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Season 4, Episode 13: She Protects Other Planets from Our Germs

Season 4Episode 13Jul 17, 2020

As we explore Mars and other places in the solar system that might have life, scientists who work in Planetary Protection are busy making sure that we don’t contaminate them.

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Planetary protection specialists

As we explore Mars and other places in the solar system that might have life, scientists who work in Planetary Protection are busy making sure that we don’t contaminate them. While engineers prepare the Perseverance Rover for launch, Lisa Pratt, NASA’s Planetary Protection Officer, is making sure that it’s not carrying too many spores — cells that could re-activate and transport Earthly bacteria to Mars. It’s especially important to keep Perseverance clean because it will collect samples on Mars that will one day return to Earth. Learn what your hand sanitizer has in common with NASA’s clean rooms, and how scientists are thinking about protecting Mars in terms of future human missions.

Jim Green: If we return a sample from Mars, can we identify life in that sample?

Lisa Pratt: Can we go there and sustain ourselves without harming Mars if there is something on Mars that could be harmed?

Jim Green: Hi, I’m Jim Green, chief scientist at NASA, and this is Gravity Assist.

Jim Green: I’m here with Dr. Lisa Pratt, and she’s NASA’s Planetary Protection Officer. Welcome, Lisa, to Gravity Assist.

Lisa Pratt: Hey. Thank you, Jim.

Jim Green: Well, you’ve had a distinguished career in biogeochemistry and astrobiology, and the Planetary Protection Officer name, that sounds really cool. In fact, I’ve received letters from kids all over the world, and one of them called your position, the Guardian of the Galaxy. I can’t help but think that every time I talk to you. But let’s start with the basics. What is planetary protection?

Lisa Pratt: Jim, I wish I could tell you that I was, in fact, the Guardian of the Galaxy, but the reality is a little more mundane. Planetary protection is focused on limiting biological contamination of other worlds with terrestrial organisms, that’s organisms from earth, and preventing the return of harmful potential extraterrestrial organisms or just organic materials when samples are returned Earth during robotic sample return or in the future when astronauts come back to Earth from exploration missions to other worlds.

Jim Green: We send things all over the place, and the next big mission is, of course, Perseverance, and it’s going to Mars. So when NASA wants to send a new rover to Mars, what do you do?

Lisa Pratt: Well, Jim, right from the very earliest phase of mission design, when that light bulb first comes on with an idea for a new mission, the Office of Planetary Protection provides advice and guidance to the engineering team on heat sterilization, or alternative chemical cleaning methods, such as vapor hydrogen peroxide. Some spacecraft materials can be cleaned and others cannot, and we want to be sure that we’re designing a spacecraft that will tolerate the cleaning procedures necessary to go to the three places we care about right now, most deeply in terms of contamination and that’s Mars, Enceladus, and Europa.

Lisa Pratt: When we have a mission that’s being assembled for one of those locations, then there’s actually an independent auditor from our office that travels to all the facilities where parts like solar panels or parachutes are being manufactured, and we take samples to determine the level of biological cleanliness.

Lisa Pratt: Every day, I actually review data on the number of spores being sampled and detected on Perseverance as we get ready for launch.

Jim Green: So Lisa, what is a spore exactly? Is it biologically made up of many different things?

Lisa Pratt: Jim, a spore is a tiny microscopic resting cell that only certain types of bacteria can make, and they make spores, a process called sporulation, when the environmental conditions get challenging and it looks like they’re going to have to shut down, they’re not going to continue to be active. But in the process of making that spore, that single-cell entity, they wrap it in layers of highly resistant biopolymers. They seal it off and thereby they create the possibility of that spore later breaking open and turning back into a viable organism that can replicate and grow. The reason going… and this goes back to Viking. It’s really the Viking planetary protection biologists that thought this through and said, “Of all of the entities known on Earth that are biological, the only thing we think that could get on a spacecraft, not be seen in an inspection and stay viable would be a hardy spore.”

Lisa Pratt: So we don’t even monitor all of the spores, which you would be monitoring if you were making medical devices like implants and things like that. For us, we actually take a wipe of a spacecraft surface, or we take a tiny little swab that looks like a slightly large Q-tip, and then we heat shock that sample to kill the wimpy organisms, because we only want to know how much contamination is there that could survive the journey, launch, travel, cruise stage and the landing and the exposure to another planet. Those are the NASA Standard Assay, the NSA, spores.

Lisa Pratt: There are international guidelines for spore cleanliness. The total requirement for all spacecraft elements impacting Mars is 500,000 spores including the rover, aeroshell, descent stage, and parachute That sounds like a lot, but the requirement is less than 300 spores per square meter of exposed rover surface. Spores are tiny, barely visible with a light microscope, so 300 spores per square meter can be imagined as just 28 tennis balls on an entire football field.

Lisa Pratt: That’s thousands of times less than our spacecraft would carry if we didn’t build them in a clean room facility, if we didn’t constantly wipe them with a cleaning fluid specific to biological cleanliness, like 70% isopropyl alcohol, which is what we all now read the labels on our hand sanitizer under the current pandemic to make sure that we’re using at least 70%, just what we use on spacecraft.

Jim Green: Well, what’s riding with Percy, and I like that nickname, Percy.

Lisa Pratt: Oh I do too.

Jim Green: So but what’s riding with Percy is the Ingenuity helicopter. This is really a fabulous idea to what we call a technology demonstration, and we hope it works. But does that also have some sort of planetary protection requirements on it?

Lisa Pratt: Yes, it does. It’s been held to about the same standards as that upper deck of the rover, but not nearly as rigorous as the sterilization for the sample tubes and drill, or the wheels. That’s because it’s a very different kind of activity. It will not, in any way, be associated with the return of samples to Earth. So part of what we’re doing with the tubes and the drill is we’re not just worrying about what we take to Mars, that’s forward contamination. We’re very concerned about what might come back in those samples, that’s backward planetary protection. Backward planetary protection ensures that we do not bring something harmful and release it into the terrestrial environment.

NASA Planetary Protection Officer Lisa Pratt with the R25 engine at Marshall Space Flight Center.

Jim Green: Well, I think I have one of these samples and a sample tube right here with me. So when I was out at JPL not too long ago, and I went into the lab where they were testing the core, I was able to walk out with one of the cores. So they had just-

Lisa Pratt: Oh, look at that.

Jim Green: Yeah, yeah. They just took this circular tube that has a cutting mechanism, and it cuts into the rock and then creates this core. Then they break it off, and then that is put into a sample tube and that’s what the sample tube looks like. As you say, these have to be cleaned really well…

Jim Green: You know, there are places on Mars I would dearly love to be able to really interrogate, and one of those places is what we believe… We call them reoccurring slope lineae. This is these long lines of dark material that appear every summer. We now know that many of them, maybe not all, but many of them actually could be briny water. What would it take for a rover in planetary protection example to be able to go over and look at that, potential water streak coming out of a crater?

Lisa Pratt: Jim, that’s a really good question, and one that I think the Perseverance rover drilling caching assembly prepares us to do because we have been successful in sterilizing at a high temperature for many, many hours in a way that would meet the requirement for going into a place where we might encounter a liquid water environment. So I actually think that what we’re learning from this mission, to prepare for sample return, is going to put us in a good place to actually design a mission where we’re going to reach towards and in some way sample one of these recurring slope lineae, which I usually just call RSLs because if I don’t, it’s a tongue twister.

Lisa Pratt: I also think that what we’re learning with the rock drilling system on Perseverance is how we might clean a drilling system that would melt drill into ground ice or rotary drill into an ice cap.

Jim Green: Curiosity landed in August of 2012, and so it’s been there many years in that environment. Do we expect many spores to have survived on its surfaces?Lisa Pratt: Jim, even if the physical entity is there, because again, it’s made out of very resilient biopolymers, it’s extremely unlikely that that spore is viable, and that’s what matters here. What matters is that an organism can come back to life, grow and replicate and spread. My feeling is, and I love it if we had the opportunity to think this through, my guess is that the Curiosity rover is now clean enough that if it were to encounter an RSL or something interesting to explore, that it would be clean enough that we as an international community, because we would probably discuss this through COSPAR, the committee on space exploration for which you are NASA’s representative to the planetary protection panel.Jim Green: True.Lisa Pratt: I think we would conclude that that spacecraft is now as clean or even cleaner than what we could ever accomplish on Earth and get it to the launch pad and get it on its way.

Jim Green: Yeah. For all the research that we have done, that really makes sense to me too.

Jim Green: Well, big discussions are going on at NASA on how we’re going to send humans to Mars. What do we have to do to protect Mars and protect the humans that are there?

Lisa Pratt: We need to get a lot smarter than we are right now, and that’s what we’re going to do with the Moon. The Artemis campaign, the Gateway orbiting facility and the sorties or extended missions down to the surface of the Moon. That’s the proving ground for Mars, Jim. If we can study how the microbes from humans leak out of the cuffs of our space suit or get out of the air handling systems in our habitats or trail along behind us on the wheels of our vehicles, then we’ll learn how to prevent that or we’ll develop technologies for sterilization of material when we’re at Mars. Then we’ll be able to do that exploration without causing harmful contamination of Mars. I say that because we don’t know right now. We don’t have the data we need to understand whether or not there’s indigenous Martian life. We’re pretty sure there’s nothing at the surface because we’ve been looking.

Lisa Pratt: We’ve been looking from orbit, we’ve been looking from rovers, we’ve been looking from platforms. We don’t see anything with the characteristics of life as we know it on Earth. But subsurface, if it was ever there and it evolved and adapted, and I think it’s quite possible it retreated into the subsurface where we believe there is to the present day liquid water below the ice table. We certainly do not want to do something that would contaminate or compete with a potential Martian life form before we’ve had a chance to study it and understand it. It would be our first contact, and that’s-

Jim Green: Yeah, right.

Lisa Pratt:…a one-time only, don’t mess it up kind of event and exploration.

Jim Green: It would be. It would be. Well, I’m going to I guess speculate, but I’m going to think about a potential future, and that is, let’s say we find life on Mars. Is it possible that we could… And it’s below the surface, it’s subsurface, maybe living in the aquifers where there’s water and there’s a lot of possibilities for that because we have an enormous amount of life below our feet too on this planet. Do you think we could get to the point where humans and these Martians could coexist, and what would that look like?

Lisa Pratt: Well, Jim, like you I’m sort of a hopeless optimist about what scientists and engineers are capable of doing, and I think it is possible. But I think we need to understand it and be aware of how we would bio barrier or very carefully control our waste and our agriculture. Because if we’re going to be up there for extended periods of time, we need to be able to grow our own food, and that’s a very different microbiome from just the human body, which we know has a signature.

Lisa Pratt: But when we start growing food, now we’ve got individual organisms that live in and on the roots of plants, mycorrhizal fungi that have a distinct characteristic, and bacteria as well. So we need to be very, very careful initially so we don’t do something inadvertent and irreversible. Then I think there is a possibility in the future that we can be there and we can study. Frankly, we’re going to have to learn if there is something in the subsurface, how to not have it get inside our habitats, and in some way present harmful contamination to us. It’s very complicated.

Lisa Pratt: Very complicated relationship—

Jim Green: It is.

Lisa Pratt:… that we’ll have to develop. But again, in the same way, the Moon is the proving ground for Mars. I think Mars is the proving ground for the extraordinary icy worlds that are out there around Saturn and Jupiter. Let’s make sure we know what we’re doing in a very dry, hostile, cold terrestrial planet before we go to an icy moon.

Jim Green: I’m going to guess that you believe there’s life beyond Earth.

Lisa Pratt: Jim, I would be absolutely flabbergasted if there was not life elsewhere in our solar system, because I think evolutionary biology has really changed over just the past two decades. Once we began to realize that there is essentially no place on Earth that doesn’t have living organisms, it makes it very hard for me to think that life only got started here. The very fact that we don’t know what the origin of life is on earth, we don’t have a geologic record that gets us back in time far enough with unaltered materials to know what the origin looked like on earth, also makes me wonder if the origin was someplace else and something arrived on Earth ready to go or partially formed, or…and any of those ideas makes me keep my mind open about life elsewhere in our solar system.

Lisa Pratt: If it’s there any place else in our solar system, then I think we will have to conclude that on the spectrum from rare to common, that it’s going to be common. If we don’t find any vestige of a life form, any place else in our solar system, that’s going to push us towards rare.

Jim Green: Well, when you look out into the solar system, where do you think we will find it first?

Lisa Pratt: I’m still cautiously optimistic about Mars because of the methane mystery. We see these pulses of elevated methane in the atmosphere. Not only do we have no explanation for where that methane comes from, we don’t have an explanation for how that methane is removed from the atmosphere. We have a great mystery on Mars right now, and that’s why as the Planetary Protection Officer—

Jim Green: Yes, we do

Lisa Pratt: I want to see us continue to explore with a very, very careful eye on forward contamination.

Lisa Pratt: That gets back to your question about, can we go there and sustain ourselves without harming Mars if there is something on Mars that could be harmed? Ultimately, I think it’s a better bet to look in the oceans beneath the ice covers in places like Europa and Enceladus.

Jim Green: Let’s say we brought the samples back from Percy, and now we’ve started to interrogate them. Do you think we know enough to be able to say these samples, we can delineate things that we brought that actually have come back from those things that are indigenous to Mars?Lisa Pratt: Jim, that would be a false positive. It would mean could we or do we need to worry about being confused and misidentifying something that made a round trip with something that came from Mars itself? I frankly, and we’ve spent a lot of time discussing this with outside experts, I have very little worry about a false positive. And the reason for that is that we are archiving samples from the spacecraft, from the facility, from the launch pad, and we are storing and saving those samples for future study so that we know a great deal about everything that could have potentially gotten on that spacecraft and flown with us.

Jim Green: Wow, that sounds great. Well, Lisa, I always like to ask my guests to tell me what was that event or person, place or thing that happened to him that got him so excited about being the scientist they are today, and I call that a gravity assist. Lisa, what was your gravity assist?

Lisa Pratt: Jim, it’s hard for me to point to a single event because I think you’re aware that I had quite a number of not false starts, but moved down one path with my education and then said, “This really doesn’t interest me that much.” I went off to college as a Spanish major.

Jim Green: Wow.

Lisa Pratt: Even though I had taken a lot of math and science in high school and knew that that was something I was good at, I didn’t see any role models, I didn’t see any way that that was going to—

Jim Green: Wow.

Lisa Pratt:… work out. Then I realized that I really still fundamentally loved biology in particular. So I started taking biology classes, and then I decided I didn’t want to be killing frogs in biology labs. This was at a time when we were still working with live animals in undergraduate labs.

Lisa Pratt: I had an inspirational moment when I decided I’m a botanist. Plants don’t bleed. So I actually transferred to the University of North Carolina as a botany major. Then if there was a pivotal gravity assist for me, it was in my senior year when I took my first geology course. The instructor, John Dennison at Chapel Hill, had a way of talking about time travel through study of the geologic record, through stratigraphy that was so all inspiring that I knew that I was even more passionate and more interested in the history of life on Earth and the evolution of life on Earth through the study of the ancient rock record. I was more interested in that than living plants.

Lisa Pratt: I guess that’s my gravity assist. It’s what serendipitously gave me dual degrees in life sciences and Earth sciences that actually positioned me ultimately to be competitive for the Planetary Protection Officer position when it was advertised and opened three years ago.

Jim Green: I was just so delighted that you applied. What made you decide to do that?

Lisa Pratt: This is a strange and wonderful story about role reversal. A number of people, both inside and outside NASA, had let me know that the position was open and I kept saying, “No. Maybe 10 years ago, it’s too late in my career,” and I made the mistake. Well, maybe it was a mistake, maybe it’s the best thing that could have happened. I was talking to my daughter about it. She’s an engineering graduate student at Stanford, and I said, “This position is open,” and that began weeks of relentless work on her part to-

Jim Green: Wow.

Lisa Pratt: Talk me into applying. I kept saying, “No, it’s just too late.” Then finally, one time on a phone call, and Jim, this was three days before the position was going to close for applications, she said to me, “So mom, following your passion and reaching for your dream job is advice you can dish out but you can’t take it yourself?” I was so shocked that this 25-year-old threw back at me what I throw at her that I actually said, “You know what, I’m going to apply. I’ll never be selected, but I’m going to apply, and for the rest of your life, you’re going to say to me, ‘I’m so proud of you for applying.’”

Lisa Pratt: Then the unexpected happened, and I’ve had the most wonderful two and a half years to date of being the Planetary Protection Officer and helping NASA find ways to not contaminate forward or backward. It’s a gift that Isabelle gave me.

Jim Green: Well, I got to tell you, I’m so proud of you for applying because I have enjoyed working with you over the last several years. It’s just been a wonderful experience for me too.

Jim Green: Well, thanks so much for tagging up with me today to discuss what a Planetary Protection Officer does and how they do it. I’ve really enjoyed our discussion today.

Lisa Pratt: Hey, Jim I’m just I’m just delighted that you asked and we had a chance. You caught me off guard with a couple of these questions, but the speculation was lots of fun, and go Perseverance.

Jim Green: Go Perseverance. Join me next time as we continue our journey to look for a life beyond Earth. I’m Jim Green, and this is your Gravity Assist.


Lead producer: Elizabeth Landau

Audio engineer: Manny Cooper