Could Life Exist on Newfound Alien Planet?

In a paper to be published in Astronomy & Astrophysics, researchers identified five possible planets around the star Tau Ceti. One of these alien worlds is within the star's habitable zone. Study co-author Steven Vogt discusses whether life could exist on the planet.

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IRA FLATOW, HOST:

This is SCIENCE FRIDAY. I'm Ira Flatow. One of the most sought after prizes in astronomy is another planet that might be like Earth, able to support life in a solar system similar to ours. And this week a team of astronomers announced a surprising discovery of five possible planets around Tau Ceti. That's a nearby star that is very similar to our own sun.

And one of the newfound planets in particular has astronomers buzzing. It's about four times more massive than Earth, but it orbits within the star's habitable zone, the Goldilocks zone, meaning an area that's not too hot, not too cold, where conditions may be just right for a liquid water to exist on the surface.

This announcement comes just a few weeks after a previous one, about the discovery of a possibly habitable planet in a different solar system. So what are the prospects of finding water or life on these planets? Steven Vogt is a professor of astronomy and astrophysics at UCO/Lick Observatory, University of California, Santa Cruz. Welcome back to the program.

STEVEN VOGT: Thank you, Ira.

FLATOW: I want to tell our listeners that they can call 1-800-989-8255 if they'd like to ask questions about it. And they can also tweet us @scifri, @-S-C-I-F-R-I. Let's go back a little bit. First, Dr. Vogt, you were involved in the exoplanet finding that was announced last month, correct?

VOGT: That's right.

FLATOW: Tell us about that one.

VOGT: Well, that's around a star called HD 10 - excuse me, 40307. I'm losing track of the numbers, there are so many stars now. And this is a system where we first tried out some of these techniques, where there were already several planets known around it, three planets known around it, and we found three more by basically being more clever in how we deal with the noise due to the star's surface activity.

FLATOW: And this was - you have a rating scale for how close to Earthlike they are correct?

VOGT: Yes, there is a rating scale set up by a fellow at the University of Puerto called the Habitable Exoplanets Catalog. It's easy to find on the Web. And he colleagues at the University of Washington and elsewhere have worked out the mathematics that describe how similar a planet might be to Earth and what its planet habitability index is.

And then they have a ranking of the top 10. So 4037G, which is the one we announced last month, ends up at number four on the scale.

FLATOW: Is that high, a higher number better or a lower number better?

VOGT: Higher number is better. Number is Gliese 581, that we talked about two years.

FLATOW: And the Tau Ceti planets, one of them, E, that you've mentioned this week, that comes in at number six?

VOGT: That's number six, and F is - there's actually two potentially habitable planets in the Tau Ceti system, yeah. There's Tau Ceti Number E, which is number 6, and Tau Ceti F, which is number nine.

FLATOW: Number nine? Tell us why that is so special.

VOGT: Well, these two planets both orbit in the classical liquid water habitable zone, and Planet E is just on the very inner edge of the habitable zone, and Planet F is just on the very outer edge.

FLATOW: Could these be rocky worlds like Earth?

VOGT: There's quite a bit of likelihood that it could be. We can't say for sure. We don't know the density of these planets or their actual diameters. We go from essentially models of all the other planets we have detected so far, and they come in certainly looking like they could well be rocky planets, or if - they might be rocky planets with some extended atmospheres or possibly a coverage of liquid water.

FLATOW: So you don't actually observe with the eye or a visible telescope actually see the planet itself?

VOGT: We don't yet, no. We don't have the capability to do that yet, though the next generation of telescopes, the James Webb Telescope, can certainly resolve these from their host star. The star is close enough, and the planets are far enough away from it that they could resolve these stars and these planets individually.

FLATOW: Would you be able to answer the question of whether there is life or water with the Webb Telescope?

VOGT: I actually haven't done the calculation, but if you can separate the light of the planet from the star, then you can do spectroscopy on it. And so you can look for the biomarkers of CO2 and methane and water and those kinds of gases, and that will tell you whether there's processes going on that generate oxygen and such, which tells a lot about whether there's biology going on on the planet.

FLATOW: This has been described as an unexpected discovery. Why was it so surprising?

VOGT: Well it was because we weren't particularly looking for planets. Based on the work we did on 40307, we realized that the activity of the star is masking a lot of the potential planet signals. So that sort of clued the lead author, Mikko, into developing a technique that can more carefully and more accurately model the activity due to spots and flares on the surface of the star.

And it - so what we decided to do then, since we didn't know anything about star activity, was to pick a star that had lots of observations, thousands of observations from multiple groups, but didn't have any known planets around it, figuring we would just be studying only the activity. And when we learned how to model that activity and removed it from the analysis, out popped five planets very unexpectedly.

FLATOW: Does this raise the hopes that, you know, you might be finding more exoplanets that are more like Earth because there seemed to be a little period going through here with astronomers that they were saying it may be a little more difficult than we expected, or there may not be as many in that sweet spot as expected?

VOGT: Yeah, I think the arc of discovery is showing us that there's actually a lot more than anyone would have hoped. And finding them this close and this soon and this easily, as we improve our techniques, is telling us that virtually every star has planets, and a lot of systems probably have planets similar to the kind we're seeing here.

And so yeah, that greatly raises the ante in terms of the likelihood that there are similar Earths out there around stars. There's more planets in the sky now than there are stars.

FLATOW: A couple of questions: Does a planet have to be like, quote-unquote, "like Earth" for it to be habitable?

VOGT: Oh absolutely not, absolutely. The biology extremophiles can exist over a wide range of temperatures and salinities and pressures and such. So no, it doesn't have to be like Earth. But that makes it easier for us to imagine that there might be life as we know it.

FLATOW: What's interesting to me, exciting to me, is the prospect of perhaps these stars are very close, are they not? They're...

VOGT: These are some of the closest stars. This one is the 19th closest star to us.

FLATOW: How close is it?

VOGT: It's about three parsecs away, about 12 light-years away, something like that.

FLATOW: So if there is intelligent life on that planet, and I'm just speculating here, it would be possible to communicate with them in real time almost, right, a lifetime, at least one person's lifetime if they could signal back and forth in 12 light-years?

VOGT: Well, and that's the reason that studying these nearest stars is so interesting. If you have a chance of contacting any intelligent beings on these things, you could have a two-way conversation easily within a lifetime around these nearest stars.

FLATOW: Or we should be hearing some of the radio noise that - of the kind that we generate, radio, TV, whatever, coming from their direction, should we not?

VOGT: Well, it turns out if you do the calculation, it's tough even from that distance to see just the hiss from NPR and the other radio broadcasts. But if they were sending out intentional beacons, that would be very easy to detect.

FLATOW: And that I guess is a commercial for us sending out intentional beacons for them?

VOGT: Absolutely.

FLATOW: Yeah, kind of search for extraterrestrial life. So do you have any other star announcements coming up soon that we might look forward to?

VOGT: Well, we're working on a number of systems. We're actually, we're doing a similar kind of analysis on Gliese 581, in the Gliese 581 system that we talked about a couple years ago, that is still very controversial. And we're applying this technique plus a lot more data to that system. That's number one on the list, to either confirm it or refute it.

So that'll be one of our follow-up things we'll be doing over the coming year.

FLATOW: Yeah, so others need to follow up what you've discovered and confirm what's happening.

VOGT: Right.

FLATOW: Dr. Vogt, thank you very much for taking time to be with us today, and happy holiday to you.

VOGT: You're welcome, thank you very much for having me.

FLATOW: You're welcome. Steven Vogt is professor of astronomy and astrophysics at the UCO/Lick Observatory at the University of California in Santa Cruz.

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