Planetary Radio: Space Exploration, Astronomy and Science - Judging a Planet's Habitability With Abel Mendez

Episode Date: October 26, 2009

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Earth, a great place for life? Eh, this week on Planetary Radio. Hi everyone, welcome to Public Radio's travel show that takes you to the final frontier. I'm Matt Kaplan of the Planetary Society. The discovery of an Earth-sized, fully terrestrial exoplanet seems to be imminent. Our guest, Abel Mendez, has come up with a system for evaluating the habitability of planets, including our own. We'll ask him how we ended up with only an average grade.

Emily Lakdawalla will use her Q&A segment to answer those who say the new definition of a planet is so narrow, maybe there aren't any. And Bruce Betts is just back from what might be called the Armageddon Conference. He'll tell us about it in today's What's Up segment featuring yet another space trivia contest. I want you to know that next week we'll start the celebration of what would have been Carl Sagan's 75th birthday. Dr. Sagan's widow and longtime collaborator, Ann Druyan, will join us once again. In the meantime, the latest news from around our universe is always in Emily's blog at planetary.org. The next couple of minutes belong to Bill Nye.

Bill has found a link between two stories you may have missed in last week's Space News, and that link is elemental. I'll be right back with Abel Mendez. Hey, hey, Bill Nye, the planetary guy here, vice president of Planetary Society. And this week, let's talk about oxygen in the ocean of Europa. Europa is one of the moons observed by Galileo originally. If you have a telescope, you can see Europa yourself. It moves every few hours. And there's evidence now that there's oxygen in what is probably an ocean on Europa. So maybe there would be living things there. Maybe we should send a space probe there and have a look around. We could maybe change the world by discovering the nature of life somewhere else. But oh no, in order to get there right now at our current level of understanding, we need electricity on a spacecraft.

And the only way we know to get a lot of electricity onto a spacecraft right now that's a real long way from the sun is with plutonium. That's right, plutonium, which is an element that does not occur in nature since we haven't lived long enough ago. Instead, we have to make it. This is where you take uranium, which has 92 protons, and transmute it into plutonium, which has 94 protons, generally the same atomic mass, 238.

And you do this in a reactor. A tricky business. It was figured out back during World War II. So that funding's cut. The U.S. Congress decided not to fund the production of plutonium. And you could say, well, that's a good thing because plutonium is so toxic. You know, I had lunch with Glenn Seaborg and he insisted that plutonium have the atomic symbol PU because it stinks and is deadly

and poisonous and dangerous. By the way, Glenn Seaborg invented or made or created the first plutonium. But even with that, even as dangerous as it is, it's cool to have a little bit of it around for spacecraft. Now, maybe if there's no plutonium, engineers will come up with some new way to drag a coil through the Jupiterian magnetosphere, the magnetic field of Jupiter, and maybe generate electricity. But that's decades away. No one's ever done that. Plutonium we know how to do now, and we know how to do it safely

as long as we don't do too much of it. So my friends, if you wanted to go to Europa and sniff around for life, it's going to be that much harder. These are the trade-offs. These are the difficult decisions you have to make as a society if you want to explore space. Think it over, my fellow taxpayers and voters. I gotta fly, Bill Nye the Planetary Guy. Almost 400 exoplanets now and still counting. Counting fast. The discovery of 32 more worlds was announced by European scientists just last week. Our tools still aren't quite sensitive enough to detect a planet that's the size of our own orbiting in that Goldilocks region called the habitable zone. Does anyone doubt that they're out

there waiting for us? And when we find them, how will we use the data to determine whether they can support life? What we need is a quantitative system for evaluating planetary habitability, and wouldn't you know, someone has come up with one. Abel Mendez is a professor of physics and astrobiology at the University of Puerto Rico's Arecibo campus. Yes, that Arecibo, the one with the world's largest radio telescope. Professor Mendez presented his study at the 41st meeting of the American Astronomical Society's Division for Planetary Sciences, held during the first week of October in Puerto Rico.

I was intrigued by the press release I read, so I invited him to join us on the show. Abel, thanks very much for joining us on Planetary Radio. Hi, thank you for having me. We are especially appreciative because, of course, doing this in English would probably not be your first choice. In fact, you just said that you just moments ago finished an interview in Spanish. I've told the audience a little bit about what you presented at DPS right there in Puerto Rico a couple of weeks ago now. Why did you begin this effort, which seems to me to be perfectly timed as the discovery of terrestrial exoplanets seems to be around the corner. Well, I wanted to precisely

evaluate the potential of life of a planetary body. So about five years ago, I started studying how the environment affects microbial life and plants. So these are primary producers for food of more complex life, like animals, including humans. So these are primary producers for food of more complex life like animals including humans. So it makes sense to me at the start that studying the habitability of simple life forms as they are needed for the rest of life. So after this study matured it was an easier step for me to extrapolate that to other planetary bodies, including solar planets.

It was mostly based on strong biology. I needed to do a lot of strong biology to include it in the models, so I can, you know, dare just to move that to other planetary bodies. I saw in your bio that it looks like you've been doing this kind of modeling for many years. Yes, yes. I started actually doing small experiments just to make sure how different microbial life get affected by changes on the environment, especially extreme temperatures and pressure environment. So I got that data, and from that data, I just moved to just completely doing modeling.

So that's one thing right now. Just a few different experiments just to test the models, but mostly modeling. How actually does this evaluation work? And this is, I don't think there's any way for this not to be slightly technical, so we'll ask the audience to bear with us, but can you take us through how, for one thing, how you classify planetary habitability? There's many ways to do it, depending on how much detail you have on the environment. The more detail you have on the environment, the better it will be, you estimate. So far I include temperature, pressure, humidity, relative humidity, pH. So the model can be very complex. But for planetary bodies, we have very limited information.

So they estimate the information we have on the planet. So for the extrasolar planet case, the estimate works by the mean surface temperature and water vapor of the ocean coverage. So if we got that basic information, that might be the only information that we would get of those planets. Then I calculate an habitability. So I created an habitability, a planetary habitability classification as a letter from A to F, just to compare the potential for life of planets. A means a better planet for life. F means not good for life.

So Earth today, in this classification, is a class C planet. I think it had two big periods in the past where it was a class B. And this surprised me, that our Earth teeming with life only gets a C in your system. Yes, yes, that's surprising. And I usually start my conference about this asking the audience, is this planet good for life? So everybody says, yes, of course, this is a good planet for life. But then I show a map of the planet with the coverage of vegetation.

And I ask again, and I say, well, it's not so good for life. And you know this. Look at this map, and you see a lot of deserts. You see a lot of polar deserts also. Imagine a planet where it was all the land coverage with vegetation, like a tropical forest all around. That would be a better planet for life. So you know this is not that good planet for life. It could get better. So I think it was like that much better for life in the past. And I mean better for

microbial life and plants. So in this classification, it takes all these details in account. So for this classification, it takes all these details in account. So for that's why it's a class A planet. So class B or class A planet will be a much better planet for life, coverage with vegetation. The ocean will also be more coverage with phytoplankton, and productivity will be higher in those conditions. What would a planet in classification A look like if we were to be able to image that planet and actually see its continents and oceans? Yeah, you will see a strong signal from vegetation. One of the things that you will also get from those measurements of the planet will be from the atmosphere,

you can get also a general idea of a vegetation index. For planets class A, it will be very dramatic. More times than Earth, you will see a signal that there is some vegetation there. So that will be something very different from here. It would be a very good planet covered with vegetation, maybe more continent, maybe it's well-balanced. If 50-50% of continents and oceans, not like today here is 71% covered with ocean,

less land. And even though we have that land, it's not even in complete coverage with vegetation. And as you've said, our data that we have so far from exoplanets, even though hundreds have already been discovered, is pretty limited. Has there even been enough data about any single exoplanet

for you to be able to apply the model and begin to refine it? You know, fortunately, we haven't discovered terrestrial-sized planet yet. All the detected planets so far are too big, like the geysers Jupiter, or too close to the star, so they are very hot. That means that they are F in my scale. But with the planet missions in the future, in the next two decades, we will be able to detect terrestrial-sized planets

in what is called the habitable zone, and therefore classify them in my scale. So by that time, that would be a good thing to do, just to classify them and see if they are above the class F planet. And that would be very surprising. That's Professor Abel Mendez. He'll be back in a minute with more about his system for evaluating a planet's ability to support life.

This is Planetary Radio. Hey, hey, Bill Nye the Science Guy here. I hope you're enjoying Planetary Radio. We put a lot of work into this show and all our other great Planetary Society projects. I've been a member since the disco era. Now I'm the Society's Vice President. And you may well ask, why do we go to all this trouble? Simple. We believe in the PB&J, the passion, beauty, and joy of space exploration. You probably do too, or you wouldn't be listening. Of course, you can do more than just listen. You can become part of the action, helping us fly solar sails, discover new planets, and search for extraterrestrial intelligence and life elsewhere in the universe. Here's how to find out more. You can learn more about the Planetary

Society at our website, planetary.org slash radio, or by calling 1-800-9-WORLDS. Planetary Radio listeners who aren't yet members can join and receive a Planetary Radio t-shirt. Members receive the internationally acclaimed Planetary Report magazine. That's planetary.org slash radio. The Planetary Society, exploring new worlds. Welcome back to Planetary Radio. I'm Matt Kaplan. Abel Mendez is a physicist and astrobiologist at the University of Puerto Rico. He recently presented his proposal for the quantitative evaluation of a planet's habitability, its ability to support life. The system looks at many factors to award a planet a rating of A through F,

with our own home world getting just a grade of C. The model seems to be by necessity geocentric, or terra-centric, if I can use that phrase. Does it in any way consider life that is potentially different from life as we know it? I don't even know how you would approach that. Well, my models are totally focused on life on Earth. So they are very based on the biology of the Earth, extraterrestrial life. The loss of biology may be universal. Life has some plasticity to adapt to extreme environments, but it has its limits. So my moment in this limit, it helped me constrain and quantify the potential environment that can sustain life in other planetary bodies. It also helped me identify potential habitats for extraterrestrial life,

but also to address those environments that can be contaminated by terrestrial life. So I don't think that this modeling effort can be just used to detect a life that identifies potential habitats, but also how will this habitat react if we contaminate it by terrestrial life. In the end, by creating models fine-tuned for terrestrial life, it also helps to identify any detected life as biologically related to life on Earth or not. So the problem is that even if we detect some life by some signal, we will get confused

if that's something related to life on Earth or not. This model, by making them very sentry, will discern very much easier if this is something related for life on Earth, or this is not, but it's still life. And I suppose that as that data continues to come in, and it's only a matter of time before we find a truly Earth-like planet. You're going to stick with this, and you will be refining the model? Oh, yes, yes. For refining the model, it's just based on terrestrial data.

That data will refine a lot the model, so I expect to do a lot of work on that, and then apply also just to the past environments and how our planet will react to global warming. So different scenarios of terrestrial life. But it has to have a lot of components from terrestrial life just to make sure that I have some sensible models that I can extrapolate to other environment. I know how it wakes related to Earth. And I think it's a very important point that this model may help us to continue to evaluate the evolving habitability of our own planet.

Oh, yes. Yes. And I want to do a lot of work on that. But the thing is, it's so complex just to evaluate right now so much data. Because as I mentioned before, I did some experiments in microbial life, but most of my data for other plants comes from the scientific literature. So I compiled a lot of database and tried to use that data from many years' experiments just to model that and convert those to habitability function that I can use to predict habitability.

So there's a lot of things to do now from that just to be able to make good predictions for the future. On a personal level, it must have been very exciting to have DPS, the Division for Planetary Sciences' annual conference, come to Puerto Rico this year. How was your presentation received? I think it was well received, especially after the comments I received during the week. Some were more intrigued about how to calculate habitability not only for extrasolar planets, but also for terrestrial or solar system applications, especially Mars. This was the first DPS conference in Puerto Rico, first time for me also, because I usually

go to the Lunar and Planetary Science Conference or the NASA Astrobiology Science Conference. But I did notice that there's less astrobiology in the DPS as compared to other planetary science conferences. There was not a section for astrobiology in the DPS as compared to other planetary science conferences. There was no exception for astrobiology, so I was put in the extrasolar planets conference. Well, at least there's some relation there. Just one other question before we let you go. I find it fascinating that your campus of the University of Puerto Rico is in Arecibo, right there where the great radio telescope is.

Is there a relationship there? Yeah, the University of Puerto Rico Arecibo is a campus in the same town of the Arecibo telescope. Everybody knows the observatory by its location name, Arecibo, but its actual name is the National Astronomy and Atmosphere Center, or NIC. Our university has an agreement of cooperation with some research and education experience with the observatory. I also share my office with an astrophysicist that is using the observatory.

So we are the university, he's the astrophysicist, I am the astrobiologist. Excellent, and I hope you get along very well. I'm not so bad. I'm just kidding. We are out of time. I want to thank you for joining us on the program today. And the best of luck, as you must be looking forward to data coming in from a terrestrial planet someplace outside of our own solar system. Yes, I expect that.

And it will come so slow for many years. But that will be a lot of fun. Abel, thanks again for joining us on Planetary Radio. Thank you for having me. Our guest, Abel Mendez, is a professor at the University of Puerto Rico at Arecibo. He has over 20 years' experience in computer modeling of physical and now biophysical phenomena and did a lot of that work before he moved on to the biocide at Fermilab. And in 2007, he was funded by the NASA Astrobiology Institute

to construct a device to measure microbial growth in extreme environments. And he worked on that with Chris McKay, a scientist who regular listeners to this program are certainly very familiar with. We'll be right back with this week's edition of What's Up after we hear from Emily. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, Part of the new definition of a planet is that it has to have cleared its neighborhood. But what about the rings and moons? Does that mean that the planets haven't really cleared their neighborhoods,

so they're not really planets either? The criterion of clearing its neighborhood is the most confusing part of the new definition of a planet to most people. And it's true that if the requirement really were that the neighborhood be empty, nothing in our solar system would be a planet. What the International Astronomical Union meant is that the body has to gravitationally dominate the area around its orbit. There are lots of particles, boulders, and moons orbiting the giant planets, but all are under the thrall of the planet's gravity. Earth's orbit is crossed by thousands of near-Earth objects which may pose a future hazard to life on Earth, but which are so

relatively tiny compared to Earth that they have negligible effect on Earth's orbital motion. So Earth is a planet. Most of the planets also have co-orbital satellites that sit at two gravitationally stable points 60 degrees away from the planet. These so-called Trojan asteroids share the same exact orbit as the planet, but they're still under the power of the planet's gravity. Pluto is one of a great many outer solar system bodies that are under the gravitational control of Neptune, orbiting the Sun exactly three times for every two times Neptune goes around. Fully a quarter of known Kuiper Belt objects share this property.

Neptune's gravity dominates this behavior, so Neptune is considered a planet, while Pluto is not. The International Astronomical Union considers Pluto, as well as fellow Kuiper Belt objects Eris, Haumea, and Makemake, to be dwarf planets. Got a question about the universe? Send it to us at planetaryradio at planetary.org. And now here's Matt with more Planetary Radio. Bruce Betts is on the Skype connection, and that means it's time for What's Up on Planetary Radio.

Welcome. Where have you been lately? I feel like I've been all sorts of places. It's been a busy week. But amongst the week, I spent part of three days in chantilly virginia chantilly lace and a pretty face and a ponytail but anyway don't get me started yeah about at a workshop talking about nuclear and kinetic impact options for asteroid deflection it was it was quite fascinating Cool. That's Armageddon time. So which did you decide to go with, the nukes or knock them? This was far from a decision meeting. This was just looking at that and also getting different communities from NASA to DOD together. And we actually looked at and are looking at lots of

other options. This just happened to be the workshop I was going to. Well, that does sound like fun, though. So tell us about the night sky. What's up there other than electromagnetic pulse? Ha! Which is not what we'd use, but okay. What's up there is Jupiter dominating the evening,

brightest star-like object in the evening, high in the south after sunset, and then moving over towards the west by later in the evening brightest star-like object in the evening high in the south after sunset and then moving over towards the west by later in the evening early the week right after this this show airs you can check it out next to the moon if you happen to catch this on the 27th or 28th we've also got in the pre-dawn Venus still visible but getting lower and lower, extremely bright object over in the east before dawn, and getting farther away from it, higher above and about 100 times dimmer, is Saturn, but still looking like a bright star. And high overhead in the pre-dawn is Mars looking reddish. It's kind of in the general neck of the woods of the gemini twin stars so check those things out

and in the meantime we will go on to this week in space history it was this week in 1971 when the uk became the sixth spacefaring nation with a launch of their own satellite jolly good right oh and uh we move on to random space fact that was lovely thank you oh you have a fact too i do hey i picked up tons of facts some of which i'll be sharing over coming weeks at this at this workshop uh this one uh courtesy of don yeomans fromPL. He talked about the fragility of comets, and in particular, Comet Shoemaker-Levy 9, of course, impacted Jupiter. And you may recall it got ripped by Jupiter's gravity into lots and lots of pieces, over 20 different pieces before the impact. Well, for Jupiter's gravity to do that, it turns out that it would have to be about fragile enough that you could have gone in there with your hands and pulled apart pieces.

It's just a big snow cone, really, a dirty snow cone. Pretty much, yeah. Okay, we move on to the trivia contest and following the LCROSS impact, we were inspired to ask you about previous lunar impacts. What was the first spacecraft to impact the moon and what was the last spacecraft before LCROSS. How did we do, Matt? This was really fun because it's a double one, and people did a terrific job getting us answers.

I think only one person was off, and that was only half off. Our winner, I will simply tell you, and I believe he's a first-time winner, although been entering for a long, long time, Ted Judah out of Petaluma, California, near where one of my brothers, brother Stephen, lives. And Ted said it was, the first one, was Luna 2, almost exactly 50 years before LCROSS, September 13, 1959. And then immediately before LCROSS, it was Japan's Kaguya, also crashed intentionally into the moon. In fact, we got some animation of that taking place from our friend Lindsay,

a regular listener down there in Australia. We did have another nomination, by the way. I should bring this up very quickly. And that was Wan Hu in the 16th century. Ed Lupin said that supposedly he launched himself up to the moon in a rocket chair of his own design and formed a crater called Wan Hu. Well, I guess that would have been the first impact

if that had happened. All right. Well, anyway, we are going to send a Planetary Radio t-shirt to Ted Judah and maybe an Oceanside Photo and Telescope Rewards card, too. And let's move on right after I tell people that for the moment, we only have large t-shirts. So find a large friend, everybody, and listen to this new question from Bruce Batts. Deep impact spacecraft impacted Comet Tempel 1. What density, average bulk density, did Deep Impact find out that Tempel 1 had?

Yeah, Tempel 1 density, that's what we're looking for. Go to planetary.org slash radio, find out how to enter. You've got until Monday, November 2nd at 2 p.m pacific time 2 p.m pacific time to get us that answer drop us a line we hope you'll enter and i guess i guess that's it one quick halloween question i hear you've been reading scary stories to children i have indeed i was at our local aquarium the aquarium of the pacific right here in my hometown long beach california which turns into the Scarium of the Pacific. And I had a great time reading scary stories to kids today, as a matter of fact.

Oh, I'm so glad it was actually scheduled at a real place. Yeah, it really was. All right, everybody, go out there, look up in the night sky, and think about Matt reading scary stories to you while you do. Thank you, and good night. Scary kiddies. I should have known that was coming. He's Bruce Betts, the director of projects for the Planetary Society.

There's no telling what he'll turn into on Halloween as we approach that all-hallows evening just a few days away as we record this for What's Up. Another reminder that my guest next week will be Ann Druyan, the distinguished writer and producer who was the wife and longtime collaborator of Carl Sagan. Planetary Radio is produced by the Planetary Society in Pasadena, California. Keep looking up. Music Thank you.