Cambridge team finds strongest hints of life beyond solar system—conversation with Prof Madhusudhan

Hello and welcome to The Print. My name is Soumya Pillai and I'm here with some very exciting news from the world of science today. The possibility of life beyond the realm of earth is something that has kept humanity excited for years and it has also kept scientists across the world busy at work. Earlier this week a research team from the University of Cambridge have found one of the most compelling hints yet of life beyond earth in an exoplanet which is outside our solar system. And as a moment of pride for all of us, this team is headed by an Indian origin astrophysicist and exoplanetary expert Professor Nikumar Dasudhan who is joining us today to have a conversation about his discovery, its significance and where it's placed in the larger narrative. Hello Professor Dasudhan, thank you so much for joining us at The Print today. Hello, thanks for having me here. Professor, just jumping into the interview head on, what is it exactly that your team has discovered? What are the findings? Yeah, so in a nutshell what we are finding are hints of one of two molecules, DMS, that's dimethyl sulfide or DMDS, dimethyl disulfide. One of these two or both of these molecules in the atmosphere of the planet orbiting another star, K2-18, the planet is called K2-18b and this system is about 124 light years away from us. Now these gases we are finding from observations of the atmosphere, of the atmosphere of the planet using the James Webb Space Telescope and this planet had already been, like we have been looking at this planet both with theoretical studies and observations for the last five years and there has already been evidence that it could be habitable, that it could be a possible Haitian world. So this new evidence adds a bit more to that narrative that this could be an ocean world and there could be life on it, but I have to be careful that this is very early science. This is telling us that it's a major step on the path to searching for life, but we cannot make a robust association to life just yet. So what we are celebrating now is having the capability to do it and the first science of it, but we want to be careful not to stretch it too far to conclusive evidence for life. Professor, you spoke about DMS and DMDS. Why exactly DMS and DMDS? How does that, these two molecules link with the possibility of life? If you could explain that a little bit. Yes, so both these molecules are known to be produced primarily by life here on earth. So over the last two decades various studies have looked at various molecules that you would look for in the search for life elsewhere and these molecules emerge as the best contenders or some of the best contenders for that claim because they're not produced, they cannot, as far as we know, they cannot be produced in large quantities by any other process but life. There have been some experiments where, lab-based experiments, that you can produce small quantities of this and you see small quantities of this in like in outer space, but you also see small quantities of molecular oxygen like on earth which is a strong biomarker also in extraterrestrial environments, but large amounts of these molecules cannot, as far as we know currently, are not produced by any other mechanism but life. So they have been predicted to be strong biomarkers including on planets like this with hydrogen-rich atmospheres and this is why we are making that association that this could be indicative of life. So when we are talking about large quantities, how large are we talking about, I mean from based on your observations? Yes, so the inferences, the initial inferences we are making is that the amounts could be at least tens of parts per million, so that is a part in 100,000. Now that may sound as a small number but if you see how much of these molecules are present in the earth's atmosphere, they're of the order of one part per billion or even lower, right, so very small quantities in the atmosphere which means what we're inferring is thousands of times higher than what we see in the earth's atmosphere and that is the significant bit and people, other teams have also done these calculations even before we made the observation and they've estimated that if you, they predicted that if you see these molecules at this level, at tens of parts per million or more, the flux, the biological flux of sulfur-based biomolecules from the ocean should be at least 20 times that than that on earth, right, so that association had already been made before the observation and that's an important point to note, it's not, you know, oftentimes you make an observation and you try to interpret it in various ways but this is different, this is, there has been a prediction already and we are making an independent observation that is confirming those predictions which is a big deal if you think about it. Professor, could you also run our viewers through the process that your team followed to get it, we do know that you used observations from the James Webb Space Telescope but if you get, if you could get a little deeper into what was the process like? So the process, so this goes through a competitive process, we apply for time on JWST and then we were successful and then I'll describe the observation process itself for this particular observation, we have been looking at this planet for the last few years, so our first observations were published two years ago in 2023 and also with JWST and we had already seen at that point evidence for, significant evidence for carbon-bearing molecules, methane and carbon dioxide and we did not see evidence for some other molecules like ammonia and carbon monoxide, now that combination of molecules is what told us that this is most likely a Haitian world, which means a world with ocean-covered surface and a hydrogen-rich atmosphere, there have been other hypotheses that have also been proposed to explain those observations but so far none of them have been able to explain all the evidence that we have, so the Haitian hypothesis is currently our best bet in terms of explanation, I mean there could be other explanations in the future but as of now that's the best explanation, so then we made this observation and the observation, these observations generally are made using what is known as the transit method, this is where you are looking at the star, you have a telescope and you can take a spectrum of the star, spectrum means light as a function of wavelength right, but when you are looking at the star as the planet transits in front of it, some of that starlight passes through the atmosphere of the planet before reaching the telescope and the molecules in the atmosphere absorb some of that starlight at different wavelengths, they absorb with at different strengths at different wavelengths, so your light is slightly lower, dimmer, when the planet is going in front of it and dimmer at different way, in different ways at different wavelengths, so based on that absorption of light and if you compare that to when the planet is not in front of the star, that difference can give you how much absorption is happening in the planet's atmosphere, so that is what is known as a transmission spectrum, absorption as a function of wavelength and based on that we can work out what are the molecules in the atmosphere and how much of those molecules need to be in the atmosphere to be able to explain that absorption spectrum or transmission spectrum that is. Professor, that I mean a bit of what you just explained was going to be my next question as well about your, I mean we've spoken about your initial observations in 2023 and then in 2024 as well, in this particular observation were you also looking at different markers or were you just looking to confirm your earlier observations with more solid observations? So yeah, so these observations are very, are entirely independent of the previous observations, this is at a different wavelength range, previous observation was what is known as the near infrared between 1 to roughly 1 to 5 micron, this is in the mid infrared between 5 to 10 micron, so there is no overlap and also it's with a different instrument obviously, so what we did is we said let's do an agnostic search, so we had a large number of molecules to begin with, we looked at about 20 molecules, that's about the largest number of molecules that have been searched for in planets like this before, so we went through this intense exercise of looking at lots of different molecules and basically we didn't pick up any of those except for these two and that is what told us that there is something there, so we did a lot of robustness test by removing these molecules and see if we can fit the spectrum, we couldn't, so then we construct a model where we include the species that we are picking up at some level of significance and including species that have been picked up previously and then we do our strict robustness test with, there's a lot of process involved in even in the data reduction, there are a lot of things you can, a lot of variables you can choose, so our approach has been to explore that entire space of possibilities on how you can reduce the data and that's what gave us the robust conclusions that we have right now. A professor who did start off by saying that you know the observations are still a little nascent, if I'm not wrong on the sigma scale it's still on a three, but if you could run us through about what more observations would you need to come a little more closer to being sure that there is a possibility that biological activity actually does exist in this exoplanet? Right, so if you looked at the spectrum that is out there that we have published, you can see like features in the spectrum just by eye, you don't even need the model, I mean there is the data and there is a model fit, but you don't even need the model to see that there are features in the spectrum, so that is always a good sign, because a lot of the times you can extract information even if you can't see by eye, statistically you can extract some information, but in this case independent of the model you're seeing features. So the first question to ask is whenever you look at a spectrum and you're trying to do interpretation, well is the data real? So however we cut it, however many analysis we did, our approach usually is to make sure we do enough to try to get rid of the data of those features, and we have failed in that, so the features stayed, but and then you do your interpretation and we are finding this at a three sigma level, and whenever you have results at a roughly two to three sigma level, we are talking about like two sigma would be like about 95 percent, three sigma is 99.7 percent, that is the sort of the gray area, like if you have a really really strong detection that would be like five sigma, if you have no detection at all that would you won't even see the feature, it will be one sigma below two sigma, but whenever you have this range between about two sigma to three, three and a half sigma, it is always a gray area in the sense that it is telling you that there are hints of something, but we are not 100 percent sure, and that is where we are right now, this is why we call them hints, right, because they're enough for us to be interested and invest resources, if it were less than let's say two sigma, then we wouldn't even bother, right, so but it's in a range where it's interesting, so then we should invest more resources and see if we can get it to that five sigma level, so this is standard scientific method, so we follow everything through the book, there is nothing that is new in all of what we are doing, so yeah, so how much time do we need for to get to that five sigma is the question you're asking, so with one observation we could get to this level, this gray region, and we estimate that in another two or three observations exactly of the type that we have done right now, I can already get us to four to five sigma, and that is the big deal, and this is why this is such a transformational moment in the history of like the search for life, is because for once we are saying that as a species, as humanity, we have the tools, and with the trivial amount of time, we can actually establish whether a potential biosignature is even there in the atmosphere of AMX, and that is what the transformational aspect of this is, so this observation took like eight hours roughly, so you need another 16 to 24 hours to get it, and that's not a lot of time with the GEMSOV space telescope, GEMSOV observes for thousands of hours every year, okay, so that's that, so we want to do that, but then even if you find the molecule at let's say five sigma, then can we claim it's robustly due to life, what we can claim is that there is a very good chance that it could be due to life, but we also want to be very careful and do due diligence to do a lot of theoretical work and experiment work on the side to establish that there is no other process, there are no unknown unknowns, right now these molecules can be only associated with life at these abundances, but we want to be open, we want to be open to other hypotheses that may come up that we didn't know so far in the field, and then that association will happen gradually, but the promise is there. Professor, my next question is going to be a two-part question and slightly more basic than what we've been speaking about so far. K218b itself has been like the focus of a lot of astrophysicists for about over a decade now, so why K218b specifically, also you started off introducing this exoplanet saying that it's about 124 light years away from earth, does that distance from earth in any way would impact the, what do I say, sustenance of life itself, could it possibly be that, like when you look at the spectrum of time, that we could be much behind and there would have been life and it does not exist now, so is that something that is part of the conversation? A very good question, so for the first question why K218b, so K218b just to give the summary, it's a planet about 8.6 times the earth mass, that's how big a massive it is, 8.6 times earth mass and two and a half times earth radius, roughly 2.6 times earth radius. Now the important bit is that this planet orbits in the habitable zone of its host star, which means if you put an earth-like planet at that distance from the star, it receives almost the same amount of radiation, total radiation that the earth receives, which means you would expect that planet to be habitable if it were an earth-like planet, but this planet is so large that five years ago no one would have called it to be even potentially habitable, because the idea we have in our minds is that in the solar system you have the earth and all the terrestrial planets, the rocky planets that are smaller than earth or comparable in the case of Venus and then you have Neptune and Uranus, which is four times earth size and about 15, 17 times earth mass and then you have nothing in between, so we don't know, this planet is intermediate right, so we don't know what these planets are like, are they rocky planets or are they ice giants like Uranus and Neptune, so previously people had assumed them to be more like mini-Neptunes, a smaller version of Neptune with a thick hydrogen-rich atmosphere, so it won't be habitable because the temperature and pressure would be way too high at the bottom of that atmosphere, but what we showed five years ago that actually if you explore the entire space of solutions, there is a solution where the planet could be covered in oceans with a thin hydrogen-rich atmosphere and you could still explain all the properties, the mass radius and temperature and all that of the planet and that is where it all started about five years ago, we published that paper and we have been looking at this plan continuously since then doing a lot of theoretical studies and these observations and we are finding right now that it's being habitable is the most viable solution, but it's not good enough for scientific evidence, we want to stay open and pursue it further and then as far as the distance is concerned, you're right that the planet being 124 light years away means that you're looking into the past, you're looking for signals that happened like 120 years ago, but from an evolutionary standpoint, that's not an issue because here we are talking about microorganisms like very basic single-cellular life biology and evolution doesn't change very much on 100-year timescales, so that's why we don't think like this makes a huge impact on the biosignature aspect of it, but we don't know if there is actually a life on it, so we have to be careful in making those extrapolations. Professor, my quick last question to you, astrophysics as a domain itself has evolved a lot, I'm sure since you started off, could you tell us how much the field itself has grown and how promising is it in the next decade or so? Yeah, so this field has gone remarkable transformation in the last three decades, so the first exoplanets outside the solar system have been found almost exactly 30 years ago, so this is the 30-year anniversary of that and when first planets were found, they were met with a lot of skepticism, was it a planet or not and so on, and today we know that almost every star should have a planet of some kind around it, so that radical shift, if you look at the night sky, pretty much every star should have some kind of planet around it, right, so that radical transformation happened in just 30 years, but for thousands of years we have been wondering about that question and then with the discoveries that we are going through now, what this is saying that maybe even the discovery of life on planets is within reach and that is an even bigger advancement, right, that's a landmark transformation in the field and even if this is not due to life, we just have to pause and think, right, five years ago if you ask someone how long would it take us to detect life on an exoplanet, the answer would have been 20 years, right, because we don't have the facility, we didn't have the facilities and we didn't have the planets, we were thinking of rocky planets like Earth and they're very hard to detect and so on, even now if you ask how long will it take to detect life on an Earth-like planet, that's another 10 years or 15 years, the next generation of facilities have to come online, but like in just the last five years and with the results like this, what we're saying is that we don't know about association with life, but at least the detection of a potential biosignature can happen anytime within the next couple of years and that transformation is a major landmark step in the search for life because never in the history of our species have we come so close to saying that the living universe is probably within reach. If there is life out there, like the kind that we are talking about here on the kinds of plants we're talking about, they are within reach, right, so and that is the important advancement here. Thank you so much for joining us, Professor Madhusudan and thank you for doing that. I'm pretty sure that you have a very, very busy schedule, especially after the massive, massive breakthrough that you have, your team has come forward with. On behalf of all our viewers at The Print, we wish you all the best for your future observations and we're really looking forward to news coming from your lab. Thank you for joining us and thanks to our viewers for staying with us through this interview. I'm Soumya Pillai from The Print and we were joined by Professor Madhusudan from the University of Cambridge. Thank you. Thank you Soumya for having me here.