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Not One, but Three 'Goldilocks Planets'?


This is SCIENCE FRIDAY. I'm Ira Flatow. It's been almost three years since astronomers found the first planet outside our solar system they called a Goldilocks planet, meaning that it's not too close, not too far, but just the right distance from its sun to potentially sustain life. And since then, more of these just right planets have been found, one at the time.

But a couple of months ago, the Kepler telescope found two in a distant solar system. And just this week, researchers announced they had found three habitable planets orbiting just one star and it's only 22 light years away from us. So how did the scientists manage to find three Goldilock planets at once? What is the potential for life on these planets? Can we detect their atmosphere? Presence of water just yet?

Joining me now to talk more about it is my guest, Rory Barnes is research scientist at the University of Washington, member of the NASA Institute of Astrobiology's virtual planetary laboratory. He joins us from KUOW there in Washington. Welcome to SCIENCE FRIDAY.

RORY BARNES: Thank you, Ira.

FLATOW: How - tell us how do you discover these planets?

BARNES: Well, these biplanets, in particular, were discovered through an approach known as the radial velocity method. And this is a method by which we observe the star, actually, move in response to the gravitational pull of the planet. So we've monitored the position of the star, and if we see it start to move and those movements seem consistent with the presence of a planet, then we can say, aha, there is, in fact, a planet there. And in this case, we saw lots of different signals. And so we were able to determine that they were, in fact, three of these planets in the Goldilocks zone.

FLATOW: How many total planets did you find at that star?

BARNES: So we know for sure there are six. There's very good evidence for a seventh. So it's certainly a full system. There's a lot of planets already in this particular star.

FLATOW: Wow. And what makes these three Goldilocks planets?

BARNES: Well, it's just what you said in the intro that they are the right distance from the star where we think the energy from the star is such that it cannot overheat the planet and not, you know, leave it too cold so that the water on the surface can actually be in a liquid form. And we think that on - we know on Earth that all life requires liquid water. And so these planets being in sort of this sweet spot makes us excited as astronomers and astrobiologists, because we think that these planets, therefore, have the potential to host liquid water and therefore, maybe life.

FLATOW: 1-800-989-8255 is our number, if you want to talk about these Goldilocks planets. You can also tweet us, @scifri. Do the planets have to be a certain size or composition to be these just right planets?

BARNES: We think so. So these - the critical thing about some of these planets, as opposed to others that have been found before, is that they seem to have a low mass. And low is, of course, relative. These are all more massive than our Earth, but these are all less than 10 times as massive as the Earth. And we think that that's an important range because if they were larger, we might think they'd be more like Neptune or Jupiter, and where they'll have these very large atmospheres made of hydrogen. But these planets look like they have a low-enough mass that maybe they can't hold on to that hydrogen. And so they might have atmospheres that are more similar to the Earth.

FLATOW: Mm hmm. Do they have any moons around any of these planets?

BARNES: Almost assuredly no.


BARNES: These - it's particular to this kind of configuration. These planets were found around a low-mass star. It's about a third the mass of our sun. And because they were close to their star, there's actually some gravitational forces that would likely remove any moons that might have formed, originally, from the planets. They would either have been repelled away and sort of lost into space or they would've, actually, collided with the planets themselves over time.

FLATOW: Mm hmm. The study calls these planets super-Earths. What does super-Earth mean?

BARNES: Yeah. It does not mean that they are better than the Earth.


BARNES: Although they might be. We don't really know yet.

FLATOW: We don't know.

BARNES: But they don't want to - we don't want to exclude that possibility.

FLATOW: All right.

BARNES: But all we mean by super-Earth is it's something that is larger than the Earth. So in this case, these planets are between about two and 10 times the mass of the Earth. And so they're super-Earths, but we want to make that distinction that they are - we use that term Earth because we don't want people to think of them as being gas giants...


BARNES: ...like Jupiter and Neptune in our solar system.

FLATOW: And how old is that solar system compared to our solar system?

BARNES: Well, that's a great question. I don't think we really have a good handle on it. It turns out that measuring the ages of stars is an extremely challenging endeavor. I can say, with good confidence, that they are between two and 10 billion years old. So that's a nice wide range for you.

FLATOW: That's pretty wide. Yeah.

BARNES: Yeah. So that's unfortunately just where we're at. I think a lot of indicators that we found for this system suggest that it's probably older than our own sun.


BARNES: But, you know, again, I don't want to speculate too much. But, you know, I - we do know its old, but we just don't know how old.

FLATOW: Well, the fact that it's old, at least, let's say our - let's give it a, right in the middle, a ballpark of our age, of our solar system.


FLATOW: And it's only 22 light years away, and you'll see what I'm driving at here - could it have intelligent life there that we might - in 22 years, you could get a signal back and forth in one lifespan.

BARNES: Right.


BARNES: You know, sure, there could certainly be intelligent life there. We don't see any evidence for that at this point, so I don't want to get anybody's hopes up but, you know, sure. I mean, it probably is old enough that, you know, there has been time for intelligent life to develop. But again, you know, we don't know how intelligent life develops in general. We see - have one example, and we don't really know how we developed intelligence. So it's hard to speculate exactly on another planet like that.

But it is old enough that perhaps if we had been living on one of these planets that, you know, we would have had enough time to form into developed intelligence.

FLATOW: Todd in St. George, Utah - let's go to the phones - welcome to SCIENCE FRIDAY.

TODD: Thanks. Hey, I was wondering, if you were on another planet or if you were on that star looking at the Earth, would Venus be in the Goldilocks zone?

FLATOW: Of our solar system.

TODD: Yeah.

FLATOW: Yeah, great question.

BARNES: Yeah. That is a great question. And I - but in our understanding, you know, we kind of define the habitable zone based on our own solar system because we have our own knowledge of what planets are habitable in our solar system. And we often define sort of the most optimistic version of the habitable zone you can imagine as the orbit of Venus just because we know that it looks like - if you are at that distance, then you're fried.

You're in this runaway greenhouse state, and your surface temperature is hundreds and hundreds of degrees. So I think it would, you know, it's kind of an interesting question, but I think, at the same time, our definition of the habitable zone is driven by our own solar system. So I think it would depend what planets are habitable in that solar system is, what their definition of the habitable zone might be. So we - Venus would be borderline, though, I would say, would be their guess.

FLATOW: Good question. Thanks for calling, Todd.

TODD: Thanks a lot. Appreciate it.

FLATOW: Yeah, yeah. If we were to look up at the night sky, could we see these planets ourselves?

BARNES: Yeah, maybe. If you had really great vision and were in a very, very dark site and waited all night, you might be able to see it. It's sort of right at the edge of what's visible to the human eye. But I still think it's fascinating to go out at night. It's a really easy location in the sky to find.

FLATOW: Where is it?

BARNES: It is right in front of the Stinger and Scorpio. And so by chance right now, Scorpio is up and visible from most of the Northern Hemisphere. So if you go out tonight and it's clear, go and look just in front of the Stinger and Scorpio. Scorpio is one of the easier constellations to find at night. It's just right in front of it. So it's in a really cool spot at the sky.

FLATOW: And the star is called?

BARNES: Gliese 667C. Isn't that exciting?

FLATOW: Another romantic name.

BARNES: I know.

FLATOW: Yeah. Do you ever change the names?

BARNES: We're scientists.


BARNES: You know, we don't do romance.


FLATOW: We're scientists. We don't do romance. I know. I've seen Sheldon Cooper. He can tell you a lot about that. How easy is it? How do you go searching? What - was this discovered by accident, or is there a certain spot in the sky say, hey, you know, it's like going through a fishing pond, I know this is where they're biting?

BARNES: Well, there's a few reasons why this particular star was looked at. One, as you mentioned, it's only 22 light years away. So it's, in fact, quite close. Relatively speaking, you know, I know 125 trillion miles doesn't sound so close in our everyday experience but, you know, astronomically speaking, it is quite close. So it's one of our solar neighbors. So that made it an interesting target. Additionally, this star has been examined for years. And this wasn't the first time that any planets were discovered around this particular star.

A couple of years ago, two or maybe three stars were discovered. There was one that was a little bit iffy that we confirmed in this study. So this was one that we already found a potentially habitable planet orbiting, and so it then became - it took the subject of more intense scrutiny and so it was - after the accumulation of more and more data that we were able to determine that there were more than just one planet in the habitable zone here but in fact three.

FLATOW: Ricky in New York, hi. Welcome to SCIENCE FRIDAY. Hi, Ricky.

RICKY: Hi. Thanks for taking my call.

FLATOW: Mm-hmm.

RICKY: So one of the big reasons that we're looking for Goldilocks planets is, of course, to see if there's other life there. And if there is other life there and it's more advanced than ours, then they - why haven't they already found us? Why aren't they doing the same things looking for other Goldilocks planets and, I guess, contacted us then?


BARNES: Yeah, alien sociology is not my specialty. I don't really know, you know, what's going on. I mean, this is a classic problem in astronomy known as Fermi's Paradox. There should be lots of planets throughout the galaxy that are significantly older than the Earth by billions of years. And so, you know, this is a question that's been posed for 50 or 75 years or so now about well, if life is out there, why haven't they found us already 'cause they presumably had billions of more years to evolve and develop technology. So, you know, I don't know.

FLATOW: Good question. Thanks for calling, Ricky. Maybe you can go up and take a look at - well, in New York it's tough to see it, streetlights (unintelligible)

BARNES: Yeah, it's a little low from there, but yeah, you can see it from there.

FLATOW: Thanks, Ricky. Have a good weekend. 1-800-989-8255. Let's to got the phones. To Tom in San Anton(ph). Hi, Tom.

TOM: Hey, Ira.

FLATOW: Hey, there.

TOM: Hey, you know, I know you're all talking about supersized planets and all that, and I'm know I probably not, you know, not catching up just quite yet but, I mean, is it considered a class-M planet? I mean, is that a term that means...

FLATOW: What - Tom, what does that mean to you, a class-M planet?

TOM: A class-M planet would support life. And who knows what life it could be? You know, I mean...

BARNES: Yeah. So we...

TOM: Like, I mean, like what kind of life lives on liquid methane on Titan? I don't know. It's...

BARNES: Yeah. Well, the short answer is we don't know either. There's a lot of possibilities out there, but what I can say is that these - that we think that life requires a whole lot of ingredients and phenomena to occur to allow the formation and evolution of life. And we don't have all the information yet on these planets. What we do know is that they look like they have about the right mass, and they're about the right distance from their star.

So these are sort of - you should think of these as the first couple boxes you might check in your laundry list for how to form an M-class planet. So we don't know if they even have water on them yet. We just - we don't know if that's the case.

So all we know is that, hey, the things that we can see today, they have at least met those requirements. And from now - from here on out, we need to try and figure out to more of these issues and hopefully we can resolve them and keep checking boxes and hopefully figure out if they are, in fact, habitable planets and maybe even inhabited.

FLATOW: Hmm. It's something to think about tonight.

TOM: Absolutely. I hope.

FLATOW: Yeah, yeah. That wouldn't - that would be fun, Tom, wouldn't that?

TOM: Right.

FLATOW: Yeah. Thanks for calling.

TOM: I appreciate it.

FLATOW: 1-800-989-8255 is our number. We're talking about extrasolar planets on SCIENCE FRIDAY from NPR. I'm talking with Rory Barnes.

How does this one compare to other Goldilocks planets, for example, how do you - how do this relate to the Kepler findings? This was not made with Kepler, right?

BARNES: That's correct. It was not made with the Kepler telescope. It's, in fact, quite a different process by which these planets are found as compared to Kepler. The Kepler spacecraft look specifically to see if planets cross in front of their stars as seen from the Earth. This is a phenomenon that we call a transit.

So what the Kepler spacecraft does is it just looks at these stars and looks for a periodic dimming of light. And that might be the telltale signature of a planet.

So in that case, you determine the period of the orbit, how - what the year on a planet is, and you also determine its physical size. But for these planets that we've discovered, it's kind of completely, you know, perpendicular kind of discovery and that we just measure the period again, the year of these planets but we - well, we can't tell their size. What we can tell is their mass.

FLATOW: Mm-hmm.

BARNES: So that's two different bits of information that we'd really like to know. If you have both of those bits information then you can determine the density, and then you can make that really critical step, which is are these planets made of rock or are they made of gas. So what we really want is to find the planet that is the perfect marriage of these two discoveries that we can both see the radius and the mass of them.

FLATOW: All right. Let's go back to Texas. To Joshua in Austin. Hi, Josh.

JOSHUA: Hey. How it's going?

FLATOW: Hey there.

JOSHUA: You actually just answered my question. To some degree, I was really curious about the transit thing. I didn't know if you (unintelligible) can lead to the other, if you can find these starts initials by, you know, the wobble technique but then watch them typically to see, you know, any of the planets' transit.

FLATOW: Could - yeah, could Kepler look at this now?

BARNES: Well, unfortunately, Kepler can't for two reasons: One is that it stares at one particular point of the sky so - and it's not going to move. And, of course, the other reason is that it died. So right now it's not working so we can't do that either.

It's possible that it could be resurrected and maybe use to look at some - look at the system. But what we - but you really want - but hit the nail on the head that we do really do want to try and put the two together in trying - put the two methods together and try and see if we can determine at these planets' transit.

And then that gives us a lot more information, and it also provides with us with a great opportunity to try and follow up and check out the atmospheres of these planets and see if they do have the right ingredients for life.

FLATOW: Do you have the tools to be able to do that with the way you look at it?

BARNES: Sure. Yeah. So the next step will be to actually try and search for these transits of these planets. So that probably has to be done from space. And there are spacecraft that have the capabilities to detect to transit. So at this point we don't if they are transiting but that will be something we're going to be following up on.

FLATOW: So it'll be great to have another Kepler up there somewhere.

BARNES: It'd be great to have lots of Keplers up there. But, yeah, right, it would be - yeah, like - and, in fact, there's a plan to do that. NASA's next Kepler-like mission is called TESS. And it is scheduled to launch in about four years, and it's going to basically do Kepler kind of observations over the entire sky. So we should get a lot more planets from that method soon.

FLATOW: And just looking at these other exoplanets, help us understand anything about ourselves or they just still hunting for extra life out there?

BARNES: Well, I think to some are both, I mean, they are certainly oddities in some way, but then at the same time it does help put our solar system and ourselves into context in the galaxy.

When we find these other planets and we see their myriad of properties, we can start to see how does the Earth fit in, how is the Earth special and how is it common. And hopefully, over time we can find enough of these planets in the Goldilocks zone where we can start to figure out, well, what really are the requirements for life, what - where do we really want to focus our efforts because, you know, at this point our technology is not advanced enough that we can just go and make these observations of atmospheres and discoveries of exoplanets cheaply. It's a really challenging endeavor.


BARNES: And so anything we can do to kind of help guide our search for life in the universe is helpful. And I think as we make that journey towards finding life beyond the Earth, that'll only necessary reflect back on us and make us understand where we're coming from and what really it means to be here on planet Earth and be alive and intelligent.

FLATOW: Great Kepler for the weekday and something to thing about this weekend. Rory, thank you for taking time to be with us today.

BARNES: That was my pleasure, Ira. Thank you for having me.

FLATOW: You're welcome. Rory Barnes, research scientist at the University of Washington, member of the NASA Institute of Astrobiology's Virtual Planetary Laboratory. Transcript provided by NPR, Copyright NPR.