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- [00:00]
Tom Whipple
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- [00:42]
Kyle McLaughlin
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- [01:49]
Tom Whipple
What if the Goldilocks Zone is for idiots? Welcome to Inside Science from the BBC World Service with me Tom Whipple. Today in a special edition, we're recording in front of an audience at the Cheltenham Science Festival. And that is the question we're going to be considering. Let me take you to the plot of the book and the hit movie project Hail Mary. It's set in the near future and the sun is dimming and no one can initially tell why. On Earth in the past decades, as in our world now, there has been a quiet revolution in the hunt for life. In the mid-1990s we found the first so called Earth like planet around a distant star. Through the 2000s there was a trickle more and then there was just a burst. I think we're now more than 5,000 exoplanets. As they're called science journalists like me put these early discoveries on the front of the paper. These distant worlds intuited from the slight dimming of the sun, that spoke of perhaps distant civilizations. And the ones we were most interested in as journalists were the small rocky ones. And of those, the ones we were really interested in, they were the ones in the so called Goldilocks Zone, where it wasn't too hot, it wasn't too cold, where liquid water could persist. There were places like ours, places we thought that life could exist. In Project Hail Mary in this Earth, they work out what's dimming the sun, and it's a small organism, they call it an astrophage, a sun eater that lives on the sun's energy itself. And obviously it was very much not in the Goldilocks Zone, very much not in a place like ours. And the hero of this book is a scientist whose PhD has a section titled the Goldilocks Zone is for idiots. So that's what we're going to discuss. What are the true limitations of alien life? How do we spot it? And have we been looking too narrowly? We're joined by Lewis Dartnall, astrobiologist at the University of Westminster, and Sarah Seager, astrophysicist and planetary scientist at MIT and author of the Smallest Lights in the A Memoir. Now Lewis looks for extremophiles, for organisms that exist in places we thought previously perhaps wasn't even possible. He's also been involved in planning for the missions to find life on Mars. Sarah is part of planning a mission to Venus, among many, many other things. On the surface of that planet, temperatures reach 500 degrees, it rains sulfuric acid. Yet in the clouds above, she thinks there could just about be life. So the mission statement of that mission might as well be the Goldilocks Zone is for idiots. Please welcome our panel. For both of you, I'm going to start with a question. So, Lewis, do aliens exist?
- [04:53]
Lewis Dartnall
Yes. So, Tom, given that my career I've chosen is in astrobiology, I'm kind of hedging my bets. But I think in my career, my lifetime, we will find signs of extraterrestrial life before I retire.
- [05:04]
Tom Whipple
Excellent, Sarah.
- [05:05]
Sarah Seager
To counter his, I will just say, scientifically, we don't know yet. But we're both, along with tons of other people trying to establish that we do see the ingredients for life everywhere we look, in the space between stars, in meteorites, where samples are brought back to Earth, and on planets in our solar system. So we definitely expect it out there.
- [05:25]
Tom Whipple
Okay, so I'm going to Come back on that. But I really want both of you to answer this question. You said we see the ingredients for life everywhere. What is life? What does it require?
- [05:37]
Sarah Seager
Well, I'll start by saying I usually avoid that question, so I will leave that for Louis.
- [05:41]
Lewis Dartnall
Everyone's looking at the biologist in the first, right?
- [05:44]
Sarah Seager
But for astronomers, we tend to focus on what we can observe, and that's more about what life does. Like we as humans, we eat food, we breathe air, and life metabolizes. And we're making an assumption that life everywhere, or some life everywhere, uses chemistry like we do, to get energy, to store energy and release that energy. And we're hoping that, like here on Earth, there's a chemical byproduct and we're looking for chemistry that is signs of metabolism.
- [06:11]
Lewis Dartnall
Lewis it's an interesting angle to ask what life does rather than what it is or what it's made out of. And fundamentally, a living system has to be able to have some kind of self description, some kind of operating manual that tells it how to run. It also needs to be able to extract energy from its environment to power itself, but also to make the Lego building blocks, the components that go into making new forms, new copies of itself when it comes to division. So that's what life does. And that's true of all life on Earth. And the chemistry that life uses to do those things, to perform those functions is using incredibly complicated molecules, great big polymers like DNA, that can store and transmit digital information, or using enzymes, which are great big proteins that can accelerate how quickly chemical reactions can be run. So when we're looking for life on other planets, we're looking for fundamentally the functions of life, something that is complicated enough to store information, something that could accelerate chemical reactions or evidence that's been going on, but not necessarily DNA itself or proteins itself, but all of this
- [07:16]
Sarah Seager
is just so complicated. So that's not actually what we're looking for. And at the risk of getting ahead of ourselves to start with, we're just looking for very, very complex organic molecules, you know, so complex that we don't think they're just lying around in nature.
- [07:29]
Tom Whipple
And so that implies what's an organic molecule?
- [07:32]
Lewis Dartnall
Yeah, so very simply, an organic molecule is just one that contains carbon. It is architecture. The structure of the molecule is made of carbon bonding to carbon. And people do talk about alternatives to organic life. There might be silicon based life out there, perhaps, although probably not, because silicon is just rubbish at doing chemistry compared to carbon.
- [07:52]
Tom Whipple
So what does the carbon. Because this is.
- [07:54]
Sarah Seager
Okay, I do have a Thing about silicon now that I've glommed onto. So the one thing about silicon is it likes to attach to oxygen. Silicon oxide is like a main component of minerals that make up rocks. Let me ask you this, does anyone here eat rock? No, you do not salt, which is kind of similar, I feel like no, because it's so hard for life to extract silicon from the environment that why would life ever use it?
- [08:21]
Tom Whipple
Okay, so, but this is. So we are carbon based life forms and we need water. And we have decided that, we've made some scientific judgments and decided that life's almost certainly going to be carbon based life forms that need water. Now there's quite an obvious argument that maybe we are over extrapolating from an n of 1. Why is it that carbon is so useful for life and silicon is something you consider but is probably less useful?
- [08:53]
Lewis Dartnall
There's more silicon on Earth than there is carbon. And Sarah's just said that the substance of the planet, that the crust, the rocks of the Earth are silicon. So life on Earth didn't not choose silicon to build itself out of because it was lacking silicon. There's more silicon here. There is carbon. It used carbon as alternative. Alternative because carbon is very good at building big bendy, flexible molecules, molecules that can do things like become enzymes or run chemical reactions. So as an astrobiologist, you try to walk this tightrope between not only looking for stuff or life that's just like us, because we acknowledge that alien life might be different, but also not just flinging ourselves off the cliff of a fantasy and trying to remain rooted as a scientist in what we know and what we can anticipate and what we can predict and what we can test for. So we tend to look for organic based life, carbon based life. But the water basedness is, and I'm sure Sarah will come back to this as well, when we start talking about life on Venus is much more of an open playing field. Maybe life would be carbon based, but not necessarily water based. Could there be other biosolvents, other wet stuff that you could dissolve complex chemistry and run that molecular machinery for life.
- [10:06]
Sarah Seager
And the funny thing is it's complicated to be a scientist at the frontier because we allow ourselves to take both sides of the argument. So in water, if you have silicon and there's water involved, remember water, H2O, then there's oxygen. So silicon and water based life is probably a no go because ultimately it wants to form rocks. But if there's another solvent that's not water, then silicon becomes slightly more of a possibility.
- [10:31]
Tom Whipple
So let's move on to the kinds of life we can imagine with these constraints. And I think probably Venus is a really good example. So tell us about your Venus mission.
- [10:41]
Sarah Seager
So Venus is the one I like to call the neglected sibling. And sometimes that ignored sibling is really truly special. But you never know because they're not getting all the attention. So Venus is incredibly curious. Its surface, as many people are taught in school, is completely unsuitable for life. It's so hot. But just like here on Earth, if you hike up a mountain or go in an airplane, it gets colder and colder. And that's also true on Venus. And 50 kilometers above the surface, way up in the clouds, it is the right temperature for life. There's also a liquid environment, which life requires, and there's energy from the sun. And that's why we think that over half a century ago, Carl Sagan first put out the idea that maybe there's life confined to the clouds. Just simple primitive life in the liquid clouds floating around. It all sounds great. And Lewis is nodding his head. He thinks it's possible. And everyone's in agreement until we remind or tell all of you that the clouds aren't made of water. They're made of acid. Concentrated sulfuric acid. It's so nasty, it will burn a hole in your clothes, in your skin. It destroys all life on Earth. That's where things have been for decades. But motivated by this reported phosphine discovery,
- [11:53]
Tom Whipple
tell us about that.
- [11:54]
Sarah Seager
So you know what, there are tons of molecules that could be a sign of life. We have oxygen on Earth that we require to breathe. If we didn't have life on Earth, if we didn't have plants and photosynthetic bacteria, we would have no life. It has to be continually produced oxygen, that is, or it wouldn't be here. It's so reactive. So we astronomers and astrobiologists, we have a long list of molecules that could be a sign of life. And one of those gases that is one of our favorites as a sign of life is called phosphine. I know very few people have ever heard of it. It's very obscure on Earth it is really only made by life. Either we make it as pesticides or bacteria in oxygen free environments make it so, hey, what a great sign of life, phosphine. It turns out that right here in the uk, Professor Jane Greaves wanted to find signs of life on Venus. And while my team was working on phosphine as a potential sign of life on exoplanets, she was purposely trying to find signs of Life on Venus by phosphine. So someone connected our two teams, really. Long story short. We reported the discovery of phosphine gas in the Venus atmosphere. We had gone through all the options of what could make phosphine, but just like on Earth, phosphine shouldn't exist on Venus. And we looked into volcanoes or. Or meteorites or lightning, and no method we examined could make phosphine, even in the tiny amounts reported. So I rushed through that, but let's just say there is a series of papers making the case for this very obscure gas on Venus and just simply saying that because there's no chemistry we know of that could make it, it leaves room for the idea of life making phosphine. Life in the clouds. But before we get to Louis, I just want to say it's incredibly controversial for so many reasons.
- [13:41]
Lewis Dartnall
Well, I was just curious to broaden the discussion on Venus slightly more that, yes, we do find life in the clouds of Earth, but it's transitory. It's up there temporarily, and it gets lofted from the oceans or from the land up into the sky, up into the clouds, sits around for little bits before settling back down again. But there's a very interesting observation that pretty much any moist niche on Earth, we find teeming with life. We find some pond scum and cyanobacteria and things photosynthesizing. We find green life everywhere on the surface. But the clouds of Earth are not green. They're not being colonized to such a great extent. Almost any percent of life is just settling back down again. So one of the main problems for life on Venus isn't just it's incredibly acidic. But can you have an entire biosphere, an entire ecosystem completely severed from the surface? You can never go down to the surface of Venus and back up again because you're sterilized as soon as you get too deep, because it's so hot, it's oven temperatures.
- [14:39]
Sarah Seager
Right. Well, I've come prepared, and I just want to have a few answers for you. But first thing I want everyone to know is, you know, the clouds of Venus, unlike Earth, where it's fragmented, on Venus, the clouds are not fragmented. They're always there. The entire planet is always covered by clouds, and they're very, very, very, very deep. So one thing about Venus is rain never hits the surface. Instead, the raindrops evaporate right below the clouds. There is a thought that if all of the sulfuric acid evaporates, it's possible that whatever life that might be there would remain just hanging loosely. It would lose all the mass. And so it wouldn't keep sinking down, but could hover just suspended like some spores on Earth can last for millions of years or longer before being revived by whatever. So there's an unknown layer of haze right beneath the Venus clouds. And it's certainly possible that when they get rained out and they end up there, they could just kind of stay there until they're brought back up. However, all that said, I just want to say that unfortunately I do fully agree with Lewis. And I would say to me, that's the biggest uncertainty is can you have life always living up in the clouds? And that's counter to the chemistry, which I think is really possible. But that all said, the second answer I come prepared with is, look, would you want to just buy into traditional science or would you want to go to Venus and see what's there?
- [16:01]
Tom Whipple
And so that's my question before we move on from Venus. You're going to Venus to see what's there?
- [16:05]
Sarah Seager
We're going to Venus to see what's there.
- [16:07]
Tom Whipple
What's it going to be?
- [16:08]
Sarah Seager
So our first mission to Venus is just a small mission and it's a probe, so it'll race through the atmosphere, slowing down by its own drag. And it has a single instrument that will shine a laser through a window, looking for autofluorescence like fluorescence to indicate the presence of organic molecules. And we'll also be measuring some. It sounds very technical, but backscattered polarization to confirm what we all think the cloud droplets are. This is Ashley Iconnecti from the Ben and Ashley I Almost Famous podcast. Ben. I've been reflecting a lot lately on how many big life moments our listeners have experienced with us.
- [16:46]
Tom Whipple
Yeah, it's pretty wild.
- [16:47]
Sarah Seager
They've watched us go from dating shows to engagements, weddings, babies, buying homes. Every stage comes with new decisions. The milestones are the fun part, but
- [16:56]
Lewis Dartnall
the planning is where things get real.
- [16:59]
Sarah Seager
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- [17:16]
Tom Whipple
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- [17:21]
Sarah Seager
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Tom Whipple
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- [17:36]
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- [18:39]
Tom Whipple
You're listening to Inside Science from the BBC World Service. I'm Tom Whipple and today I'm with a live audience at the Cheltenham Science Festival and we're discussing some out of this world science on the topic of whether or not we're alone in the universe. Lewis, talk to us about your work on extremophiles and how that informs things like Mars and the sibling that's noticed normally.
- [19:02]
Lewis Dartnall
So my research is mostly looking at some of the hardiest forms of life on Earth, kind of survival superheroes that we call extremophiles. So life that loves or can tolerate at least very hostile, very dangerous environments that will kill your eye pretty much instantly. And so as a whole body of organisms, these extremophiles teach us something very, very interesting. They teach us what are the outer limits of life on Earth? What is the boundary of our biosphere on our planet? And therefore what could be considered to be habitable environments on other places? Is Mars today on its surface a habitable environment? Or was it 3 billion years ago when both Earth and Mars were primordial worlds? Or is the ocean we now know exists beneath the icy surface of Europa or Enceladus moons orbiting Jupiter or Saturn? Are they habitable places? Do they have the right kind of conditions for life to be able to survive?
- [20:02]
Tom Whipple
So tell us about hopes now for finding life on Mars. What are we doing next?
- [20:07]
Lewis Dartnall
There's a very, very exciting mission coming up that the European Space Agency ESA is about to launch in the next Year or two, which is the ExoMars Rover. And up until now, NASA probes have had a little drill that's basically the length of your pinky, and it's driven around and stuck its little finger into the side of rocks and extract that material to analyze, which with ExoMars, we're going to get 2 meters underground, a substantial distance underground, and I'm going to pull up handfuls of that Martian dirt where hopefully it's been protected underground, and then scrutinize and analyze and not just look for the building blocks of life, but hopefully find biosignatures, unambiguous signs of life itself.
- [20:48]
Tom Whipple
I want to move on to life outside of our solar system. Now. I said, as a science journalist, I've written more exoplanet stories than I can think. So there's that period where we were just getting an exoplanet a day. And there came a point where you said, fine, this is, you know, this is in the Goldilocks zone, however we define it. And it's Earth like, but actually it's 100 light years away or it's 200 light years away. We're never going to get to it. So, Sarah, will we ever. Will we ever know the truth that's out there?
- [21:18]
Sarah Seager
Well, we may or may not ever know the truth, but the hunt is on for sure. And we'll at least have. I know it's not extremely satisfying, but we will have signs of life. That's why we name it biosignature. We don't name it like an actual life.
- [21:33]
Tom Whipple
And so what do we look for? How does it. Now that we found these exoplanets, how do we start categorizing the ones that might just be the civilization?
- [21:42]
Sarah Seager
Well, it's not easy. And I think we can appreciate from Lewis's wonderful descriptions of Mars just how complicated it is to sort of. And what makes it even harder for exoplanets is they're so far away, we can't send spacecraft there. We don't know what their surface is like. We don't know what's inside. They're really just a point of light or less. So we use remote sensing. We can look at spectra. We can see the gases in the atmosphere of these planets. And if we're lucky, we can see a bunch of gases. And we try to, using computer codes and general laws of chemistry and physics, kind of piece together what's there. I think you can tell by the way, say, piece together. It doesn't sound very certain, but we're looking for gases that don't belong, that are far outside of equilibrium with the rest of the atmosphere. So here on Earth, we have oxygen, and oxygen is so reactive, it shouldn't be here at all unless it's continually produced. And so on Earth, life is pumping so much oxygen into our atmosphere that oxygen, despite being highly reactive, can always be there. We astronomers have come up with a long list of gases that could be signs of life. But along the way, we've come up with a bunch of problems. One is whatever gas I can think of that could be a sign of life, you will be able to come up with a counter argument. Given that there's so much we don't know about these planets, a large number of these counter arguments. For example, the molecule could be produced in a volcano. If the interior of the planet is different from Earth, it's really hard to push back on those. Second, we've come up with some problems with contamination from the star itself, because stars like our sun, they have star spots and flares and other problems, and those are messing it up. While I can assure you our search is on, it turned out to be way harder than we imagined.
- [23:30]
Tom Whipple
Lewis, it sounds to me like this is actually going to be deeply unsatisfying and a recipe for eternal academic debate. Just keeping you guys in jobs for literally the rest of humanity.
- [23:42]
Lewis Dartnall
Well, the joke always made if someone is paying for you to look for something, don't find it too quickly. This is the big astrobiology conspiracy.
- [23:52]
Tom Whipple
Now, in our last bit, I want to pose. If we can't yet find them, there is one other option. Now, in 2018, the Barcelona music festival Sonar did something a little unusual. It pointed a transmitter at an exoplanet, one of the rocky ones in the habitable zone, and it blasted songs by Jean Michel Jarre at them. The organizers of the festival may not have known, but they were engaging in a pretty active debate. For years we've had the SETI project, the Search for Extraterrestrial Intelligence, which has been listening out for signals. So not looking for biosignatures, but. But looking for an advanced civilization sending messages. There has also been proposal to do the reverse, to do METI messaging. Extraterrestrial intelligence. Why not say hello was the proposal. Some think it'd be a nice way to get some advice and meet these advanced civilizations. Some think, as Stephen Hawking put it before he died, that when advanced civilizations meet less advanced civilizations, it doesn't normally go terribly well for the less advanced one and maybe will be lunch anyway. Jean Michel Jarre is on his way. He has not yet arrived. He is four years before introducing the great electronica alien apocalypse of the2030s. Louis, let's start with you talk through the issues of this. Should we be talking to the aliens?
- [25:19]
Lewis Dartnall
There's one argument that perhaps we don't want to start announcing our presence to the rest of the galaxy. The analogy is if you're walking through a dark forest, maybe shut the hell up and keep shouting and attract attention of the lions or tigers or whatever. And this, this is an idea that's been played around with quite nicely in science fiction. And the three Body Problem, for example, deals with this kind of scenario. Where it doesn't quite hold water for me is I don't think we would need to shout our presence for extraterrestrial civilizations to already know about us, because all the sort of technology that Sarah's just been talking about, we have been obviously a biological planet, a life bearing planet for very, very long period of time now. And yet that has apparently attracted no one's attention. And I'm discounting sightings of shiny UFOs as evidence that anyone has, anyone has visited the Earth trying to find where this life is. So we don't seem to attract anyone's attention. That could either be there is no other life out there to have its attention attracted, or we are just one of a multitude of alive planets, of biological planets, and we're just one many, and no one's picking us out as being particularly special. And both of those extremes are kind of equally terrifying. But what's so exciting is we are right on the brink now of starting to understand where we are on that scale with the next generation space telescopes, not just detecting Earth like planets orbiting other suns, but starting to characterize them. Do we see oxygen in their atmosphere? Are they alive? Maybe we'll have a shopping list in the next 20, 30 years of our closest Earth like planets near to us.
- [26:58]
Tom Whipple
Sarah, do you think we should?
- [27:00]
Sarah Seager
Well, once in a while, astronomers get together and come up with a plan and sometimes even with money to have a campaign to develop messages and send them out. But every time that happens quite it happens every few years, another group of astronomers squashes it and the first group succumbs to peer pressure and doesn't do it.
- [27:18]
Tom Whipple
And so which way are you pressuring your peers?
- [27:21]
Sarah Seager
I just don't get involved because I agree with Louis that if there's intelligent life out there, more intelligent and capable than we are, they already know we're here.
- [27:30]
Tom Whipple
Well, let's go and see if anyone in the audience has met any aliens and can contradict that.
- [27:35]
Lewis Dartnall
Are there any aliens in the house?
- [27:38]
Tom Whipple
Have we got any questions? Louis, you said at the start that you think that we might find alien life at some point within our lifetimes. I'm just wondering what that moment would actually look like. Because in science fiction it's when the spaceship comes to Earth or whatever. I'm thinking of scientific discoveries in my lifetime. It's more like a PowerPoint presentation where someone says, we found the Higgs boson. What would that moment actually look like?
- [28:00]
Lewis Dartnall
My impression is it will be a relatively small, slow protracted dawning and realization of rather than sudden flash, light bulb flash moments. Unambiguously demonstrating existence of life is an incredibly hard thing to do. There are always lots of ifs and buts or counterexamples or other possibilities. And looking for life on Mars. What we will almost certainly want to be able to do, to be sure, is not try to send an entire miniaturized laboratory with wheels on the bottom, solar panels on the top, which is effectively what a Mars rover is to analyze samples there. We want to grab the most promising samples of the Martian surface, bring them home, bring them back to the Earth, and then use all the laboratories and all the highest tech analytical equipment around the planet to scrutinize that sample and hopefully get something that approaches unambiguous proof.
- [28:52]
Tom Whipple
Thank you for that. And let's take another question.
- [28:56]
Sarah Seager
Thank you very much. You've spoken a lot about the potential of life outside our universe and Venus and Mars and other satellites. But what about our own moon?
- [29:05]
Lewis Dartnall
Do you think we've gone digging around enough within astrobiology? The Moon has definitely never been alive. It has never had liquid water on the surface. It's never had an atmosphere, it's never been a habitable environment. But that doesn't mean the Moon isn't potentially of great interest astrobiology, because it's almost like the attic for our planet. And every time there's a big impact into the surface of the Earth, it splashes up lots of material. Meteoritic stuff from the surface of the Earth gets splashed up into space, some of which will be swept up by the Moon and then preserved for very, very long periods of time on the surface. So it's a very interesting proposal. If we could start finding ancient terrestrial rocks on the Moon, they would be much better preserved than anything our own planet's been able to do, because it's got a very dynamic, constantly changing surface with plate tectonics. So there might actually be a much better record of the history of life on Earth on the moon than our own crustal rock record.
- [30:01]
Tom Whipple
That's all we have time for. I am going to go and enjoy the Furious. I have left before the Jean Michel jars, fearing aliens come to eat us with their death stars. Thank you for being with us. And it's goodbye from me and goodbye from the panel.
- [30:13]
Lewis Dartnall
Thanks.
- [30:14]
Tom Whipple
Cheers.