

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Water.

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00:38:15,800 --> 00:38:20,800
Everybody knows the story of Goldilocks and the three bears.

340
00:38:22,800 --> 00:38:27,800
She sneaks into their house and tries to hit their porridge.

341
00:38:30,800 --> 00:38:33,800
The first ball is too hot.

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00:38:36,800 --> 00:38:40,800
The second ball is freezing cold.

343
00:38:45,800 --> 00:38:50,800
It's only when she tries the third ball that she's happy.

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This one, Goldilocks says, is just right.

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00:39:00,800 --> 00:39:07,800
When we look around the universe in the search for life, we are looking for conditions that are just right.

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00:39:08,800 --> 00:39:14,800
And just right in this case, is defined by the presence of this stuff.

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Water.

348
00:39:22,800 --> 00:39:27,800
Water transports the essentials for life around the planet.

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And around every living body.

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It's the most important substance in the universe.

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Because water is so familiar to us, it's not until you really stop and think about it that you realize how weird it is.

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Water is made up by one oxygen atom and two hydrogen atoms.

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And because of the nature of the elements and the way they're bound, we have a net negative charge at the oxygen side and positive on the two hydrogen.

354
00:40:15,800 --> 00:40:22,800
This means that every hydrogen in a molecule can interact with the oxygen on the other molecules neighboring.

355
00:40:22,800 --> 00:40:30,800
And that's why we have to replicate this attraction for billions of neighboring molecules and you get a substance that is very sticky.

356
00:40:31,800 --> 00:40:38,800
And water molecules don't just attract each other, they attract to almost any other molecule they come in contact with.

357
00:40:40,800 --> 00:40:46,800
They pull other substances apart, break them down and dissolve them.

358
00:40:53,800 --> 00:41:01,800
Water is the universal solvent because of its unique ability to dissolve nutrients and chemicals.

359
00:41:13,800 --> 00:41:19,800
It seems certain the first spark of life on Earth happened not on land.

360
00:41:19,800 --> 00:41:23,800
But in water.

361
00:41:29,800 --> 00:41:36,800
Deep underwater in the primordial oceans, the chemical ingredients for life were swirling around.

362
00:41:37,800 --> 00:41:42,800
What was needed was a place to concentrate these ingredients.

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00:41:43,800 --> 00:41:48,800
To allow the chemical reaction that would eventually lead to life.

364
00:41:50,800 --> 00:41:55,800
That place could have been a hydrothermal vent.

365
00:41:58,800 --> 00:42:08,800
Water interacts with hot rocks deep underground and comes gushing back up into the freezing sea water carrying nutrients and chemicals.

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Little bubbles of life.

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00:42:16,800 --> 00:42:20,800
The link between water and life is so strong.

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00:42:21,800 --> 00:42:27,800
It's hard to imagine any life anywhere in the universe existing without it.

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00:42:28,800 --> 00:42:33,800
It's mind-boggling to think how life can find a way in very extreme places.

370
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Very hot, very cold.

371
00:42:35,800 --> 00:42:37,800
And at the end is all about the water.

372
00:42:37,800 --> 00:42:40,800
If there's liquid water, you'll find life.

373
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Water on Janus is scarce.

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00:43:04,800 --> 00:43:07,800
It either freezes as ice,

375
00:43:10,800 --> 00:43:13,800
or evaporates into the wind.

376
00:43:17,800 --> 00:43:22,800
But there's just enough liquid water for life to take hold.

377
00:43:23,800 --> 00:43:30,800
And for the toughest of creatures to adapt and survive.

378
00:43:41,800 --> 00:43:44,800
At NASA, they have a saying,

379
00:43:44,800 --> 00:43:49,800
if you want to find life, follow the water.

380
00:43:53,800 --> 00:43:58,800
How might life adapt on a different world?

381
00:43:59,800 --> 00:44:01,800
One with two stars.

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00:44:04,800 --> 00:44:08,800
Where there's more energy than on Earth.

383
00:44:11,800 --> 00:44:15,800
A planet perfect for life.

384
00:44:52,800 --> 00:44:55,800
NASA

385
00:45:22,800 --> 00:45:25,800
You