Newly Discovered Exoplanet Ripe For Life

Gliese 581g, a planet orbiting the dwarf star Gliese in the constellation Libra, is Earth-like in a few key ways. It's not much bigger than Earth, and its temperature seems mild enough for liquid water. Steven Vogt, of the University of California, Santa Cruz, explains how he found the planet.

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IRA FLATOW, host:

When it comes to porridge, Goldilocks was looking for a bowl that wasn't too hot, wasn't too cold - you know what it was - and astrobiologists like their exoplanets the same way, and astronomers may have dished up just that for them.

Reporting in The Astrophysical Journal, astronomers say that they have found a new planet that seems just right. It's called Gliese 581g, such a nice name for a new little planet. It's in the constellation Libra, about 20 light years away, so no one's going there at any time soon. And its distance from the sun makes it ripe for having liquid water on its surface, the astronomers say. And it's what's making them so excited.

And here to tell us more about the newly found planet is one of its discoverers. Steven Vogt is a professor of astronomy and astrophysics at the Lick Observatory at the University of California, Santa Cruz. Welcome to the program, Dr. Vogt.

Dr. STEVEN S. VOGT (Professor of Astronomy and Astrophysicists, Lick Observatory, University of California, Santa Cruz): Good morning, Ira.

FLATOW: Why is this planet not too hot, not too cold, just right for you?

Dr. VOGT: Well, an important ingredient for life of the kind that we think we understand - carbon-based life, organic life - is that water exists on the surface of a stable place for billions of years in liquid form, 0 to 100 centigrade or 32 to 212 Fahrenheit. It's difficult to get that exact temperature range in the universe. You're either out between the stars and you're at basically 2.7 degrees Kelvin and your atoms are hardly moving; or your near a star, in which case you'll fall in and explode into a cloud of plasma. You won't be long around the universe.

So being in an orbit around a star at just the right distance is an extremely important place to be if you're life.

FLATOW: Mm-hmm. And so scientists have been quoted as saying that they're really quite sure - very, you know, they like to stake their reputations, I guess - that this planet may really have water on it. And if it has water, it might have some form of life on it.

Dr. VOGT: Yeah, we don't have any direct evidence that there's water, but we do know that there's water all through our solar system. There's water on the moon now, water on the Earth, of course, water in the clouds of Venus, a lot of water on Mars...

FLATOW: Mm-hmm.

Dr. VOGT: ...under the surface probably, in the moons of Jupiter and Saturn and also at in the interstellar medium. There's some characteristics about this particular system that also tell us water is probably there too. These planets - there's so many planets that are close in, we think they probably migrated from farther out where they would have formed in what's called the ice area where the water would exist in liquid form.

FLATOW: Mm-hmm. Now one of the - some of the excitement about this is that scientists have been saying, gee, we found this so quickly, it took us only 11 years.

Dr. VOGT: Well, and that was - that's basically my takeaway message from the thing, is not that it's the first. Somebody will always be the first. The point is that when I look at this discovery and I began to think about what it means, what it really means is we found this way too soon, way too nearby, which means we're either just incredibly lucky and we won't find another one again for a long, long time, if you believe that, or if you're like myself and you don't believe in luck, you realize the statistics are telling you that there's probably a lot of these things out there.

FLATOW: Mm-hmm. Yeah, you know, there have been - there's been debate over the years about whether the Earth is such a privileged position and that we're not going to find all those planets with possible life on it that the Drake equation says we might. But now you're - you seem to be saying that it might be more abundant than we thought, at least finding those planets.

Dr. VOGT: That's right. I think the - what this is telling us is that these kinds of places, stable orbits, stable planets and stable orbits that are about the right size and the right temperature to have liquid water for these kinds of things to occur are probably a lot more common than we had dared hope. And so that's the message of this...

FLATOW: Mm-hmm.

Dr. VOGT: ...particular discovery.

FLATOW: How did you find this one? How do you find these planets?

Dr. VOGT: Well, we have a target list of about 1,500 stars that we've been monitoring for some 15 years. In the last four years or so, as we've begun to realize, largely based on results from a competing Swiss group, that the number of planets is really quiet high. The incidence of planets is high around stars. We began to focus our search mainly on the nearest stars, and particularly on N-type stars, stars that are smaller than the sun, knowing that that's where we'd probably likely find habitable planets. So we've been focusing on about 400 stars with great detail and just trying to get enough observations to be able to see these really weak signals.

FLATOW: Can you actually see the planet itself or do you look for evidence that the planets are there?

Dr. VOGT: No, we don't ever see the planets themselves. I mean, we have now gotten some direct images of planets through various techniques. They're giant planets, very young in their evolutionary scenario. But most of the planets, the 500 planets that have been detected out there have no images. They simply are sensed by watching the effect that they have on the star that they orbit. They cause the star to move on - in its own little orbit. And we can sense that.

FLATOW: And how many - this is a little planetary, sort of a little solar system of itself that you found. There's more than this one planet in it, correct?

Dr. VOGT: Right. The Swiss had already found four planets in the system, and what we added were two more basically. And if you look at this system, it's kind of - it's eerily reminiscent of our own solar system in several ways: One, the orbits all very nearly circular, which is like our own solar system. There's an inner clutch, kind of a tight inner clutch, a group of sort of like four or five planets in pretty close and then kind of loner, much farther out. So this solar system looks kind of the same way. It would have like sort of like a Jupiter farther out.

But the whole thing fits within the orbit of our Earth, basically. If you could put our own solar system on top of it, it would all be within the orbit of our Earth. So it's a scaled down version of our own solar system in some ways.

FLATOW: You made a statement and you've been quoted that you think the chances of life on this planet are 100 percent.

Dr. VOGT: Yes. I've been roundly criticized for that, and I'm taking a lot of flak for that. You know, I guess I should have taken the Zeno's paradox answer, which is if you take a half a step towards a wall each time, you'll never get there. And so maybe I should have used something like 99.999 or whatever. But I tried to qualify that. Basically, that is my personal opinion. It's no better or worse than anyone else's and someone asked me for my personal opinion, so I gave it. But I feel quite certain that the chances are very, very high that there - that life could take a foothold here. In fact, many of my colleagues are saying it's much easier for a life to take a foothold on this planet than it was on the Earth.

FLATOW: Because?

Dr. VOGT: Well, there's a lot of reasons for that. One of the reasons is that it's slightly more - it has slightly more gravity than the Earth. So it would probably hold on to its atmosphere better. Another reason is that it probably has a little more internal heat from tidal heating and from just having more mass. So that would make its plate tectonics more efficient. And that's important in maintaining the carbon-dioxide cycle or carbonate-silicate cycle. So there's a number of things like that that go into it - have to do not only with the size of the orbit but also the mass of the planet.

And the third thing is stability. This system would offer a large range of very stable, what I would call eco-longitudes. Since it's tightly locked to the star probably, it has one side that faces the star all the time and is always in daylight. The other side faces the dark sky, and is always in night. That's where the astronomers live. And then you have everything else in between.

So there's a wide range of temperature - temperatures available, climates on the surface that you could pick by just picking your longitude. The most pleasant place would be right along the terminator, the line between light and dark. And at that place, you'd be right at a nice intermediate temperature and the sun, or your star, would always be sitting right on the horizon. You'd have eternal sunset or sunrise, depending on whether you're an optimist or a pessimist.

FLATOW: So you're sticking by your prediction?

Dr. VOGT: Well, you know, I'm - it's - I have no crystal ball for any of these things. But this is as good as it gets in terms of having the conditions for life. And I, personally, myself, believe just based on how fast life appeared in under the incredibly difficult situations that it occurred - probably multiple times on Earth early on - that it's pretty hard to stop life when you give it half a chance.

FLATOW: Yeah. I remember that line from "Jurassic Park": life will find a way. Yeah.

Dr. VOGT: Yes, yes. I think so.

FLATOW: Yeah. All right. Well, thank you for taking time to be with us. And good luck with your planet.

Dr. VOGT: You're welcome.

FLATOW: Will we give it a different name, do you think so?

Dr. VOGT: Well, the name I use is my wife's name, Zarmina's(ph) World. I think that's a lot more euphonious than Gliese 581g.

FLATOW: All right. Zarmina's World.

Dr. VOGT: Yeah.

FLATOW: Okay. It sounds like - it's got this nice ring to it. We'll stick with that.

Dr. VOGT: Sure.

FLATOW: Thanks, Steven.

Dr. VOGT: Okay, Ira. And nice to be with you.

FLATOW: And thank you. Steven Vogt is a professor of astronomy and astrophysics at the Lick Observatory at the University of California at Santa Cruz, talking about Zarmina's World.

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