Ever since the first exoplanet, 51 Pegasi b, was discovered, the hunt for life outside the solar system has begun. With the development of technology and science, search methods are also changing. So, astrobiology today has become a flagship in the search for signs of life in distant worlds. Today, when scientific articles about certain discoveries appear almost every day, there is nothing surprising in the unification of seemingly different disciplines. Thus, astrobiology is a relatively young branch in science, combining astronomy, biology, chemistry, physics, and much more.
Adam Frank is a professor of astrophysics at the University of Rochester, New York, whose real passion lies precisely in the search for life beyond Earth. In addition, he is the author of several popular science books, among which is the bestseller Light of the Stars. Alien Worlds and the Fate of the Earth "(Light of the Stars. Alien Worlds and the Fate of the Earth, translated by the author). Dr. Frank proudly calls himself an astrobiologist and is confident that soon we will be able to find signs of life by studying the atmospheres of exoplanets. Naked Science was able to talk with the professor about how exactly the signatures of life can be found in the atmosphere of a distant planet, how important it is to understand life on Earth in these studies, and much more.
You are a physicist and astronomer, but you have also repeatedly stated in various interviews that in recent years you are increasingly interested in astrobiology. Why Astrobiology?
- It's just that astrobiology is the coolest thing about it (laughs). In fact, I've always wondered why people are not interested in astrobiology. What other question can be more important or will have more consequences than the question of the existence of life in other worlds? I once had a joke with a friend who studies condensed matter physics, telling him: "Seriously, which is more important - the number of balls that you can put in a bag, or the existence of life in other worlds?" To which he replied: "Well, yes" - and was offended for fun.
I mean, this is a really fundamental question for us. Even if this is an unreasonable life, just its very presence somewhere else, the understanding that this is not the only planet on which there is life (which is possible) is one of the most scientific and philosophical questions that I can imagine and for which you can find the answer. It is as significant as the question of the origin of the universe.
When you think about very important scientific issues, most often it is about the origin of the universe, which is inside a black hole. Speaking about the origin of the Universe, I do not think that this question will ever be given an exhaustive answer due to the nature of the question itself, since it collides head-on with philosophy. But in the case of the existence of life on other planets - we can answer this. The origin and existence of life, if we expand this question to civilizations, we can find clear answers to this that will touch upon the deepest philosophical questions about who and what we are.
How does understanding life on Earth help you in your research?
- In fact, we have only one example of life.People often say, “Astrobiology? How can this even be a real topic if we only have one example? " But, as I always say, if you treat it this way, then you can miss how much of everything relevant and important we have learned. Astrobiology is the study of life in its planetary or cosmic context. And we've learned a lot about this over the past few years. Obviously, one of the most important things here is understanding the history of life on Earth in great detail. As I say, there have been three revolutions in astrobiology: the discovery of other planets orbiting other stars, then the exploration of the solar system, during which we visit and study all types of objects in it, and the exploration of 4.5 billion years of Earth's history.
We have a really good idea of the entire history of life on the planet, although many questions still remain. One of the things that becomes clear when looking at the data is how many different planets the Earth has managed to be. Once upon a time there was a water world, almost or completely without continents. We were the "snowball" Earth. And even a jungle planet. In each of these changes, life played an important role, and sometimes even provoked them. So in a sense, by studying the history of the Earth, you get several different planets with life on them - and all this can be explored.
Of course, the mechanism of life, genetics in this case are always the same. But if you are wondering how life can interact with the planet and change it, then we see many different modes that are useful for research. How do they usually say? "Anything that is not prohibited by the laws of physics and chemistry is likely to happen." So we have to be careful when we study life on other planets, because the probabilities are infinite. But I believe that in this way you learn about "circuits", get an overview of how life and planets can go hand in hand. This is extremely important.
Since this is a relatively new offshoot, what are the most insurmountable difficulties you face in your search for life in space?
- One of the main things that people do not realize is how close we are to conducting a real scientific search for life in the universe. Amazing, isn't it? People have wondered if life has existed anywhere else in the universe since the days of the ancient Greeks, whose philosophers speculated about the existence of life on other planets and elsewhere. And throughout history - and this is at least 2500 years - an endless dispute lasted. Someone said: "Well, yes!" And he answered: "No". It was a dispute with no data.
But for several years now we have been on the way to obtaining direct data relevant to this question. And we will get them thanks to exoplanets. Space is littered with exoplanets, and we are learning how to characterize their atmospheres. We will be able to obtain information about the chemical composition of their atmospheres. And this is exactly what will help to understand whether there is life on them. In other words, we will be able to find out if these planets have a biosphere. Over the next 10, 20, 30, 40 years, we will have relevant data. Yes, we will argue about their meaning, but these will no longer be guesses, but direct information.
This will be related to the so-called atmospheric characteristic and understanding how to read the signals of the biosphere by means of light passing through the atmosphere of an exoplanet orbiting another star. Now everyone is focused on this, everyone is striving for this. There are also a million sub-tasks associated with this. For example, I am working on the study of exoplanetary atmospheres during the evolutionary stage. And this is extremely difficult, since a similar idea originates from James Lovelock and his Gaia Hypothesis. Back in 1965, he deduced that oxygen is present in the Earth's atmosphere due to life, and the Earth's atmosphere is not in equilibrium, since life on the planet constantly consumes oxygen and throws it back out. It turns out that if life disappears, oxygen will disappear along with it.Lovelock was the first person to understand this.
In essence, the atmosphere is a sensor for the presence of life. For a long time it was believed that if oxygen and methane are found in the atmosphere, therefore, there is life on the planet. But we realized that everything is much more complicated. Speaking of difficulties, we now face a difficult task: to determine which chemical compounds are biosignatures.
What are the most intriguing discoveries of recent years that have helped in the development of astrobiology as a separate branch of science?
- The most shocking and surprising discovery was the exoplanets themselves, since it was the answer to a question that is 2, 5 thousand years old. But it's not only that. The point is not just the discovery of exoplanets. We just got to the point where we started wondering how many exoplanets there are. How many stars do you need to count to stumble upon one with an exoplanet? How many stars do you need to count to find one that has an exoplanet in the right place for life to appear on it or liquid water on its surface? And we also answered these questions.
You must be familiar with the Drake equation. The second and third variables in this equation are the number of stars that have planets and the number of planets in the habitable zone. And today we know the answers. Every star in the sky - every one! - there are planets, which in itself is an incredible discovery. One in five stars has at least one planet located in a suitable place for life to emerge. Discoveries like these change everything - they completely reimagine our approach to finding life.
In addition, our understanding of the climate is important. It's funny when someone in the US says the word "climate", people think it's about politics. No, we're talking about how the planets function. By studying Venus, Mars, Earth, Titan (Saturn's giant moon), we are studying how the climate works. Climate and life go hand in hand. This is one of the fundamental things. Studying the history of the Earth, we even understood how planets without life work. I like the saying that climate is how planets take sunlight and try to do something interesting with it. So now we already have a good understanding of how the climate works on lifeless planets. And thanks to the Earth, we know how the climate functions on a planet that has life - this is also an important transition. That is, now we understand how to think at the level of the planet - this will also become a large part of understanding systems.
There are many other points as well. All the work we've done, studying life in extreme conditions and diving into Antarctic subglacial lakes (talking about really cool people in science), thanks to it, we now know that there are versions of life on Earth that can withstand incredible types of conditions.
Not so long ago - less than 100 years ago - we realized that the Universe is much larger than the Milky Way. And the first exoplanet was discovered just 27 years ago. How would you describe the development of space research until the end of the 21st century?
- For me, exoplanets are a huge part of space research - a lot of work will be done in this area. If young students were to ask me for advice on which field is the best place to go, I would say: something related to gravitational waves. This is a completely new window - we suddenly have a completely new way of observing the skies. That discovery was so overwhelming not only because scientists discovered gravitational waves, but, in part, because of the immediate impact this discovery had on astronomy. Hardly anyone expected to receive a signal from two merging black holes. So gravitational waves are definitely going to be big, and so are exoplanets.
As far as cosmology is concerned, there is no longer the enthusiasm that used to be. A lot of work has already been done with the available data - in particular, with those relating to the early universe - and I don't think we will get much new data in the future.Of course, my cosmologist friends will object and say: "Yes, this is ridiculous!" However, there is much more to learn about the large-scale structures of the universe. For example, baryon acoustic oscillations are a way to see imprints of events in the early universe and how they influenced the propagation of galaxies. Also today, star formation is still going on - this is also a very interesting and promising area. Supernovae, too, are still not fully understood - we still do not understand exactly how they explode. This is with regard to astronomy.
Big data will change a lot. This is especially true for the time domain. Traditionally, astronomers point a telescope at the sky, observe one point for a while, and receive data. Previously, we simply did not have the opportunity to observe, in fact, the entire sky, then observe the entire sky the next night and the next night. The heavens are changing and some things are difficult for us to keep track of. It is with this that we have difficulties - registering phenomena in the sky that change. Now, with telescopes like LSST (Large Synoptic Survey Telescope), we can observe the sky every night, collect data, process it - and who knows what we'll find? A lot of things will come up that we can't even imagine right now - this often happens when new tools are launched. So there will be breakthroughs in the time domain, as well as in the use of machine learning to process the received data.
As for space exploration directly, speaking of the solar system - forget about exploration, exploitation comes into play (here Professor Frank used consonant words: exploration - exploration and exploitation - exploitation. - Author's note). If commercial enterprises start to work actively in space, if an economy can form there, then a person can literally be present in space. I can't wait to start drilling asteroids. Sign me up - I'll be the first asteroid miner!
As far as we know, you are very fond of science fiction and, in particular, the television series "Expansion" ("Space"). Given that there are already companies like Planetary Resources and Deep Space Industries that are developing asteroid mining equipment and planning missions, what do you think are the prospects for humanity in exploiting space resources?
- I am a clear supporter of this. I believe that nothing can be cooler than this! But it is not clear if everything will turn out as it should. It is not clear whether an economy could actually emerge there. Yes, regarding this topic, I am a hobbyist enthusiast. I happened to read the work of some people in which they set out their ideas about mining from asteroids. Apparently, water will be easier to extract, but rock drilling will be more difficult. And here we still need to figure out what exactly means “simple”. It is also not known if it makes sense to develop this economy - it is not clear if it will be viable.
When people talk about the interplanetary economy, it is primarily about companies working for their countries that conduct space research. For example, the extraction of water from asteroids will require the presence of some kind of base on the Moon or in its orbit, which will be serviced by private companies. This will be the first step. The second step could be space tourism. But if we talk about the full economy - I have no idea how it will turn out. I hope everything works out.
It's easy to imagine what could go wrong. Just a couple of enterprises that will not cope with the work, or they will have an accident, an explosion, is enough. And everyone will just say, "Oh no, it's too expensive." It is even worth looking at the US space program: we are approaching the 50th anniversary of the landing on the moon, but have not left Earth's orbit since then. Of course, the only reason we went there was the Cold War and the accompanying space race.
To summarize, I would say that the development of the solar system will be a prize for overcoming climate change. If we can survive this and become a stable, technologically advanced civilization, then the next step for us will be the solar system. But, of course, I can easily imagine how it will fail. So let's keep our fingers crossed and hope for the best.
“Do you think we can actually travel to other worlds, or will we have to send machines because of radiation and other problems associated with deep space exploration missions?
- Yes, robots are so much cheaper than humans! There are many reasons why sending people into space seems like a pointless idea, but I think we will still send people. At least we will try. This is very expensive and highly dependent on whether we can provide it. We've been saying for 50 years that we will do it. It's like exploring Mars - sometimes you need an astronaut on the surface to do the research. I am convinced that we should do it, I think we will do it, but it all hinges on the ways of accomplishing this task. Every US president says: "We are flying to Mars!" - but we are not flying anywhere. As much as I love the idea of billionaires controlling the cutting edge of science, I'm very glad that there are people like Elon Musk because they are pushing this entire industry. And, probably, this was to be expected. There is a famous story - "The Man Who Sold the Moon." It is a work from the golden age of science fiction, published in the 1950s. And it describes how businesses have tried to arrange things.
It's funny, but I expected you to ask about the journey to the stars. And then I'm just full of skepticism. I believe that if we are lucky, then approximately the next 1000 years of human evolution will be the history of the solar system - about how we and our technology will be able to populate different places in the solar system. But the stars are so far from us. And things like the warp drive are not quite aligned with reality. Take, for example, the Alcubierre engine, which requires negative energy. I have read papers that say that when you reach your destination and turn off your Alcubierre engine, it can produce such intense gamma rays that it can easily destroy the system you are trying to get into - this is clearly not the result that needed.
There is also the idea of a generational ship - a classic sci-fi idea of a ship carrying three to four generations of people. There is also hibernation, when everyone sleeps in hibernation chambers. Will any of this work? Recently, by the way, I read a very interesting work on the cost of a generation ship. Its author carried out all the calculations and summed up: to build a ship of generations, the entire economy of the three solar systems would be needed.
I think it's entirely possible that one solution to the Fermi paradox is that interstellar travel is simply too difficult. The stars are very far apart. We are limited by relativity.
Thus, at least with our lifespan, interstellar flights are impossible, because if it takes 150 years to get somewhere, and then wait another 20 years for signals from one end to the other, then this is no longer civilization. but just a bunch of outposts that can communicate with each other from time to time. So I'm oddly pessimistic on this issue. But I will be glad if the opposite is proved.
What do you think about terraforming Mars? Is this even possible in the long run, or is it nothing more than a sci-fi dream?
- Again, I hope this is possible. And I have no ethical problem with that. Mars is essentially a dead planet. It's an interesting question if we can find active microbes there. But you need to think biospherically.If we manage to terraform Mars, it will not be us, but the earth's biosphere. We will simply be intermediaries through which the green shoots will move from one planet to another. Regarding whether this is possible: there was recently an article that there just isn't enough carbon dioxide. Again, I don't think it would be a big problem to get a couple of comets in there (laughs). It all depends on our technology: if we find a way by which we can move something large, then we could eventually deliver comets to Mars.
It also makes sense to consider the option of covering a crater with a canopy. Many Martian craters have fairly tall walls - about a mile or so high, I'm not entirely sure I need to verify this information. Speaking of science fiction, this was done in the anime Cowboy Bebop - a great show! That is, you can do something like this: it is not necessary to immediately terraform the entire planet, you can cover several craters with a canopy, and you will already get several hundred square miles of area with normal pressure suitable for life. Who knows what else we'll come up with?
Speaking of technology, that's why I'm saying that the next 1000 years will be the story of humanity's adventure in the solar system. That is, without inventing something out of the ordinary like negative energy, but using only our engineering skills and programming, we can achieve a lot. And you don't have to terraform something - you can develop something large-scale like domes or other structures in which you can live. And also don't forget about radiation. Let's see.
What do you think about life in the solar system outside the Earth - for example, on Enceladus and Europa?
- Why not? Especially considering that most of these worlds are likely geothermally active due to tidal forces that continually squeeze and stretch their rocky insides. So there must be deep rifts there. We found that life on Earth can exist so deep under water that sunlight plays absolutely no role there. And it is quite possible that it was in such places that life was born - in these chemical plants. I think there is something there. We need to land probes on Europa and drill the ice. Maybe if we go down under the ice and look around, we will be able to detect signs of life. In the case of Enceladus, it's even easier - you just need to fly through the geysers and get samples. Moreover, in the course of a mission that was not tuned in to study Enceladus, it was already found out that these geysers are salty. Plus we have Titan - it's a wonderful world: methane lakes, rain of liquid methane. This is all just crazy! Yes, it will be very cool.
To what extent is astrobiology focused on looking for signs of carbon-based life? Are there any models or theories related to the search for other types of organic compounds?
- In this case, you must first of all pay attention to the metabolism on a non-carbon basis. Even so, when you are looking for signs of life in the atmosphere, you are looking for signs of disequilibrium chemistry first - that’s what really matters. There have already been various studies on what metabolism might be. And yes, on the one hand, this is all mostly carbon-based. But similar things can be done with silicon. That is, if you want to build a biosphere based on silicon, then you need to understand how it would develop. I know that there are people who are dealing with this issue. It is necessary to look for chemical compounds that cannot be formed here, but it is possible to extrapolate what the chemical pathways for the formation of biomolecules can be.
The interest in silicon is due to the fact that this element, like carbon, can be very heterogeneous chemically. It has connections that allow you to make different connections with it. But carbon is very heterogeneous and can bond with many other elements.This is why we think that basically life takes on a carbon form. Carbon is everywhere in the universe.
One of the closest exoplanets to Earth - Proxima Centauri b - is considered a candidate for the presence of life on it. How do you view this assumption?
- People think that the Sun is a typical star, but it is not. In fact, it is a relatively heavy star. The most common type of star has a mass of about half that of the sun - these are M-class stars, dwarfs. They are smaller than the Sun, not as bright as the Sun, colder than it. All this means that the habitable zone is located very close to the surface of such stars. And of course, the reason we pay so much attention to dwarfs is because they are the most common type of stars, there are quite a few of them in the vicinity, and they are also very suitable for studying atmospheres, which I mentioned earlier.
The dilemma is that these stars have an active atmosphere - flares and storms constantly occur on them. That is, a planet orbiting such a star is constantly bombarded with high-energy radiation. From this follows the question: can the atmosphere on the planet be preserved in such conditions? Or if she has life on her, can she survive? So far, this is an open area of research. I and my group are doing just that. We study the atmospheres of planets rotating in so-called hot orbits - orbits close to a star. In such conditions, part of the atmosphere will evaporate directly into outer space. Now we are studying larger planets, but eventually we will reach planets the size of the Earth.
How do you assess the chances of humanity to save our world and species?
- Oh, well, it's 50/50! (laughs) Most of my work is about climate change and the future of humanity, so I get asked this question quite often. I like to say that I am optimistic, because the alternative is not so rosy (laughs). Of course, I think we can handle it. Climate change is a kind of Great Filter. Any civilization that reaches our level will face climate change. The question is whether we can survive it. And the answer depends either on the evolutionary heritage and behavior of the species - whether it is a collective intelligence, a social species, and so on - or on the ability to learn new behavior.
It's safe to say that we haven't developed many good habits over the course of evolution. No, we are not alien to such behavior as curiosity and everything else, thanks to which we can do science. But if we talk about coherence, then things are not so good - that is why we are at war. So it all comes down to whether we can draw conclusions, or rather, whether we can develop new social behavior in the time it takes to survive. And this is an open question. Again, I think we can. There is no reason why we couldn't. But will we do it, are we mature enough? Basically, we are space teenagers and are now in a transitional age towards maturity. Some teenagers never grow up. How do you like this answer?
Vladimir Guillen, author of Naked Science.