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Season 4, Episode 19: Life in the Clouds, with David J. Smith

Season 4Episode 19Oct 9, 2020

While more research is needed, Smith and others are fascinated by the possibility that airborne microbes could also be found elsewhere in the solar system, and beyond.

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NASA astrobiologist David J. Smith

High above our heads, even beyond 120,000 feet up, scientists have found tiny organisms called microbes. These high-flyers were swept up from the ground by winds and storms, or spewed out through volcanic processes. While most of these high-altitude microbes are dead, some are still alive, or have produced material called spores that could activate in the future. David J. Smith, an astrobiologist at NASA’s Ames Research Center, uses airplanes to collect these microbes, analyze them in the laboratory, and expose them to even higher altitudeswith balloon experimentsto see how they will respond. If microbes can inhabit our clouds, what about other planets? While more research is needed, Smith and others are fascinated by the possibility that airborne microbes could also be found elsewhere in the solar system, and beyond.

Jim Green: Did you know the smallest form of life can travel enormous distances? How do they do that? How do microbes fly in the upper atmosphere?

Jim Green:Hi, I’m Jim Green, chief scientist at NASA, 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. David J. Smith from the NASA Ames research center, and David is an astrobiologist. But he has significant experiment

Jim Green: He’s founded the aerobiology laboratory at the NASA Ames Research Center. And David is an astrobiologist but he has significant experience in ecology and evolutionary biology. David spent the first portion of his NASA career as a principal investigator and project scientist specializing in microbiology. He founded the Aerobiology Laboratory at NASA Ames Research Center. Now I also want to mention that David won the 2019 award, the Presidential Early Career Award for Scientists and Engineers.

Jim Green:Welcome, David, to Gravity Assist.

David Smith: Thank you, so much, Jim. I’m happy to be here.

Jim Green: Let’s start out with what are we talking about? What do we mean when we’re talking about microorganisms, and why are they so important in the search for life?

David Smith: When we talk about microorganisms or microbes, we’re really talking about small life. Life so small that you can’t see it with your own eyeball. In some cases, we’re talking about single-celled microbes. And the reason we’re so fascinated by microbes is because they’re so successful on this planet.

David Smith: You could argue that Earth is a microbial planet. And I say that because microorganisms were the first to arrive on this planet, the first to emerge in the evolutionary history of our planet. For billions of years, it was a microbial planet. And even today, when we look at the types of life on Earth, most of it is microbial in terms of the sheer diversity. And so, microbes are really successful, both in the total amount of microbes on this planet, and the adaptations of microbes in nature, the resilience to changing environmental conditions. And for those reasons, we expect them to be perhaps, in the solar system and other places where we’re interested in looking for signs of life.

Jim GreenYeah, that’s a really important point, you know, when our Earth had microbes for 4 billion years or so, and, and survived many mass extinctions that went on, you know, perhaps that’s what happened on other planets. And this is why we’re looking for microbial life on those planets.

Jim Green: I remember when microbes were found at high altitudes. And this was really mind boggling.

Jim Green:How would these tiny organisms really get lofted into space? You know, they can’t fly, right. So, they have to take off somehow.

David Smith:You said it, they don’t have wings, but they can drift due to natural convection and winds that move in Earth’s atmosphere that in a sense, connect the Earth’s surface to the atmosphere. And all of these patterns are because of prevailing winds around the globe. If you’ve ever been to the ocean, of course, as soon as you arrive at the beach, you smell it, you smell the salt, you smell the ocean, right? Those are aerosols, a lot of those aerosols are reaching your nose because of wave action and winds on the coastline. So you also get microbes that live in the ocean, pushed into the atmosphere with those same patterns.

Jim Green:What type of microbes have we found?

David Smith: We see the same kinds of microbes in the atmosphere that you would see if you went outside and scooped up some soil, a representative sample. The reason for that is maybe easier to understand if we just talk about how microbes move in air, right? So, if you were to sneeze, and I were to microbiologically sample what’s coming out of your sneeze, more or less it would be representative of the microorganisms in your mouth.

David Smith:Now in the atmosphere, you could think of geological and meteorological processes, in effect causing the Earth’s surface to sneeze. And therefore, the same signal we get in the atmosphere is representative of what was on the surface. And so the exact signal of microorganisms really depends on where we’re sampling, how high we’re sampling. the season we’re sampling and the local topography. And so it’s a complicated question to give a simple answer to, but more or less, because the microorganisms are being swept up from the surface. The samples that we get in the atmosphere are representative of that surface, albeit in a much lower concentration.

Jim Green:So this is going to be pollens and it’s going to be you know, fungi. And well, even bacteria and viruses, right?

David J. Smith is an astrobiologist at NASA's Ames Research Center in California's Silicon Valley.

David Smith: Absolutely, all of the above, Jim. We see fragments of pollen and other pieces of biological debris in the atmosphere as well, too. And, you know, speaking of sneezing, anybody that suffers from seasonal allergies is acutely aware of pollen in the Earth’s atmosphere. You may not know that if you suffer from seasonal allergies, you too are an aerobiologist. But that’s just to say that, you know, we, we have been impacted in a lot of ways by the movement of airborne microbes, whether or not we’ve had the systems to actually start to understand all of these complicated patterns of dispersal. It’s a really exciting time to be an aerobiologist, start to answer some of these questions about what is above our head?

Jim Green Indeed, I’m fortunate, I don’t have allergies. So I am not an aerobiology detector. But what I want to know is how high do these get? What’s the what’s the altitude range and do we see different types at different altitudes or is it a mixture?

David Smith:In general, the concentration of bioaerosols decreases, the higher you get above the Earth’s surface. We’ve seen reports anywhere ranging from about 5, even to 50% of the total aerosol signal for aerosols that are larger than about two and a half microns derived from biological particles.

David Smith: Now we can use airplanes, we can use balloons, we can even use sounding rockets. And there’s really just been a handful of studies published in peer reviewed literature, that have been able to make detections in Earth’s stratosphere, which is very high up above the surface, more or less, above 40,000 feet. And the highest report ever was done not using an aircraft, but a sounding rocket, all the way up to about 250,000 feet in the mesosphere. Now, that was just a single study that was published in the 1970s. And it hasn’t been repeated. But it’s an interesting and intriguing result, I would put more confidence in a handful of other studies flown using large scientific balloons, were are also able to measure a microbiological signal at around 120,000 feet in Earth’s middle stratosphere.

Jim Green: Wow.

Jim Green:Well, it’s also above the ozone 120,000 feet is really up there, which means, you know, they’re going to get also get bombarded with ultraviolet light from the sun. How do they survive?

David Smith:In fact, most of the biomass that we collect in the upper atmosphere we think, is dead. We can still detect its presence based on its DNA signal. But most of the bio aerosols that gets swept up into the atmosphere, particularly above the troposphere and into the stratosphere, are not living. Now, some still can withstand those conditions. So there is a portion of really resilient microbes, mostly spore forming bacteria that have been recovered from the middle stratosphere, which is truly extraordinary based on the environmental conditions, that location, and you mentioned it it’s very strongly irradiated at that altitude above the ozone in particular, it’s freezing. And it’s really dry. And all of these things make it even more remarkable that we can recover any, what we call viable signal life that is still hanging on, probably hunkered down in a state of dormancy.

Jim Green:Well, do some of these microorganisms carry disease?

David Smith:I would say first and foremost that the vast majority of microorganisms are harmless. And in fact, most microorganisms in nature are helpful. And so I want to dispel any worries people may have about microorganisms moving in the atmosphere. Now that said, there have been a few reports of potential correlations between the movement of winds across adjacent agricultural fields and the spread of certain plant pathogens. There’s also a lot of interest in the so-called meningitis belt and whether or not you can have human diseases moving along, moving along with winds across continents.

David Smith:Now, there’s going to be a lot more work required to actually establish such associations. But before we can do any of that we need more efficient methods for making collections in the atmosphere. And so there’s still much work to be done before we start to monitor and perhaps even predict movement of diseases in the atmosphere if in fact, it’s happening. Now, I wouldn’t say to worry about what’s above your head, keep your windows open, I would say the aerobiology of the indoor environment is a lot more likely to be harmful to your health than the aerobiology of the open air outside.

Jim Green:We hear so much about, you know, the transmission of COVID, a virus, you know, and we know that when you sneeze particles move away and can go many feet. So do they immediately go up? Or what happens to them in general?

David Smith:Yeah, most of the particles coming out of your sneeze are large enough that they’ll fall to the ground pretty quickly. But that said, wear your face mask. It’s important.

Jim Green:Of course, aerosols do have effects on the weather. Would microbes also affect the weather in any way?

David Smith:Whether or not the microbes or pieces of microbes, if they’re damaged, whether or not they’re living or dead, they can still influence precipitation and the weather. Now, for precipitation to occur, you need to have a nucleus for water to nucleate onto and that can occur through a biological particle.

David Smith:Now, there’s a famous, well studied at this point bacterium, Pseudomonas syringae, which has been examined for its common occurrence and cloud water. And also precipitation that’s collected at high Alpine observatories, why do we keep finding this particular bacteria? Turns out that it’s got proteins on its outer membrane that actually in produce nucleation more efficiently and particles that are not biological. So this is just absolutely fascinating. It could in fact, be an evolutionary outcome that this plant microbe which resides on the surface of leafs and gets commonly swept up into the atmosphere, may have through natural selection figured out a way through proteins on its outer membrane, to really build its own parachute for returning to the surface quickly.

Jim Green: Wow. Well, you’ve done a lot of experiments not only from aircraft but from balloons, too. Can you give an overview of what you’ve been doing with those platforms?

David SmithThe first thing I wanted to do was follow on Dr. Dale Griffin’s pioneering studies on NASA’s ER-2 aircraft. And so after his landmark paper in 2004, we flew another mission on NASA’s ER-2 aircraft over the open Pacific Ocean, the same altitude around 66,000 feet. And, sure enough, we were able to verify the same findings that Dr. Griffin’s team reported earlier, which was not only a signal of microbes over the open ocean at 66,000 feet, but living bacteria and fungi. So despite my skepticism, we were able to verify those results. And it really motivated me to continue making samples using NASA aircraft.

David Smith: Starting three years ago, using a different NASA aircraft, a Gulfstream Jet called the C 20-A, which can’t fly as high, but can still reach about 40,000 feet in altitude, we were able to modify a system that more or less was already in place on the aircraft for measuring the vehicle’s airspeed, just a tube that sticks out of the window of the airplane and into the open atmosphere. And we were able to optimize that too, in such a way that we could get very efficient volumes of air moving through our system.

David Smith:I would encourage any curious listeners to go take a look at those surveys, which report all the kinds of diverse microorganisms above our head at altitudes, ranging from 10,000, all the way up to 40,000 feet using this new system.

David Smith:So how do you get even higher? That’s where the NASA large scientific balloons come in. And so we’ve also flown a series of missions, both from New Mexico in the United States and even Antarctica, on large NASA scientific balloons that can reach all the way up to about 120,000 feet, and can linger at that altitude for hours and in some cases, weeks. So what we do with those studies, instead of trying to make collections at that altitude, we intentionally carry known types of microorganisms, some of the same types of bacteria that we commonly find in the aircraft surveys, we take them to the middle stratosphere on NASA balloons, expose them to that environment, and then return them to the lab after the exposure to measure: Did anything survive? And if so how? And so we’re using a variety of platforms to address some of those larger questions in aerobiology that remain poorly understood still.

Jim Green:Well, this really brings me to one of the recent discoveries, you know, that’s been reported by a series of scientists that see phosphine, you know, at 60 kilometers in the Venus atmosphere. And so, we know that the surface pressure is just enormous on Venus, you know, 90 times ours and the temperature is hot enough to melt lead, but it that, that altitude, you know, it’s like an atmosphere. Looking at that, do you think that’s possible? Could microbes be living in in that altitude on Venus?

David Smith:Well, I’ll say, the idea of what a habitable zone is, has certainly changed substantially even in my lifetime. And more generally, in the field of astrobiology, you know, when I was in school, we were taught, you know, there was sort of a Goldilocks zone of where a planet could be habitable. And then suddenly, we started discovering all of this life in the subsurface of Earth. And that totally shattered the idea of what a habitable zone could be, and where we should look for signs of life in the universe.

Jim Green:Yeah, and hydrothermal vents in the ocean too, you know, the hydrothermal vents are just pouring, pouring out material that life loves.

David Smith:Sure, and we do know, based on our own solar system, that atmospheres are relatively common. So you would expect more planets or maybe more moons with atmospheres as well throughout the universe. And so for that reason, I think it’s really important to consider whether or not the atmosphere, clouds could, in a sense, be an ecosystem. If not here on Earth, perhaps it’s possible with other environmental circumstances and other planetary bodies. Now, the discovery that’s been reported at Venus is certainly motivating a lot of scientific debate. And I think that is just such a positive thing.

Jim Green: It is.

David Smith: I think that a lot of important work will come from interdisciplinary conversations and dialogues that are occurring as a result of that study. You know, I see astronomers now debating with microbiologists, I see atmospheric chemists debating with geologists. I think all of these things are so wonderful and so healthy for a vibrant and stronger field of astrobiology.

David Smith:So, as I mentioned before, it’s a great time to be an aerobiologist on Earth, because we’ve got plenty of difficult questions, both here over our head, and certainly as we look elsewhere, for signs of life in the universe.

Jim Green:Well, you know, David, I always like to ask my guests to tell me, what was the event or person, place or thing that kept them so excited about being a scientist, that it propelled them forward and they became the scientists they are today. I call that event, a gravity assist, and many people have had more than one gravity assist along the way. So David, what was your gravity assist?

David Smith:Oh, I very much I’ve had multiple gravity assists. I’ve been fortunate to slingshot around a few planets, if you will, on my trajectory to wherever I’m heading. So I would love to give thanks to, back in my public school system in Colorado, some great science teachers, Judy Whitman, who helped me fall in love with the field of biology, Tim Lenczycki who was so patient with me when I was failing my physics exams and probably wanted nothing to do with science. But you know, in his own free time and lunch breaks, he was able to coach me back into the fold, and help me understand some of the physical principles I was struggling with when I was younger. And then when I got to college, I had just an outstanding thesis advisor who introduced me to doing microbiology, T.C. Onstott. And I was so fortunate to cross paths with T.C., and he introduced me to how I could really make a career out of astrobiology and encouraged me to go to graduate school.

Davis Smith:And then I would give my last major gravity assist shout-out to Bill Parsons, former Center Director at Kennedy Space Center, who saw something in me that I certainly didn’t see in myself, which was going to work for NASA, to me just seemed so out of reach. But Parsons was able to convince me otherwise encouraged me to come start work at Kennedy Space Center. And so I’m so grateful to him, and anybody listening to this conversation that has the dream of coming to work for NASA, I want you to know you can do it. You’ll need some great mentors along the way. Your gravity assist will be there. And don’t hesitate to reach out to people because they are willing to help.

Jim Green:Indeed, yeah. And I want to thank you too, because I’m just delighted you’re working at NASA Ames. And got that new laboratory up and running.

Jim Green:Well, David, thanks so much for joining me and discussing this fascinating topic.

David Smith:It was my pleasure, Jim, thanks for the opportunity.

Jim Green: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.

Jim Green:If you like Gravity Assist and want even more great podcasts, check out the new season of NASA’s Curious Universe.

Jim Green:Curious Universe takes listeners on exciting adventures with top NASA experts like astronauts, scientists, and engineers. In their second season, you’ll tour the International Space Station, investigate how black holes form, and much more! Here’s a sneak peek of what you can expect to hear.

AMBER STRAUGHN:The thing about astronomy is that it gets to the heart of the big questions that we have as human beings. Where did we come from? Are we alone in the universe?

HOST PADI BOYD: Our universe is a wild and wonderful place. Welcome to NASA’s Curious Universe. In this podcast, NASA is your tour guide.

ASTRONAUT SAMANTHA CRISTOFERETTI: For the past twenty years, we have been a spacefaring civilization. If you were born after the year 2000, you haven’t lived a single day without human beings in space.

DANTE LAURETTA: Almost seventeen years of my career has been focused on this one day to make sure everything goes according to plan.

HEATHER ENOS: It really all happens in less than twenty seconds.

SAM DOVE:Think of something that’s moving very slow, around .8 or .9 miles an hour, moving this big rocket down the road.

JOHN GILES: It just goes Brrrrrrr and it just gets louder and louder.

JEREMY SCHNITTMAN:We actually think there are close to a hundred million black holes just in the milky way alone all sprinkled around dead ashes of stars.

AMBER STRAUGHN: It’s those mysteries that are out there in the universe that we haven’t even dreamed of yet. I think the universe is going to surprise us.

HOST PADI BOYD:NASA’s Curious Universe season two. Coming to your ears this October.

HOST PADI BOYD:Subscribe right now, and get ready for a grand adventure.

Jim Green:You can listen and subscribe to NASA’s Curious Universe on your favorite podcast app at


Lead producer: Elizabeth Landau

Audio engineer: Manny Cooper