AZoQuantum spoke with Sascha Quanz, an exoplanetary scientist who will be co-leading the search for life beyond our solar system as part of the new Centre for Origin and Prevalence of Life at ETH Zurich.
Please could you introduce yourself and your professional background?
My name is Sascha Quanz. I'm a professor of astrophysics, specifically exoplanets and habitability, at ETH Zurich. My background is also in physics; I studied in Heidelberg in Germany, and then graduated with a Ph.D. from the Max Planck Institute for Astronomy. I then left academia for two years and went into Management Consulting at McKinsey and Company, but then came back to academia and to ETH Zurich.
In 2019, I was given the chance to start my own group with a professorship focusing on Exoplanet Science. What we primarily do in our group is work on detecting extrasolar planets and building instruments. We are involved in ground and space-based instruments to detect these planets and characterize them, working on algorithms to analyze the data and using modern approaches to data science.
I attended a very inspiring symposium in 2013, almost 10 years ago, where, as a postdoc, I was exposed to a breadth of different scientific disciplines including Chemistry, Biology, Environmental Science, Earth Science, and Astrophysics, and talks occurred about how we can all work together to make progress. They looked at some of the most fundamental questions related to the origin and prevalence of life, and that really got me into that topic. It was one of the most exciting conferences I've ever been to.
I was amazed, and that was really it for me, a trigger that inspired me or motivated me to be more open-minded and also to try to find connections with other disciplines, not only within astrophysics.
Recently, ETH Zurich opened the ‘Centre for Origin and Prevalence of Life’. What are the questions that inspired the creation of this center?
I think a lot of it is actually really in the title: Origin and Prevalence of Life. It has to do with the fact that we really have no clue about what life actually is - we don't know when it arose, where it arose, or how it arose. How do you go from chemical non-living matter to biochemical living matter, and at what point do you decide whether it's living or not living? Does or did life exist on other celestial bodies other than Earth? All of these questions remain unanswered.
I think one of the realizations in many of the disciplines that are working on this topic was that in order to really make progress, you have to talk to other disciplines because there is a limit as to what you can do within your own.
Let's take the chemists, for example. They are trying to answer questions such as what the building blocks are that can be used to replicate life. They will observe some reactions and see whether some of the precursor molecules of more complex molecules show up. They're not yet replicating life, but rather the building blocks to DNA or RNA molecules, for instance.
However, one of the most important questions is under what conditions these reactions take place. You would need to have the same conditions that existed on early Earth, and if you are experimenting with the reactions in a clean room in your lab, that's probably very different. So there's a very strong connection already to Earth and Planetary Science: What are the temperatures? What is the atmosphere? How wet is it? What's the pH range of your environment? All of these things are important because they have an influence on the chemical reactions.
It is worth noting, however, that not all of the themes in our Centre will feed into all of the different sub-disciplines. Often you will have a case where two disciplines are very tightly interlinked and maybe a third just a little bit, but it's going to be very difficult to find one thing where everyone has to be involved.
For instance, we can look again at these steps from non-living matter to living matter. I have very little to provide there as an astrophysicist. It's again the question of what raw material is available on a planet early on, but it's up to the Planetary Scientists and the Chemists to continue the research.
Let me briefly explain the four pillars of our Centre. One is indeed defining those chemical and physical processes that generate those building blocks that allow you to go from non-living to living matter. That's going to be fundamental. This is primarily driven, I believe, by Chemistry, Chemical Biology, and some Earth and Planetary Science questions. However, the second pillar is trying to characterize the diversity of Planetary Environments, and then we start making the step toward Planetary Science.
The first management team of the new research Centre consists of Roland Riek, Didier Queloz, Cara Magnabosco and Sascha Quanz (from left to right). Image Credit: Marco Rosasco Photography / ETH Zurich
We try to understand under what conditions life may have arisen on Earth, then we try to extrapolate these to other planets and moons in the solar system, but also to other extra-planetary systems. So, what are the different environments where such a process could have happened or could not have happened?
Then it's about trying to understand how different environments support life and how life influences those environments. There's a tight interplay between the biosphere of our planet and the composition of the atmosphere. We had one example already with oxygen, but also there's an interconnection with the geosphere between the land mass and the oceans.
All of this is a gigantic interlinked system. You cannot have one without the other. Understanding this interplay, and again trying to understand what influences what in what way, is going to help us to understand better how to look for life on other planets and under what conditions life can function.
Non-standard life and extreme environments are where you can really push it. How extreme can you go in terms of conditions for life as we know it to still thrive? And then you're again asking the question about different stellar environments and different planetary environments, but non-standard life could also mean maybe there's a different kind of life. All life on Earth functions exactly the same way - you can trace it all back to a last universal common ancestor, and this is still for me absolutely amazing. It doesn't mean that life arose only once, but all we know right now is that there's one time that is the starting point of all life as we know it today.
That's another big question: is it just one time that it happened? Did it happen many, many times and just one was lucky to survive?
So, the extremes may also include things that are not the way we think of living entities right now.
You are currently the principal investigator for LIFE – the Large Interferometer for Exoplanets – how does this role relate with the initiative of the Centre of Origin and Prevalence of Life, and how will the different research areas facilitate your exploration of exoplanet atmospheres?
When we look for life on extrasolar planets, that is planets orbiting stars other than our Sun, we are going to be using indirect methods and looking for signatures that life leaves in the planets' atmospheres. The oxygen in Earth's atmosphere, for instance, comes from living plants, and you can look for those signatures on other planets. As well as this, we need to understand questions like: Is life a unique source for that signature? Could there be other sources? And again, these are not astrophysical questions - these are questions for Environmental Scientists and also maybe for Atmospheric Scientists.
Then we need to talk to the biologists, because we need to understand the gases that are produced by metabolism. Maybe there are other metabolic cycles that produce other molecules that we could also detect, again something I don't know. If we learn from the biologists what the signatures are that we are looking for, we can design instruments that actually try to look for these traces in the atmospheres of other planets.
With the LIFE mission, this is in a very early phase, and nothing has been built. We are still in the concept phase. We need to understand things like: How many spacecrafts do we need? How big do they have to be? What is the right wavelength coverage that we need? What are the signatures that we are looking for?
These are still things that are in flux; we have a first idea, but this needs to be refined. There are technical aspects that we are trying to tackle in our group, but also through collaborations with other groups. Then there are the scientific questions, and I would hope that there are natural connections to the atmospheric scientists, etc., to better understand what the signatures are that we are actually looking at.
This is ultimately where you close the loop and start answering the question of the prevalence of life outside the solar system, so this is where I see our group contributing the most, at least for the coming few years.
Specifically what kinds of bioindicators are you hoping to find in exoplanet atmospheres?
We are going to start off easy in the sense that we are going to look for things that we understand from Earth. A lot of people would say, "Well, it's going to be very unlikely that there's another planet out there that is exactly like Earth." I agree that's very unlikely, probably not going to happen. But, we have to start somewhere before we start putting out hypotheses.
What we are looking for, primarily, is the signatures or molecules in those atmospheres where we know that they are either exclusively or primarily produced by biological activity. Oxygen, as mentioned, is a very good example for a planet like Earth.
There are other ways, however, where conditions can produce an atmosphere in a planet under more extreme conditions. For instance, closer to a star, the starlight could break up CO2 or water molecules. The carbon or hydrogen atoms would then go away and you would accumulate O2 in the atmosphere. However, this is not happening on a planet like Earth at a certain separation from the star.
Also, most methane on earth comes from biological activities, and then there's more trace gases like nitrous oxide (N2O), another great candidate for bio-signatures that is at very low levels in our Earth's atmosphere, but it's going to be hard to detect.
Image Credit: Dotted Yeti/Shutterstock.com
The interesting bit about oxygen and methane, at this point in time, is that combined the simultaneous detection of both of these molecules is considered the strongest signature for life, because from a chemical perspective, methane and oxygen are very reactive when put together. So, if you would stop life on Earth right now, it will take a few 10,000, maybe 100,000, years for the molecules to fully react. Having those two together at the same time means that something is continuously replenishing those features in the atmosphere - this is life.
From an astrophysics perspective, such disequilibria is what we are looking for, and then we need to understand if there are other sources, other molecules, that life can produce. This is a part of our research that we are not doing yet in our group, not yet in the Centre, but other groups including NASA are looking into this very strongly while also trying to understand what false positives there could be.
In terms of false positives, I gave the example of water molecules being broken up by strong radiation in ultraviolet light, where the hydrogen is then escaping and the oxygen accumulates in the atmosphere. That's one example that we know already, but maybe there are other examples, other chemical reactions that can take place, and this we also need to understand.
Are you, therefore, looking for the existence of current life on exoplanets or just evidence that there ever was any? Are you more likely to find evidence of existing life than evidence of something that died out thousands of years ago?
All the exoplanets that we will be able to investigate in greater detail are going to be in the immediate neighborhood of our sun. So, in terms of light years, that will be maybe out to 60 - 70, or so, light years. This is still a very large distance for us, but for astronomy or astrophysics, this is nothing. It's literally the stars you can see with your eye that we are going to look for planets around, and if there are planets, we would like to understand what those planets are made of.
The time that it takes light to travel from there to here, that's just a few tens of years. So when we see it today, you can basically assume that unless something catastrophic happens, it's still going on. So it's indeed an indication of active present life. It's not an indication of past life like you would look for on Mars where we know that there's no life happening right now, but maybe a few billion years ago.
There's an interesting point here because then the question becomes, "all right, so maybe there are so many planets and we're just unlucky that the life on them has already gone." This is why, for us, it's important to understand for how long in the history of Earth we can find atmospheric signatures of life. We know that the oxygen level that we have today, which is being produced by algae and plants, is not the same as it was two billion years ago for instance.
There's an evolution in the signatures because of the co-evolution of life, oceans, and atmospheres. All of this, as I said, is interlinked. So we did some first calculations and tests and we believe that depending on what sort of instrument or space mission you're going to use, at least for half of the lifetime of Earth, maybe a little bit longer, those signatures were strong enough to be detected remotely on another planet if they were at the same level as in Earth’s history.
This is fantastic news. We know that life probably started maybe 500 million years after the Earth's formation, so it has been evolving for the last four billion years, and for half of that time we could detect that. The stars out there in our neighborhood, they have roughly the same age as the sun, so a few billion years.
So, for whatever reason, if similar processes took place on those, I think there's a fair chance that we could actually see it. This is what is important for us; the chances of looking at those signatures is not so strongly dependent on if it’s happening right now. Because, yes, life evolved, but those signatures there can be robust and long-lived.
What are some of the methods and equipment you will use to analyze these exoplanet atmospheres? In particular, what role will the ELT – Extremely Large Telescope – play?
Let me start with the James Webb Telescope. James Webb wasn’t designed to do exoplanet science, but it will do fantastic exoplanet science.
Today we already know of some exoplanets that are sort of rocky and have roughly the same size and mass as the Earth, and they happen to orbit around stars that are much smaller than the sun. These are easier to analyze because their suns don't have this overwhelming glare from the luminosity that makes it difficult to understand what's happening on the planets.
The James Webb Telescope. One dozen (out of 18) flight mirror segments that make up the primary mirror on NASA's James Webb Space Telescope installed at NASA's Goddard Space Flight Center. Credits: NASA/Chris Gunn More
So we know those planets already, but we don't know if any of these other terrestrial exoplanets have atmospheres. We think so, we assume it, but that would be a very important measurement that James Webb could probably do to be sure. A lot of these small stars produce a lot of hard radiation in the UV range, so in principle, they could evaporate those atmospheres very, very quickly.
In terms of looking for biosignatures, I think it is going to be extremely hard if not to say impossible with James Webb, because although the planets are small and James Webb is a gigantic telescope, it's also not as big as it would need to be to do that science. So, this brings us then to the next generation of ground-based telescopes.
The ELT, Extremely Large Telescope, is going to be a European-led project, and it's currently being built in the Atacama Desert. It's going to have a 39-meter primary mirror, which is almost a factor of five bigger than the current largest telescope you have on the ground.
The size is important because it increases your collecting area; in terms of the photons you collect from those planets, if you have a bigger bucket you're going to collect more of them. At the same time, a bigger telescope also means you have better spatial resolution, so you are much better able to separate the planet from the star directly on your detector.
With current telescopes, these are smeared together and are indistinguishable, and this is why we cannot take a picture of a planet yet. But, with the ELT, we're going to separate those two signals. This is for me the fundamental step that the ELTs will do. We will take the first clear picture of a terrestrial planet.
To summarize, James Webb will do indirect measurements, investigating the planet as it passes in front of the star, but as it's an indirect method it will not take a picture of the planet directly. The ELT can take pictures of a planet.
I'm very optimistic; I cannot prove it to you, but this is why we want to build this - to show at one point in time a picture and say, “This is the star, there's the planet”, and then maybe we can get some idea of what that planet is made of.
Ultimately, though, you have to combine two approaches; you also have to build gigantic telescopes out in space. If you have an ELT in space, you can combine the calm environment of space together with a high spatial resolution of a gigantic telescope. You would combine light from several telescopes that are acting as one; each telescope itself would probably be smaller than the James Webb Telescope, but if they fly a few hundred meters apart, they can act as one gigantic telescope. Then you have all you need in space. Those few small telescopes are enough to look for dozens if not hundreds of planets, and many of them will be similar to Earth in size and temperature. This the driving motivation for the LIFE mission.
For the LIFE mission that we are currently pushing here in Europe, it's the question of investigating terrestrial exoplanet atmospheres, not just one or two, but doing statistics in order to address questions of how often it happens that a planet, like Earth, Venus, or Mars evolves. You cannot do this without large space missions. NASA is looking into similar ideas, with a different mission concept using a slightly different wavelength regime and different techniques, but the same goal.
In my dream world, NASA will build a mission that will look at, as we call it, reflected light. It will measure the light that is reflected by the planet. So, the light is emitted by the star and the planet reflects the light like a mirror. Alternatively, you can measure the intrinsic radiation from the planet because of its temperature at mid-infrared wavelengths. This is our approach for the LIFE mission.
Reflected light has information that thermal emission doesn't give you, and thermal emission has information that reflected light doesn't give you. Just imagine those missions flying in 20 to 25 years, where at the same time you can get a much more complete picture of those planets and a much more robust identification of potential biosignatures. That's the ultimate motivation for those bigger telescopes in space that are needed; you're not going to get it from the ground, unfortunately, even with the next generation of gigantic telescopes.
Do you think your goal is possible within the projected 25-year timeline?
We joke because 25 years is roughly the time of my retirement, so I always say, "I want to see that thing launched before I retire. It's fine if I'm retired, but please invite me to the launch party!" I think it is not completely unrealistic - for me, it's a question of priorities. We need to get people, agencies, donors, private industry, etc. interested and to join forces to address this question.
When I say it is a question of priorities, I mean that at the end of the day it's funding. I think there's no physical law that prevents us from building that mission, but can we get sufficient support in different areas?
Scientific processes like this are slow because many countries and agencies are involved. So for me, the biggest question is: Do we manage in the coming few years to get the support we would like to have? Are we convincing enough that it's not only astrophysics but also those other disciplines that are involved?
We have a foot in the door at the European Space Agency where they came up with a rough timeline for three future L class large missions, and they have a 2035 to 2050 time frame. This gives you an idea of what timescales we're talking about. We have managed to put our science on the map of the European Space Agency that doesn't mean it's going to fly, it doesn't mean it's going to be funded and implemented, but it's the first foot in the door.
The feeling I have is that there's so much enthusiasm about this topic, not only here but literally throughout the world, and not only from astrophysicists or biologists and chemists but also from so many people. I think it's possible, we just have to do it right. We have to be nice to each other, collaborate with each other, and make everyone understand that this question is bigger than any one of us.
One legitimate question we always get is, the money you're spending, what is it good for? Does it benefit society, and can we not use that money for something else? And that's an absolutely relevant question. Just look around us, right? The world is crazy right now. There are so many issues, so many challenges and I couldn't agree more. But, I think what is important is that you're not losing money by doing these kinds of things. You provide some inspiration not only for the next generations, but you open the minds of people to see the bigger picture. You see that there are questions that relate to all of us on this planet equally. If we have the means to fulfill ourselves by investing in this, I think it will and can only be beneficial in the long run.
It's going to be hard; it's going to be difficult, but at the end of the day, I believe we can make this work.
How many people are going to be involved in this across different disciplines?
In the new ETH Zurich Centre, for now, the number is about 40 Professorships. Professorships at ETH Zurich mean typically a group size of 15 - 20 people; not all of them are devoting all of their time to that topic, but there's a common interest amongst all of those professorships.
This is not a closed club, and we welcome everyone within the ETH Zurich community to participate and join our discussions.
What is personally the most exciting part of this new initiative to you?
What I'm really excited about is learning new things. I think about being able to sit down in those seminars and meetings again with all the great colleagues here but also in other centers and really educate yourself about chemistry or biology. I'm going to enjoy this. I really like learning and there are so many things I have simply never heard of or learned before. It's going to be great to feel like a student again and be absolutely open.
Another big thing is to see the students, to see the eyes of the younger generation coming in. When you mention the program here on campus or in a lecture, you can see that a lot of the younger generation understand that this is a really important question, and you get emails asking: How can I contribute? Is there a project already? Can I do a Ph.D.? So, seeing and hopefully inspiring and giving the energy to the next generation is going to be fascinating to see.
Do you have faith we will find evidence of life on other planets?
I do. I cannot prove it to you, but the reason I'm optimistic is the following. From exoplanet science, we know that there are so many planets out there, and especially that there are so many terrestrial planets out there.
We can even look at our nearest star. It's called Proxima Centauri, and it has a small planet roughly at the right separation from the star to be at a temperate regime where in principle liquid water could exist...and that's the nearest star. So, chances are that many of those nearby stars do have these planets. Otherwise, it would be a really big coincidence. And this is what the statistics of exoplanets tell us.
So, there's reason to be optimistic that our immediate neighborhood is full of small terrestrial exoplanets, with roughly the right size and temperature, and so on. That's one thing. The other thing is that, and I mentioned this at least to some extent already, life started so early on this planet. Again, we don't know how or when exactly, we don't know if it's just one incidence or several, but it started relatively early and then it lasted for such a long time. So many things could have happened, but life was robust. It occupies all niches you can think of. It is everywhere. You're breathing life right now. This tells us that life is resistant and will adapt - once you have it, it's very hard to get rid of it.
This together with the amazing number of planets that we know are out there makes me optimistic that by building the right instruments and the right missions, we can make an empirical assessment.
This is why you need to make sure the number of planets you can investigate is large enough that not finding any evidence of biological activity on those planets is useful. If you look at two, maybe you're just unlucky. So this is why James Webb and the ELTs will do fantastic things, but it's not going to cut it. We need those bigger missions to make the sample large enough so that the null result, as we would call it, is telling us something very profound and important for ourselves and our planet.
For me, it's not so much a "yes" or "no" answer. I'm not going to be disappointed if it turns out that many of those planets do not show signs of life, because the empirical assessment tells us something about our planet, and how special we are. It means that maybe life is even more precious than we thought because then this is the only place in the immediate solar neighborhood where life indeed managed to survive for billions of years. This is important to know too.
So I'm optimistic, but a negative answer would be equally scientifically important. And I'm happy to take either answer - I just want one!
About Sascha Quanz
Sascha P. Quanz is an exoplanetary scientist, an Associate Director of the Centre for Origin and Prevalence of Life and Head of the Exoplanets & Habitability Research Group in the Department of Physics at ETH Zurich. He is driven by the long-term goal to search for indications of life on extrasolar planets (i.e., planets orbiting stars other than our Sun). Researchers in his group carry out astronomical observations on state-of-the-art telescopes, design powerful data processing algorithms and statistical frameworks to interpret the data and contribute to the development of key technologies and instruments for world-leading facilities on ground and in space to enable the direct detection and characterization of extrasolar planets.
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