Gravity Assist: What is Astrobiology? With Mary Voytek

From NASA’s Gravity Assist podcast, hosted by NASA’s Chief Scientist Jim Green.

How did life originate and evolve here on Earth? What form could life take elsewhere – and where else could life survive beyond our planet? These are questions that scientists called astrobiologists tackle every day. By using space telescopes, doing laboratory experiments and studying extreme environments on Earth, astrobiologists hope to uncover new insights about what it means to be “life” and get more clues to the ultimate question: Are we alone in the universe? Mary Voytek, head of NASA’s astrobiology program, discusses in this episode.

Season 4, Episode 1: What is Astrobiology?

Jim Green: Are we alone? What is NASA doing to answer that very important question?

Jim Green: Let’s talk to one of the top astrobiologists in the country.

Mary Voytek: As we look for unusual life here on Earth and life elsewhere, we look for the unexpected.

Jim Green: Hi, I’m Jim Green, NASA’s Chief Scientist, and this is “Gravity Assist.” On this season of Gravity Assist we’re looking for life beyond Earth.

Jim Green: I’m here with Dr. Mary Voytek, she’s the lead scientist for astrobiology at NASA headquarters, and she manages the entire astrobiology program for NASA. Welcome Mary.

Mary Voytek: Thank you so much for asking me to do this, Jim.

Jim Green: Well, you’ve been doing this now for many years and the concept of astrobiology is really coming on strong. We talk about it all the time in science, but what really is astrobiology, what does it mean?

Mary Voytek:NASA defines astrobiology as understanding how life emerged and evolved here on Earth and where it could possibly exist elsewhere beyond Earth.

Jim Green: When I talk to the public and I say, “NASA is looking for life beyond Earth,” the first thing they think of is, “Wow, we’re looking for little green men.” But are we really doing that?

Mary Voytek: So NASA’s strategy for looking for life has been informed by what we understand about Earth.

Mary Voytek: We think there’s been life on this planet for maybe about 4 billion years, but that’s been single cell microbial life. It’s only been in the last few hundred thousand years or several hundred million years that we’ve had forms of life that would be more recognizable and would be able to be seen without the unaided eye.​

Mary Voytek: So most of the time on this planet, the only life that was here was microbial, single cell, very, in terms of form and structure, very simple. And so in terms of searching for life, just in terms of probabilities, it is more likely that we would find microbial life on other worlds.

Jim Green: So what are the kinds of things that we’re doing in terms of looking for life here at Earth?

Mary Voytek: One of the most important things is an understanding how you go from a planet where there’s no life to a planet that is teeming with life, is to look at those transitions and the condition of the planet, as well as how it affects the processes that are steps towards the emergence of life. So we’re looking at things like, what are the physical and chemical conditions on early Earth that would be conducive to the production of molecules that end up becoming extremely important in life? And that includes molecules that can provide energy, as well as molecules that can be built on to provide structure and function, and basically the components that we see in life today.

Jim Green: Well, one aspect has really excited me, and that is looking for life in extremes. You look out into the solar system and it’s hot or it’s really cold, or the environments are so much different than ours. And so extreme environments are really important. And I know we do that here on Earth.

Mary Voytek: Absolutely. And in fact, in addition to understanding the steps towards life emerging and looking for the earliest signs of life here on Earth, we also want to understand those limits to life because as you said, the environments in our own solar system beyond Earth are not Earth-like, they’re not the conditions that we all find pleasant. It’s not the lovely climate of California out on those planets, and so we need to understand how life can actually persist in something that is beyond our comfort zone.

Mary Voytek: So our comfort range is, we know what room temperature is, we know what standard pressure is. And so organisms that seem to thrive and enjoy or love conditions that are more extreme than that or outside our comfort zone are called extremophiles. We can certainly live in cold temperatures, but not without putting on cold weather clothing and building shelters and generating heat for ourselves. But there are organisms that don’t have coats, microorganisms that aren’t hooked into the power grid and generating enough heat to live, and they’re called psychrophiles because they love the cold.

Mary Voytek: And then there are organisms that really love the heat that can live at temperatures above the temperature at which water boils, so that’s 100 degrees C. And so these allow us to start looking for environments that would be suitable to support life, even if it’s extreme life.

Jim Green: Well, one of the common threads between all those extreme environments is water. No matter where we go, where we find water, even in small amounts, we have the opportunity to find life.

Mary Voytek: Yeah. We always struggle amongst scientists with definitions of life. And in fact, I usually like to say if you ask 100 scientists what is life or how to define life, you’ll get 120 definitions. But one thing is really common to all definitions is it requires a solvent.

Jim Green: Mary, what do you mean by solvent?

Mary Voytek: Well, in chemical sense, it’s a medium or a solution that allows reactions to take place, and so it facilitates transfers of electrons and modifications to chemistry. It also provides a liquid, also provides structure, and we are mostly water. And so that solvent or that liquid actually is responsible for our structure as well.

Jim Green: So we are what we eat and at the end of the process—

Mary Voytek: We are what we drink.

Mary Voytek: Here on Earth, the life that we know requires water. It’s how it moves materials around, it allows the fluidity within cells so that cells can actually function. And so that has been one of the primary strategies at NASA for looking for places that could support life. So we go to extreme places here on Earth, like the dry valleys of Antarctica or the Atacama Desert where to the eye, it appears as if there is no water, but even a tiny bit of water, as you mentioned, life can take advantage of.

Mary Voytek: And so as we go beyond Earth, we’re now then looking at environments on say, Mars that might have the same level of water that we see in these deserts here on Earth.

Jim Green: I remember the day you came into my office and we had this great discussion on how we would define life and how that should be viewed and a definition that would encompass all kinds of different life, things that we can’t even imagine right now, life not like us. You told me it had three basic parts. What were they?

Mary Voytek: Well, of course it required a solvent to support a particular type of chemistry. It requires a mechanism to acquire energy, because everything requires energy to do anything. And then it had to be able to reproduce. I guess I’m going to extend it a little bit to four.

Jim Green: It sounds like it.

Mary Voytek: It needed to be able to evolve because our environment is not static. And as Earth has changed, life would not survive if it weren’t able to adapt and evolve to actually be able to thrive in the new environment.

Jim Green: Well, I know you were really excited about that definition because it’s all encompassing in the sense that it doesn’t require that it be water or that it requires a carbon-based life form. But I was in the doldrums because indeed I can’t run out and build an instrument that measures reproduction and evolution and then a have that operated on some planet. So that’s really tough. But the water theme for us, for life like us, or the liquid aspect of it really helped us start a process of looking for life beyond Earth.

Jim Green: Well, why should we care about this particular topic?

Mary Voytek: I’m going to break down the question to something a little bit different, which is, are we alone? That’s a really compelling question. It’s philosophically important, it challenges our identity as human beings. And I think people in general are just fascinated by that question and they want to have that question answered.

Jim Green: Yeah. Me too. Right.

Mary Voytek: In addition, we now know more about how our own cells function. Some of the work that we do in astrobiology informs us about how cancerous cells may have actually played a role in a positive way towards evolution because it’s kind of growth out of control, and maybe that’s what you need to initially establish yourself on a planet.

Mary Voytek: And so it has all these ramifications for just understanding biology here on Earth. And I have to say, I’d be extremely excited for us to find something that was different than life on Earth because in science, you learn often the most when you find something to contrast.

Mary Voytek: And so any kind life is going to be exciting, but finding something that is very different would be really exciting as well.

Jim Green: Even here on Earth, we’re looking for that. We’re looking for something really different, something, maybe not carbon-based and maybe not requiring water, but still another liquid. Where are we in that search and have we found anything?

Mary Voytek: Well, I like to tell people that when we define life or we understand life here on Earth, we’re looking at the winner. So the very beginning of life as it started to emerge, there were probably a lot of different solutions to what kind of solvent, what kind of molecules were important for structure. What kind of energy was it acquiring? What form it took? What elements it actually may have used. And at some point in time as life continued to reproduce and evolve, there was a form that was the most successful here on Earth given Earth’s conditions. And we call that the last universal common ancestor. And at that point, most of biology, if not all of biology have those basic things.

Mary Voytek: But at the same time, there could be less successful organisms that exist still here on Earth, but the challenge in finding them on a planet that is overwhelmingly populated by all of those successful forms that come from that winner is a real challenge.

Mary Voytek: And so looking in extreme environments allows us to start looking for that.

Mary Voytek: We think about at some point in time on Earth, life became so predominant that it affected planetary processes, and you start seeing evidence of it. So you don’t see growth and reproduction, but you see a change in the composition of our atmosphere. We went from an environment that was anaerobic to an atmosphere dominated by oxygen, and that was because of microorganisms. And so as we look for unusual life here on Earth and life elsewhere, we look for the unexpected. We learn more and more about how planets and planetary bodies function, we have an expectation of what their surfaces will look like and we understand what we expect from an atmosphere if it has one.

Mary Voytek: And then we look for something that just isn’t what we expect. We look for a disturbance in the force, you might say, something that is just unusual that we can’t explain any other way. And that’s where we begin. And that’s to some extent, in our enthusiasm for searching for life, some mistakes we’ve made in the past where we thought we understood what we were looking for and didn’t spend quite enough time dispelling any other possible explanation.

Mary Voytek: But we’re much smarter now and that’s exactly how we take how we approach the search for life.

Jim Green: Well, we’ve done so much work in this area and there’s so much detail, why haven’t we found life yet?

Mary Voytek: That’s a really good question, and I pause because it just swims around in so many ideas in my head for why that’s possible. And one is, of course as we’ve already discussed, the challenge of, if life is not as we know it. And so again, how do you look for life as we don’t know it? The other issue is, it is pretty clear that based on life as we know it, that Earth is the premier planet. It is perfectly situated in relationship to its Sun, it’s got a magnetic field that protects it. It’s gotten many, many environments across the entire surface and into the subsurface that can support life as we know it. It is just an incubator, a perfect incubator.

Mary Voytek: And so as you start looking into environments, even on Earth where say nutrients are limiting or there’re extreme physical conditions, you notice that the number of cells decreases. And so as we look beyond Earth and we look at places like Mars or we look even beyond to the moons of Saturn and Jupiter, these environments are much more extreme than Earth, much less hospitable. And so just because of what we know about Earth, the inhabitability of an environment can control how much life you see, we would predict the amount of life on any of those other bodies is going to be very dilute, there isn’t going to be much of it.

Mary Voytek: Finding something very small, it’s like looking for a needle in a haystack. Relative to the bulk of materials on these bodies, life is going to be a small component. It’s going to make less of an impact on the environment. And so detection limits are essential. And really, really refining where we go to look for life is going to be essential because in biology, one of the things we do is grab a sample and grind it up and then analyze it. We can’t take a giant sample of Mars and just grind it up and hope we find a cell in it. We have to be very smart about where we think it might be and figure out how we can most effectively look at that very, very small signal.

Jim Green: Well, there’s another dimension to this that I’ve come to realize and appreciate, and that dimension is time. When we go out to planets and we’re looking at their current environments, because the solar system is 4.6 billion years old, things have changed over time. And so that dimension is really important. So how do we think about how life might exist in the past on other objects?

Mary Voytek: Particularly now that we have exoplanets to look towards, the possibility has really exploded in terms of what environments might support life. And one of the strategies for people who are interested in exoplanets has been to look at the environments on Earth over time. At the very beginning, the solar system was kind of a violent place to be situated, with bombardments from objects out there like asteroids and comets. And that changed the Earth both on its surface and its atmosphere.

Mary Voytek: There’s also just the differentiation or the evolution of the planet itself. And it turns out that’s a huge, huge deal for organisms dealing with oxygen. On one hand, of course we know we can’t live without it, but when that change first happened, it was a toxin. Oxygen is a way that we actually get rid of organics. Hydrogen peroxide is an oxygenated compound that we use to sterilize things. And so organisms had to figure out how to deal with that first. And then as a result, once they were able to adapt to oxygen, it turns out that oxygen is a fantastic molecule to pair with other molecules to actually generate energy.

Jim Green: So this really exciting. What do you think are some of the best payoffs that we’ve gotten by making this kind of research viable for NASA?

Mary Voytek: Well, I think that there are a number of areas that we’ve had a major impact, as NASA has in general. A lot of our scientists that we fund to work on origin of life questions are also doing medical research and they’re quite related. I also mentioned synthetic biology. And synthetic biology is where basically we look at what organisms have managed to do on their own and modify them to our own needs to make them do things that we need to have them do.

Mary Voytek: So for example, bio-remediation. The best way to clean up oil spills or contaminants in groundwater in particular is to apply organisms that can use those contaminants either as an energy source or food for making materials in the cell. And in the process, they convert it from something toxic to something that is benign. In addition, we have an instrument that we developed from a researcher out at Ames, Dave Blake that’s called CheMin. It looks at the mineralogy of systems and their oxidative states.

Mary Voytek: And one of the things that’s currently being used for is… Well, there are two interesting ones. One is it’s used in the detection of counterfeit drugs, which is a gigantic problem for the World Health Organization. And in addition, they’ve used their instrument to detect fraudulent artwork. And so you can use this to understand minerals that go into paints that weren’t present, say during the Renaissance. It’s important in terms of paint restoration, but also in detecting actually, you may all know that that canvas is for painting were reused multiple times, and so you might find a Rembrandt that has multiple layers of different paintings.

Mary Voytek: And some of this, the CheMin was the tool that could be used for the materials that were generated in that paint, and any kind of change may lead to other kinds of detection for looking for things like that as well.

Jim Green: And that instrument is on Curiosity on Mars.

Mary Voytek: Yeah. Go Curiosity.

Jim Green: Right. And it’s doing fantastic. Well, where are you most excited to look for life and why?

Mary Voytek: I have two answers to that. One is in our own solar system. As the head of the Astrobiology Program, I’m excited about all places, but I’m very, very much intrigued by the news-

Jim Green: You love all of children equally, as I like to say.

Mary Voytek: You know. Absolutely. I love all of my habitable environments equally. I’m very excited to learn more about the moons of Saturn and Jupiter. I just think that between the possibilities with Europa and Enceladus and the fact that we are sending out missions to study them better and just how bizarre Titan is, which is a moon of Saturn, with the only other body in our solar system that has liquid on the surface, but that liquid is methane and ethane and it’s not water. And so what kind of biology can you expect from something like that? If we find life there, it’s going to be, I just can’t even imagine, it’s going to be so different than life here on Earth.

Mary Voytek: One of the most amazing discoveries we made in the end of the ’70s, so right around the time that Viking had landed on Mars looking for life, was discovering weird life here on Earth. And that was life that we found kilometers away from the surface at the ocean floor, at hydrothermal vents systems. And this was the first time we discovered that life could be supported by energy other than the Sun. Up until that point, we thought every single thing on the planet ultimately derived from energy provided by the Sun, but we find this oasis of really odd organisms supported entirely by chemistry, chemical reactions that can generate the energy necessary for organisms to thrive.

Mary Voytek: And so on these ice-covered oceans, we expect that we could possibly have the same system. We have evidence, at least in one of them, that we definitely have hydrothermal activity, that is, water interacting with rock of the planet or the planetary body at higher or elevated temperatures. And that causes a certain kind of chemistry than on our own planet has led to supplying molecules necessary for the energy that can support life. And so we think that that could be happening on either Saturn’s moon in Enceladus, or Jupiter’s moon, Europa.

Mary Voytek: And then of course, the possibilities that have recently in the last five to 10 years with the number of exoplanets we’ve detected. Oh my goodness, it’s almost any planet you could imagine. I feel like it’s almost, we’re at the point of having a video game or a game where you just dial different things and you create a planet and it could support life, “Oh, I want it a little warmer. I want it a little colder. I want more water, less water. I want to have this mineral present or not.”

Mary Voytek: I just think that the possibilities are just astronomical and I mean that intentionally.

Jim Green: That’s a really neat idea because as you turn around and turn those dials and create that planet, that planet exists out there somewhere.

Mary Voytek: It does, I think.

Jim Green: That’s right. I just never thought of it that way, but we’ve got like four thousand planets that we’ve identified and that number is just going to increase over time.

Mary Voytek: Well, those are ones we’ve identified. If you go by what we predict, if you look up in the sky now, we’re not looking at stars anymore. We’re looking at solar systems.

Jim Green: So Mary, with all this said, what do you think, are we alone?

Mary Voytek: I think, absolutely not. I believe that, I’m not sure when we’re going to find life, but I am certain that there is life beyond earth.

Jim Green: Yeah. I am too.

Jim Green: Mary, I always ask my guests to tell me what was the event or person, place or thing that got them so excited about them being the scientists they are today, and I call that event a gravity assist. So Mary, what was your gravity assist?

Mary Voytek: I think I can identify a person that helped me, pushed me forward, and that was my mom. And although she was not a scientist, she was extremely bright and very interested in the natural world and very interested in science fiction. So I have memories as a child going to the beach in the summer and being encouraged to set up aquaria and to study the organisms in the ocean. And I have memories of every Thursday night, I think it was, I might be wrong about the day, assembling with my four other siblings to watch Star Trek on TV with the entire family.

Mary Voytek: And so I think that the very force of personality that my mother had, the hope, the imagination is what really sent me into science and really nurtured and stimulated my curiosity that led me to where I am today.

Jim Green: Mary, let’s say one of our scientists calls you up and says, “I found it. I think I have found life on this planet,” what do you do next?

Mary Voytek: So extraordinary claims require extraordinary evidence, and that comes from our most famous and inspirational scientists, Carl Sagan. And in fact, this happened to us in 1996 — a scientific group out of Houston came to us with evidence, four lines of evidence that they thought that they had actually found evidence of life in a Martian meteorite. And very good scientists, excellent, reputable scientist, respectable scientists said they had the evidence and it came out in a peer-reviewed publication, and after that the entire scientific communities started examining it and challenging it.

Mary Voytek: And one of the things that we discovered is you can do great work, but you can still be wrong. And in fact, I like to say that astrobiology is 60 years of doing research, proving ourselves wrong as we move towards understanding what life is and how we can detect it. And so the first thing that I would do is find out what that evidence is. We’d make sure that it was put to the test by other scientists before we would do anything with that. So the peer-review process and publications is the start. We’ve learned too that some people can be so enthusiastic that we might even need greater challenges, but we would basically take it to the global scientific community and put it to the test.

Jim Green: Okay. And then if it turned out to be true?

Mary Voytek: Once I stop screaming with excitement, we would go back onto… I think that a lot of us have talked about what would be the next step.

Jim Green: Well, we certainly wouldn’t keep it a secret.

Mary Voytek: No, absolutely not.

Mary Voytek: One of the things Astrobiology Program does is, we have talked to individuals about what it would mean to you to find life, does it challenge your religious beliefs? Does it challenge how you think about yourself, or whatever? Are you frightened by the concept?

Mary Voytek: And so, it would be really important to think about how to deliver that messaging, and I think that there is tremendous excitement that we could convey. I think we can convey hope and leading to a better understanding about ourselves. I think we’d also need to know like, “So, where did you find it and how can we find out more?”

Mary Voytek: Initially, after I stop screaming myself, it’s like, “I want to get some more of that. I want to go to wherever that came from. I want to… “ More work, more science, more characterization, more to understand.

Jim Green: It’s the next set of questions you now want to ask.

Mary Voytek: Absolutely. Absolutely. That’s what I’d do after I stop screaming. What about you Jim?

Jim Green: Oh, what would I do?

Mary Voytek: Yeah, if it’s you.

Jim Green: I’d be screaming too.

Jim Green: Well that’s fantastic, and Mary, thanks so much for joining me today and talking about, of course, one of my favorite subjects too, astrobiology.

Mary Voytek: Thank you so much, Jim. This has been a blast.

Jim Green: You’re very welcome. Thank you. Well, join me next time as we continue our journey to look for life beyond Earth. I’m Jim Green and this is your “Gravity Assist.”

Credits:
Lead Producer: Elizabeth Landau
Audio Engineer: Emanuel Cooper

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