Clara Sousa-Silva is a quantum astrochemist at Harvard. Please support this podcast by checking out our sponsors:
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EPISODE LINKS:
Clara's Twitter: https://twitter.com/drphosphine
Clara's Website: https://clarasousasilva.com

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OUTLINE:
0:00 - Introduction
1:39 - Discovery of phosphine on Venus
14:16 - Phosphine gas
24:29 - Searching for molecular fingerprints
35:26 - What does a quantum astrochemist do?
50:31 - Spectroscopic networks
54:56 - Biosignature gases
57:49 - UFOs and aliens
1:11:06 - Alien civilizations
1:28:42 - Programming
1:35:57 - Why science is beautiful
1:39:50 - How to be productive
1:50:09 - Books
1:51:41 - Meaning of life

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The following is a conversation with Clara Souza Silva, a quantum master chemist at Harvard, specializing in spectroscopy of gases that serve as possible signs of life on other planets, most especially the gas phosphine.

She was a co-author of the paper that in 2020 found that there is phosphine in the atmosphere of Venus and thus possible extraterrestrial life that lives in its atmosphere.

The detection of phosphine was challenged, reaffirmed, and is now still under active research.

Quick mention of our sponsors, Onnit, Grammarly, Blinkist, and Indeed.

Check them out in the description to support this podcast.

As a side note, let me say that I think the search for life on other planets is 1 of the most important endeavors in science.

If we find extraterrestrial life and study it, we may find insights into the mechanisms that originated life here on Earth.

And more than life, the mechanisms that originated intelligence and consciousness.

If we understand these mechanisms, we can build them.

But more than this, the discovery of life on other planets means that our galaxy and our universe is teeming with life.

This is humbling and terrifying, but it is also exciting.

For most of our history, we explored the surface of the Earth and the contents of our minds.

But now, with space-faring vessels, we have a chance to explore life beyond Earth, their physics, their biology, and perhaps the contents of their minds.

This is the Lux Friedman Podcast, and here is my conversation with Clara Sousa Silva.

Since you're the world expert in, well, in many things, but 1 of them is phosphine, would it technically be correct to call you the Queen of Phosphine?

But you still rule by Love and power, so, but while having the doctor title.

In September 2020, you co-authored a paper announcing possible presence of phosphine in the atmosphere of Venus, and that it may be a signature of extraterrestrial life.

There was some pushback, of course, from the scientific community that followed, friendly, loving pushback.

Then in January, another paper from University of Wisconsin, I believe confirmed the finding.

So where do we stand in this saga, in this mystery of what the heck is going on on Venus in terms of phosphine and in terms of aliens?

I think you and the rest of the public are now witnessing a pretty exciting discovery, but as it evolves, as it unfolds, We did not wait until we had years of data from 10 different instruments across several layers of the atmosphere.

We waited until we had 2 telescopes with independent data months apart.

But still, the data is weak, it's noisy, it's delicate, it's very much at the edge of instrument sensitivity.

And so We still don't even know if it is phosphine.

We don't even really know if the signal is real.

I think at the more philosophical end of how this happened, I think it is a distinction and myself and other co-authors were talking about this.

It's a distinction between hypothesis generation and hypothesis testing.

Now, hypothesis testing is something that I think is the backbone of the scientific method, But it has a problem, which is, if you're looking through very noisy data and you want to test the hypotheses, you may, by mistake, create a spurious signal.

The safest, more conservative approach is hypothesis generation.

You see some data and you go, what's in there with no bias.

Now this is much safer, much more conservative.

And when there's a lot of data, that's great.

When there isn't, you can clean the noise and take out the signal with it.

The signal with a bathwater, whatever the equivalent of the analogy would be.

And so I think the healthy discourse that you described is exactly this.

There are ways of processing the data, completely legitimate ways, checked by multiple people and experts where the signal shows up and then phosphine is in the atmosphere of Venus, and somewhere it doesn't.

And then we disagree what that signal means.

If it's real and it is an ambiguously phosphine, it is very exciting because we don't know how to explain it without life.

But going from there to Venusians is still a huge jump.

LRW So that would be the title for the civilization, if it is a living and thriving on Venus's Venusians.

CMH Until we know what they call themselves, that's the name, yes.

So this is the early analysis of data or analysis of early data.

It was nevertheless, you waited until the actual peer-reviewed publication

Of course, and analysis of the 2 different instruments months apart.

So that's ALMA and JCMT, the 2 telescopes.

I mean, it's still, I mean, it's really exciting.

What did it feel like sort of sitting on this data, like kind of anticipating the publication and wondering and still wondering, is it true?

Like, how does it make you feel that a planet in our solar system might have phosphine in the atmosphere?

I've been working on phosphine for over a decade.

Before anyone could spell it or heard of it.

And at the time people either didn't know what phosphine was or only knew it for being just possibly the most horrendous molecule that ever graced the Earth.

And I'd been considering looking for it because I did think it was an unusual and disgusting but very promising sign of life.

I really didn't think to look in the solar system.

I thought it was all pretty rough around here for life.

And so, I wasn't even considering the solar system at all, never mind next door Venus.

It was only the lead author of the study, Jane Greaves, who thought to look in the clouds of Venus and then reached out to me to say, I don't know phosphine, but I know it's weird.

And so the telescopes were looking at, so this is visual data.

mean by visual, you wouldn't see the phosphine.

It's remote, you're observing, you're what, zooming in on this particular planet.

I mean, what does the sensor actually look like?

It'd be nice to kind of build up intuition of how little data we have based on which.

I mean, if you look at like, I've just been reading a lot about gravitational waves and it's kind of incredible how from just very little, like probably the world's most precise instrument, we can derive some very foundational ideas about our early universe.

And in that same way, it's kind of incredible how much information you can get from just a few pixels.

So what are we talking about here in terms of based on which this paper saw possible signs of phosphine in the atmosphere?

So phosphine, like every other molecule has a unique spectroscopic fingerprint, meaning it rotates and vibrates in special ways.

I calculated how many of those ways it can rotate and vibrate, and it's 16.8 billion ways.

What this means is that if you look at the spectrum of light, and that light has gone through phosphine gas on the other end, there should be 16.8 billion tiny marks left, indentations left in that spectrum.

We found 1 of those on Venus, 1 of those 16.8 billion.

So now the game is, can we find any of the other ones?

They're all in terrible places in the electromagnetic spectrum.

And the instruments we use to find this 1, can't really find any other 1.

There's another 1 of the 16.8 billion we could find, but it would take many, many days of continuous observations and that's not really in the cards right now.

I mean, how do you, there's all kinds of noise, first of all.

So how do you separate all of that out to pull out just this particular signature that's associated with phosphine?

So the data kind of looks somewhat like a wave

a lot of that is noise and it's a baseline.

And so, if you can figure out the exact shape of the wave, you can cancel that shape out and you should be left with a straight line and if there's something there, an absorption, so a signal.

We tried to find out what was this baseline shape, cleaned it out, and got the signal.

If you do this wrong, you can create a signal.

But that signal is at 8.904 wave numbers, And we actually have more digits than that, but I don't remember by heart.

And ALMA in particular is a very, very good array of telescopes, and it can focus on exactly that frequency.

And in that frequency, there are only 2 known molecules that absorb at all.

We look at that exact spot where we know fossil absorbs.

If there is extraterrestrial life, whether it's on Venus or on exoplanets where you looked before, how does that make you feel?

Or is it only, not only, but mostly, possibly to understand something fundamental, something beautiful about life in the universe?

You would have to bring on a poet or a philosopher on the show.

I feel those things, I just don't know if those are the right things to feel.

I think it's rather silly to feel scared.

Sometimes in the movies, don't go near it, don't interfere.

I think 1 of the things with Venus is because of phosphine, now there is a chance that Venus is inhabited.

We should be very careful with messing with them, bringing our own stuff there that contaminates it.

If there's life there, it's probably the remains of a living planet, the very last survivors of what once was potentially a thriving world.

And so, I don't want our first interaction with alien life to be a massacre.

So I definitely wouldn't want to go near out of a, let's say, galactic responsibility, galactic ethics.

And I often think of alien astronomers watching us and how disappointed they would be if we messed this up.

So I really want to be very careful with anything that could be life.

Humans are plenty capable of killing 1 another.

We don't need extraterrestrial help to destroy ourselves.

But this life, if there is life there, it does seem just like you said, it would be pretty rugged.

It's like the cockroaches Or Chuck Norris, I don't know.

It's the some kind of, it's something that survived through some very difficult conditions.

That doesn't mean it would handle us, you know?

You come just because you're resilient in your own planet doesn't mean you can survive another.

Even our extremophiles, which are very impressive, we should all be very proud of our extremophiles, they wouldn't really make it in the Venusian clouds.

So I wouldn't expect, because you're tough, even Chuck Norris tough, that you would survive on an alien planet.

And then from the scientific perspective, you don't want to pollute the data gathering process by showing up there.

How heartbreaking would it be if we found life on another planet and then we're like, oh, we brought it with us, it was my sandwich.

And it's certainly a problem with Mars because we visited the, if there is life on Mars or like remains of life on Mars, it's always going to be a question of like, well, maybe we planted it there.

It's harder, because when we try to go to Venus, things melt very quickly.

Yeah, well, in terms of Elon Musk and terraforming planets, Mars is stop number 1, then Venus maybe after that.

So, can we talk about phosphine a little bit?

You'll be surprised here, it wasn't taken already.

You already mentioned it's pretty toxic and troublesome.

So maybe, what are some things that make it interesting chemically and why is it a good sign of life when it's present in the atmosphere like you've described in your paper, aptly titled the phosphine as a biosignature gas in exoplanet atmospheres.

I suppose you wrote that paper before Venus.

And no 1 cared, you know, in that paper, I said something like, if we find phosphine on any terrestrial planet, it can only mean life and everyone's like, yeah, that sounds about right, let's go.

And then Venus shows up and I was like, are you sure?

Now that it's right here, I'm less sure now that my claims are being tested.

So it's shaped like a pyramid with a phosphorus up top and then 3 hydrogens.

It's actually quite a simple molecule in many ways.

It's the most popular elements in the universe, carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur.

When you add hydrogen to them, it makes quite simple, quite famous molecules.

These are all molecules people have heard of.

You do it to phosphorus, you get phosphine.

People haven't heard of phosphine because it's not really popular on Earth.

We really shouldn't find it anywhere on Earth because it is extremely toxic to life.

It interacts with oxygen metabolism and everything you know and love uses oxygen metabolism.

And it interacts fatally, so it kills in several very imaginative and very macabre ways.

So it was used as a chemical warfare agent in the First World War and most recently by ISIS.

Even life that might not avoid it, so life that doesn't use oxygen metabolism, anaerobic life, still has to put crazy amounts of effort into making it.

It's a really difficult molecule to make, thermodynamically speaking.

It's really difficult to make that phosphorus want to be together with that hydrogen.

When they're not avoiding it, it's extremely difficult to make.

You would have to put energy in, sacrifice energy to make it.

And if you did go through all that trouble and made it, it gets reacted with the radicals in the atmosphere and gets destroyed.

So we shouldn't find it anywhere, and yet we do.

It's this kind of weird molecule that seems to be made by life and we don't even know why.

It's not the only molecule that life is willing to sacrifice energy to make, but we don't know how or why life is even making it.

So absolutely mysterious, absolutely deadly, smells horrifically.

When it's made, it produces other kind of diphosphenes, and it's been reported as smelling like garlicky, fishy death.

Once someone referred to it as smelling like the, let me see if I remember, the rancid diapers of the spawn of Satan.

And so it's just this horrific molecule, but it is produced by life.

And when it is produced by life, it's done with enormous sacrifice.

And so it's this strange contradictory molecule that we should all be avoiding and yet seems to be an almost an ambiguous sign of life on rocky planets.

So on rocky planets, what, is there biological mechanisms that can produce it?

And is there, you said that why is unclear, why life might produce it, but is there an understanding of what kind of mechanisms might be able to produce it, this very difficult to produce molecule?

The enzymatic pathways of phosphine production by life are not yet known.

This is not actually as surprising as it might sound.

I think something like 80% of all the natural products that we know of, so we know biology makes them, we don't know how.

It is much easier to know life produces something because you can put bacteria in a Petri dish and then watch and then that gas is produced, you go, oh, life made it.

But that's much easier to do, of course, than figuring out what is the exact metabolic pathway within that life form that created this molecule.

No 1 had really heard of it until now-ish.

What you were presenting is the fact that life produces phosphine, not the process by which it produces phosphine.

Like if you were to try to understand the mechanisms, the, what did you call them, enzymatic pathways that produce phosphine, how difficult is that of a problem to crack?

If I'm not mistaken, even the scent of truffles, obviously a billion dollar industry, huge deal.

Until quite recently, it wasn't known exactly how those scents, those molecules that create this incredible smell were produced.

As you can imagine, there is no such pressure.

There's no phosphine lobby or anything that would push for this research.

And it isn't crazy because we know that phosphine is really hard to make.

We know it's really hard for it to happen accidentally.

Even lightning and volcanoes that can produce small amounts of phosphine.

It's extremely difficult for even these extreme processes to make it.

So it's not really surprising that only life can do it because life is willing to make things at a cost.

So maybe on the topic of phosphine, what again, you've gotten yourself into trouble.

I'm gonna ask you all these like high level poetic questions, I apologize.

When did you first fall in love with phosphine?

It was somewhere between a long relationship and Stockholm syndrome.

When I first started my PhD, I knew I wanted to learn about molecular spectra and how to simulate it.

I thought it was really outrageous that we as a species couldn't detect molecules remotely.

We didn't have this perfect catalog ready of the molecular fingerprint of every molecule we may want to find in the universe.

And something as basic as phosphine, the fact that we didn't really know how it interacted with light and so we couldn't detect it properly in the galaxy, I was so indignant.

And so initially I just started working on phosphine because people hadn't before, and I thought we should know what phosphine looks like.

And then I read every paper that's ever been published about phosphine.

It was quite easy because there aren't that many.

And that's when I started learning about where we had already found it in the universe and what it meant.

I started finding out quite how little we know about it and why.

And it was only when I joined MIT and I started talking to biochemists that it became clear that phosphine wasn't just weird and special and understudied and disgusting.

It was all these things for oxygen-loving life.

And it was the anaerobic world that would welcome phosphine, and that's when the idea of looking for it on other planets became crystallized.

Because oxygen is very powerful and very important on Earth, but that's not necessarily going to be the case on other exoplanets.

Overwhelmingly, most planets are oxygen poor.

And so, finding the sign of life that would be welcomed by everything that would live without oxygen on earth seemed so cool.

But ultimately the project at first was born out of the idea that you wanna find that molecular fingerprint of a molecule.

And that's connected to then looking for that fingerprint elsewhere in a remote way.

And obviously that then, at that time, where exoplanets already, when you were doing your PhD, and by the way, I should say your PhD thesis was on phosphine.

It was all on phosphine, 100% on phosphine.

With a little bit of ammonia, I have a chapter that I did where I talked about phosphine and ammonia.

But no, phosphine was very much my thesis.

But at that time when you're writing it, there's already a sense that exoplanets are out there and we might be able to be looking for biosignatures on those exoplanets?

Pretty much, so I finished my PhD in 2015.

We found the first exoplanets in the mid to late 90s.

And from there, it's not a big jump to think, well, if some have atmospheres, some of those might be habitable and some of those may be inhabited.

So how do you detect, you started to talk about it, but can we linger on it?

How do you detect phosphine on a far away thing, rocky thing, rocky planet?

You've kind of mentioned the wave, but what are we supposed to think about?

You can crack that light open with a prism or a spectroscope or water and make a rainbow.

That rainbow is all the colors and all the invisible colors, the ultraviolet, the infrared.

And if that light was truly pure, you could consider that rainbow to just cover continuously all of these colors.

But if that light goes through a gas, we may not see that gas.

We certainly cannot see the molecules within that gas, but those molecules will still absorb some of that light.

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Clara Sousa-Silva: Searching for Signs of Life on Venus and Other Planets | Lex Fridman Podcast #195