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0:25

Almost 800 million miles away

0:27

from Earth, the moon Enceladus orbits

0:30

the gas giant planet Saturn.

0:32

Enceladus is tiny,

0:34

only 314 miles in diameter.

0:36

That's small enough to fit

0:38

entirely inside the borders of Texas.

0:42

Back in June, an international group of

0:44

scientists announced they found evidence that

0:46

suggests Enceladus has all the

0:48

necessary building blocks for life,

0:50

meaning this small, icy moon

0:53

could be habitable. It has

0:55

a global subsurface ocean

0:57

that's salty that's underneath this icy

1:00

shell. That's Wall Street Journal science

1:02

reporter Aylan Woodward. And

1:05

past evidence from missions from

1:07

NASA and other international space agencies have

1:09

found five key ingredients

1:11

of typical Earth life. But they hadn't found

1:13

the sixth key ingredient, phosphorus, and

1:15

phosphorus is sort of a very rare element. And

1:18

with that last checkbox,

1:22

it basically indicates that Enceladus

1:24

is potentially habitable and a really

1:26

great place in our planetary neighborhood

1:28

to look for life.

1:30

Aylan says this recent finding is evidence that

1:32

life could be more common in our solar system

1:34

than we once thought, and also

1:36

perhaps on exoplanets.

1:39

Those are planets found outside our

1:41

solar system. In

1:43

the 31 years since the first exoplanets

1:45

were discovered, astronomers have found more than 5,500.

1:49

They're still finding new ones, and new

1:52

technology is helping scientists learn even

1:54

more about them.

1:55

If ocean worlds in

1:57

our planetary neighborhood do seem to have

1:59

conditions. that are typical

2:01

of Earth's life, it's plausible

2:04

that there are similar conditions on other ocean worlds

2:06

outside of our solar system on these

2:08

extrasolar planets or exoplanets that

2:11

we should also be looking for. Take

2:13

the exoplanet K2-18b. It's 124

2:16

light years away from Earth and

2:19

was first discovered in 2015. Earlier

2:22

this month, NASA announced that the James

2:24

Webb Space Telescope spotted signs of carbon

2:27

dioxide and methane there, which

2:29

suggests it might be an ocean world. And

2:32

an ocean world with all the elements

2:34

for life could be habitable. But

2:37

habitable for some life forms doesn't

2:39

necessarily mean that humans could survive

2:42

there.

2:42

There's plenty of places on Earth where

2:45

microbes are totally happy

2:48

and we would die immediately.

2:51

Chris Impey is an astronomer at the University

2:53

of Arizona and author of the book, Worlds

2:55

Without End. Exoplanets, Habitability,

2:58

and the Future of Humanity. He

3:01

says what we consider habitable for life here

3:03

on Earth might not be the same for other

3:05

planets in our solar system or

3:07

even in the rest of the galaxy. And

3:10

that could have major implications for what our

3:12

understanding of life is. The

3:15

uncomfortable fact of this field is

3:17

that life might be so strange that

3:19

it's unrecognizable and then how

3:22

do you define an experiment to detect it or find

3:24

it? From the

3:26

Wall Street Journal, this is the Future of Everything.

3:29

I'm Danny Lewis. I spoke

3:31

with Chris Impey about how astronomers are hunting

3:33

for exoplanets and how new technology

3:36

is giving them a better glimpse of far-off worlds,

3:39

which could change how we search for life in

3:41

our own solar system and elsewhere

3:43

in the universe. Stay with us.

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4:32

Chris Impey, welcome to the future of everything. Pleased

4:35

to be with you. People have been imagining

4:37

other worlds and what they might be like for thousands

4:40

of years, but we only started

4:42

finding proof of planets outside our solar system

4:44

called exoplanets in the early 1990s. Why

4:47

are they so hard to find? Well,

4:49

planets don't emit their own light. They

4:52

reflect a little bit of the light of

4:54

their star. So you're trying to detect something

4:56

that's hundreds of millions or billions of times fainter

4:58

than its parent star. And it's like looking for

5:01

a firefly that's right there in

5:03

the stadium floodlights. It's

5:05

been more than 30 years since the first exoplanets

5:08

were discovered, but detecting what

5:10

an exoplanet's atmosphere is made of is

5:12

another thing. It's really hard to do and

5:14

it's only been done for about a hundred exoplanets.

5:17

Why is it so important to get this data? Well,

5:20

we're trying to answer an incredibly profound

5:22

question about the universe, which is, is

5:25

there life beyond Earth? Is this sequence

5:27

of events that led to us, where

5:29

biology started about four billion years ago,

5:32

is that unique to this rock

5:34

around this star in this part of the Milky Way?

5:37

Everything else about the history of astronomy would

5:39

suggest we're not special, but we still don't know

5:41

the answer and that's a that's a big one. So

5:43

the traditional astronomical definition

5:45

of a habitable planet is one that's in the

5:48

so-called Goldilocks zone. That

5:50

means the planet surface temperature is one where water

5:52

is able to exist in liquid form. It's

5:54

not too hot, it's not too cold. But

5:57

is that too restrictive, especially since life

5:59

is fast?

5:59

in some pretty extreme environments right

6:02

here on Earth. So the lesson of the

6:04

Earth is that life does not need

6:06

a star. We have life on

6:08

Earth that exists deep in the oceans. That's

6:10

not part of a photosynthetic food chain. We

6:13

have life inside deep rock. We have life

6:15

that can handle higher than boiling point

6:17

of water, lower than the freezing

6:19

point of water. So the bounds on life on Earth

6:21

are pretty wide. We've got

6:24

Europa, the icy and watery

6:26

moon of Jupiter that's very far out. We

6:28

have Enceladus, the little moon of Saturn that's

6:30

even further out that has ice jets and

6:33

subsurface liquid or water. We

6:36

have Titan, which is a bizarre moon

6:38

of Saturn that might have a different form of life

6:40

based on ethane rather than water. So

6:44

the solar system has examples

6:46

where there could be biology. How would

6:49

you define a habitable planet? I don't

6:51

even know that I can do it very

6:53

well because we're kind of stuck doing

6:55

the most obvious thing, which is we look

6:57

for the thing we know. We look for life

7:00

as we know it on this planet when that may

7:02

not be the full spectrum of what you

7:04

might call biology in the universe. We

7:07

look for life that uses liquid water

7:09

as a medium when that may not absolutely

7:11

be true everywhere. So we

7:13

just make these assumptions and you sort of

7:15

do the experiment you can do because you have to know

7:18

how to recognize it. The uncomfortable

7:20

fact of this field is that life

7:22

might be so strange that it's unrecognizable,

7:26

and then how do you define an experiment

7:28

to detect it or find it?

7:30

All right, so just in our own solar

7:32

system, we've got gas giants like Saturn

7:34

and Jupiter. Venus is kind

7:36

of like Earth if it was way

7:39

hotter and had a carbon dioxide atmosphere.

7:42

Plus there are several moons that scientists think

7:44

could be habitable scattered throughout the solar

7:46

system. And that's a lot of variety

7:49

just for our own neighborhood, so to speak.

7:51

What are astronomers learning about what kinds

7:53

of exoplanets are out there so far? Some

7:56

of the things we're learning suggest that our solar

7:58

system may not be typical. The most

8:00

common type of exoplanet is actually

8:03

a super-Earth. Well, we don't have a super-Earth

8:05

in our solar system. So the most common type

8:07

of exoplanet in the galaxy doesn't

8:09

exist in our solar system. And it leaves us

8:12

scratching our heads and wondering, you know, are we

8:14

typical? What is a super-Earth?

8:16

It's roughly two to three times Earth's size

8:19

and six to eight times Earth's mass.

8:22

And so it's a heftier version of the

8:24

Earth. And it'll have probably a thick atmosphere.

8:27

It'll almost certainly have active geology.

8:29

They're probably super-habitable. So they're

8:31

of great interest. They're actually a little easier to

8:33

study than Earth themselves. There

8:35

aren't any missions planned to go to exoplanets.

8:38

But space agencies are planning several

8:40

missions to moons in the outer regions of our

8:43

solar system. One of these, the

8:45

European Space Agency's Jupiter Icy

8:47

Moons Explorer, or JUICE mission,

8:50

launched in April and should reach the planet

8:52

in 2031. What does

8:54

this have to do with habitable exoplanets

8:56

or exomoons? Well, the JUICE mission

8:59

is going to inspect several moons of

9:01

Jupiter. But probably the most exciting one

9:03

to most people is Europa. It's not

9:05

going to land on the surface or drill

9:07

through the ice. It drops a probe and

9:10

then sniffs the gas or ice

9:12

that splashes off and looks for organic material

9:15

and possibly life. Because the outer solar

9:17

system doesn't get a lot of attention. It takes a

9:19

decade to plan a mission, a decade for it

9:21

to get out there. They're all expensive, multi-billion

9:24

dollar missions. So we just don't go there very often.

9:26

So this is a valuable one. Let's

9:29

put some numbers on it. The JUICE mission is

9:31

going to cost about $1.7 billion

9:33

by the time it's complete. And another mission

9:35

that NASA is working on, the Europa Clipper

9:38

mission, which is just going to study one

9:40

of Jupiter's moons, Europa, is

9:42

scheduled to launch in 2024. And

9:45

that will probably cost at least $5

9:47

billion once everything's all said

9:49

and done. What do you say to people who

9:51

wonder why we should spend so

9:54

much money on missions like these? You

9:56

have to put it in the scheme of things when

9:58

that public is asked, what fraction of their

10:00

tax dollar goes to NASA, they always

10:03

overestimate, you know, they say, oh, it's a dime

10:05

or a nickel of my tax dollar. Well, it's not, it's

10:07

like a few tenths of a cent and only a fraction

10:09

of that goes to planetary science and the things we're

10:11

talking about. It's really a very small

10:14

amount of what we spend, especially on military things.

10:17

For context, in the 2023 fiscal year, the

10:20

US Department of Defense budget was more than $816 billion.

10:24

NASA was given $25.4 billion. That's

10:28

a lot smaller, but it's still a lot

10:30

of money. So when we're talking about missions

10:32

then to Jupiter and its moons, what

10:34

would we have to learn to make these missions

10:36

worth it? You know, we sort of want

10:39

to answer the question the most direct way

10:41

and say, yes, there's microbes,

10:43

there's DNA, and it's either exactly

10:45

like our form of life or different, either way,

10:48

that's interesting. But really,

10:50

we're just iterating towards that

10:52

answer. These missions are not profound

10:55

enough. You just can't send a full biology

10:58

lab to the outer solar system.

11:00

So you have to put a compact package

11:02

together and learn as much as you can and sort of

11:04

just see if the ingredients for life are

11:07

there. And so what might we learn from

11:09

studying some of these moons around Jupiter

11:11

that could be applied

11:14

to the search for exomoons outside our

11:16

solar system? Planetary scientists

11:18

think there are probably a dozen habitable

11:20

locations in the solar system, which

11:22

includes the objects we talked about, but also some

11:24

of the moons of Uranus and Neptune further out

11:27

that we don't know much about, maybe even Pluto itself.

11:29

These are places where there's no liquid water,

11:31

of course, on the surface, but under the

11:34

pressure of ice and rock and heated by

11:36

the rocks from the interior, you can have liquid water.

11:38

You've got organic material, the local energy

11:41

source, that's all you need for life. So if

11:43

you have a dozen habitable spots

11:45

in one solar system, but only

11:47

one habitable planet, Earth, then

11:50

that's an order of magnitude more places

11:52

where there could be life in the universe. Just

11:55

ahead, how new technology is helping

11:57

astronomers take a close look at distant-

14:00

do that experiment and then maybe by

14:02

next generation of space telescopes. You

14:04

have to design and build your optics

14:07

really well within the telescope to

14:09

occult the central star and

14:11

blot it out and then you can

14:13

extract the little signal from

14:15

the reflected light of the star. What

14:18

does that mean for us here on Earth? It's

14:21

an interesting dichotomy. Either life

14:23

on Earth was a unique accident and we're alone

14:26

in the universe or we're not.

14:29

So we're really just trying to look for other forms

14:31

of life beyond Earth and we're looking

14:33

for the most simple forms of life, microbes,

14:36

bacteria. The only way we

14:38

really have a handle on simple forms

14:40

of life is when they're pervasive

14:42

enough to alter a planetary atmosphere

14:45

completely. That happened on the Earth because

14:47

the oxygen we breathe was produced by microbes

14:50

billions of years ago and there's one part in

14:52

five of our air. That's a pretty dramatic

14:55

imprint on an atmosphere. So

14:57

we'll do the same kind of experiment with exoplanets.

14:59

We'll look for oxygen, we'll look for ozone, we'll

15:02

look for methane and we'll look for water vapor

15:04

of course because we want to know that there's water

15:06

since life on Earth all depends

15:08

on water. What are the chances that

15:11

we'll find other forms of life on exoplanets

15:13

or exomoons? Well I would

15:15

say it's at a very interesting stage. We've

15:17

already found planets that are as close to Earth

15:20

as we're likely to find and so this experiment

15:22

of inspecting the atmosphere and looking for

15:24

alteration due to biology, that's a

15:26

game that probably will succeed or fail

15:29

in the next five to seven years. It's

15:31

not going to be a clean, crisp answer

15:33

because these spectra are going to be kind of

15:35

ratty, kind of noisy, a little

15:38

ambiguous to interpret. You're not going to get

15:40

the smoking gun of life. It's not

15:42

going to be that simple. One

15:44

example probably won't convince you because there's

15:46

always uncertainty and so you'll probably want six

15:49

or eight or ten. And once you get up to

15:51

that number, if you find nothing on

15:53

any of them and they were all very habitable

15:55

as far as you knew that life on Earth could

15:57

survive these environments, start

16:00

to think, well, maybe what happened on Earth was

16:02

kind of unique or a fluke or special. And

16:05

if we find many or

16:07

several from that first sample,

16:09

then game on. We have a whole new field

16:11

of science, and then you're really excited. And

16:14

then the question you want to ask is, are they

16:16

the same as life on Earth? Or is it some

16:18

different variation on that? Does

16:20

natural selection, as articulated

16:23

by Darwin, does that operate on these other

16:25

worlds? Do they use the same replicating

16:27

molecule, DNA and RNA? Do

16:30

they organize themselves in cells the

16:32

same way our biological

16:34

life forms do? We have all these questions.

16:37

And of course, if you have microbial life

16:39

in a lot of places, then why wouldn't you have intelligent

16:41

technological life? So the

16:44

sheer abundance of habitable worlds,

16:46

it makes it incredibly unlikely that

16:48

we're alone. But microbes, you know,

16:50

front page headline, the general public

16:52

will probably get excited for a week and then it'll

16:54

fade into the news cycle. Scientists

16:58

will be excited for a long time. That'll change everything. It'll

17:00

change biology. It'll change astronomy. But

17:03

it still begs that second question.

17:06

If you've got microbes

17:07

and you know that on Earth that eventually

17:10

led to us, how often do you get something

17:12

like us? And if it's

17:14

life that, you know, doesn't look anything

17:16

like us, I mean, how

17:18

would we even recognize that, you

17:21

know, as life? I

17:23

think that's exactly the right

17:25

question. And that's an unfortunate question

17:27

because you, you know, you look

17:29

for the things you can detect. So

17:32

it's quite possible that alien

17:34

forms of biology will be inscrutable,

17:37

unrecognizable, so different

17:39

that we're not designing the right experiment to

17:41

even look for them. That's even

17:43

been true of Mars. People have argued

17:45

going back to the pioneer, going back

17:47

to the first Mars missions, that

17:50

those early life detection experiments only

17:52

looked for terrestrial metabolism

17:55

mechanisms. And if it had been some

17:57

slightly bizarre mechanisms, they

17:59

would. wouldn't have found life. And

18:02

so the null result of the experiment was

18:04

not meaningful. So aside from whether

18:07

or not life has evolved elsewhere in the universe, what

18:09

else can we learn from studying exoplanets?

18:12

Well, planets change over cosmic time.

18:14

And so there are natural forces that change

18:17

the atmosphere and the interior of a planet.

18:19

And so exoplanets are all little

18:21

object lessons in how planets like

18:24

ours evolve. And so I think we'll

18:26

learn a lot about the evolution of

18:28

habitable worlds, independent of

18:31

what the human footprint on a habitable

18:33

world is. And that's going to be helpful. So I

18:35

think it's safe to say that I'm never going

18:37

to be able to visit an exoplanet in my lifetime.

18:39

And chances are, probably neither

18:42

will my kids or my grandkids, right?

18:45

It's really cool to know that there are these other

18:47

planets out there in the universe. But do

18:49

these discoveries really change anything for

18:51

us here on Earth? I think they will

18:53

only change something if we find intelligent

18:56

and technological life elsewhere. That

18:59

could change something. Because then

19:01

you're communicating through light. You're

19:03

not imagining that you would travel there because the distances

19:06

are so large. If there are microbes

19:08

elsewhere, that may or may not inform

19:10

us about terrestrial biology. I mean,

19:12

it would to a biologist. But it may not affect

19:15

how we live on this planet. If we

19:17

find intelligent life, of course, we've got a lot of

19:19

questions to ask. University

19:23

of Arizona astronomy professor Chris Impey.

19:30

The Future of Everything is a production of the Wall Street

19:32

Journal. Stephanie Ogan Fritz is the editorial

19:34

director of The Future of Everything. This

19:37

episode was produced by me, Danny Lewis.

19:40

Our fact checker is Aparna Nathan. Michael

19:42

Laval and Jessica Fenton are our sound designers

19:45

and wrote our theme music. Catherine

19:47

Milsop is our supervising producer. Aisha

19:50

Al-Muslim is our development producer. Scott

19:53

Salaway and Chris Inslee are the deputy editors.

19:56

And Philana Patterson is the head of news audio

19:58

for the Wall Street Journal.

19:59

Like the show? Hi friends! And

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leave us a five-star review on your favorite platform.

20:05

Thanks for listening.