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(stimulating orchestral music)

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Today, the advent of cutting-edge

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observational instruments is shedding light

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on amazing facts about life and the universe.

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In this first of two episodes,

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we'll explore an alien planet that is filled with life.

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Where is that planet?

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Far beyond our solar system.

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A location that astronomers

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previously paid little attention to.

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Near the kind of star that is most common

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in the universe: a red dwarf.

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Planets revolving around such stars

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may be the best candidates for hosting alien life.

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In particular, to try to find small planets

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transiting small red dwarf stars,

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planets that might of the kind to host life.

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On this planet,

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what is natural on Earth does not apply.

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Strange trees grow on the land, drenched with red light.

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Half the planet is in perpetual light ...

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the other half locked in an endless, icy darkness.

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But planets like this are still likely to host life.

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And life on these worlds has had much more time

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to develop than on Earth.

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There may be lifeforms that have evolved far beyond us.

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(creature growling)

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If there are intelligent beings over there,

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it's a great perk to be living on such a planet.

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(rocket rumbling)

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To further the search for planets hosting life,

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NASA launched a new space telescope and began observations.

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Among these myriad stars,

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are any of them home to extraterrestrials?

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In this episode, we'll explore an alien planet

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overflowing with life.

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(mysterious string music)

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In late 2017, the world's scientific community

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was excited by the discovery

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of a mysterious object in space.

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The UFO whipped across the night sky at a furious speed.

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It was dubbed Oumuamua, a Hawaiian word

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meaning "first messenger from afar."

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Observations showed that it was about 400 meters in length,

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with the long, narrow dimensions of a cigar.

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No asteroid of this shape had ever been observed before.

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What in the world was this strange object?

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Astronomers throughout the world

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tried to determine the nature of Oumuamua.

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One of these scientists was Abraham Loeb

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of Harvard University.

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The properties of Oumuamua are very different

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from the properties of asteroids and comets.

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Asteroids and comets that come close to Earth

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move in orbits that lie within the solar system.

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But Oumuamua was different.

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Using its speed to calculate its flight path

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revealed that it came from outside the solar system.

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This was the first time that humanity

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had encountered a visitor from interstellar space.

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Moreover, as Oumuamua approached the sun,

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it experienced a mysterious acceleration.

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In the case of a comet, the extra push

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comes from the evaporation of ice on the surface of the rock

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that creates out-gassing that is pushing on the rock

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and giving it an extra acceleration.

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But in the case of Oumuamua,

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we didn't detect any gases around the object.

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And, moreover, we didn't see

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any cometary tail of dust behind it.

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Oumuamua did not produce a comet's gas trail.

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So, how did it accelerate?

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After making his calculations,

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Loeb reached a rather incredible hypothesis.

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And so, the questions is whether it could be artificial

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and some other civilization was using light sails

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to produce spacecrafts that are floating in space

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for some purpose, and this is one of them.

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While most astronomers believe

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it is a natural body, Loeb argued that it was

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an artificial object made by aliens, or could be.

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And its mysterious acceleration can be explained

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by imagining a space yacht powered by the light of the sun.

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There is a reason Loeb made his hypothesis.

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Astronomy has recently opened up new frontiers

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in the search for life in the universe.

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Over the past decade or so, there was a revolution

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in our understanding of the abundance of planets.

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We now know that almost every star

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has a planet like the Earth.

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These frontiers lie

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far beyond our solar system.

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The stars that shine in our night sky

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burn and emit light of their own, just as our sun does.

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We now know that planets orbit these stars.

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These are called exoplanets, and astronomical observation

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is increasingly finding evidence of their existence.

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If there are planets around each and every star we see,

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there could be a trillion planets in our galaxy,

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the Milky Way.

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Life in some form is thought to exist

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on an untold number of these worlds.

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Most astronomers now believe

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that extraterrestrial life does exist.

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My basic premise is modest.

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Out of modesty, I believe that we

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are not unique and not special.

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And so, if you roll the dice billions of times

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in the Milky Way galaxy, surely there's a good chance

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that what we see here on Earth will be reproduced.

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From the time we humans first entered space,

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we've been searching for extraterrestrial life.

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We've explored numerous planets

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and moons in our solar system

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but have yet to find any trace of life.

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But extraterrestrial life must exist somewhere.

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Some 40 years ago, a young girl

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became entranced by that dream.

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From the first time her father took her star gazing,

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Sara Seager would never forget the sight of the stars

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in the heavens, away from the city lights.

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(gentle orchestral music)

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She wondered, "Somewhere among those stars

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"there must be someone like me

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"gazing at the glittering sky."

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Carrying this thought with her, Seager became an astronomer.

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She now leads a major project

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that hopes to find a yet undiscovered planet

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teeming with life.

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Why are we here?

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Why does our universe exist?

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How did Earth form and evolve?

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How and why did life originate and populate our planet?

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The second question that we often think about

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is are we alone?

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Is there life out there?

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I'm here to tell you just how close we're getting

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to finding out the answer to this question.

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It's the first time in human history

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that this really is within reach for us.

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This space telescope, TESS,

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is assisting Seager's search for life in the universe.

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And I can guarantee that, in the next generation

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of space telescopes, and the second generation,

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we will have the capability to find

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and identify other Earths.

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And so, I envision that our descendants

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hundreds of years from now will embark

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on an interstellar journey to other worlds,

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and they will look back at all of us

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as the generation who first found the Earth-like worlds.

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Thank you.

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(audience applauding)

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Seager spent 20 years

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working to realize her vision.

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She wanted to build a space telescope

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to search for other Earths outside the solar system.

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(soft orchestral music)

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As a graduate student, Seager studied physics.

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During that time, a major discovery

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helped to determine the course of her life.

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In 1995, news broke of a momentous event.

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Far outside the solar system,

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in the direction of the constellation Pegasus,

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a planet was discovered revolving around a star.

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(stirring orchestral music)

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At that time, no one expected that planets

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beyond the solar system could be detected,

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so this was an astonishing development.

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The discovery was later recognized with a Nobel Prize.

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Moreover, the planet was revolving around a star

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about the same size as our sun.

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This discovery spurred astronomers around the world

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to search for planets outside the solar system.

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To date, more than 4,000 such exoplanets

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have been identified.

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However, most of these planets are too close

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to the star they orbit, and so are scorching hot.

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They are not planets with water, like Earth.

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In other words, they cannot sustain life.

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But then came a new discovery that thrilled Sara Seager.

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It was early in 2017.

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Planets were found that could support life,

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in a place where no one expected them.

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Well, with this discovery, we've made a giant,

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accelerated leap forward in the search for habitable worlds

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and life on other worlds, potentially speaking.

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40 light years from the Earth,

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in the direction of the constellation Aquarius,

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there is a small, read star known as TRAPPIST-1.

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Seven planets were found the be orbiting the star.

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(intriguing percussive music)

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Surprisingly, three of them are cool enough to contain water

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and maybe even oceans.

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One of the reasons astronomers are so excited about it

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is it's a veritable laboratory for studying planets

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orbiting very cool, very small, very dim red stars

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that are so incredibly different form our sun.

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TRAPPIST-1 is a small, red dwarf,

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a type known as an M dwarf.

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It is very different from our own sun,

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which burns at a fierce 10,000 degrees fahrenheit.

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Typical red dwarfs are much smaller than the sun,

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with surface temperatures about 2,000 degrees cooler.

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Three habitable planets exist there,

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in part because the star is so cool.

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Whether liquid water can exist on a planet

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depends on its distance from the star.

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If it's too close, water will evaporate as a gas.

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If it's too far away, it will freeze into a solid.

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(ice creaking)

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Only at the right distance will water remain as a liquid.

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Because a red dwarf is cooler,

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at a distance where our sun would scorch a planet,

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liquid water can still exist.

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Until recently, astronomers believed that life

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could only exist on planets that orbited stars

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similar to the sun.

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As a result, they didn't even make observations

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of red dwarfs, considered too small and dark.

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People hated M dwarf stars.

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But that's the evolution of the field.

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Initially, it's like it has to be

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just like Earth, just like our sun.

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But that's very hard to do, and so now,

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that's like in my talk when I was asking

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how do we find another Earth?

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We're taking this shortcut,

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like a shortcut to just get there.

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But of all the stars in the night sky,

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only a minority resemble the sun.

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On the other hand, red dwarfs make up

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most of the stars in the Milky Way.

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There are hundreds of billions of them.

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(dramatic orchestral music)

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If a space telescope targeted these stars for observation,

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it should find large numbers of habitable planets.

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How many could support life?

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Seager made an estimate based on current theory.

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She took the number of observable stars

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and calculated the probability of an exoplanet

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being in the habitable zone around each star,

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as well as other factors.

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Her result was ...

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7.5

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let's round that up to eight.

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Okay, let's call it 7.5, but we don't have half planets,

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so we'll call that eight.

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So we could have eight.

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So, although initially I feel discouraged

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that the numbers are so small,

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it's actually wonderful that we have any chance at all

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to make the first efforts to try

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to find signs of life out there.

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So I am encouraged by the numbers.

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I try to make it so it's not zero.

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(soft orchestral music)

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A space telescope could be used

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to find habitable planets.

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Seager believed that was the best path

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to finding extraterrestrial life in the universe.

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This was the origin of the TESS space telescope mission.

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The standard search for planets

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has been carried out by telescopes

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exploring limited areas of the sky, one zone at a time.

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But TESS will be different.

267
00:16:47,330 --> 00:16:50,570
It will search the universe in all directions,

268
00:16:50,570 --> 00:16:55,520
rotating its four cameras to tile images of outer space.

269
00:16:55,520 --> 00:16:57,470
It's an unprecedented approach

270
00:16:57,470 --> 00:16:59,623
to the search for habitable planets.

271
00:17:03,980 --> 00:17:06,730
Despite its revolutionary promise,

272
00:17:06,730 --> 00:17:09,623
TESS was almost aborted due to lack of funding.

273
00:17:10,690 --> 00:17:12,833
But Seager would not give up.

274
00:17:13,810 --> 00:17:17,510
She traveled throughout the United States, giving lectures

275
00:17:17,510 --> 00:17:20,493
and arguing that the project was indispensable.

276
00:17:23,260 --> 00:17:27,130
Her passion bore fruit, and private sector organizations

277
00:17:27,130 --> 00:17:29,690
agreed to donate funds.

278
00:17:29,690 --> 00:17:31,163
The mission moved ahead.

279
00:17:32,490 --> 00:17:36,260
In 2013, TESS was officially recognized

280
00:17:36,260 --> 00:17:38,123
as part of NASA's mission.

281
00:17:40,190 --> 00:17:44,323
More than 10 years passed since the initial research began.

282
00:17:48,140 --> 00:17:51,380
April 18, 2018.

283
00:17:51,380 --> 00:17:54,700
A special day had arrived for Sara Seager,

284
00:17:54,700 --> 00:17:57,103
the launch of the TESS telescope.

285
00:17:58,260 --> 00:17:59,770
It's a whole mix of emotions,

286
00:17:59,770 --> 00:18:02,450
just excitement and nervousness

287
00:18:02,450 --> 00:18:04,693
and just hoping everything goes well.

288
00:18:08,160 --> 00:18:09,510
Seager and her family

289
00:18:09,510 --> 00:18:12,840
came to the Kennedy Space Center, eager to witness

290
00:18:12,840 --> 00:18:16,033
a major step in the realization of her dream.

291
00:18:17,600 --> 00:18:19,818
Three, two,

292
00:18:19,818 --> 00:18:23,830
one, zero.
(rocket rumbling)

293
00:18:23,830 --> 00:18:24,920
Liftoff.

294
00:18:24,920 --> 00:18:29,000
SpaceX Falcon 9 carrying TESS, a planet-hunting spacecraft

295
00:18:29,000 --> 00:18:31,800
that will search for new worlds beyond our solar system.

296
00:18:34,398 --> 00:18:37,315
(crowd applauding)

297
00:18:38,840 --> 00:18:39,810
Fantastic launch.

298
00:18:39,810 --> 00:18:40,940
It was the perfect launch.

299
00:18:40,940 --> 00:18:42,190
It went up into the sky.

300
00:18:42,190 --> 00:18:43,380
Beautiful.

301
00:18:43,380 --> 00:18:44,820
Yeah, it was pretty cool.

302
00:18:44,820 --> 00:18:47,570
I mean, it's nothing like we've ever seen before.

303
00:18:47,570 --> 00:18:48,922
Yeah, it was really cool.

304
00:18:48,922 --> 00:18:52,509
Definitely better than playing Fortnite at home.

305
00:18:52,509 --> 00:18:55,342
(rocket rumbling)

306
00:18:57,440 --> 00:19:00,093
The launch was flawless.

307
00:19:01,340 --> 00:19:05,163
TESS headed toward an orbit in outer space.

308
00:19:05,163 --> 00:19:08,746
(dynamic orchestral music)

309
00:19:14,040 --> 00:19:17,010
Far darker than any spot on Earth,

310
00:19:17,010 --> 00:19:19,390
the position is ideal for observing

311
00:19:19,390 --> 00:19:21,993
the faint light of red dwarfs.

312
00:19:23,530 --> 00:19:26,263
The search for habitable planets is on.

313
00:19:27,120 --> 00:19:29,000
The dream space telescope

314
00:19:29,000 --> 00:19:31,763
is about to begin its observations.

315
00:19:36,151 --> 00:19:39,984
(intriguing orchestral music)

316
00:19:42,400 --> 00:19:44,483
July 2018.

317
00:19:45,880 --> 00:19:48,280
The time has come for the first pictures

318
00:19:48,280 --> 00:19:51,970
from the TESS space telescope to reach Seager and her team.

319
00:19:58,700 --> 00:20:01,380
In this image, taken with four cameras,

320
00:20:01,380 --> 00:20:04,530
of an area near the south celestial pole,

321
00:20:04,530 --> 00:20:08,513
there are 2.8 million red dwarf stars.

322
00:20:12,740 --> 00:20:14,239
I was amazed.

323
00:20:14,239 --> 00:20:15,490
I was just ...

324
00:20:15,490 --> 00:20:19,070
It's just incredible how many stars TESS sees,

325
00:20:19,070 --> 00:20:22,540
and also it's really beautiful

326
00:20:22,540 --> 00:20:25,040
and just this really wonderful snapshot

327
00:20:25,040 --> 00:20:28,030
of a huge swathe of the sky.

328
00:20:28,030 --> 00:20:30,660
So, I was amazed that we could see so much of it

329
00:20:30,660 --> 00:20:33,400
in such great detail all at once.

330
00:20:33,400 --> 00:20:35,140
When I saw this image for the first time,

331
00:20:35,140 --> 00:20:37,340
I was just happy.

332
00:20:37,340 --> 00:20:38,570
It's incredibly beautiful,

333
00:20:38,570 --> 00:20:40,920
more beautiful than you could imagine.

334
00:20:40,920 --> 00:20:42,830
And it shows you some detector effects

335
00:20:42,830 --> 00:20:44,030
when there's a very bright star,

336
00:20:44,030 --> 00:20:47,090
but on the whole it's just absolutely stunning.

337
00:20:47,090 --> 00:20:48,300
So, honestly, our real goal

338
00:20:48,300 --> 00:20:51,020
is to just find the best targets,

339
00:20:51,020 --> 00:20:55,283
the best potentially habitable planets.

340
00:20:58,340 --> 00:21:00,390
How can planets be found

341
00:21:00,390 --> 00:21:02,333
among these endless stars?

342
00:21:03,770 --> 00:21:06,093
Planets do not emit light themselves,

343
00:21:06,940 --> 00:21:10,130
but when one passes in front of a burning star,

344
00:21:10,130 --> 00:21:12,683
the star's light is partially blocked.

345
00:21:13,550 --> 00:21:16,770
Observing this tiny drop in emitted light

346
00:21:16,770 --> 00:21:19,474
reveals the presence of a planet.

347
00:21:19,474 --> 00:21:23,474
(intriguing instrumental music)

348
00:21:26,500 --> 00:21:29,663
This drop-off in light is called a transit.

349
00:21:31,220 --> 00:21:33,860
The orbital cycle of a planet can be calculated

350
00:21:33,860 --> 00:21:36,673
from the interval between transits.

351
00:21:37,550 --> 00:21:40,960
To that end, TESS will continue to take photographs

352
00:21:40,960 --> 00:21:45,033
of the same areas of the sky again and again.

353
00:21:49,397 --> 00:21:52,470
(soft electronic music)

354
00:21:52,470 --> 00:21:54,463
Eight months after the launch.

355
00:21:55,430 --> 00:21:58,440
In this meeting, the team tried to identify

356
00:21:58,440 --> 00:22:01,763
possible planets from the images sent by TESS.

357
00:22:03,240 --> 00:22:06,433
This is an image taken by the space telescope.

358
00:22:07,550 --> 00:22:09,063
What did the team think?

359
00:22:10,040 --> 00:22:11,829
I would be suspicious

360
00:22:11,829 --> 00:22:13,810
of the secondary eclipse.

361
00:22:13,810 --> 00:22:15,610
Looking at the ...

362
00:22:15,610 --> 00:22:18,110
Oh, 'cause there's like a little bump here?

363
00:22:18,110 --> 00:22:18,943
Yeah.

364
00:22:18,943 --> 00:22:19,803
One transit.

365
00:22:21,637 --> 00:22:23,637
Let's get a closer look.

366
00:22:27,680 --> 00:22:31,230
There were 170,000 red dwarf stars

367
00:22:31,230 --> 00:22:32,133
in this image.

368
00:22:33,020 --> 00:22:36,600
When they were analyzed, one of the stars

369
00:22:36,600 --> 00:22:39,383
showed a fluctuation in emitted light.

370
00:22:40,710 --> 00:22:45,180
It's the red dwarf LHS 3844,

371
00:22:45,180 --> 00:22:47,843
49 light years from Earth.

372
00:22:51,890 --> 00:22:53,060
I really like this.

373
00:22:53,060 --> 00:22:54,200
All right, so this is actually a really exciting one.

374
00:22:54,200 --> 00:22:55,570
That's a good catch, yeah.

375
00:22:55,570 --> 00:22:57,130
Good candidate.

376
00:22:57,130 --> 00:22:57,963
All right.

377
00:23:00,370 --> 00:23:01,880
When the data on the starlight

378
00:23:01,880 --> 00:23:03,870
was examined more closely,

379
00:23:03,870 --> 00:23:07,183
the level fluctuated only at certain times.

380
00:23:08,130 --> 00:23:12,383
This phenomenon occurred regularly, at 11-hour intervals.

381
00:23:15,700 --> 00:23:17,970
They had discovered a planet

382
00:23:17,970 --> 00:23:21,213
on an 11-hour orbit around the red dwarf.

383
00:23:22,944 --> 00:23:27,368
(dramatic orchestral music)

384
00:23:27,368 --> 00:23:29,760
On this day, the team analyzed

385
00:23:29,760 --> 00:23:33,010
a total of 40 planet candidates.

386
00:23:33,010 --> 00:23:35,773
And TESS's observations have only just begun.

387
00:23:39,180 --> 00:23:42,130
These particular planets are not gonna be habitable.

388
00:23:42,130 --> 00:23:44,220
However, these are a faint set of stars.

389
00:23:44,220 --> 00:23:45,110
They're relatively faint.

390
00:23:45,110 --> 00:23:47,140
And so, it will be really not as easy,

391
00:23:47,140 --> 00:23:50,360
kind of challenging to find a habitable planet around them.

392
00:23:50,360 --> 00:23:53,270
We're definitely on track to finding habitable planets.

393
00:23:53,270 --> 00:23:55,406
It's really just a matter of time.

394
00:23:55,406 --> 00:23:57,260
(ethereal music)

395
00:23:57,260 --> 00:23:59,390
TESS is continuing its efforts

396
00:23:59,390 --> 00:24:02,833
to search for planets that orbit red dwarf stars.

397
00:24:03,840 --> 00:24:07,770
But research increasingly indicates that these alien worlds

398
00:24:07,770 --> 00:24:11,223
contain entirely different environments than Earth.

399
00:24:14,800 --> 00:24:16,720
Because these planets around the tiny star,

400
00:24:16,720 --> 00:24:19,590
they're so close to the star, the year of someone

401
00:24:19,590 --> 00:24:22,610
on that planet would just be literally a few days.

402
00:24:22,610 --> 00:24:25,530
And just incredible to think how all the things

403
00:24:25,530 --> 00:24:27,230
we've talked about about red dwarf stars

404
00:24:27,230 --> 00:24:29,030
are even more extreme with these planets.

405
00:24:29,030 --> 00:24:30,330
It's a very extreme place.

406
00:24:33,400 --> 00:24:34,550
The surface temperature

407
00:24:34,550 --> 00:24:37,840
on red dwarfs is relatively low.

408
00:24:37,840 --> 00:24:41,460
As a result, planets must be quite close to the star

409
00:24:41,460 --> 00:24:44,063
for water to remain in its liquid state.

410
00:24:50,060 --> 00:24:52,630
Because these planets are so close,

411
00:24:52,630 --> 00:24:54,280
they are strongly influenced

412
00:24:54,280 --> 00:24:56,973
by the gravitational forces of the star.

413
00:24:57,940 --> 00:25:00,690
This causes the planet's orientation to the star

414
00:25:00,690 --> 00:25:05,033
to be fixed, a phenomenon known as tidal locking.

415
00:25:07,920 --> 00:25:11,260
A tidally locked planet always faces the star

416
00:25:11,260 --> 00:25:12,603
from the same side.

417
00:25:13,630 --> 00:25:16,280
Thus, it's divided in two.

418
00:25:16,280 --> 00:25:20,130
Light falls on one hemisphere, which is always day,

419
00:25:20,130 --> 00:25:23,443
while the other hemisphere is always night.

420
00:25:28,140 --> 00:25:31,430
Perpetual day and perpetual night.

421
00:25:31,430 --> 00:25:36,319
Is it possible for such an unusual world to host life?

422
00:25:36,319 --> 00:25:38,400
(upbeat percussive music)

423
00:25:38,400 --> 00:25:42,240
NASA scientist Tony Del Genio believes that life

424
00:25:42,240 --> 00:25:45,453
does exist on these tidally locked planets.

425
00:25:46,420 --> 00:25:50,503
But for some reason, he first took us into a pizzeria.

426
00:25:58,912 --> 00:26:01,997
(fire crackling)

427
00:26:01,997 --> 00:26:02,830
Here you go.

428
00:26:02,830 --> 00:26:03,663
Thank you.

429
00:26:03,663 --> 00:26:05,190
Enjoy, bon appetit.

430
00:26:05,190 --> 00:26:07,860
We used to think that tidally locked planets

431
00:26:07,860 --> 00:26:09,333
were something like pizzas:

432
00:26:10,930 --> 00:26:14,223
hot on one side, with lots of good stuff ...

433
00:26:15,770 --> 00:26:19,853
but not much going on on the other side of the planet.

434
00:26:20,780 --> 00:26:22,840
But now we know that tidally locked planets

435
00:26:22,840 --> 00:26:24,333
are much more dynamic.

436
00:26:26,450 --> 00:26:28,410
What is this world like,

437
00:26:28,410 --> 00:26:31,380
if it's more dynamic that the simple dichotomy

438
00:26:31,380 --> 00:26:33,602
of the top and bottom of a pizza?

439
00:26:33,602 --> 00:26:37,269
(spirited orchestral music)

440
00:26:38,180 --> 00:26:41,090
Del Genio uses computer simulations

441
00:26:41,090 --> 00:26:44,203
to study the climate on a tidally locked planet.

442
00:26:45,220 --> 00:26:48,020
His simulation shows that large amounts of heat

443
00:26:48,020 --> 00:26:51,870
are transferred from the day side to the night side,

444
00:26:51,870 --> 00:26:55,053
a dynamic circulation of the atmosphere.

445
00:27:02,090 --> 00:27:05,030
So, every planet with an atmosphere,

446
00:27:05,030 --> 00:27:10,030
the atmosphere, the main job of the atmosphere on any planet

447
00:27:10,440 --> 00:27:14,140
is to move warm air to cold places

448
00:27:14,140 --> 00:27:16,060
and cold air to warm places.

449
00:27:16,060 --> 00:27:17,310
That's what weather does.

450
00:27:19,322 --> 00:27:22,510
A tidally locked planet is not cleanly divided

451
00:27:22,510 --> 00:27:25,773
into worlds of blazing heat and frigid cold.

452
00:27:29,150 --> 00:27:33,473
A planet bathed in the red light of a red dwarf star.

453
00:27:34,750 --> 00:27:36,920
Let's take a look at the circulation

454
00:27:36,920 --> 00:27:39,483
of water and atmosphere that takes place here.

455
00:27:45,870 --> 00:27:49,203
On the day side, where light shines endlessly,

456
00:27:50,150 --> 00:27:53,920
at its center, where the light falls most intensely,

457
00:27:53,920 --> 00:27:57,530
a super giant cumulonimbus cloud forms.

458
00:27:57,530 --> 00:28:00,750
(rain pouring)

459
00:28:00,750 --> 00:28:04,323
Rain falls like a waterfall suspended in the air.

460
00:28:05,250 --> 00:28:08,000
But before that rain reaches the surface,

461
00:28:08,000 --> 00:28:09,723
it's vaporized by the heat.

462
00:28:10,890 --> 00:28:15,210
That water vapor carries heat across the entire planet.

463
00:28:15,210 --> 00:28:18,460
(delicate piano music)

464
00:28:20,841 --> 00:28:23,040
And that warm air goes up

465
00:28:23,040 --> 00:28:26,090
and then starts drifting over the poles,

466
00:28:26,090 --> 00:28:28,880
over to the night side, and then over to the dawn

467
00:28:28,880 --> 00:28:31,743
and dusk sides of the planet, and over to the night side.

468
00:28:33,490 --> 00:28:34,890
On the night side,

469
00:28:34,890 --> 00:28:37,440
where frigid temperatures are expected,

470
00:28:37,440 --> 00:28:40,810
the warm air carries heat that raises the temperature

471
00:28:40,810 --> 00:28:44,400
in places above -20 degrees celsius.

472
00:28:44,400 --> 00:28:46,623
That's -4 degrees fahrenheit.

473
00:28:47,850 --> 00:28:50,800
And there is one area on a planet like this

474
00:28:50,800 --> 00:28:54,890
where lifeforms would be most likely to thrive.

475
00:28:54,890 --> 00:28:59,370
This is the border between the day side and the night side:

476
00:28:59,370 --> 00:29:00,783
the twilight zone.

477
00:29:03,540 --> 00:29:07,453
It is believed that a superb climate takes form here.

478
00:29:08,390 --> 00:29:12,720
Average temperature range from zero to 20 degrees celsius,

479
00:29:12,720 --> 00:29:15,763
or 32 to 68 degrees fahrenheit.

480
00:29:17,080 --> 00:29:21,860
The area is bathed in the perpetual red glow of twilight.

481
00:29:21,860 --> 00:29:25,023
Its sun never moves from its position in the sky.

482
00:29:27,910 --> 00:29:30,320
At times, rain falls,

483
00:29:30,320 --> 00:29:32,663
bringing its blessings to living things.

484
00:29:33,870 --> 00:29:38,030
This environment that could be agreeable to life

485
00:29:38,030 --> 00:29:41,757
covers as much as 20% of the planet.

486
00:29:41,757 --> 00:29:45,257
(gentle orchestral music)

487
00:29:46,510 --> 00:29:49,280
The net result of all of that

488
00:29:49,280 --> 00:29:52,540
is that a larger fraction of the planet

489
00:29:53,430 --> 00:29:56,930
could be habitable than what we initially imagined.

490
00:29:56,930 --> 00:29:58,890
I'm absolutely certain that there is life

491
00:29:58,890 --> 00:30:00,190
elsewhere in the universe.

492
00:30:02,060 --> 00:30:04,490
Life almost certainly exists

493
00:30:04,490 --> 00:30:06,663
on such tidally locked planets.

494
00:30:07,700 --> 00:30:10,183
But what form does that life take?

495
00:30:19,240 --> 00:30:21,700
We paid a visit to David Aguilar,

496
00:30:21,700 --> 00:30:23,636
who studies extraterrestrial life.

497
00:30:23,636 --> 00:30:24,860
(uncanny instrumental music)

498
00:30:24,860 --> 00:30:27,050
He has participated in space missions

499
00:30:27,050 --> 00:30:30,893
such as the New Horizons probe sent to Pluto and beyond.

500
00:30:32,260 --> 00:30:34,460
Based on the latest scientific thinking,

501
00:30:34,460 --> 00:30:38,433
he is exploring what extraterrestrial life might be like.

502
00:30:42,420 --> 00:30:45,520
We thought Earths like we live on

503
00:30:45,520 --> 00:30:48,850
would be the most common planet out there for life,

504
00:30:48,850 --> 00:30:50,053
and we were wrong.

505
00:30:50,900 --> 00:30:54,030
So, maybe our little Earth is an oddity.

506
00:30:54,030 --> 00:30:57,140
And the most common planets for life

507
00:30:57,140 --> 00:31:00,922
will never see a sunset, a sunrise.

508
00:31:00,922 --> 00:31:03,620
(bright piano music)

509
00:31:03,620 --> 00:31:06,040
Aguilar has been considering the lifeforms

510
00:31:06,040 --> 00:31:08,570
that might live in the twilight zones

511
00:31:08,570 --> 00:31:11,303
of planets that orbit red dwarf stars.

512
00:31:12,370 --> 00:31:15,303
To that end, he traveled to MIT.

513
00:31:16,880 --> 00:31:17,924
It's me again.
<v ->Hello.

514
00:31:17,924 --> 00:31:18,757
Hi, David.
Hi, Sara.

515
00:31:18,757 --> 00:31:19,590
How are you?

516
00:31:19,590 --> 00:31:20,423
Come on in.

517
00:31:20,423 --> 00:31:21,570
It's been a while since the early days.

518
00:31:21,570 --> 00:31:23,730
He came to see Sara Seager,

519
00:31:23,730 --> 00:31:26,860
as one of the leaders of the TESS space telescope project.

520
00:31:26,860 --> 00:31:28,490
(Sara chatting)

521
00:31:28,490 --> 00:31:31,593
What types of life does she imagine we'll find there?

522
00:31:32,590 --> 00:31:34,723
Hot, cold.

523
00:31:36,060 --> 00:31:38,130
I'm always thinking we're gonna find something

524
00:31:38,130 --> 00:31:39,550
right around in here

525
00:31:39,550 --> 00:31:41,770
that may be adapted to go into the cold,

526
00:31:41,770 --> 00:31:44,390
maybe adapted to venture into here.

527
00:31:44,390 --> 00:31:46,690
You know, these M dwarf stars, they are kind of faint.

528
00:31:46,690 --> 00:31:48,150
And through a very thick atmosphere,

529
00:31:48,150 --> 00:31:50,040
there might not be too much light.

530
00:31:50,040 --> 00:31:51,990
So what if you had creatures, lifeforms,

531
00:31:51,990 --> 00:31:54,150
like birds with giant wings,

532
00:31:54,150 --> 00:31:57,266
that the wings themselves could carry out photosynthesis?

533
00:31:57,266 --> 00:31:59,410
(intriguing instrumental music)

534
00:31:59,410 --> 00:32:01,730
Seager believes some planets

535
00:32:01,730 --> 00:32:04,640
might have denser atmospheres than Earth

536
00:32:04,640 --> 00:32:06,143
and high air pressure.

537
00:32:08,680 --> 00:32:11,410
And so if you had that dense air over water,

538
00:32:11,410 --> 00:32:15,890
there could be life that can transfer from water to air,

539
00:32:15,890 --> 00:32:17,783
just like we have amphibians that go from water

540
00:32:17,783 --> 00:32:18,616
and they can live on land,

541
00:32:18,616 --> 00:32:20,952
there could be fish that truly fly.

542
00:32:20,952 --> 00:32:24,952
(intriguing instrumental music)

543
00:32:28,900 --> 00:32:31,802
Under their small red suns,

544
00:32:31,802 --> 00:32:34,320
tidally locked planets.

545
00:32:34,320 --> 00:32:38,053
What kind of life might inhabit the twilight zone?

546
00:32:39,520 --> 00:32:42,520
Aguilar tries to give shape to the lifeforms

547
00:32:42,520 --> 00:32:45,823
that might be suited to the environment on these planets.

548
00:32:49,250 --> 00:32:53,070
This is a red dwarf, one of the most numerous

549
00:32:53,070 --> 00:32:55,413
and common stars in the universe.

550
00:32:56,710 --> 00:32:58,840
Let's go take a look at the spectacles

551
00:32:58,840 --> 00:33:01,343
that unfold on this living planet.

552
00:33:02,880 --> 00:33:04,770
Riding the air currents that flow

553
00:33:04,770 --> 00:33:08,040
from the day side into the night side,

554
00:33:08,040 --> 00:33:10,860
a world wrapped in perpetual darkness

555
00:33:10,860 --> 00:33:12,903
unfolds into the distance.

556
00:33:15,230 --> 00:33:18,610
The temperature is -10 degrees celsius,

557
00:33:18,610 --> 00:33:21,335
or 14 degrees fahrenheit.

558
00:33:21,335 --> 00:33:22,668
(uncanny instrumental music)

559
00:33:22,668 --> 00:33:25,390
(ground rumbling)

560
00:33:25,390 --> 00:33:27,023
Something is swelling.

561
00:33:27,960 --> 00:33:30,873
And now, it begins to float.

562
00:33:30,873 --> 00:33:34,400
(creature whistling)

563
00:33:34,400 --> 00:33:37,113
It's one of the creatures that inhabit this planet.

564
00:33:46,300 --> 00:33:49,740
They feed on microorganisms that ride the wind

565
00:33:49,740 --> 00:33:51,590
and live by taking advantage

566
00:33:51,590 --> 00:33:53,440
of the circulation of the atmosphere.

567
00:34:00,460 --> 00:34:03,508
They're heading toward the border between the night side

568
00:34:03,508 --> 00:34:06,293
and the day side, the twilight zone.

569
00:34:12,720 --> 00:34:15,920
These large creatures can glide in the sky

570
00:34:15,920 --> 00:34:17,970
because hydrogen gas is produced

571
00:34:17,970 --> 00:34:20,410
when they digest their food.

572
00:34:20,410 --> 00:34:22,310
Stored in their bodies,

573
00:34:22,310 --> 00:34:25,163
it allows them to float like balloons.

574
00:34:27,540 --> 00:34:30,840
When they expel the gas, they move at will

575
00:34:30,840 --> 00:34:34,103
into the perpetual red glow of the twilight zone.

576
00:34:44,040 --> 00:34:46,143
Let's descend for a look around.

577
00:34:50,290 --> 00:34:54,893
This is an oasis with the water that is essential for life.

578
00:34:56,700 --> 00:34:59,763
Strange plants grow in profusion.

579
00:35:00,620 --> 00:35:04,100
Much of the light from the red dwarf is infrared,

580
00:35:04,100 --> 00:35:07,943
so photosynthesis is different from what occurs on Earth.

581
00:35:14,580 --> 00:35:18,103
The red sun never shifts its position in the sky.

582
00:35:19,090 --> 00:35:21,700
As a result, all of the vegetation

583
00:35:21,700 --> 00:35:23,633
faces in the same direction.

584
00:35:27,500 --> 00:35:30,820
We feel comfort when we see beautiful green

585
00:35:30,820 --> 00:35:35,603
and fields of green, and forests, and valleys.

586
00:35:36,770 --> 00:35:39,210
Those would be there, too, but they would be

587
00:35:39,210 --> 00:35:44,210
beautiful black forests in magenta fields.

588
00:35:44,760 --> 00:35:48,023
It would look very odd to us.

589
00:35:56,440 --> 00:35:59,807
This creature lives on land and in the water.

590
00:35:59,807 --> 00:36:03,653
(gentle piano music)

591
00:36:03,653 --> 00:36:06,250
Because the atmosphere is dense,

592
00:36:06,250 --> 00:36:09,923
it has evolved to move freely between land and water.

593
00:36:15,982 --> 00:36:18,982
(creature chirping)

594
00:36:24,580 --> 00:36:28,190
On this planet, where the atmosphere circulates

595
00:36:28,190 --> 00:36:30,980
in a dynamic fashion, the twilight zone

596
00:36:30,980 --> 00:36:33,600
has the most stable environment,

597
00:36:33,600 --> 00:36:35,630
a paradise for living beings.

598
00:36:35,630 --> 00:36:38,630
(creature growling)

599
00:36:40,530 --> 00:36:44,580
But this creature's wingspread is three meters.

600
00:36:44,580 --> 00:36:47,670
Its exoskeleton is hard and thick,

601
00:36:47,670 --> 00:36:49,653
covering its body like armor.

602
00:36:50,860 --> 00:36:54,653
It evolved into this shape in order to capture its pray.

603
00:37:00,424 --> 00:37:03,922
(creature roars)

604
00:37:03,922 --> 00:37:07,005
(creatures chirping)

605
00:37:09,257 --> 00:37:11,590
(splashing)

606
00:37:15,020 --> 00:37:17,640
Perhaps the intense struggle to survive

607
00:37:17,640 --> 00:37:20,243
serves as a spur to develop intelligence.

608
00:37:24,660 --> 00:37:28,480
We reach out and we realize that we're quite special,

609
00:37:28,480 --> 00:37:31,510
and this planet is very special,

610
00:37:31,510 --> 00:37:34,540
but there's going to be more mystery out there.

611
00:37:34,540 --> 00:37:37,640
There's going to be worlds that will just dazzle us,

612
00:37:37,640 --> 00:37:41,957
amaze us, and they're just waiting for us to find them.

613
00:37:44,520 --> 00:37:46,150
One feature in particular

614
00:37:46,150 --> 00:37:48,083
promotes the evolution of life here.

615
00:37:49,290 --> 00:37:51,590
The lifespan of a red dwarf star

616
00:37:51,590 --> 00:37:54,030
is much longer than our sun,

617
00:37:54,030 --> 00:37:57,723
which burns out 10 billion years after its formation.

618
00:37:58,830 --> 00:38:01,520
As a result, life on this planet

619
00:38:01,520 --> 00:38:05,010
is able to evolve over a longer period of time

620
00:38:05,010 --> 00:38:08,293
than it took us to develop intelligent life on Earth.

621
00:38:11,220 --> 00:38:13,930
M dwarfs are unique because they can live

622
00:38:13,930 --> 00:38:15,510
a very long time.

623
00:38:15,510 --> 00:38:18,490
They can live for billions or tens of billions of years.

624
00:38:18,490 --> 00:38:21,933
And so that gives life longer to evolve.

625
00:38:26,130 --> 00:38:28,820
Now, at this very moment,

626
00:38:28,820 --> 00:38:31,610
scientists are continuing their efforts

627
00:38:31,610 --> 00:38:33,973
to find extraterrestrial life.

628
00:38:35,010 --> 00:38:38,110
The TESS space telescope continues its search

629
00:38:38,110 --> 00:38:40,783
for planets outside our solar system.

630
00:38:41,840 --> 00:38:44,780
It sends new images form its observations

631
00:38:44,780 --> 00:38:47,065
to Earth at a steady pace.

632
00:38:47,065 --> 00:38:51,170
(dramatic orchestral music)

633
00:38:51,170 --> 00:38:55,063
The TESS team met one year after the telescope was launched.

634
00:38:57,320 --> 00:38:59,010
Do you have other planets?

635
00:38:59,010 --> 00:39:00,190
Yeah, there's one other one.

636
00:39:00,190 --> 00:39:02,550
There's an interesting case, actually.

637
00:39:02,550 --> 00:39:05,880
This is the other star that I've requested time on.

638
00:39:05,880 --> 00:39:06,713
Oh, yeah, this is--

639
00:39:06,713 --> 00:39:07,546
Okay.

640
00:39:07,546 --> 00:39:08,379
So, this is an M dwarf.

641
00:39:08,379 --> 00:39:10,630
This is a much cooler and fainter star.

642
00:39:10,630 --> 00:39:11,463
Nice, very nice.

643
00:39:11,463 --> 00:39:12,406
Yeah.

644
00:39:12,406 --> 00:39:13,790
(upbeat electronic music)

645
00:39:13,790 --> 00:39:18,790
The candidate star they found was L 98-59,

646
00:39:19,100 --> 00:39:22,533
a red dwarf some 35 light years from Earth.

647
00:39:23,840 --> 00:39:27,710
It is orbited by not one but three planets

648
00:39:27,710 --> 00:39:29,860
the same size as Earth.

649
00:39:29,860 --> 00:39:33,027
(dynamic brass music)

650
00:39:36,090 --> 00:39:39,790
Today, TESS is capturing images of planets

651
00:39:39,790 --> 00:39:41,263
heretofore unknown.

652
00:39:44,040 --> 00:39:45,860
The exciting thing, I think, about that

653
00:39:45,860 --> 00:39:47,910
is, even though we release them in chunks,

654
00:39:47,910 --> 00:39:51,163
and so we release like 20 at a time and then 40 at at time,

655
00:39:52,280 --> 00:39:53,830
if you divide it over the course of the year,

656
00:39:53,830 --> 00:39:56,405
it's like we've been finding a planet a day almost.

657
00:39:56,405 --> 00:39:57,238
A planet candidate.

658
00:39:57,238 --> 00:39:59,488
Yeah, a planet candidate.

659
00:40:00,337 --> 00:40:02,100
These are planet candidates

660
00:40:02,100 --> 00:40:03,903
that TESS has identified.

661
00:40:05,628 --> 00:40:09,378
(uplifting orchestral music)

662
00:40:12,420 --> 00:40:15,973
The number of candidates has passed 1,000.

663
00:40:23,570 --> 00:40:26,070
As you know, in exoplanets everything's incredible.

664
00:40:26,070 --> 00:40:27,800
It's so diverse.

665
00:40:27,800 --> 00:40:30,540
Planets are all sizes and masses and orbits.

666
00:40:30,540 --> 00:40:32,890
And so, we try not to have preconceived notions.

667
00:40:32,890 --> 00:40:35,260
We're just trying to go out there and see what's there,

668
00:40:35,260 --> 00:40:38,703
and that's the sense of why it's like true exploration.

669
00:40:39,610 --> 00:40:42,000
At the same time, another effort

670
00:40:42,000 --> 00:40:46,153
to find direct evidence of extraterrestrial life has begun.

671
00:40:47,663 --> 00:40:50,250
(dramatic instrumental music)

672
00:40:50,250 --> 00:40:54,013
Through photosynthesis, plants create oxygen.

673
00:40:58,290 --> 00:41:02,320
Animals emit carbon dioxide and methane gas.

674
00:41:02,320 --> 00:41:04,820
(gas hissing)

675
00:41:06,480 --> 00:41:10,360
Finding these substances in the atmosphere of exoplanets

676
00:41:10,360 --> 00:41:14,283
would provide direct evidence of life.

677
00:41:17,253 --> 00:41:19,680
(waves crashing)

678
00:41:19,680 --> 00:41:23,913
This is the island of Tenerife in the Canary Islands.

679
00:41:24,770 --> 00:41:29,000
Here, Japanese astronomer Norio Narita

680
00:41:29,000 --> 00:41:31,640
uses a ground-based telescope

681
00:41:31,640 --> 00:41:35,113
to more closely observe the planets TESS discovered.

682
00:42:00,150 --> 00:42:02,602
This is the camera that Narita developed.

683
00:42:02,602 --> 00:42:06,602
(impressive instrumental music)

684
00:42:09,550 --> 00:42:12,350
When a planet crosses in front of a star,

685
00:42:12,350 --> 00:42:14,000
light passes through the layer

686
00:42:14,000 --> 00:42:15,743
of atmosphere around the planet.

687
00:42:21,600 --> 00:42:25,120
By analyzing this minuscule amount of light,

688
00:42:25,120 --> 00:42:28,313
the components of the atmosphere can be deduced.

689
00:42:31,600 --> 00:42:34,360
The attempt to find the first hard evidence

690
00:42:34,360 --> 00:42:37,223
of extraterrestrial life continues.

691
00:42:43,200 --> 00:42:45,863
On the other side of the globe, in Chile,

692
00:42:47,120 --> 00:42:51,170
in 2019, one of the world's largest instruments

693
00:42:51,170 --> 00:42:54,923
for analyzing atmospheric gases went into operation.

694
00:42:56,400 --> 00:43:00,190
David Ehrenreich declares that the day we capture evidence

695
00:43:00,190 --> 00:43:03,163
of life in the universe is certain to come.

696
00:43:06,910 --> 00:43:11,210
My dream is to find traces of life

697
00:43:11,210 --> 00:43:13,940
in the atmosphere of another planet.

698
00:43:13,940 --> 00:43:15,940
We should be open to find life

699
00:43:15,940 --> 00:43:19,650
in completely different forms in completely different place.

700
00:43:19,650 --> 00:43:21,320
The challenge of that is that,

701
00:43:21,320 --> 00:43:26,303
how are we going to recognize that this is actually life?

702
00:43:27,810 --> 00:43:29,230
Throughout the world,

703
00:43:29,230 --> 00:43:31,510
a friendly competition is on

704
00:43:31,510 --> 00:43:34,100
to be the first to discover evidence

705
00:43:34,100 --> 00:43:36,993
of extraterrestrial life.

706
00:43:42,928 --> 00:43:44,850
(mysterious music)

707
00:43:44,850 --> 00:43:49,251
And what about that visitor from outside the solar system,

708
00:43:49,251 --> 00:43:50,084
Oumuamua?

709
00:43:51,150 --> 00:43:56,150
NASA clocked it at 196,000 miles per hour

710
00:43:56,180 --> 00:44:00,663
as it sling-shotted past the sun on September 9, 2017.

711
00:44:02,160 --> 00:44:04,320
Its rapid acceleration led some

712
00:44:04,320 --> 00:44:05,820
to believe it was a spaceship.

713
00:44:07,670 --> 00:44:10,653
Where did the strange object originate from?

714
00:44:14,930 --> 00:44:18,503
A research team in Europe is working to solve that riddle.

715
00:44:22,660 --> 00:44:25,050
The scientists have followed the trajectory

716
00:44:25,050 --> 00:44:26,903
of Oumuamua's flight path.

717
00:44:28,330 --> 00:44:30,770
They have identified a number of stars

718
00:44:30,770 --> 00:44:33,850
in the direction of the constellation Cetus

719
00:44:33,850 --> 00:44:35,263
as possible sources.

720
00:44:37,732 --> 00:44:41,315
(rousing orchestral music)

721
00:44:43,050 --> 00:44:46,150
And then there are some smaller, fainter objects

722
00:44:46,150 --> 00:44:48,710
that are also more red, and for example this one,

723
00:44:48,710 --> 00:44:50,543
and these are what we call red dwarfs.

724
00:44:50,543 --> 00:44:52,413
They are smaller stars, older stars.

725
00:44:53,260 --> 00:44:54,940
All of the points you see here

726
00:44:54,940 --> 00:44:58,360
are stars that may have been the original system

727
00:44:58,360 --> 00:44:59,660
where Oumuamua was formed.

728
00:45:03,510 --> 00:45:07,310
Whether Oumuamua is a cigar-shaped asteroid

729
00:45:07,310 --> 00:45:12,014
or a spaceship, what might its home planet look like?

730
00:45:12,014 --> 00:45:15,431
(rousing operatic music)

731
00:45:24,660 --> 00:45:26,440
Could it be this planet,

732
00:45:26,440 --> 00:45:28,943
bathed in the light of a red dwarf star?

733
00:45:35,550 --> 00:45:37,523
Is this an alien planet?

734
00:45:43,430 --> 00:45:46,610
Somewhere in the vast expanse of space,

735
00:45:46,610 --> 00:45:51,240
there may be a civilization far more advanced than ours,

736
00:45:51,240 --> 00:45:53,303
gazing out at our plant.

737
00:45:58,828 --> 00:46:01,400
(gentle guitar music)

738
00:46:01,400 --> 00:46:04,613
Sara Seager continues to search for exoplanets

739
00:46:04,613 --> 00:46:06,503
with with the TESS telescope.

740
00:46:07,820 --> 00:46:09,640
On one of her days off,

741
00:46:09,640 --> 00:46:12,343
she and her family went out stargazing.

742
00:46:15,664 --> 00:46:16,817
The telescope looks quite small,

743
00:46:16,817 --> 00:46:18,320
but it's a fantastic lens,

744
00:46:18,320 --> 00:46:20,690
so things we'll see are incredibly sharp.

745
00:46:20,690 --> 00:46:22,860
The young girl who was entranced

746
00:46:22,860 --> 00:46:26,783
by the starry skies holds true to her vision.

747
00:46:28,640 --> 00:46:30,360
But when I look at the night sky,

748
00:46:30,360 --> 00:46:32,700
I look at the stars, and I wonder,

749
00:46:32,700 --> 00:46:34,930
are there any planets around those stars?

750
00:46:34,930 --> 00:46:38,700
And I wonder if there's any intelligent life

751
00:46:38,700 --> 00:46:40,310
around the planets around those stars,

752
00:46:40,310 --> 00:46:43,453
looking back at our sun and wondering the same thing.

753
00:46:43,453 --> 00:46:46,790
(gentle piano music)

754
00:46:46,790 --> 00:46:50,740
Pursuing planets with extraterrestrial life.

755
00:46:50,740 --> 00:46:55,493
For Sara, her childhood dream lives on.

756
00:46:59,918 --> 00:47:03,585
(gentle instrumental music)

757
00:47:47,946 --> 00:47:51,113
(creature vocalizing)