Gravity Assist, Season 5, Episode 24: Do Other Planets Make Pollution?

Is there intelligent life beyond our solar system?

And how are we ever going to find it?

No one signal is a good signature of technology or biology.

You need a combination of things.

Hi, I'm Jim Green, and this is Gravity Assist, NASA's interplanetary talk show.

We're going to explore the inside workings of NASA and meet fascinating people who make space missions happen.

I'm here with Robbie Canup and he is a scientist at NASA's Goddard Space Flight Center who thinks a lot about the signs of life and what they might be on a planet outside our solar system.

We call that planet an exoplanet.

Robbie makes climate models of exotic far away worlds and investigates how we could detect biology, but also technology coming from these exoplanets.

Welcome, Robbie, to Gravity Assist.

Thank you, Jim.

I'm super excited to be here.

Well, you know, I heard that you used to study something completely different, gravitational waves.

What are those, and and why did you stop working on that particular topic?

Yes.

So, I did my PhD in physics in the field of gravitational waves.

To give a brief summary, imagine your throwing a rock into a clear water, and the ripples after you throw the rock into the water, the ripples coming from there are essentially what we think of as gravitational waves coming from an object.

Any object in this universe has gravity.

And so, gravitational waves are essentially when you have a moving object, a very dense moving objects going around each other or, you know, exploding stars.

They emit these space time waves, you know, Einstein theorized that there could be a space time, right?

So, these are the space time waves traveling across the universe.

Why did I leave this field?

I was at Penn State working as a postdoc on gravitational waves, but at that time I heard about these new field of science that's just coming out, exoplanets.

And I was like, okay, wait, this sounds interesting.

And the main thing I wanted to do is like can I explain my work to my mother?

And and if she asks me, hey, Robbie, what are you doing?

And I'll say, oh, I'm working to find alien life.

And that's simple for me to explain to her.

And it was exciting, and my daughter used to say that, you know, my dad finds aliens.

I felt like a Hollywood star.

And so, I said, okay, let's go ahead and do it.

And then that's how I started.

Well, that's fantastic.

But you're really doing it in a very important way, and that is looking at atmospheres of exoplanets, and not just any old atmosphere.

How did you end up making that decision?

Right.

So, the reason why I study these atmospheres of exoplanets is because I think the ultimate goal of answering our the question, are we alone in this universe, with the existing telescopes and existing instruments is to look at the atmospheres of these exoplanets because they're so far away,

it's uh really uh not likely anytime soon for us to travel to those uh planets, right?

And so, the best thing we can do at this point is to point our telescopes, collect the light coming from the atmospheres of the planet, and then look what kind of gases they are.

And that was exciting to me.

And so, I started working on the climate models of these uh planets.

Well, why do you think, and I believe it's the majority of planetary scientists and astrophysicists, think that there could be complex or intelligent life on planets beyond our solar system?

So, just to give you an idea, right now, we know more than 5,000 exoplanets, planets orbiting other stars.

On an average, now we think there is at least one planet for every star in our galaxy.

And our galaxy has at least a minimum of 100 billion stars.

So, there are at least 100 billion planets in our galaxy.

And imagine the statistics of having so many planets around in our galaxy, and many of them could be smaller Earth-sized planets that could host life.

Well, I know you've done some really fascinating work on exoplanet climate models.

What are some of the climate conditions you expect on these exoplanets?

If you asked me this question 30 years ago, I would say, oh, all of them are going to be Earth-like conditions or maybe, you know, Jupiter-like planets because how else planets are going to form other than our solar system like arrangement,

right?

Right.

Come on, who would everyone should look like us, right?

So, of course.

But then what?

Guess what happened in 1995 when they first found the exoplanet, the first exoplanet around a Sun-like star.

It's a Jupiter-sized planet in a 4-day orbit around a Sun-like star.

Wow.

And yes, and and it was unexpected, and that's why we wanted to see how these planet conditions are going to change from star to star.

What we are seeing is only a small subset of the climate conditions that we are discovering right now.

Super hot, small size planets, large size planets, and also habitable Earth-sized planets are also we found them in with lots of different kinds of missions.

One important thing, though, Kepler mission, which was launched in 2009, found that the most common type of planets is somewhere in between Earth and the Neptune size.

And we don't have that in our solar system.

Yeah, we call that a super Earth or a mini Neptune.

Exactly.

Yeah, so something happened as our planets evolved that that one of those didn't form.

What do you think that was?

Those kind of planets are uh somewhere in between uh transitioning between a gas giant and a rocky planet.

Uh they don't have as dense atmospheres as Jupiter or Neptune or they don't have completely thin atmospheres like our Earth.

They have somewhere intermediate between uh both the planets.

They may have a little of hydrogen, little of uh you know, uh carbon dioxide or ammonia, but not too much, but not too little.

That's what makes them fascinating that we don't see them in our own solar system.

But we can see them around other stars.

Well, are there any exoplanets that you're really excited about right now?

Yes, actually.

Our closest star is Proxima Centauri.

And uh 4 or 5 years ago, uh astronomers have discovered a planet, an Earth-sized planet in the habitable zone around Proxima Centauri.

It's called Proxima Centauri b.

So, this is what I'm really excited about that opportunity right now.

Well, that star and the planet is only about 4 light years away.

There's another uh planetary system a little further that I'm also excited about, and that's TRAPPIST -1, and that's at about 40 light years away.

What can you tell us about the TRAPPIST-1 system of planets?

So, you asked if I'm excited at what kind of a planet I'm excited about.

I said Proxima Centauri b.

Well, we won't be able to characterize uh or at least look at the atmospheres of the planet in the next decade or so.

But with TRAPPIST we have James Webb Space Telescope up there, and it is one of the primary target in the habitable zone planets uh with James Webb Space Telescope.

So, uh the there are seven planets in that system.

TRAPPIST-1 system has three habitable zone planets uh in it.

We would like to see if the planets themselves can retain the atmosphere because the star is pretty small, and these small stars usually have a very high flaring and ejections of very high intensity X-rays and the UV rays.

So, we would like to see first of all, do they have any atmosphere?

And if they do, do they have water-based atmosphere?

Because water is essential for life.

It turns out that star, as you said, is a small dwarf star.

Those planets are really close, and like our moon, are they tidally locked?

Do they always have one face pointing to the star and the other pointing away?

Yes, they are uh tidally locked.

In fact, I would even go ahead and say they are synchronously rotating.

Essentially, what it means is what moon is doing to us, always facing the same side uh of the planet to the star.

Uh and because of that, so this is exactly what I do in my research work, in my climate modeling.

We model these tidally locked planets around these cool stars.

And and because these planets are tidally locked or or synchronously rotating, facing only one side all the time, the climate and the weather is completely different than what how we have it on Earth.

For example, if you are on that planet, there is always a thick cloud cover right in front of the Sun side of the planet.

Always, all the time.

And because of that, uh that cloud will uh try to protect or at least try to not increase the surface temperature as much uh as uh it wouldn't have if you if you don't have the cloud cover.

And so, the climate is totally different.

Well, what is the concept of this habitable zone around a star?

So, uh the way we define in the exoplanet uh field uh the habitable zone is uh it's the region around a star where a rocky size planet with suitable atmosphere has liquid water on its surface.

And you can see how I carefully try to craft this definition.

Well, liquid water is essential for life, and so we want to see if there is a liquid water on the planet.

Why surface?

Why not sub surface?

Uh well, these planets are exoplanets.

They are quite far away from us.

So, within our solar system, there are Jupiter's uh moons and Saturn moons where we think there are there is sub surface liquid water.

So, we had the luxury of sending missions to those planets and see if we can find the water under these moons.

We don't have that kind of luxury for exoplanets.

So, we have to focus only on the surface liquid water, and that's the reason why we focus a habitable zone concept on that.

We have to understand that our Earth's example is only one possible way of having life and intelligent life.

So, every planet's evolution would be uh different.

So, that that that's something that uh when we have to look when we are looking for exoplanet life.

Yeah, in fact, one can also think that we actually co-evolved with the Earth.

We were in the right place, the right time.

Our moon helped us in many different ways.

Our climate was great, and that really enabled us uh to develop into an intelligent beings.

This brings up a really fascinating topic, and that is uh how might we detect signs of technologies developed by intelligent beings on other planets around other stars?

And we call that technology techno-signatures.

So, what kind of techno-signatures should we be looking for?

So, we know already one techno-signatures that several of our colleagues are doing, the radio techno-signatures, the radio it's called the SETI, search for extraterrestrial intelligence.

There are other ways that we can do.

For example, pollution uh on uh in on the planet produced by industrialized civilizations.

Uh maybe they have some sort of a uh laser pulses sending as a uh beacon towards us.

We can also detect them with the night side city lights.

Every civilization needs energy to produce and, you know, to sustain.

If we can build a telescope and look at the planet and uh if we detect night side uh city lights, we know they that's a one of the techno-signatures.

So, there are several of them like that.

Chlorofluorocarbons, the CFCs that we use in our refrigerants.

There is nothing in the nature that we know of and that we can think of that can produce CFCs naturally, biologically, or a even abiotically.

There is only one way to do that, and that's through technology that we know of.

That begs the question, then, what would be the next set of observations you would then make?

Okay, this is even another excellent point.

No one signal is a good signature of technology or biology.

You need a combination of things.

Okay?

So, if you find CFCs and you think, oh, maybe that's a technology, then you want to find corresponding uh other kind of pollutants in in in your data.

And maybe for that you need to have a different kind of a telescope to do that because not everything will be seen at the same time.

And so, if you find several different signatures of gases, if you do find other pollutants, then you know, hey, you know, there's something going on on that planet.

Uh that's great.

One of the important things that we have to do is remove or identify false positives.

Now, what do you mean by that?

Ah, that's a good point.

And and also false negatives, I'm going to say about both of them.

Okay?

The false positive is that you detect a signal, and you think it is your the signal that you want, you know, I found an alien techno-signature or something.

But then it turns out to be oh, something the nature produced or maybe some instrumental problem.

So, that's a false positive.

False negative is you detect something and you say that, oh, it's a instrumental noise, it's nothing there, it's from coming from the star, but it's actually is a signal from the thing that you want to detect.

Yeah, I'm concerned about that, too, as you probably know.

You know, we have to be able to be confident, you know, create a level of confidence in each one of the observations.

But what's exciting about the field is we make these uh analyses on signals, we get that out, the scientific community uh thinks of new and inventive and creative ways to either disprove the idea or enhance the idea.

And that's the process of science that we want to have.

Well, I have to tell you, you know, there'll come a time when we may have to say, we're very confident that we have seen signs of extraterrestrial life.

Do you think we, humans, as a civilization here on Earth, are ready for that news?

I think we are ready.

I I I 100% believe we are ready.

And I'll tell you why.

Okay, because I've been asked that and I've said I don't think we're ready.

Okay.

So so I'm I'm very fascinated to hear your response.

Okay, so so I I like to say this with the discoveries of exoplanets and with the discoveries of you know, habitable zone Earth, we we're with water on Mars and every aspect of science,

we are not suddenly breaking out.

It's not 30 years ago if you say that, oh, we found a life on other planets, then everybody oh, what what did you do?

No.

So here we found we were saying that okay, we found several thousands of planets, we are inching closer and closer.

So we are getting everyone ready to accept to the point that hey, you know, that's we are finding lots of neighborhoods, we are finding lots of houses.

It's just a matter of time before we find people in those houses.

Okay.

So I think we are ready.

All right.

Uh I don't think we're ready.

And the reason why is I'm not sure what the observations are that will will be the smoking gun that tell us what we have really found when we actually make the announcement.

And and that's going to require a lot more educating everyone as to what we've really measured and why we really think we have a high level of confidence to determine that it's life.

Okay, that's a scientist's problem, not the general public's problem.

Okay.

Okay.

Well, you know, I've also heard that you've been involved in looking at unidentified aerial phenomena or UAPs.

And and you're approaching that from a scientific perspective, of course.

Can you tell us a little bit about that?

So this is what I say when we talk about the UAPs and search for life.

They're two completely independent topics.

We cannot combine them unless we have super compelling information that okay, they are somehow connected.

For me, the search for life is what we just talked about all this time, exoplanets and telescopes and instruments and whatever.

UAPs are something that are in our skies and we don't know what they are.

And essentially that's where I stop and say okay, because we don't know what they are, we have to observe them with different instruments, collect the data, analyze, and then you figure out what they are.

Apart from that, everything else is speculation.

And this is what I call a scientific applying a scientific methodology to studying the UAPs.

These UAPs may not be technological in nature.

The many possibilities are atmospheric events or other natural phenomena.

We just don't know yet.

Well, do you have an update to make a determination or or do we still lack a lot of knowledge and observations of UAPs to make a determination?

I think we do need a lot of data collection of data before we do any kind of a determination.

And That's where we are right now, collecting the data.

Well, Ravi, I always like to ask my guests to tell me what that person, place, or event was that got them so excited about being in the sciences that they are today.

And I call that event a gravity assist.

So Ravi, what was your gravity assist?

My gravity assist to there were two of them.

One before I entered my PhD program, I I'm a big fan of Star Trek and I felt that that was a community where I could relate to and I wanted to study life from,

you know, other planets.

And that really really motivated me since I was in eighth or ninth grade.

And and that really motivated me to pursue science, math, physics, and I I was told to do well in those to become a scientist.

And I kept that goal all the time all all through my life.

The second one was that happened about nine years ago when I was writing a paper and the paper was about how common are Earth-like planets in our galaxy.

And I found I did some calculation and I found that there are more than what I expected.

And I literally jumped out of my chair, like literally.

I was like, this can't be possible.

I'm standing in front of history that's happening right now that we for the first time in our life, we know how common are Earth-like planets.

And and that really motivated me to study you know, how do we find even more?

How okay, if they are so common, where can we find this life?

And that's really motivated me to pursue more and more opportunities and that's why I'm at NASA Goddard because this is where the missions happen.

This is where we try to find life on other planets.

And that's that's my second gravity assist, I would say.

Well, that's fantastic.

You know, your excitement about the science and the things that you learn propel you to keep going and it accelerates you.

And hopefully you'll be the one to announce that we have found life beyond Earth.

Oh.

I I hope you will be with me at that time, Jim.

I'll at least be able to interview you.

Well, Ravi, thanks so much for joining me for this fantastic look at finding habitable worlds in other solar systems.

Oh, thank you so much, Jim.

This is wonderful.

Thank you.

Well, join me next time as we continue our journey to to look under the hood at NASA and see how we do what we do.

I'm Jim Green and this is your Gravity Assist.