 So Dr. Giada Arney is a NASA postdoctoral program fellow at the NASA Goddard Space Flight Center and a member of the Virtual Planetary Laboratory. She recently received her PhD from the University of Washington where she worked on photochemical climate and spectral simulations of worlds and traveled by global haze decks. And so this is a really exciting thing about that she's having a chance to study is what these exoplanets are like. And her colleague is Dr. Eddie Schwedermann. He's a NASA postdoctoral program fellow, also with the NASA Astrobiology Institute, alternative Earth's team at the University of California, Riverside. He also received his PhD from the University of Washington, Seattle. And his research has included modeling the spectral appearance, climate and photochemistry of terrestrial exoplanets, which is of course what we're really, really looking for. So we wanna find those astrobiology, those biosignatures. And so Eddie and Giada are gonna share with us about their work to do that. And so please welcome Drs. Giada Arney and Eddie Schwedermann. Okay, hi everybody. So I'm gonna go ahead and share my screen. So Giada's just gonna load up the presentation and then we're gonna go, we're gonna kind of trade off a little bit as we go because we're giving this joint presentation and presenting little bits of aspects from both of our works and also a general overview. And so since Brian already gave us that great introduction, I think we can just move to the next slide and kind of outline what we're gonna talk about tonight. And so the first thing we're gonna do is sort of talk about the state of characterizing exo-Earth or planets we might expect could be habitable, could be like the Earth. Of course, a lot of it's a perspective investigation and Giada's gonna talk about missions and how we might observe Earth-sized planets orbiting other stars. Then I'm gonna talk about biosignatures. What is a biosignature? How might we recognize it on exoplanet? We're gonna talk then about the Earth through time. So the Earth has represented different states throughout its history. It would have looked quite different two billion years ago than it does today. And so all of those, we have evidence for that in a geochemical record. And all of those states are, of course, plausible states for Earth-like planets to exist in. So Giada's gonna talk about that. I'm gonna talk a little bit about potential false positives for life or how we might be fooled by abiotic processes that could generate what we might think are biosignatures in exoplanet atmospheres and how we could basically stop that before it happens and rule those scenarios out. And then finally, Giada and I are gonna talk about the case of Proximus and Tori B. And it's an incredible discovery. We're so looking forward to learning more about this planet. We don't know a lot about it now, but we do know, what we do know is it's the closest it could possibly be for an exoplanet in a Hubble zone around another star. And that's just amazing news. And so if you just move to the next slide here, this is why we're talking about it. Potentially habitable planets are being discovered. This is a great graphic produced by the Planetary Habibi Lab. And this sort of gives a little bit of an overview and with artist conception images of what these planets that have been detected either through transits or radial velocity, what they might look like. So this is a two scale representation of these planets. We know at most they're mass and radius. In some cases we only know they're radius or only they're mass. And so we have to guess at the other thing. But we're pretty sure that most of these have a rocky composition, likely a secondary outcast atmosphere. Maybe not, but they definitely orbit within a range of distances from their star in which if they had an appropriate atmosphere, they could maintain liquid water on their surface. And so now that we have this growing list of potentially habitable planets, we really have to start thinking about how we're gonna characterize them. And so now I'm just gonna drop it off to Jada who's gonna talk about what missions are coming up. Yeah, so we're in a really exciting time because not only do we know about these exoplanets now, we're actually starting to find small terrestrial size, so Earth-sized exoplanets, which are obviously really interesting when you wanna think about planetary habitability. But just around the corner are missions that are not just gonna be able to find these planets and give us really basic information about their properties. Like Eddie was saying, we know their masses, sometimes we know their radii, their distance from their stars, but that's it. And so when you're concerned about planetary characteristics and just really understanding these planets as unique worlds, we need more information. And so there's a couple of missions on the horizon. One that I wanna point out is JVST or the James Webb Space Telescope, which is a 6.5 meter diameter telescope that would mainly be able to take infrared observations. Now, the James Webb Space Telescope will be able to observe exoplanets as they cross in front of their stars. So as the planet, you know, as you have your star, the planet passes in front of the star and blocks out a little bit of that starlight and the James Webb Space Telescope could potentially measure features in the planet's atmosphere as it looks for absorption of the starlight that's being backlit behind the planet passing through the planet's atmosphere. But these are really hard observations for JVST to make because JVST was not designed for exoplanets. We hardly knew about exoplanets when we started building this telescope. And so at most, if we're lucky, we might be able to characterize one or two transiting so when it passes in front of the star Earth-sized planets with JVST. In the more distant future, there's a couple other missions, but the most exciting mission or group of missions to me is what on here is called New World's Telescopes. There's a lot of different concepts for this telescope. This is a telescope that has not yet really been, it's still in design. There's a couple of different competing designs through what this New World's Telescope could be. One of the designs is being worked on is something called HAB-X, which is the habitable exoplanet finder, I think it's called. This is a telescope that would be somewhere on the order of four to six meters, four to 6.5 meters in diameter, so potentially a little smaller than the James Webb Space Telescope. And it's mainly looking for signs of habitability on a few Earth-sized planets. But the mission that I get really excited about and the mission that's actually being worked at NASA Goddard, which is where I'm at now is one called Louvoir, which stands for the large UV optical infrared telescope because astronomers love acronyms. So this would be a really huge telescope, something like nine to 16 meters in diameter. And this telescope is designed to detect tens of Earth-sized planets in the habitable zones and search for signs of life. And both HAB-X and Louvoir would be looking at reflected light from these planets. So they'd be able to block out the star and directly see the planet. And in order to do that, you need advanced techniques such as things called coronography or star shades, which are occultures that would fly in front of the telescope. And these are challenges because we've never done coronography. We never had to block out something with a contrast ratio as extreme as it is between planets and stars. A Earth-sized planet is about 10 billion times dimmer than its star. And so there's a lot of photons from the star you have to block out in order to see the tiny planet. But fortunately, missions like Louvoir are quite big. So here's putting it into context. The left image on this slide, you can see the telescope had HDST or the High Definition Space Telescope. That's another name for Louvoir. You can see how much bigger it would be than JWST. And on the right side, you can see a simulated image of what an exosolar system, our solar system, might look like from a great distance using this telescope. And of course, the observing time with these things is going to be expensive, like literally expensive. These are expensive telescopes, but a mission like Louvoir is designed, potentially designed to be a long-lasting, serviceable telescope that might be operable for something like decades. All right. Great. So thanks, Jada, for that. And this is a segue. Since observing time is going to be so expensive, we really want to know how we're going to recognize a planet that's habitable. And if so, if it's inhabited. And of course, the sooner that we can recognize whether the planet's habitable or inhabited, the more we can spend the time on the interesting targets. Or if we could, for example, rule out the habitability of a planet, we could go to the next target. And so here's just an image from Cassini of Saturn. And then on the lower right there, you can see a pale blue dot that's Earth. And so this is just sort of to give you perspective that when we're going to be looking at exoplanets, we're not going to have any spatial information about the planet. We're just going to have a pixel of light that's going to be a certain color. But we can unfold the light spectrum from that planet and look at evidence that there's different gaseous molecules there or maybe evidence for different surface features. So if we can go to the next slide. I just wanted to get through some definitions here. I mentioned habitability and biosignatures. And what I mean by that, of course, is that they're different. Habitability means there's evidence that the planet can or does maintain surface liquid water. That's the definition of habitability that we have. And yes, there are cases where you can imagine some kind of like exo-europa or something. But those planets, whatever potential biosphere would be there, would be completely unobservable from interstellar distances. So we really take surface liquid water to be the determining factor. Biosignature is a positive indicator of life. So something that life is producing that you would expect to be produced by life. And anti biosignature is something that maybe shouldn't be there if life is present. Life would, for example, remove it if life was present. And then what I'm going to call a false positive indicator, and I'm going to get into that later, is evidence for a process that would abiotically generate something that you would otherwise think is a biosignature. So if you saw that a biosignature and the false positive indicator, that could mean that you don't actually have a real biosignature. So if we could go to the next slide. And so here are the requirements for planetary biosignatures. I said we're going to be looking at these planets across vast distances. So whatever evidence that life produces to change the composition of the plant's atmosphere or surface has to be observable over interstellar distances. That means it's probably global in extent, has to produce observable features. So if it's, for example, gas, like oxygen has to interact with light in such a way to create a stamp or a fingerprint that can be observable. It has to build up to detectable amounts and it has to be separable from abiotic processes. So that's important. So if you think of an application form for a biosignature, let's say it's methane, we're going to ask it a few questions. Are you produced by life? OK, yes. Methane is produced by life. Bacterium, cows, for example. OK, let's move on to the next question. Do you have experience with vibrorotational transitions? So this is just a fancy way of saying, can you interact with light? And methane, you can. OK, so now we'll move on to a tough question. Have you ever been mistaken for a geological process? And unfortunately, methane fails there. Methane is produced by many geological processes on Earth. It is a major constituent in the Moon Titan. We're pretty sure that there is no Earth-like biosphere on Titan. And some of those other abiotic processes include chemical interactions at hydrothermal vents. And so methane alone is present, of course, and also in all the giant planet atmospheres. It's not alone a very good biosignature. So if we go forward, so one approach we can take to this is called an Earth-based approach. And this just means that when we're thinking about biosignatures, we kind of look to the Earth for an example. And there's advantages to that. The Earth-based biosignatures automatically pass the first few tests. We know they're produced by life. We know they're detectable and can build up. We can use existing data and models of the Earth system to sort of explore what they look like. And we'll always have more information about our own planet than any exoplanet, because we have these ground truth values. We have so much richness here on the planet we live on. OK, so this is just an infographic I put forward about the different types of planetary biosignatures. And you can categorize them basically based on how they'd manifest themselves to an observer. And so I'd start with gashes biosignatures, which are, as the name suggests, compounds produced by life that can survive in the atmosphere and build up to detectable quantities. And so the big exemplar here is oxygen, which is produced by photosynthesis. So photosynthesis is a process that takes water on the surface and carbon dioxide in the air. It combines it with plentiful photons from the sun to generate biomass. Or this is a very simple empirical formula for carbohydrates there. And oxygen as a waste product. And that oxygen as a waste product in our atmosphere over many billions of years has built up to a detectable amount. And there's also byproduct of that oxygen, which is ozone, which is also potentially a detectable gas. It's OK, we can go to the next one. So if your atmosphere is somewhat clear, photons can interact with the surface and get reflected back. And so one example, and so if life is at the surface, it can interact with that light. And so one example of that is called the vegetation red edge or VRE. And it's basically this phenomenon that occurs when you look at the wavelength dependent reflectance of leaves. You notice the green bump that they're more reflective in green wavelengths and other wavelengths. But what you don't notice with your eyes is that they're very reflective in the infrared, just redder than your eyes can see. And this is actually something that's been used by Earth observing satellites to map forests and vegetation farmland on Earth. And conceivably, it could be used to find kind of exo-vegetation on an exoplanet if you had adequate data and if the surface coverage was significant enough. And then the last thing I'll talk about here is temporal biosignatures. And so you might think there's a gas that's not by itself a biosignature like carbon dioxide is produced by volcanoes. There's carbon dioxide, of course, to a lot of Mars planets that are not habitable. But there's a geochemical cycle on Earth that recycles that carbon dioxide. There's also an interaction with the biosphere. So in northern hemisphere, during the growing season, the biosphere is sucking up carbon dioxide and reducing it slightly in the atmosphere as biomass builds up. And then as the winter drags on, the biomass dies and it's not sucking up as much CO2. Some of that CO2 is released and you end up with an increase in CO2. And so that modulation is actually observed on Earth. And if it was big enough and you could get it on exoplanet, that might also be a biosignature. And so this kind of analysis was done by the Galileo spacecraft on a gravity assist flyby in the early 90s. And Carl Sagan wrote this up in a nature paper. And many people have probably heard of this. But if you haven't read it, it's a real treat because he writes it as if he has never visited Earth. And we're going to it for the first time and we're looking for evidence that there's life there. And so the Galileo spacecraft trained its instruments on Earth and found evidence of oxygen, of methane, of nitrous oxide, which is laughing gas, all compounds produced by life and seem together, established something called chemical disequilibrium. And so if we just go to the next slide, chemical disequilibrium next slide is just the idea that you have two compounds or gases that should just react together immediately or soon within a short climb scale. And that's true of methane and oxygen. They should annihilate each other. But the fact that we see both in the atmosphere suggests there's an active source for both of them. So that's a strong biosignature on Earth. And oxygenic photosynthesis, just to mention this again, is a leading biosignature candidate. People talk about it all the time because it is the potential to most energetic metabolism on Earth. It only needs very simple ingredients, water, carbon dioxide, some trace nutrients, and light from the star. To, of course, I'm papering over a lot of complicated biochemistry that needs to evolve on that planet also and biochem and the geology that needs to occur on the planet for the oxygen to build up. But it is one of the primary things we're looking, we're gonna be looking for. Yeah. Okay, and then besides oxygen, there are other gases that we might look for. I've listed some here, sulfur compounds, methyl chloride, methylmercaptin, ethane. These are some biosignature gases that maybe some of them seen alone might not be quite evidence for life, but seen with other things might be evidence. And some alone would be very intriguing. And so this is just to say that there are many different gases besides oxygen we might look for. And if we go to the next slide, we can just see that this is just a graph that shows you the gases that are emitted to Earth's atmosphere with life, that's the left side, and without life on the right side. And you can see all these gases would have much different fluxes in the atmosphere without a biosphere present. Of course, this doesn't include the actual absorption features of all of these gases and that creates some complications, but we wouldn't expect an exoplanet with a biosphere to necessarily be exactly like the Earth. So we've got to keep an open mind for all these other gases too. And then finally, you can kind of look at habitability markers in the same way. You might tell whether the planet is habitable. The fact that you don't find a biosignature doesn't necessarily mean it's not inhabited, that there's no life, but it might mean just mean that you got unlucky. And, but we certainly would like to know if the planet is habitable, we'd want to look for water vapor in the atmosphere. We'd want to look for nitrogen and carbon dioxide that show there could be a sufficient greenhouse gas, greenhouse effect. SO2 could be an indicator of volcanism. Surface features could tell us directly there's liquid water if we can observe the glint effect from the ocean. Surface heterogeneity implies continents and oceans and that could be very intriguing. We want there to be clouds and if there are variable clouds, that's great. And so, and so here is a model, but this is a pretty well-validated spectrum of the Earth from the visible all the way through the middle thermal infrared. And so you can see here, again, this is the brightness of the planet as a function of wavelength. Okay, and so the blue in the blue square is the reflected light and in the red square is the emitted light, the Earth is emitted because it's hot. It has a temperature and you can see that there are signatures from ozone. That's O3 and oxygen O2. There's that lambda to the negative four is Rayleigh scattering effect. That's why we have a blue sky and also why the Earth is blue from a distance as I showed you in that Cassini photo. And we can see evidence of both CO2 and methane as well. Okay, so I'm going to turn it over to Jada now. All right, so obviously the sort of holy grail for exoplanet science is we want to find Earth-like planets. But I think when we think about Earth-like planets, it's an interesting notion because a lot of the time when we talk about finding Earth-like planets, we're talking about finding planets like modern-day Earth, right? We want to find planets that have Earth-like atmospheres with oxygen and nitrogen and trace amounts of methane and CO2 in them just like modern-day Earth. But Earth through time, what you're seeing here, so this is a sort of pie chart that shows the different epochs of Earth's history has looked very, very different compared to modern-day Earth. So you can see the box at the top, right? Like that's now, that's humans. And if we go back into the past, say to the protozoic, there were no large macroscopic life forms on our planet through the protozoic. So that's a huge chunk of Earth's history. And then if we go even farther back into the Archaean which ended at about 2.5 billion years ago in the Archaean, as well as in the Hadean, there was very, very little oxygen in our planet's atmosphere. And as Eddie was just telling you, oxygen is sort of this canonical biosignature that we're searching for. But oxygen didn't even start to build up in our atmosphere to detectable quantities until about 2.5 billion years ago at the start of the protozoic during something called the Great Oxygenation event. So when we think about what an Earth-like planet the spectrum looks like, and we think about modern-day Earth, if we rewind the clock and go back through time, Earth is gonna look very, very different in these different epochs. And so this slide is just to sort of illustrate different sort of cartoon images of the Earth through time. And what I've seen a lot of my time-during research on and a big part of my PhD dissertation involved looking at Archaean Earth, which was again sort of that pink part of the pie chart. So between about 3.8 and 2.5 billion years ago, Archaean Earth would have been a very different world compared to modern-day Earth. It would have had a lot fewer continents compared to modern-day Earth. And a big thing in the atmosphere is that, like I said, it would have had an anoxic atmosphere because even though there was oxygenic photosynthesis operating during the Archaean, the oxygen in the atmosphere hadn't yet built up to large quantities. So there were many orders of magnitude less oxygen in the Archaean compared to modern-day Earth. And because oxygen and methane react together and they wanna destroy each other, an interesting thing about the Archaean is because you don't have the oxygen in it, you could have orders in magnitude more methane in that planet's atmosphere than you could in the modern-day atmosphere. So methane and Archaean Earth's atmosphere would be a lot more detectable compared to the modern-day atmosphere. And an interesting thing about methane-rich atmospheres is that if you had a ratio in the atmosphere of methane to CO2 greater than about 0.1 or 0.2, which is a lot more methane than we have today, you can actually trigger the formation of a global organic haze similar to the haze that's in Titan's atmosphere. An analogy I like to use for what this haze is qualitatively like is put a chemical smog. So if you've ever been to LA or any other large cities on a day where there's not a lot of atmosphere circulation, you probably have seen smog, sitting low on the horizon, close to the cities. So imagine this smog lofted tens of kilometers up in the atmosphere and enshrouding the whole planet and it would be a sort of orange color. And this is what Earth may have looked like for some periods in the Archaean. The entire Archaean would not have been hazy, but we do have geochemical evidence suggesting that this haze existed at some times in the Archaean. So here's a picture of hazy early Earth next to Saturn's mean Titan, which has a similar organic haze in its atmosphere. Now, as I was mentioning, methane is interesting, but it's also really slippery to deal with because methane can be produced by both biological and geological processes. So the biological process that produces most of the methane in Earth's atmosphere is called methanogenesis. Now, methanogenesis is a really simple metabolism. It uses really simple stuff like H2 and CO2. It's a metabolism that evolved really, really early on. We have evidence of it in the geochemical record dating back to about 3.5 billion years ago, and it likely evolved earlier than that. So it's possible that similar simple methane producing metabolisms could evolve on Earth-like exoplanets. But of course, methane can also be produced by geological processes, as Eddie mentioned. And the dominant geological process that produces methane on Earth is something called serpentinization, which occurs at the seafloor, and it's when water hydrates certain types of rocks at the seafloor, and one of the byproducts of the chemical reaction that occurs is the release of methane. And so serpentinization is itself interesting because it's a process that requires liquid water, which is a sign of habitability on a planet. And so because the dominant sources of methane on Earth-like planets are either life or the serpentinization process that needs liquid water, I think methane is a really interesting gas to detect because it signals some really interesting things that could be going on on that planet. So we're looking for these paleboudocs right now. So if you can imagine you're a little purple alien and you're looking through your giant 16-meter telescope at an exoplanet and you see it's a paleboudoc. You might get really excited because you may think, oh, this is a planet like the one I live on. This is an Earth-like planet. But what if it looks like something else? What if it's a pale orange dot? Like what if it's an Archean Earth analog planet with a haze in its atmosphere? Would we be able to recognize that planet as quote-unquote Earth-like and correctly deduce that it might have habitable conditions and possibly life on it? So I've thought a lot about this question, doing a lot of modeling with different climate and photochemical models to generate atmospheric states for hazy early Earth. And I've generated also a spectra of what the remote observables of hazy early Earth would look like. So I'm gonna show you some reflection spectra of what this planet might look like from a distance with a haze in its atmosphere. Okay, so here are these reflecting spectra of Earth with three different haze thicknesses in its atmosphere. So the black spectrum that you see here is a planet with no haze in the atmosphere and this is an Archean spectrum. So it lacks oxygen and ozone that our modern day spectrum has and it has a lot more methane in CO2. The blue spectrum is a spectrum with a thin haze, what I call a thin haze in it. And the orange spectrum is what I call a thick haze spectrum. And I've also labeled some gaseous absorption features. So you can see where methane and water vapor absorb in this spectrum. You can see there's a lot of methane observing in the spectrum. And a thing to notice, right, is there's a huge qualitative morphological difference between the spectrum with no gase and the spectrum especially with the thick haze. And that's because the haze absorbs this blue light very, very readily. So these short wavelengths, these blue and UV wavelengths, you can see that the reflectivity on the y-axis for these hazy planets is really, really down for the thick haze planet because the haze is such a good blue and UV absorber. This blue absorbing propensity of these haze particles is the reason why Titan is orange and the reason why early Earth, if it had a haze in its atmosphere, it would also be orange. And a cool thing about this feature, right, you can see it's a really, really strong broad feature here is that it's even stronger than the spectral features for methane itself. And so it's potentially an indirect way of detecting methane in a planet's atmosphere if you don't have access to the methane spectral bands themselves. So this is the kind of spectrum that say, luvoir or habex might be able to collect. So if you can directly image an exoplanet and detect its reflected light, but with something like the James Webb Space Telescope, you're actually gonna be observing the planet in transit transmission when it passes in front of the star. So between you and the star and the telescope could be directly in the middle of it. And the starlight would be passing through the edges of the planet. So the planet would be backward by the star. So what I'm showing you here are some transit transmission spectra. The y-axis here is showing you the altitude that the light from the star can get down to into these planets atmospheres before it's absorbed. So notice how at the shorter wavelengths for the thick case spectrum, for example, if you look at say 0.4 microns, that the light can only get to about 80 kilometers into the planet's atmosphere above the planet's surface. Whereas in the no-haze spectrum, the light can get much, much deeper down into the atmosphere, somewhere around say 30 kilometers at 0.4 microns. And you've got this very strong spectral slope in the thick case spectrum, where you can see much more shallowly into the atmosphere at short wavelengths compared to longer wavelengths where you can see deeper into the atmosphere. So this slope is a characteristic of these organic cases. And so if we see similar exoplanets that have these very sloped transit transmission spectra where their planet is much more opaque at shorter wavelengths compared to longer wavelengths, because again, these organic cases are much more absorptive at the short UV and the blue wavelengths compared to longer wavelengths where they're much more transparent so light can penetrate deeper down, that would be a strong indicator that you have an organic case in the atmosphere as well as if you saw these methane bands. So you can see here these methane absorption features in these spectra, which are these bumps you see in the spectrum. And the reason why they appear as bumps here is because when you have an opaque molecule in the planet's atmosphere, you're not gonna see as deeply into the planet's atmosphere. If you look at it at a wavelength where methane absorbs, you might say no one will see down to 40 kilometers versus if you look at the place where the methane is not absorbing, you might see much more deeply. So that's why the absorption features are bumps here. And so with the James Webb Space Telescope, we can actually go out to even much more even longer wavelengths. So before I was showing you out to 1.6 microns, which is in the near infrared, but the James Webb Space Telescope is designed to study infrared astronomy. So it could go out to potentially much longer wavelengths. Now, the problem with getting to these much longer wavelengths is that the star itself gets much, much dimmer at these longer wavelengths. And so your sizzle of noise drops off very, very steeply as you push farther and farther into the infrared. In practice, you probably couldn't take observations of exoplanets at wavelengths longer than 10 microns. But I do wanna point out that this, there's a feature at about six microns that you can see labeled their haze. So that is an absorption feature that you see is that bump in the orange spectrum compared to the other two spectra. And that feature is due to the haze itself. And so this would be potentially another way of directing organic haze in a planet's atmosphere. Now, organic haze, again, it's interesting because methane itself is interesting. Methane can signal these fascinating processes like biological processes and also the serpentinization, this process that needs liquid water in order to produce methane from geology. And so how on earth would we figure out what's going on in these planets? So this complicated counter plot, I promise it's not that complicated, is showing how we might start to disentangle what's going on if we see an organic haze in a planet's atmosphere. So the color bar is showing you sort of optical depth of the haze. So how thick is the haze? How much is it actually affecting your spectrum? The Y axis is the amount of CO2 in the planet's atmosphere. The more CO2 you have in general, the more difficult it is to form a haze. And the more methane you need to form that haze. And the X axis is the flux of methane at the planet's surface that's going into the atmosphere. And then the solid line with the zeros is where you have an optical depth of unity. So this is a log plot, so log zero is one. So that's where you have an optically thick haze. Now, in the Archean, we think the amount of CO2 in the atmosphere was somewhere in the range of this box. And what we find is that for Archean-like CO2 levels, you need methane flux rates on the order of about somewhere around 10 to 11-ish molecules per centimeter squared per second being produced at the surface in order to have enough methane in that planet's atmosphere to form a thick haze that's going to strongly impact your planet's spectrum. And this is actually really interesting because for these thick hazes, this is consistent with the production of methane by biology on Earth. And so if you saw a thick haze and simultaneously we're able to measure the amount of CO2 in a planet's atmosphere, you could argue that you need a methane production rate that's at least consistent with known biological methane production rates on Earth. And it's higher than known abiotic methane production rates on Earth. So on Earth today, the production rate of methane from abiotic processes, like surpritinization, is one to two orders of magnitude lower than the biological production rate. Now, of course, this isn't a smoking gun because on an exoplanet, we don't know what the abiotic production rate is. And of course, we also don't know what the biological production rate is. But again, at least we could say that using these sort of photochemical, geochemical constraints that we infer from what our own planet does that organicase in the presence of high CO2 could indicate methane production rates that are consistent with biology, even if we can't say it's biology for sure. And then we'd start to stare at the planet harder to try to see other signs of habitability. Like, does it have water? Does it have other biosignatures? Does it have these sort of temporal and surface biosignatures that Eddie was mentioning earlier? And that could start to sort of nail down the question of what exactly we're looking at. And again, these cases are cool because they have such a strong, really great detectable spectral feature. So back to Eddie now. Okay, thanks. And I might move through this section just a little bit quickly because we're running low on time. But I'm gonna talk about pulse positives for life. So how we might be fooled by what we might think are biosignatures, but in reality, are results of abiotic processes. So if we go to the next slide, sort of the conclusion at the beginning of this, at the beginning of the millennium, was that there are only a very narrow set of circumstances where you could produce oxygen, which again is a very interesting biosignature because it's produced by a synthesis. That this range of commissions is very narrow and that primarily would occur in regions outside of the solar system. It might occur inside the inner edge because you're so hot, you're evaporating all your water and your water goes into your upper atmosphere and the hydrogen is cleaved off that water by UV radiation and escapes, potentially leaves that oxygen behind. And so when the first papers about the runway greenhouse came out, and they sort of talked about this possibility why it didn't happen on Venus and if Venus potentially had more water, it could have had an oxygen atmosphere. And then there have been papers on the outer edge of the habitable zone and how if you had a ice covered surface, you can't react your photochemical products. So again, cleaving oxygen off of CO2 or water, you couldn't react that with the surface as it happens on Mars where the oxygen that's liberated from those reactions gets combined with the surface, which is why it's rusty. But if you were prevented from doing that, you might build up some oxygen in the atmosphere. So if we go to the next slide, but recently there have been many more potential difficulties here because there have been all these other proposals for how this might happen inside the habitable zone. And so if we just go to the next slide and talk about specifically, CO2 from CO2-photosis, which is probably one of the most easy of these mechanisms to understand. And if we go to the next slide. So this is just saying, if you can just click, yeah. So we're just highlighting this reaction here. CO2 plus a photon as H new goes to CO plus O cleaving an oxygen off of a CO2 molecule. And those oxygen atoms can recombine into a oxygen molecule. Now this process is strongly disfavored on the earth. And in fact, most of almost all of our oxygens from CO2 synthesis, this process is very ineffective. But if we just look at some spectra for different stars and advance here, we can see that different stars have different UV spectra. And so then they drive this reaction in different ways. And so while this is true, while it's true that this reaction and this process for building up oxygen is strongly disfavored on a planet around a sunlight star, it's actually more favored on planets or bring different kinds of stars. So if we go to the next slide, this is just sort of showing the strength of the UV ozone band, the Hartley Hurley bands on the left side there. The left upper corner is reflected light as Jada kind of illustrated different reflected light and transmitted light. So the upper left is ozone and reflected light. The bottom left is ozone and transmitted light. The upper right is oxygen in reflected light and then the bottom right is oxygen and transmitted light. And you can see the strength of these features. So this is all assuming, this is using a photochemical model and assuming that no biotic process is going on, just the photochemical reactions in the atmosphere assuming different spectral types that you'd end up with potentially detectable amounts of oxygen for certain types of stars. And so that's a good thing to know. We go next. But there's gonna be what's what I called before a false positive indicator here in the sense that while you're cleaving off these oxygen atoms from your CO2 molecule and then those later can become oxygen molecules, you're also generating a lot of CO and that CO could potentially be detectable. So on the left hand side here is just a simulated spectrum of this process happening. So it's self consistent with the photochemical model. And then we've pretended that JWST is observing this planet transiting another star where this process is favored and we're calculating what it might see. And so you can see that both the CO2, if we advance here, the CO2 is visible and then if we advance again we can see that the CO also produces bands. Now this is actually more observable than the oxygen itself. So if you saw this for a planet it might tell you that this is a planet where an abiotic process is going on. It's generating potentially abiotic oxygen. So you shouldn't be fooled by that if we go advance here. So there are other methods for doing that. One is if we advance again, just this concept that if you lack a substantial enough atmosphere you're not gonna cold trap your water like earth waters cold traps. So most of our water cleans close to the surface. It doesn't go all the way up into the atmosphere because there's enough other air around that makes that process disfavored. And so but if you remove a substantial amount of nitrogen for example from our atmosphere and if we didn't have oxygen from photosynthesis then you could potentially put your water into the upper atmosphere and have the same UV reaction happen where you cleave off oxygen from water and potentially generate oxygen. That would generate itself enough to self limit. Again, cold trap the water. So that's an equilibrium state where you have almost as much oxygen as we do on earth abiotically. But again, the way that if we advance the way to rule this out is to detect directly to tech nitrogen. And so we've kind of demonstrated that for the earth at least we can detect nitrogen in our spectrum and in the spectrum. And it would be enough to rule this process out. And if we go forward again the final thing is a little bit more complicated to understand, but it's this fact that for stars that are significantly dimmer than our sun they have a very bright pre-main sequence phase. And so they're much brighter as the planets are forming and that means that they're much more liable to lose their atmospheres, including the hydrogen that would have been part of the water. And so if we go forward, for M stars especially this is a big problem. They could lose a lot of water in the beginning of their history. That also leaves behind a lot of oxygen. Now that oxygen could react with the surface or it could build up in the atmosphere. Now if that happened, if we advance the question is just distinguishing a lot of oxygen some oxygen from a lot of oxygen and the whole history of the planet earth we've had at most 0.3 bars of oxygen. And this graph sort of shows that if we go forward again there are signs of what are called O4 bands which are when two oxygen molecules combine or collide they generate an observable signature. And so we could look for that. That would show that there was a massive oxygen atmosphere that's too massive to just be from photosynthetic life. So if we go forward, this is just again an example of what JWST would see in that circumstance if you had a very high massive oxygen atmosphere and you looked at it in transmission you would see these O4 bands come up and that's a very big counter indicator for photosynthetic life. And if we go forward again we can also see this in reflected light. The black spectrum is sort of an earth-like atmosphere and then the other bands are more massive atmospheres. And so wanted to get a little bit in on Proxima Centauri so we can go forward. And so, okay, so this one just to say that there are things to look for that would rule out these false positives. And if we could find them or rule them in or rule them out and if we could find them then we could be much more confident about our designation that the oxygen came from biology. So if we go forward we can talk about Proxima for a bit. All right. So we've probably heard of Proxima Centauri B it was announced in August and it is an earth-sized planet in the habitable zone of the closest star. So what a jackpot. Super exciting. It was discovered with the radiovelocity method. So you're measuring the Doppler shift of the light from the star as a star wobbles from the planet circling around it and giving the star a little tiny tugs. And so this method allows you to measure the planet's mass and also its distance from the star. And you know, again, that's about it. We know very little about this planet. But you know, just because it's in the habitable zone and just because it could be habitable you know, it doesn't mean it actually is. We don't have the knowledge yet to be able to say what exactly Proxima Centauri B is. But what we can start to do is think about whether or not we can actually discriminate between different atmospheric states. This planet could be a lot of different types of things. So we need to start anticipating what the spectral observables of those states are so that we can start to build the instrumentation and data reduction pipelines that we need in order to characterize this thing in the future. Okay, so one possibility is just like I described. Proxima is a very late type star. It's an M type star and it was much brighter in its early history than it is now. And so that means that Proxima Centauri probably lost a lot of water. And if it did, then it has this capacity to potentially, according to recent studies build up oxygen. So if we just advance, as I sort of showed before, this would produce observable signatures that would let us know that that oxygen could not have been from biology and was a primordial from this early history of the star. And so that's the main point of this slide. Okay, so what if it's like early Earth for the haze or perhaps without a haze? So I ran our photochemical climate model to simulate our Kean type atmospheres, both without a haze and with a haze. And not all stars are able to form a haze. However, Proxima Centauri does have the right amount of UV radiation to form a haze. And so if there's a haze on this planet, we'll be able to see it because it'll produce a whopping big spectral signature. And if it's like modern Earth, there are some complications and actually exciting aspects of this. So the fluxes into the atmosphere from biology is one part of the equation, but also how those gases, what their lifetimes are and what their abundances are is dependent on the incident spectrum. So we found when modeling photochemically an Earth-like atmosphere is that you would actually have a lot of buildup of methane, which is really good news because you would have both detectable oxygen and detectable methane. So methane is strongly favored to build up on Proxima Centauri if it had sort of an Earth-like atmosphere to begin with. So if we advance the slide, you can just see how clear this is. So the only difference here is the, so one set of lines is the spectrum of the Earth Sun and one is Earth Proxima. And you can see these big differences due to different methane bands. And so we assume the same flux of methane into the atmosphere, the photochemical lifetimes are just very, very different and that allows for methane to potentially build up to really high quantities in Proxima. All right, so we want to actually figure out how observable is this thing going to be with future instrumentation. What you're looking at on the slide is a modern-day Earth and a lot of planet orbiting Proxima Centauri. And of course, that's what we would love for it to be as observed by a lukewarm simulator. The solid colored lines you see are IWAs or inner working angles. And they are different, so the choreography that is used to nullify the starlight, to block out the starlight has a wavelength-dependent behavior and its ability to block out the starlight sort of falls off a cliff at what's called the inner working angle after which you see the star again and you can't see the planet again because it's totally outshined by the star. And so these are sort of wavelength cutoffs for how good the IWA could be. We don't know what the IWA is gonna be for any future instrumentation, so these are just different assumptions of what it could be. Ideally, you'd want something like the green line that would be the best because that'd give you the biggest spectrum and the most spectral information, but it could be something like the red line which would cut you off at like one micron which would give you a lot less information. You'd see a lot fewer, say, methane bands. You wouldn't be able to see CO2 anymore. And also notice that you actually get pretty good signal to noise. So these are error bars on the box and notice how the errors are pretty small in the near infrared just because Proxima's send emits most of its light in the near infrared, because it's quite a red star, but even in the visible region, there are larger error bars. Havax is a smaller telescope and IWAs for smaller telescopes are a lot smaller. So unfortunately, Havax would have a much more difficult time characterizing this. The best case scenario for a smaller telescope like Havax is that it might be able to get out to a little bit beyond 1.1 microns. So here in Louvre, you can see it gets out to something like almost three microns with the most optimistic IWA. So you're losing a lot of information and more realistically, we'd probably be dealing with an IWA of something like two lambda over D, which is the blue line, which you can see really does not get you much information. You can see Rayleigh scattering, but that's about it sadly. Do you want to do this one, Eddie? Well, I kind of want to just leave these up so that we can talk about questions, but this is just a cool plot put together by one of our colleagues that shows the color of the planet orbiting Proxima Centauri if it had an Earth-like atmosphere. So you're combining the red light from Proxima with sort of the blue Rayleigh scattering from Earth and you get sort of a purple lavender color. And then if you had a hazy arcane Earth, you'd just color it pink. So I think this is a great time for questions. So maybe I can just answer the first one. So I'll answer the have there been any studies of what non-carbon based life forms might be look like and what its biosignatures might look like. And so that's an intriguing question. The thing is we don't actually even know what non-carbon based life forms, what their biochemistry is even like. And so if we don't know what their biochemistry is like, we don't necessarily know what gases they put in the atmosphere and therefore what we should look for in the exoplanet atmosphere. I will say that there have been studies in what life would look like on Titan and there's been some progress in thinking about what a membrane would look like to exist in that cold liquid hydrocarbon solvent. It's called an azosome and it's made artificially in the lab. And so there's a little bit of progress there, but we're kind of looking at this earth based strategy right now just because that's what we know best. All right, it looks like there's another question or comment it looks like that Mars is also orange without haze and yeah, it is because iron oxide is another strongly blue absorbing thing. In fact, iron oxide is so you can almost sort of think of it as a false positive for haze because it has a similar spectral behavior. The difference there is Mars's atmosphere is a lot less reducing than a methane rich atmosphere would be. So when we're dealing with these exoplanets, we need a lot of spectral contextual information to figure out what we're looking at. So ideally what you wanna see is that haze signature that blue UV absorption combined with methane bands. And that would really clue you went on the fact that you're actually looking at haze and you're not looking at something else like iron oxide absorption. Yeah, it looks like we've got a question coming in. They couldn't quite get to the Q and A. It looks like Michalos would like to know a little bit more about the background spectrum and how it can be subtracted to study the signal. Could you get a little more information about that question? I think it's about how you're isolating the spectrum from the planet from the star, which is much brighter. And so maybe a little bit more about the techniques to isolate the starlight. Yeah, so I think you might be asking about how are we going to see the tiny little firefly next to the giant floodlight? That is the star, where the firefly is the planet. We're working on that. We don't have the technology yet that can do that, but there's two different techniques that are being studied. One is a coronagraph. The coronagraph is an internal occultor that lives inside the telescope. It's a sort of mask inside the telescope that is designed to block out the starlight. So it's designed to block out the light that would be hitting the center of the aperture. So you position the telescope such as the star's light hits the center of the aperture and you put some sort of mask there. This is difficult. We don't yet have coronagraphs that can perform at the level of precision that you need to remove all the photons from the star, except one in every 10 billion that you need to see the planet. But there is a lot of people actively working on this problem right now. And then the second one is a star shade, which is an external occultor. So this would be something that would fly outside of the telescope and it would position itself between the star and the telescope at a pretty large distance. I don't want to make up a number, but like thousands of kilometers or more, distance from the telescope. And this is something that, again, blocks out the starlight. So it would hide the field of view from the center. So you block out the starlight that way. Okay, great. Well, it looks like we have time for, we have one last question that came in. And this is an interesting question, as Jeff asked, will good candidates with reasonable biosignatures for habitability be sent radio hello messages? So we can say hello to the potential biosignatures. Yeah, okay, I'll answer that. So we've been focusing on biosignatures, sort of the agrobial biosignatures. So how life interacts with the atmosphere. And we kind of look at sort of setting signals as technosignatures. And one of the reasons that we're kind of separated that, it's not that we don't think setting is a bad idea. We think it's a great idea. It's just a very different set of expertise needed to characterize an exoplanet atmosphere versus a detector radio signal from an ETI civilization. I will say this, if we look at that history of life on Earth plot that Jada had up earlier, I don't know if she can go back to it. Basically, the history of life on Earth is four and a half billion years. And for a substantial amount of that time, microbial life was interacting with the atmosphere and potentially generating an observable signature in the atmosphere. And only like 0.00000001% of the time was there a communicable civilization generating radio signals. So my opinion is that ETI is a microbe and it's trying to contact us through it through the changes it makes to its planet's atmosphere. All right. Well, it looks like we're right at the top of the hour, about a minute past. And so Jada would like to go ahead and stop sharing your screen. And so then we can wrap the ball. Thank you very much. This is really fascinating, this whole idea about being able to figure out how the atmospheres are like of all these exoplanets. It's very exciting. I think it's great. So basically that's gonna be it for tonight. You'll be able to find this webinar along with many others on the Night Sky Network under the outreach resources section just for the webinar. You'll post tonight's presentation on the Night Sky Network YouTube page by the end of the week, where you can also find some other videos from past webinars as well.