Cosmic Queries – Life on Exoplanets with Sara Seager

Welcome to StarTalk, your place in the universe where science and pop culture collide.

StarTalk begins right now.

This is StarTalk.

I’m your host, Neil deGrasse Tyson, your personal astrophysicist.

And this week is a Cosmic Queries edition, the always popular Cosmic Queries.

And the topic, the always popular search for life in the universe.

And I’ve got with me is my co-host, Matt Kirshen.

Hey, hey, Neil.

I spent all day yesterday trying to memorize the name of your podcast.

It’s probably science.

Did I get it right?

It is.

I always confuse you for another variant.

I stumbled in my efforts there.

I found a podcast called Sometimes or Mostly Science.

It’s a whole other podcast.

Oh, we hate them.

No, we’ve got a running rivalry.

You totally have a rivalry.

I’ve got to make sure I get your stuff right.

It’s going to come to violence at some point.

Probably violence.

I know a little bit about the search for life, but not as much as our guest today.

Our guest today is Sara Seager.

Sara, welcome to StarTalk.

Thanks for having me today.

Sara, let me get your full title up here.

You’re a professor of aeronautics and astronautics, physics and planetary science at MIT.

No, they left out a few categories.

No, it’s because exoplanets and the search for life is an incredibly interdisciplinary topic.

It draws upon all those different fields.

Excellent.

But between you and me, you’re a planetary scientist, right?

Yes.

My home is really in astrophysics.

You can call me an astrophysicist or a planetary scientist or both.

In the club.

I guess the search for life in the universe has to necessarily include the search for exoplanets, right?

They go together.

But is that part of our bias?

Not necessarily.

We’re definitely teracentric.

We definitely are narrow-minded.

But at the same time, yeah, like earth-centric, you know, and on Earth, we believe that for the origin of life, we need a place for ingredients to concentrate.

And it’s hard to imagine ingredients just, you know, concentrating in the vastness and that low density of outer space.

OK, so this concentration thing, I think, is under-celebrated out there.

I mean, in the public, people, we take it for granted that we have rocks and buildings and mountains and people.

And for in our greater universe, nothing is together.

Mostly it’s mostly empty.

And where it’s not mostly empty, it’s highly rarefied.

And so planets are really special places.

Is that right?

They are very special because they do concentrate complex molecules.

They concentrate elements, nutrients and everything we need.

Am I right in thinking they are substantially less special or at least less rare than we thought they were even five, ten years ago?

Yes, actually.

We are slowly making ourselves less and less precious, less and less special.

No, Sara, it’s okay to know that.

You’re not just supposed to tell people that.

I think that’s nice about science.

I like the fact that scientists sort of switch between going, you’re incredibly special and you’re not special.

Well, we do.

We love thinking back to the Copernican Revolution, where before Copernicus, the model of the universe was that our Earth literally was at the center of the universe.

All the planets and the sun and the stars, apparently all orbited Earth.

I think I’ve heard, is it Andrewian described this sequence, some combination of her and the Carl Sagan camp, referred to it as the sequence of great demotions for whatever we imagined ourselves to be.

Plus, there was some rebuttal to that.

I forgot the fellow’s name, but he wrote, I think convincingly, that the idea that we are in the center is not necessarily an elevated place, if heavens are above us.

So the center could be the slag heap of where everything collects, and your ultimate goal is to ascend from that to greater places.

But in either case, the location was unique, I think.

Interesting.

So in his mind, we are like the plug hole of the universe.

We are sort of a drain.

So Sara, was it natural to transition from exoplanet discovery to the search for life?

Or did someone have to sort of nudge you, or was it just obvious as the next thing to do?

You know, every scientist is different, and I’ve sort of been the random walk type of scientist.

Like, work on a problem and see a more interesting problem, and then move over slowly.

Do you like the dog being distracted by the squirrel?

Squirrel.

But when you started out in the late 90s, we didn’t know many exoplanets, and even those that we did, it was fun to think of aliens on them, but there was no research program there yet.

So it seems to me you were there at the birth of this, if not having birthed it yourself.

Yes, and in fact, but just to go back even further, before my time, perhaps even before yours, but in the decades past, since…

Even before Neil!

There is no such thing.

No, okay, well, you know, what’s interesting is if you look back, like even just after the time of Sputnik, like in the early 1960s, there’s actually a report from a think tank kind of company, and it actually talks about planets and exoplanets and the chance for other Earths.

And even in the decades after that, you know, there were always studies on how would we go about finding another Earth.

And so when exoplanets was born in the mid 1990s, and yes, I was there, I was a graduate student working on exoplanets at the time, you know, they were hot Jupiters, they were not suitable for life in any way, but slowly those two things came together, you know, all the past decades of thinking about Earths, then switching gears to the hot giant planets.

And so the thought of finding Earths in life, it was kind of always there in the background, even though it might have been a bit of a stretch.

And just to be clear, the Jupiters that you’re referring to being hot, was it was easier to find really massive planets first, compared to low mass planets.

So you’re going to find a Jupiter first, and they’re hot because why?

Because they’re very close to the star, so close to the star that as heated by the star, they’re just hot.

Okay, so the Jupiters, but they didn’t look like our Jupiter.

So there again, we were not.

So we thought we were representative of the universe and we’re not.

I mean, at least our solar system.

Right, right.

We always expected to find a Jupiter where our Jupiter is, which is, you know, five times further from our sun than Earth is.

And instead, we found Jupiter mass objects within a few, you know, few day period orbits of the star.

So even our bias, which shows up every day in race relations and sexism, it even shows up in astrophysics.

It did, yeah.

And, you know, the funny thing is, just to take that a level further, when we people first found these hot Jupiters so close to the star, we just assumed that they had the same albedo, the same reflectance properties as Jupiter itself.

Jupiter is quite bright.

You know, you see it in the sky because it’s got icy clouds.

And we couldn’t see Jupiter in reflected light.

And with a little more thought, we realized, wow, these hot Jupiters, they’re incredibly dark.

They’re very absorbing.

They have no reflective clouds.

Okay.

So they’re not only…

So they’re big Jupiters that don’t look anything like Jupiter.

Like, I mean, yes and no.

They don’t appear like their atmospheres aren’t like Jupiter, but they’re kind of bulk composition.

They’re mostly made of hydrogen and helium.

That part’s the same.

So if you come to this as an astrophysicist, planetary scientist, and now you want to think about life, you got to start knocking on the doors of biologists.

So when did all that happen?

Remarkably, it really, it started happening for me when I had my first staff position.

I worked at a place called the Carnegie Institute of Science, and I was in Washington, DC.

And it’s quite interdisciplinary there already, and they were already part of working on the somewhat new field back then of astrobiology.

So I started interacting with biologists there, and the funny thing was is I got a postdoc there, and I signed him up to work with me.

And it literally took us like nine months before we could even understand each other, because our language was so different.

So you need the coffee lounges, you know, between at the intersections of departments, because otherwise we just live in our stovepipes and discoveries go unattended to.

It’s true.

And later on I attended an astrobiology conference, and I met a remarkable person there who became one of my closest colleagues.

And so then through him, him being a biologist, I was able to learn and create more collaborators.

And so, I mean, you have a fascinating story.

I only recently learned that you’ve actually collected that together in a kind of a memoir, The Smallest Lights in the Universe.

So congratulations on that memoir, published by Crown in 2020.

And because we’re all distracted by big explosions and big lights and big things, but maybe the smallest lights in the universe, I guess these are the exoplanets, or it could be metaphor for other things in the book, that it’s just to call attention to other previously underserved domains of the cosmos.

Thanks.

So let’s get straight to this.

What is life?

You know, in Exoplanets, we have a good excuse for completely avoiding that question.

I’ll run it by you.

Because we have telescopes and we can see atmospheres of other planets.

We’re hoping with our next generation telescopes to see atmospheres of small rocky planets.

And we’re going to look for signs of life by way of gases that might be attributed to life that have accumulated in the atmosphere.

So we prefer to think about what life does.

Life metabolizes.

And it may give off gases during that chemical process of metabolism.

So we conveniently sweep that under the rug and we just talk about what life does.

And you sweep it under the rug because you can’t do anything about that question anyway.

We can’t do anything about it.

And it’s just a question that no one wants to agree on what the answer is.

So you sweep it under the rug and say, let’s do what life, let’s observe what life does.

So you’re the atmospheric gases equivalent to the people who study animal poop.

For example, it’s things that life does, even if you’re not studying the life itself.

That’s right.

Not to equilibrate your study with the study of feces.

And actually, Neil, that has never been done before.

So that is brand new.

It’s a brand new analogy.

So you’re saying atmospheres on planets are kind of the animal remains of the galaxy?

Well, the gaseous effluences, I guess.

Yes, actually, that’s a great way to look at it.

So, Sara, but clearly there are gases out there.

And I want to get to the Q&A because Matt has them lined up.

And I don’t want to lose any time on that.

But clearly there’s some gases, let’s take methane, for example, that we know is the byproduct of life, not all life, of course, but some bacterial life on Earth.

We know that.

So now let’s look to another place, like Saturn’s moon Titan.

Oh, my gosh, it’s completely covered in methane.

So it must be teeming with life.

So, but it’s not.

So, how, what, Hugh?

Yeah, that’s the single most biggest problem, that we need to be able to see other gases in the atmosphere and put the gas in question in context with what else is there.

But even doing that will be, it’ll still be hard.

It’ll be very, like a forensic crime scene, you know, how do we pick out what is really life, what is really not made by life?

So the gases you list that are the products of life are necessary but insufficient to prove that there’s life.

Yes, actually.

And that is the sort of, let’s call it the dirty secret of the whole field.

Because that will never be able to prove it.

So in forensic crime scene terms, you’ve sort of got to distinguish between blood that was caused by the crime and blood that was just previously existing sort of decorative blood in that room.

Precisely.

Just blood that someone had put there that would just naturally be there on the walls.

The normal blood that exists in the room.

I’m sure Sara is going to put that analogy in her next research paper.

Just put just an equation and that’s all science is, right?

If it’s an equation, it’s legit.

Yeah.

And so on our earth, we have methane produced by life, by bacteria, by cows.

But we also have methane coming out of mid-ocean ridges.

So in a lot of cases, it is definitely ambiguous.

And methane is natural gas that we have in our stoves.

And I’m pretty sure what’s coming out of your stove is not cow farts.

It’s come from another location on earth.

So Matt, we have a couple of minutes left in this segment.

Let’s see if we can squeeze in a question.

Okay, great.

Well, this one, I love the questions that come from our younger listeners.

The questions are all from Patreon today.

This one comes from Carrie Jenkins, an eight-year-old fan.

Eight?

I know.

How long do you think it will take for us to find other life in the universe?

Yeah, how close are we, Sara?

How many more years?

What do we got here?

Well, we actually will have, we like to say we’ll have the key.

I’m not purposely trying to evade all your questions, honestly, but I would like to say that we will have the capability to find signs of life very soon with the launch of the James Webb Space Telescope.

But whether we find life, that really depends on what’s out there.

You know, if every planet has life, if life is extremely common, life that makes gases.

So, if you want a concrete answer, I could say anywhere between two years and 30 years, let’s say.

Okay, so this would be the life, the usable life expectancy of the James Webb Space Telescope.

Well, I was putting the James Webb, whose nominal life expectancy is five years, maybe ten.

I was thinking of future telescopes beyond the James Webb.

Okay, and possibly missions to the icy moons of Jupiter, where there might be life beneath the surface or even life beneath the surface of Mars, right?

I mean, why not?

You’re not looking for that life, but you got other people, top people doing that as well.

Right.

Okay, so we might find life or definitely know there isn’t life as we know it in the lifetime of this eight-year-old girl.

Well, maybe this eight-year-old girl will carry the torch.

If all the searches we’re doing now are exhausted, maybe she’ll be the one to think of the next new idea.

Oh, maybe you all aren’t clever enough and we need her to come along and solve all the problems.

All right, we got to take a quick break.

When we come back more StarTalk Cosmic Queries with my friend and colleague, Sara Seager.

We’ll be right back.

Hey, I’m Roy Hill Percival, and I support StarTalk on Patreon.

Bringing the universe down to Earth, this is StarTalk with Neil deGrasse Tyson.

We’re back, StarTalk, Cosmic Queries, the Search for Life edition.

I got with me my co-host, Matt Kirshen.

Matt, where do we find your podcast?

Oh, just all the podcast places.

All your nearby stores have it.

Any of them, yeah.

Go to your local podcast supplier and just ask for Probably Science, and they’ll find it somewhere in the back there.

Excellent.

They’ll go through their files.

Do you also do stand-up comedy?

I do, well, I used to when indoor things existed.

Right now, I talk into Zoom recordings and pretend I’m doing stand-up.

Okay, this is during the COVID lockdown.

That’s what it is.

Yeah, that was my day job, and hopefully will be again.

Excellent, excellent.

And we have as my special guest, Sara Seager, who’s an astrophysicist, planetary scientist, and is searching for the exoplanet, searching for life.

And she’s our resident expert in this moment to field these questions that Matt has solicited from our fan base.

And this is the Patreon fan base.

So what more do you have, Matt, for us?

Also, by the way, we should mention that our guest today isn’t the only one with a new book out.

And you’ve got a book based on cosmic queries that has a chapter that talks about the search for life.

Oh, yes, indeed.

So thanks for mentioning that because I almost forgot.

I probably wouldn’t have forgotten by the end.

But there’s a book called Cosmic Queries because this format was so successful.

We said we’ve got to do more than just put it out there as a podcast.

So there’s a book called Cosmic Queries that takes all the biggest questions, including this one.

And much of Sara’s research that informs this field is contained in that chapter.

And so in a celebration of Cosmic Queries as a thing and the search for life as a sub thing of the bigger thing, we’ve got Sara Seager.

So, Sara, thank you again for being on StarTalk and for checking in for this.

So, Matt, what do you have for us?

Well, I’ve got to do another Cosmic Query question from another young Patreon listener.

This comes from Violetta and Violetta’s mom, Izzy.

Violetta is a 12 and a half year old astrophysicist here in Birmingham, Alabama.

12 and a half.

When you’re young, those halves are important.

And I asked Professor Seager, I want to know, firstly, what exactly are biosignatured gases?

And secondly, what biosignatured gases would Earth give off that would be detectable by extraterrestrial life who might be looking for inhabited planets like ours?

Perfect question.

Yes, Sara, ready again.

Or would ETs not need to look for our biosignature gases because our existence would be pretty obvious because, duh, space junk.

Yes, well, a biosignature gas is a signature of life.

It’s a gas produced by life that can accumulate in an atmosphere of a planet to a level that we can detect with our telescopes.

You know, I love to imagine, you know, there are intelligent aliens on a planet orbiting a nearby star, and they have the kind of space telescopes we’re building or hoping to build.

They would look at our Earth, and they would definitely see a very strong biosignature gas, and that’s oxygen.

And oxygen fills our atmosphere to 20% by volume.

But without plants, without photosynthetic bacteria, we would have literally virtually no oxygen.

So if all the plant life went away, you know, walked off the Earth today, how long would it take for our oxygen supply to sort of drop to zero?

And why would it drop at all?

Why wouldn’t it just stay there?

Well, we also have bacteria that make oxygen, so I’m not sure, you know, what the division is all about.

No, no, no, just take away everything that’s making oxygen.

Take everything away.

And so now we’ve got 20% oxygen.

What happens to it?

Well, what happens to it is oxygen is a highly reactive gas, and it will just react away with other molecules in the atmosphere, with lots of things on the surface, you know, with gases coming out of vents and volcanoes, and that oxygen just won’t be there.

And how about how much time would that take?

Would it happen like next week or in a year?

No, no, it wouldn’t happen next week.

It probably wouldn’t happen in a year.

It’s probably more like thousands of years.

Okay, or more.

Okay, so if we kill all the life, the oxygen pollution life, we can still live out our lives with oxygen.

Subject generation will suffocate.

Yes, probably we could live out our lives.

Okay, so what you’re saying is even though this 20% has been stable over the, mostly stable, it’s not actually a stagnant number because we are constantly producing it and constantly removing it and it just happens to be balanced at this number.

Is that a fair way to say it?

That’s a fair way to say it.

Okay, okay, cool.

All right, Matt, give me another one.

All right, this comes from Grumsetuff, one word, I hope I’m pronouncing that even close to correctly.

Whatever you did is better than what Chuck does with names.

Chuck can’t pronounce anything.

What is your most optimistic explanation of the Fermi paradox?

I like that question.

Oh yeah, I think we all have our favorite answer to that one.

Well, tell me what it is first.

The Fermi paradox is the idea that if, if there is intelligent life that can harness energy and get in spacecraft and journey beyond their planet, that they should have colonized the entire galaxy by now.

Because once they can get to one planet and colonize that, they can just keep going.

And so the Fermi paradox is summed up by the question, where are they?

So what you’re saying is in the lifetime of the galaxy, it doesn’t really take that much time, if you’re intelligent by our measures, to build spacecraft and start traveling to planets, even if you can’t travel at the speed of light.

Right, right.

That over time, you would eventually reach planets and colonize.

Okay, so all right, so where are they?

Okay, so there’s the explanation I think is the real one, and then there’s the one that I hope is the real one.

So Matt, her explanation would be, they’re already here.

Yeah, that’s the funnest answer, but go ahead.

So, you know, one answer is that it just takes too much energy.

Like we, as humans, we know now what it takes to get in a spacecraft and go somewhere.

That’s a lot of resources.

So perhaps they’re just not doing that.

There’s another answer that the intelligent civilization will unfortunately and inevitably self-destruct.

They’ll destroy their planet, they’ll kill each other, they won’t ever reach that kind of place.

Would that be the definition of not being intelligent?

Yeah, well, it would be…

My explanation that I love is I’ll put it to you this way.

Just imagine an ant colony in your house, you know, what you might have or your apartment.

And the ants, they appear kind of, you know, dumb, but they’re somewhat clever, right?

Because they have a society and you see them doing like a reconnaissance mission.

But just to be clear, just to make sure we’re all on the same page, by ant colony, you mean like one of those ant habitat module things where you can see…

No, I just mean it could be that ant colony habitat or it could just be the ants like in your house.

Oh, just ants in the house, okay.

And I don’t know if you’ve ever had this, but you’ll see like a few of them kind of looking around and they might come across like a piece of cat food on your counter or something.

And then shortly thereafter, you have a huge stream of them and they’re all coming to get this cat food in like a little river.

Well, you can mess them up if you like wipe away their trail for a moment.

They kind of get lost.

But I want you to imagine, you know, Neil, Matt, having a conversation with those ants.

Like tell them about the universe.

Tell them about the Hubble Space Telescope and the vastness of the number of stars and galaxies.

And tell them about calculus and geography.

Yes, yes, yes.

So what I love to imagine is that to these intelligent aliens out there, that we are like the ants.

Like why and how would they contact us?

Okay, so Matt, Sara is bumming us out.

First we’re insignificant, now we’re just plain stupid.

Well, also I think it is worth pointing out there are different, I mean, like Sara was eluding to, there are very different types of intelligence.

You know, I’ve been to university, you’ve both spent a lot more time in academia.

But we’ve all met people who are incredibly smart in specific ways and otherwise idiots.

Okay.

So, you know, maybe they have the ability to travel across galaxies, but they’re not the ability to not shoot themselves within a very short amount of time.

The official answer to the Fermi paradox, where are they?

They think we’re idiots.

Either they think we’re idiots or we think they are for having self-destructed before they could get here.

Touché.

All right, so Matt, give me some more.

So along the lines of interacting with other civilizations, Eric Gross asks, let’s say we discover proof of life not in our own solar system, but on some distant celestial body.

Would there be any meaningful scientific value of the discovery or opportunity to expand upon the knowledge?

It may, of course, have broad societal and emotional effects, but would science practitioners have any real hope of gaining more information about life forms that are at a minimum of 4.3 light years from Earth?

I love that question.

Matt, who asked it?

That was Eric Gross.

Eric Gross.

Okay.

Yeah, so, Sara, I love that question because generally when we think of scientific discoveries or advances, we think, okay, in five years or ten years, engineers will get a hold of it and they’ll make some new device and we’ll all be living better and differently.

And so, life somewhere else that you can’t actually have a conversation with, even if it’s intelligent, are you getting secrets from them?

I mean, if you can’t, or can you?

Are we missing something here?

It’s such a great question.

I mean, we are so wrapped up in the emotion and the excitement of the journey of exploration and of being the first who can try to find out what’s out there.

So, in a practical sense, not really.

I mean, we’re not doing this to find anything practical.

That said, wouldn’t it be amazing if there is life, intelligent life, on the nearest star system for light years away, and we could have a very slow conversation.

We could imagine.

No witty repartee there.

Right.

Send them a message and, you know, four years later, you’ll get their message back, and we could exchange ideas about technology.

So, if we want it to be practical, like, that’s probably the most practical avenue.

So, but in terms of biology, unless we learn from them through these radio signals what their sort of biochemistry is like, we wouldn’t get to compare DNA or if they have DNA at all.

You wouldn’t be able to do any sort of in-situ kind of comparisons to advance biology on life, I would guess.

Is that correct?

No, that’s correct.

That’s correct.

Yeah, but I don’t want to sound like who was that philosopher 150 years ago who said, the stars, they’re just lights on the sky, and we can know, you know, how bright they are in the location, but we will never know what they’re made of.

Right, and think about this, like, we’re just here now.

Imagine a thousand years from now, you know, 10,000 years from now.

We may have a way to get to this.

Imagine if there’s intelligent life on that planet and we do, like, a sample return.

We fly something by, they send something up, we grab it, we, you know, gravitational slingshot around their star and we come back.

So, all right, I’ll just think a thousand years from now, rather than next week.

Well, what you just said, that answer segues quite neatly into this question, which I like.

And I’m going to combine two different questions from what Tom says, who asks, what forms of communication are most likely to be able to cross between the stars?

And Trumpet Womb, who says, how do you think we will overcome the language barrier if we ever meet another sentient life form?

I love it.

And Sara, remember that movie, Arrival?

So, I got in trouble for…

And I knew I was going to get in trouble for saying this.

I said, in the movie Arrival, they brought a physicist and a linguist to try to communicate with the alien when they should have brought an exobiologist and a cryptographer.

And I got so much shit from the linguist out there.

Because this is their one time to appear in a movie.

And there I am just dissing them.

But what is your opinion about how we would actually communicate?

I mean, I love that movie.

I love the concept that it may be so difficult that we may not find a way to communicate.

Okay, so, Matt, she just swept that one under the rug.

Do you hear that?

Neil doesn’t like any of my answers.

She’s sweeping it.

I don’t know how big her rug is in the middle.

But how about mathematics?

How about symbology?

How about, I mean…

I like all those answers.

You’re okay with them or not?

I like it, I like it.

It would have to be something that is fundamental in a very mathematical way.

I agree with that.

Because math apparently applies across the universe.

So if they discover something that is cosmic universal, it will have to be the cosmic universal things we discovered as well, I presume.

So I wonder, so I think one of our greatest triumphs is the periodic table of elements.

If we can like show that to them and see if they have a version of it.

Because there’d be a lot of pantomiming initially, I would guess, before anybody actually communicated.

So it is funny that, you know, aliens often just spoke English, you know, in the movies.

Right, right.

That’s why the Arrival is so great.

Because it’s the first time they have these beings that have no way to really interact with us.

Right, right, right.

So Matt, give me one more question before we wrap up this middle segment.

I will do.

And for the people who are watching the video rather than just the audio, I apologize for the other life form that keeps walking across my lap while we’re trying to record.

I have no way of communicating with him.

Well, so I’m also going to combine these two questions because they’re in similar themes.

So Rob Carter asks, when searching for life on other planets, is there a priority of what type of life you look for?

For example, would a land-based life form take precedence over an aquatic species and so forth?

And then Jonathan R.

Brown asks, carbon-based life on Earth developed in the oceans and diversified exponentially from there, spreading to land and beyond.

Life on other worlds may develop from a different elemental base and begin on land or in other environments.

Could ET life be too alien for us to recognize as life, and what is the baseline?

And we’ll get to that after this break.

See what I did there?

So those are brilliant, amazing questions that are the foundation of so much science fiction storytelling.

But Sara, you have the commercial break to figure out what the answer is before you sweep this one under the rug, okay?

When StarTalk Cosmic Queries returns.

StarTalk Cosmic Queries, the Search for Life edition.

Our guest today is Sara Seager.

Sara, are you active on social media?

Do you have a Twitter account?

Yes, I do.

It’s a ProfSaraSieger, P-R-O-F.

ProfSaraSieger, and S-E-A-G-E-R.

Okay, excellent.

So we can all follow you there.

And I assume you talk about fun stuff, and your research, and the like?

Yes.

And Facebook as well.

You can just search for my name, Sara Seager, on Facebook as well.

Okay, excellent, excellent.

So Matt, we left off with a brilliant pair of questions.

Tell me the two names who asked it again.

Yes, that was Rob Carter and Jonathan R.

Brown.

And they were both asking about the types of life forms that you might find on other planets, whether land-based, aquatic, and so on, and whether we’d even be able to recognize those things as life.

And must they be based on carbon?

Yeah.

Yes, well, we won’t have a chance to see that life.

We’ll only see what life does.

We’ll see the byproducts of that life.

Because the telescopes aren’t good enough yet.

Right, right.

We’ll only see the planet far away.

We won’t even see it in some cases.

It’ll be a pale blue dot, or we’ll just see its atmosphere as backlit by its star.

So we won’t see the animals.

So the point is, when you study the chemistry of the atmosphere, it’s a remarkable feat of observational astrophysics, because the light from the star behind it passes through the transparent atmosphere, and then the molecules leave their fingerprint, and that’s what you’re studying.

Right, that’s the way we’re studying exoplanet atmospheres today.

So we’re a long way off from you watching something wave to you in the telescope lens.

We are, but you know, funnily enough, it doesn’t stop us.

Well, I was going to say, it doesn’t stop us from speculating about what life might be like.

I want you to just imagine for a moment, because there are, exoplanets are so diverse.

They’re different masses and sizes, and we’re imagining their atmospheres are all different.

Imagine a planet where the atmosphere is so massive and heavy that it’s a similar density to water.

So imagine you have a water ocean, and above that is a heavy, dense atmosphere.

You could imagine things like flying fish that can just move between the atmosphere and the water because it’s the same density.

Wow.

We love to imagine a planet that is somewhat dark because of the massive atmosphere.

And we like to imagine this idea of birds with giant wings that are photosynthetic, that the wings are like giant plant leaves.

They can fly up to where there is sunlight and gain energy from the sun that way.

Sara, that reminds me, some science fiction writer, forgive me for not remembering, there was a punchline in it where the aliens come to the Earth, they see what we all do here, and then they return to their home planet and they report on what they discovered.

And they said, they’re all made of meat.

And because we basically eat each other, right?

Life eats other life, unless you’re a plant, in which case you eat sunlight.

So, I mean, just think about that.

So, if you are a bird that has photosynthetic wings, then to eat, like you just said, you just go to an altitude where you get the sunlight and then come back down and you’re not killing anything for your survival.

But then you would presumably be prey for whatever is in the lower levels because they aren’t accessing that sunlight.

You’d want to make sure they’re photosynthetic, too.

But imagine a whole world where that’s the case and they come visit us and we have all these slaughterhouses and not just us, other animals eat other animals.

And this would look like a really bloody nasty place to them.

I mean, you guys ever think about that?

Okay, so tell me also about a carbon-based life.

How important is that?

Yeah, because Sam Couch actually asked this specifically while we’re doing that.

Sam asked, is it possible to have life elsewhere that is not carbon-based?

And if so, what would that look like compared to carbon-based life?

And what would be the requirements for that life to survive?

Yeah, there really hasn’t been a lot of solid work done in that area.

It’s really hard to construct, you know, a biochemistry of like a completely different type of life out there.

We’re not sure if silicon-based life is even really possible.

We think silicon, you know, a lot of our silicon here on Earth, for example, it’s locked away into rocks and there’s just not a lot of silicon.

We think silicon compounds are often, they dissolve in water too easily.

So I think the jury is still out on that one.

Okay, so even though silicon makes the same families of molecules as carbon does, because they’re top and bottom to each other on the periodic table, as we learned in high school chemistry, they’ll all make the same kinds of molecules.

But you’re saying the other properties of silicon molecules make them wholly different from what carbon is giving us.

So our search for life is justifiably carbon-based, not to put words in your mouth, but that’s kind of what you’re saying.

Yeah, you said it well.

That’s right.

Matt, did she sweep any of that under the rug?

No, I think that rug is fully lifted and the items underneath it are exposed to the elements.

All right.

This one’s pitting host against guest here.

Josh V asks, Dr.

Tyson has spoken in the past StarTalk episodes about the idea of Goldilocks zones being antiquated at best and possibly the wrong approach to searching for life.

What is Professor Seager’s opinion on the use and definition of Goldilocks zones as it applies to what galactic locations are prioritized in searching the vast cosmos?

Wow, actually, this is one where Neil and I agree, actually.

So just to go into some detail, the habitable zone is a good construct, the Goldilocks zone.

It helps us think of where we should be looking for planets.

But in reality, I think it really depends on the individual planet.

Like, I want you to imagine a planet that instead of having an atmosphere like ours that is mostly nitrogen and it has a good amount of oxygen, imagine a planet that has a hydrogen atmosphere dominated by hydrogen.

Did you know hydrogen is a nasty, potent greenhouse gas, way worse than any of the gases we have on our planet Earth?

So a planet with hydrogen, it turns out it could still be the right temperature, far outside to what we think of as this traditional Goldilocks zone, because it has such a powerful greenhouse.

And they wouldn’t call it nasty.

They would be thankful for it.

They would need it.

Yes, they would need it.

Right, right.

So I like to think of habitability concept as being, you know, planet independent, not your location in the galaxy or your location in your own planetary system, but dependent on the properties of the planet.

So that’s an enlightened, modern view of the concept of a zone.

So the zone is not a…

it’s a virtual zone in that sense.

Because it can take…

it can be in places that are not just in the narrow minded swath that’s around the Sun.

So that’s good.

I hadn’t thought about these other kinds of Goldilocks zones you’re referencing.

So, yeah, and for all we know, even the definitions we’ve come up with now, 20, 30 years from now, Carrie and Violetta, the 8 year olds, or the 8 and 12 year olds listening to this, in their day, they might look back at our definition, broadened definition of a Goldilocks zone and say, what do they know?

Because for all we know, they could be like life inside of volcanoes or something.

I mean, who knows?

But right, right, and we haven’t observed any rocky exoplanet atmospheres yet.

We’re just beginning.

So right, right, right.

Very good.

Very good.

So what I want to do now is go into a semi lightning round.

And so, Sara, pretend you’re on the evening news and the whole interview is going to last just a couple of minutes.

And so, so this is your sound by quiz.

Can you give us a sound?

You’ve been very good in this program up till so far.

So I think you’ll come out in flying colors.

So Matt, let’s see how many questions we can squeeze in before we call it a day.

We’ve actually got a few questions left if that’s…

Okay.

I think I know the answer to this one.

But Andrew Gundrow asks, my question is about the probability of life in the universe finding each other.

If we think of the universe as infinite and the axis of time as infinite, does it stand to reason that the probability of life in different areas of the universe finding each other on both axes time and space approaches zero?

Ooh, I like that.

My guess is no.

But I want to hear from the scientists.

Yeah, I didn’t totally get that the last part of that.

So he’s saying if everything’s infinite, life should find each other.

So why shouldn’t find each other?

I think I think the question is, if we’re dealing with an infinite universe and a finite amount of life, would that not be so far apart from each other that it couldn’t find each other?

No, he had he added another dimension.

Let’s say life is there and we’re here, and we go there when we find them.

Okay.

If space is infinite, that reduces the likelihood that they’re just going to be there.

They’re going to be probably much farther away from us.

That’s the first axis on this.

The other axis is maybe the life is there now, but they’re not going to be there in a hundred years.

So you have to intersect not only in time, but in place.

And if both the time axis and the place axis are infinite, what hope do we have of ever making contact?

I think I got his question.

I think you got it.

I think that is the question.

Yes.

Yes, yes.

It really all depends on how common life is.

If life is rare, then yes, that question is an answer is valid.

But we all want to believe that we will we see.

But we see the ingredients for life everywhere.

And so we have every reason to hope that on each rocky planet, that’s the right temperature, that there’s a chance for life there, in which case life is, yeah.

Okay, and but but in terms of how far we’ve actually searched, my favorite reference there is an analogy given by a Jill Tarter of the SETI Institute.

And I’ve been so good, I’ve given this 100 times since then.

And we got her to say it on StarTalk.

So we have it bronzed in our archives.

You can ask how much of the universe has researched before we start saying there’s no life here.

And if you look at all the parameter space, time, space, frequency of bandwidth, right?

You could be trying to say hi in one frequency, and they’re trying to say hi in another frequency, and there’s ships passing in the night, and you both conclude that there is no sign of intelligent life.

So she said, it’s like going up to the ocean, scooping a cup, an empty cup, filling it with ocean water, looking at it and saying, there are no whales in the ocean.

So in terms of how much total volume of space-time frequency is searchable.

And so that was depressing but fascinating at the same time for me.

Right, right.

But at the same time, now I’m going to turn the tables and do the opposite of trashing all the comments.

Like, if you’re scooping up that one glass of water, surely there is some kind of life in there.

So we’re thinking that we can look at the nearest stars and the nearest planets and that the ingredients for life are everywhere and that they should come together often enough that we have a chance of finding signs of life.

Excellent, excellent.

So that’s like taking a scoop of anywhere soil on earth is going to be life in it no matter what.

Right, or any air, air parcel.

Even air, very cool.

Very cool.

Matt, let’s slip in a couple more questions.

All right, John David Newman says, Is it possible that the galaxies we observe relatively easily are less likely to have life than the dwarf galaxies or wandering stars in deep space which are more difficult to see?

Could wandering stars or dwarf galaxies in deep space be less threatening to life?

Well, at the moment, we’re only able to observe the very nearest stars.

We can’t see other galaxies.

So that question is out of our purview at the moment.

However, each star is fairly isolated and each star has its own planetary system as far as we can tell.

So it shouldn’t matter which galaxy the planet is in in relation to whether life is there or not.

And we see the same kinds of stars in most galaxies.

There are differences, of course, but that repeats enough, so I agree with you.

We will be perfectly happy searching stars in our own galaxy without having to go to others just to wonder if it’s different.

But another point implicit there is there are some galaxies that have very rocking active nuclei with very deadly radiation coming out.

And it could be that some galaxies are hostile to the formation of complex molecules and more peaceful galaxies like the dwarf galaxies that they may be more hospitable.

I mean, we don’t really know this yet.

And I agree, Sara, there’s still much more searching to go before we start creating a galactic model for what life would or should be like.

Let’s get one more question, Matt, see if we can get it.

All right, well, I’m going to combine these two then, because I’m really on a combining kick today.

These are both quite philosophical.

Jett Thomas asks, we as a species love to stimulate our senses by watching movies, listening to music, telling stories and more.

Assuming an alien civilization is interested in leisure, can we hypothesize what a stimulation of different senses would look like outside of our familiar five and look for evidence of such things?

And then Chris Hampton says, what effect do you think the discovery of alien life would have on society?

Would borders eventually dissipate and self-identification move from Russian, American, etc.

to Earthling?

How long would the initial pandemonium last?

So music, society, culture and art, how would everything change?

In one sound line, Sara.

I think I was going to ask Neil for that because Neil is so articulate and good at speaking.

I think you should take a crack at it.

I’ll take a quick crack at it.

It is interesting when you find something that’s more other than you are from among yourselves, it does act as a kind of binding force.

And sometimes for the good, sometimes not.

But I had hoped that we would have had this kind of binding force in the face of battling COVID.

COVID was like an alien that it doesn’t care what your skin color is or your gender or gender expression.

It doesn’t care.

It’ll infect you.

And that would be a good place to band together and fight it.

And we failed that test.

So I wish I had more confidence than I currently do in how we would react collectively as a species to an alien, be they friendly or hostile.

And the other question was what?

It was about what kind of version of stories and art and music and civilization have and how would it differ from ours?

Sara, do you guys Sara, do you guys think much about the senses that an alien might have?

No, I mean, is that is that something that you could look for?

Look for evidence of or ways that they could have changed their environment to accommodate the different ways that they that they interact with each other?

No, I mean, if you think about it for a moment, our oxygen on Earth, life on Earth, bacteria, cyanobacteria, billions of years ago, they re-engineered our atmosphere.

They completely changed our atmosphere.

So it was unrecognizable.

So we can see giant things like that.

But small things like that animals do or that aliens would do, those are out of our possibility for now.

Yeah, but you’re being like straight scientists there.

But now let me ask you, Sara Seager, the human being who watches science fiction movies, can you imagine if an alien had another sense, what might it be?

Yeah, that’s a tough one.

I don’t have a good answer for that.

I can take any answer and have to be good.

Well, sometimes I do like to think about our own planet Earth and all the intelligent life here, you know, like the dolphins and octopus.

And there’s a lot of creatures here that we think are highly intelligent.

And so I do like to think about how they interact with each other, what signs they give each other.

My favorite New Yorker comic was there were two dolphins swimming together and they’re looking up at two humans talking to each other, looking out of the water and they see them.

And one dolphin says to the other, they face each other and make sounds, but it’s not clear that they’re actually communicating.

Dolphin with brains bigger than ours.

Sara, it’s been a delight to have you on.

And we neglected to even mention that you were co-author on the recent discovery of phosphine, a molecule in the upper atmosphere of Venus, a possible product of life.

I know that that result is still getting contested, but it’s fun to watch science at its best when ideas come forth and people try to explain it in multiple ways.

So just good luck on that.

It was great to see you active in that.

And in your part memoir, The Smallest Lights in the Universe, it’s a delight to see that it contains a firsthand account, not only of your life, but the birth of an entire cottage industry in our beloved field of astrophysics, the search for exoplanets and the search for life itself.

So great to have you on and good luck with that.

Thanks for having me.

All right.

And Matt, always good to have you, man.

Oh, it’s a pleasure.

Thanks for having me.

And we’ll look for you on Probably Science.

Yes, please.

I got it straight.

And also your book as well, Neil.

We’ve got to give that another plug.

Oh, sorry.

Another plug for Cosmic Queries.

If you like this format, and if you’re listening, you probably do, because it’s one of our most popular.

We just put it all in one book.

It’s got the deepest questions.

What is life?

And what is the universe made of?

And how did it begin?

How will it end?

And are there multiverses?

And so we’re very proud of that book as a StarTalk community, because a lot of it has been inspired by shows like this, where you write in and ask your deepest questions.

And that inspired us to put the book out there, and it’s a product of the StarTalk family.

This has been StarTalk Cosmic Queries.

I’m Neil deGrasse Tyson, your personal astrophysicist, as always.