On a special episode (first released on Wednesday, June 26th) of The Excerpt podcast: The age-old question has been debated for centuries. Might we soon get an answer? The planet that is the current focus of international inquiry is called Gliese 12b, an Earth-sized exoplanet that’s only 40 light years away. The first step in answering this question has to do with determining a planet's habitability. In this respect, Gliese 12b shows some promise. What’s next on the road to solving one of mankind's oldest riddles? Michael McElwain, a NASA scientist at the James Webb Space Telescope center, joins The Excerpt to share insights regarding this revolutionary new development.

Hit play on the player below to hear the podcast and follow along with the transcript beneath it. This transcript was automatically generated, and then edited for clarity in its current form. There may be some differences between the audio and the text.

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Dana Taylor:

Is there life on another planet? The age-old question that has been debated for centuries might soon get an answer. Hello and welcome to The Excerpt, I'm Dana Taylor. The planet that is the current focus of international inquiry is Gliese 12 b, an Earth-sized exoplanet that's only 40 light years away. It might even be habitable. What's next on the road to answering these and other exciting questions? Joining us today to share insights regarding this exciting new development is Michael McElwain, a NASA scientists at the James Webb Space Telescope Center. Thanks for joining me today, Mike.

Michael McElwain:

Thanks so much for having me.

Dana Taylor:

You were part of this international team who discovered Gliese 12 b, how exciting of a moment was this for you? Was this a career high?

Michael McElwain:

Yeah, this is a tremendously exciting new exoplanet. Gliese 12 b is the nearest transiting temperate Earth-sized planet that we found to date. And this was actually, it was a long process for discovering this planet. So it was initially identified as a exoplanet candidate by NASA's TESS mission. That's a mission that's been operating for about six years now, looking at approximately 200,000 stars and is looking for this characteristic dimming of the star for when a planet passes in front of the star. And so TESS has actually discovered 7,000 planet candidates to date, about 400 of them have been confirmed and I was part of a team that confirmed the exoplanet status for Gliese 12 b.

Dana Taylor:

Let's get to some of the basics about Gliese 12 b. First, what is an exoplanet and what are the biggest factors you look for in determining a planet's habitability?

Michael McElwain:

So there are eight planets in our solar system orbiting the sun. Our sun is an average type star. There's planets orbiting other stars, and we call those other planets exoplanets. And we're actually in the middle of an exoplanet revolution right now. It's happening. The first exoplanet discovered was orbiting around the sunlight star was in 1995. And over the past 30 years, we've discovered over 5,000 exoplanets. So if you go outside at night and you look up at the sky and you're looking at different stars, we now know that on average every star has at least one exoplanet orbiting around it. And one in five of those stars have planets that are orbiting at the right separation where they could have liquid water.

Dana Taylor:

So as part of what helps determine a planet's habitability, does it have to do with whether liquid water exists or also atmosphere?

Michael McElwain:

There are a lot of factors that contribute to habitability. We think liquid water is an essential ingredient for life here on earth, and for complex life we think liquid water is required. It's the key element for chemical reactions that take place in animal and plant cells. For habitability on the Earth, there are a lot of factors. So we think that the atmosphere plays an important factor, we also think the Earth's magnetic field is an important factor as well.

Dana Taylor:

So if Gliese 12 b doesn't have an atmosphere, if that's the case, do we just move on?

Michael McElwain:

Interestingly, the Earth's initial atmosphere that it was formed with we think was stripped away. And so what we have now is actually called a secondary atmosphere, or in the case of the Earth, actually even a tertiary atmosphere. And so our atmosphere is primarily composed of material that was outgassed from the interior of the earth. We think that Mars and Venus had atmospheres that were also secondary atmospheres. For rocky exoplanets, we're just at the very beginning. We just now have the capability of observing these exoplanets and determining whether or not they have atmospheres. And Gliese 12 b is a terrific candidate to do those measurements to determine whether or not it has an atmosphere. Right now, the observations that we've made today, we don't know whether or not Gliese 12 b has an atmosphere. We think there's a very good chance that it does. This is a really key question for Gliese 12 b. We had the ability to make these observations with the James Webb Space Telescope that was launched at the end of 2021 and is now doing exoplanet atmospheric characterization. If there's time awarded to do these observations with the James Webb Space Telescope, we'll have a spectrum of Gliese 12 b's atmosphere in about two years.

Dana Taylor:

I was going to ask, without sending a team to the planet to do this research, how does your team go about answering these kinds of questions? Is the James Webb Telescope the only way to get the answers right now?

Michael McElwain:

The initial discovery of this exoplanet was using a method called the transit method. And so this system happens to be oriented such that the planet passes this directly in front of the star and actually blocks out some of the starlight. So some of the listeners might have participated in the total solar eclipse or observed that. So it's rather than blocking out the entire star, it's actually just a very small fraction of the starlight that gets blocked. So you could take on the order of 1%. Those systems that transit are actually amenable to characterization of the atmosphere. So we first see that the planet is transiting, then we have the ability to go back and make very precise measurements. Light that is emitted from the star passes through the atmosphere of the planet, if it exists, and some of that light is filtered and we can actually observe the composition of the atmosphere.

Dana Taylor:

So let's play a few hypothetical scenarios here. Let's say the Gliese 12 b ends up having an atmosphere similar to Earth's and it also has liquid water, where do you go from there?

Michael McElwain:

So for Gliese 12 b, we won't be able to determine if there's liquid water on the surface. So in the atmosphere we'll be looking for water vapor. We know based on our current observations that Gliese 12 b orbits in what we call the habitable zone, planets need to orbit at the right separation from their stars so they're not too hot and they're not too cold, so there can be conditions where liquid water exists on the surface. And we think that Gliese 12 b is in the range where it could have liquid water on the surface. With the James Webb Space Telescope, we will not be able to determine conclusively if there is liquid water on the surface. So what we can look for is signs of water in the atmosphere and other indications that the temperature is such that we could have liquid water on the surface.

Dana Taylor:

And are there other exoplanets that you're studying right now that might be habitable?

Michael McElwain:

So there are a handful of other exoplanets known that are transiting in a medieval to atmospheric characterization with the James Webb Space Telescope. And those are being observed as well. In fact, the James Webb Space Telescope just observed the very first atmosphere of a rocky exoplanet 55 Cancri e. So that was a exciting discovery. That planetary atmosphere was actually, we think has a magma ocean and there's some outgassing of material that's creating this secondary atmosphere. And so that's just the very first step. You had mentioned before whether or not we could actually travel to this planet, Gliese 12 b. So the planet we know is 40 light years from Earth, and that's actually interstellar travel is something that we haven't done before. We've sent probes to every planet in the solar system. And so that's enabled us to have new information about those planets. We know that the nearest star Proxima Centauri has a planet Proxima Centauri b that's also orbiting in the habitable zone.

We've measured that indirectly with a radial velocity technique. So we're unable to make atmospheric characterizations like we are with Gliese 12 b. But that object is only four light years away. And so there is a team that's working on sending probes to that Proxima Centauri b, that project's called Breakthrough Starshot. And what's happening there is they're actually very small spacecraft that would have a solar sail that are sped up by laser light that can speed them to about 20% the speed of light. And so if they were able to achieve those speeds with this fleet of small spacecraft, they could arrive at Proxima Centauri in 20 years. Then after they arrive, they could take data. It would take four years to send that data back to Earth. Gliese 12 B is 40 light years away. So it would take about 200 years to send the small spacecraft out to Gliese 12 b, and then it would take 40 years to send that data back. So that's a very long time to wait. We have observatories now that we're using like the James Webb Space Telescope, and we're also planning future telescopes that can make even more precise measurements and look for other exoplanets.

Dana Taylor:

So Mike, you're telling me to be patient. Does habitability at all answer the question of whether or not there is life on another planet?

Michael McElwain:

We now know that about 20% of stars have planets that orbit in the right separation such that they could have liquid water. We know that there are about 100 billion stars in our galaxy, and so that means that there are about 20 billion stars that have planets that are orbiting in the right separation, have liquid water. So there's a lot of opportunity for life to exist. Back in the early 1960s, there was a famous scientist named Frank Drake, and he actually came up with this pretty simple equation to estimate how likely it is for life to exist on another planet. And so you need to know the number of stars, the number of stars that have planets orbiting in this habitable zone, the frequency of which life exists on those exoplanets, and then the frequency of which life becomes complex and intelligent, and finally the frequency of the civilizations that exist now.

And so there's a tremendous abundance of exoplanets and opportunities for life to exist. So NASA has just started designing a new space telescope called the Habitable Worlds Observatory, and it is actually setting out to discover Earth-like exoplanets and study their atmospheres for signs of life. And so if you were to go far away from earth and observe its atmosphere, you would know that life exists here based on what you see in the atmosphere. And so we're applying the same principles to study other planets with direct imaging with this Habitable Worlds Observatory.

Dana Taylor:

And then what excites you the most about what you might discover with this project and other projects going forward?

Michael McElwain:

So the Habitable Worlds Observatory is NASA's next flagship mission. It's going to follow the Roman space Telescope that is set to launch at the end of 2026. And the goal of the Habitable Worlds Observatory is to study the atmospheres of at least 25 exoplanets looking for signs of life. And that is going to happen in the next 25 years or so and will help us answer this question of whether or not life is common in the universe and whether or not we're alone here in the universe.

Dana Taylor:

And what's your best guess?

Michael McElwain:

Yeah, I'm optimistic. I really think we as humans have thought that the Earth occupied this special space, and the more we've learned, the more we've been able to look. We know that now exoplanets are very common. We know that a lot of them exist in the habitable zones. And so I think that it's very likely we will find other Earth-like planets that show signs of life and humanity will be able to continue exploring and someday we will go to those other worlds.

Dana Taylor:

Mike, thank you so much for being on The Excerpt.

Michael McElwain:

Thanks for having me.

Dana Taylor:

Thanks to our senior producer Shannon Rae Green for production assistance. Our executive producer is Laura Beatty. Let us know what you think of this episode by sending a note to [email protected]. Thanks for listening. I'm Dana Taylor, Taylor Wilson will be back tomorrow morning with another episode of The Excerpt.