Life Beyond Earth, Part 3: Natalie Batalha

Thank you very much for having me. Kepler, exoplanets. NASA is on a quest to find evidence of life beyond Earth. Do not doubt.

It is the one of the grand questions, “Is there anybody out there?” One of the grand questions that drives strategic planning for NASA astrophysics, right. There are three paths that we can take to get us there, to find evidence of life beyond Earth. One is solar system exploration. This beautiful image of the plumes of Enceladus, the landscapes of Mars the Curiosity shows us, compels us to explore the solar system and see if there is life lurking in any of these nooks and crannies, in a subterranean cave on Mars, in a subsurface ocean on Europa or Enceladus. Whether or not we find life? Maybe we'll find death, in fossils, in extinction. Regardless, the implications are profound.

The second path is the SETI search, ears to the universe, listening, searching for signals that are not astronomical as we understand them. Signals that are big surprises that might be due to technology, might be due to intelligent life depicted by the Allen Telescope Array up in Northern California.

But there's a third path and that's looking for the cradles of life as we know it, looking for planets like Earth that could harbor surface liquid water and could give rise to life as we understand it here on Earth, carbon-based life. Well, this path was made possible 20 years ago with the first discovery of an exoplanet orbiting a normal main sequence kind of star like our Sun, and I just happened to be at that conference, I was a young graduate student at the time, and it was a conference on stars, not planets, that field of study didn't exist at all! It was cool stars, stellar systems and the Sun, no exoplanet in the title, right? In fact, that talk wasn't even on the agenda. But next thing we knew, Michel Mayor, a Swiss astronomer, went up to the stage, cameras were there, and announced the discovery of 51 Peg b, and it blew our mind! It was unlike anything we understood, right? We understood the solar system; close to the star you've got the small rocky planets; further out, you've got the ice and gas giants, right? That's how solar systems are supposed to form, that's how they're supposed to lay out, our own solar system says it is so.

And yet, here we had a planet discovery, a planet almost as large as Jupiter, with a four-day orbital period around its star, blasted by stellar radiation. Theorists did not know how to make a planet like that. And that's basically how the field of exoplanets has been ever since. We have uncovered an unparalleled diversity of worlds. But what we want to look for, what NASA wants to look for are worlds not like this gas giant blasted by stellar irradiation where surface liquid water cannot exist; we're looking for the cradles of life. And so we fast forward to March of 2009.

(NASA): Three, two... engine start... one, zero and lift off of the Delta II rocket with Kepler.

On a search for planets in some way like our own. NASA's first mission capable of detecting potentially habitable earth-sized planets. A space telescope launched into orbit about the Sun, pointed toward one field of view about the size of my hand near the plane of the Milky Way galaxy, focusing on about a 150,000 stars there, measuring their brightnesses with very high precision. Because for some of those systems, planets that are in orbit about the star will pass directly between the disk of the star and the telescope, and the telescope will perceive the presence of that planet as a momentary dimming of light, a dimming of light that repeats once every orbital cycle.

This is Kepler's first light image. Every tiny speck you see, every tiny pinpoint on that image is a star in this one hand print on the sky in the constellation of Cygnus and Lyra. There are 4.5 million stars in this one footprint. Kepler observed 150,000 of them. The precision that's required to see an Earth-sized planet transit across the disk of a Sun-like star, can be described with the following thought experiment. Imagine the tallest skyscraper in New York City, maybe something like 80 stories high, I don't even know how tall the highest skyscrapers in New York City anymore, but let's pretend it's about 80 stories high, and it's occupied, every single room is occupied, and it's nighttime, all the windows are open, every light is on. And one person in that building goes to the window and lowers the blinds by about a centimeter. That's the precision that's required to see this tiny diminution of light caused by an Earth.

So what I'd like to do is give you kind of the big picture of what exoplanets have been discovered since that historic meeting in 1995 in Florence, Italy where the first exoplanet was announced. And I'm gonna do that with a scatter plot. Kepler doesn't take beautiful pictures of planets, right? We don't find planets by pointing our telescope up into the sky and saying, “Aha, there's one!” We must infer their existence by measuring some property of the star itself, okay? So in this scatter plot, it's going to be radius or diameter of the planet versus orbital period, okay? And we're going to animate this plot, adding discoveries as they're made, and I'm going to first show you those discoveries that have been made by every other team around the world except Kepler. There will be some horizontal... There will be some horizontal lines to give you some reference. Earth sized has a horizontal line, Neptune sized and Jupiter size. They're color coded by the technique that was used to find them, but I want you to just get a general feel for the patterns that are emerging. 2005, 2006... Earth is there for reference at the orbital period and size. 2011...12... We start to see some patterns. There is a swarm of blue points up there on the left, Another larger swarm of pink points in the upper right. For reference, Jupiter would have an orbital period of just over 4,000 days, so 1,000, 2,000, 3,000, 4,000, up to the line that is Jupiter, and you see we have found some Jupiter analogues out there in the distant environs of the solar system.

So this is what the scene looks like, barring Kepler. Over 85 percent of those discoveries are planets larger than Neptune. Now I'm going to show you what Kepler has added after analyzing four years if its data. Through this technique of transit photometry, measuring brightness, Kepler has found over 4,200 transiting objects; 90 percent of which, or more, are going to be bona fide exoplanets, planets orbiting other stars in our galaxy. Our blinders have been lifted to small planets. The landscape has changed dramatically, right? Now more than 85 percent of the known planets or the planets known to humanity, are smaller than Neptune, instead of larger, which just goes to show that our technology, we were hampered by our technology. Every time you build a new piece of technology, you learn a tremendous amount. Moreover, you can see that there are some yellow points kissing that Earth locus at one Earth diameter and 365-day orbital periods.

So Kepler has begun to find Earth, true Earth analogues. The big question that Kepler set out to answer is, “What fraction of stars in our galaxy harbor potentially habitable Earth-sized planets?” We want to get a feeling for the ubiquity of planets like Earth, these cradles of life, these potential cradles of life. Are Earths common? Are they are they prevalent in our galaxy or is our own Earth somehow special? So what have we learned from Kepler? From Kepler, we can now with this large sample of planets, we can ask the question, Okay, what is the population of planets out there? What is their diversity? What is the population? How far do I have to go out into the galaxy before I happen upon a potentially habitable Earth-sized planet? You can ask this question because of Kepler. And so the answer is, if we were to take our own galaxy and we were to shrink it down to the size of the continental United States, and you stand on one coast, maybe here in Washington, D.C., you look out over the continent and you ask yourself, How far is the nearest potentially habitable Earth-sized planet? The answer is, about a stroll across the National Mall, between about the Capitol building and the Lincoln Memorial, or about 15 light years. Which is very close, given the fact that the galaxy is 100,000 light-years across.

Okay, so what's next? So we're kind of learning that Earth-like planets are pretty common; that's good. That means that exploration, finding evidence of life, following this path, has great potential. So, what's next? Well here on the left, I'm showing you an image actually taken of Venus transiting our own Sun. This is an actual image of a planet in our own solar system transiting across the surface of our Sun. The Hinode spacecraft took this image, and I'm showing it to you because I want you to see the very thin layer of orange hugging that planet. Do you see that? That's the Venusian atmosphere. It's very thin; it's only five kilometers thick. I think that's about the scale height we call it, very thin. In terms of area, if you collected that whole area, it's only 1/200 the area of the disc itself. So it's very, very thin, but here's the thing: the sunlight, shining on the planet from behind is filtering through that atmosphere that's hugging it. And when it does that, the atmosphere itself is leaving a fingerprint on that light. If I'm on the other side, I can collect that light, I can spread it out into a spectrum, I inspect it, and I can disentangle the fingerprint that that atmosphere left on the light. Which means, I may have the ability with enough sensitivity to disentangle what that atmosphere was made of.

On the right-hand side of this image is cyanobacteria, it's like algae, and this microscopic picture of cyanobacteria was caught in the act of metabolizing and producing a tiny burp of oxygen; the very process which created the oxygen on our own planet and gave rise to more complex life forms. So, that's the kind of signature that we would want to see by catching the light filtering through the atmosphere. That's called transmission. Now that's very tough, but the James Webb Space Telescope is going to do that very thing for maybe larger planets, more like mini-Neptunes. Another technique that I'm looking forward to is imaging. What we really want, talking about big dreams, what we really want is to catch the light reflecting off of the surface of a planet.

Here you've got the Blue Marble on the left, an iconic image taken by the Apollo astronauts leaving Earth on the way to the moon. That's an image that was taken from 22,000 miles away; the first full disk image of our planet. And you can see the reflected light, the light from the Sun that's reflecting off the planet and into the camera of the Apollo astronaut.

On the right-hand side, it's the pale blue dot of Earth, taken by the Cassini spacecraft from 900 million miles away. It's unresolved; you don't see the surface features, but the information is there. If you look at the Apollo image, the way light reflects off of every element of that disk is different, right? The way it reflects off ocean is different than the way it reflects off land, which is different than the way it reflects off forest. And those features, those peculiarities, will be present in the light, even if it's unresolved. It will be present in the light if we can take it with enough sensitivity, we can spread it out into a rainbow, and we can see the indications of those surface features. It's tough; these planets are faint. 10 billion times fainter than the star they orbit. We are overwhelmed by the glare of the parent star. How are we going to see this faint, little smudge that is an Earth-like planet, potentially habitable Earth-like planet? Well, the way that we think about doing it is kind of like the way I would see you out here in the audience. I'd have to put my thumb over these lights. Oh, wow, that works! We block out the light of the parent star. The problem is, you know that the little planet, it's like a little gnat orbiting a big searchlight or a spotlight, right? A lighthouse; so, I take my thumb and I cover it and then, maybe I can see the gnat flying next to it. But light bends, it bends around obstacles; it still kind of introduces this diffraction, this interference, so I have to be careful about the way that I design my thumb, you know I need to be kinda fancy about it. But that kind of technology is being developed today as we speak, and here's a little clip showing some of that technology happening at JPL.

This is an animation of what the thumb would look like. You launch a system, a space telescope that has connected to it, a sunflower. The petals that you see unfurling are a star shade, that's the thumb that you hold up. You fly it out some thousands of kilometers away, and you use it to perfectly block the glare from the star, thereby revealing the faint gnats orbiting the lighthouse.

So, I'll end with this image. 500 light-years away, there is a star called Kepler-186 in the constellation of Cygnus; that's Cygnus Lyra region. It's a red star, a star that's cooler than our own Sun, and Kepler has found five planets so far orbiting that star. The fifth planet out, at an orbital period of about 192 days, is within the uncertainty the same size as the Earth to within 10 percent. So what you're seeing here, is not an image of that planet, remember Kepler does not take pictures of planets, it infers its existence and so we have to put a little bit of our imagination into this. We tell everything that we know to the artist and let him bring this world to life, but I ask myself the question, “You know, if you have water, you're likely to have at least simple life forms, simple microbes, maybe single-celled things; how does life begin? Does it begin with a spark, a sputter, a smolder? Does it evolve slowly? Or is it that when you have simple-celled organisms, microorganisms, when they take hold, does life begin by igniting, transforming the global landscape?”

We don't know which it is or if it's someplace in between. But what I know is we creatures, we are these creatures, these portals to the universe, we are the universe become self-aware, right? Our bodies are these portals to the universe observing itself and as such, by our self-awareness, by definition that means that by necessity, we reach out. So when we do find a planet that harbors life, that is a habitable environment, that has biosignatures, and this is possible within the next one or two generations, maybe two or three, by necessity, we are going to want to reach out. And I wonder what potential will be unlocked when we go, what potential will be unlocked when we connect. Thank you very much.