Could This Exoplanet Harbor Life?

Want to be a top notch candidate for hosting alien life? Then there's a few key requirements you should be aware of: Ideally, you're a large object like a moon or a planet; scientists suspect you also have an atmosphere and water; plus, you should orbit your star from a nice mid-range distance — in the "Goldilocks Zone" of habitability. Until recently, you would be competing against TRAPPIST-1 e. It's a planet outside of our solar system. TRAPPIST-1 e is also only 40 light years away, rocky and the same size as Earth, which prompted researchers to investigate whether it also has an atmosphere — and the potential for alien life. A team of researchers has been investigating TRAPPIST-1 e to learn more about its potential. Their answers, recently published in the Astrophysical Journal Letters, say a lot not just about this exoplanet, but about how scientists should refocus their hunt for alien life. Interested in more space science? Email us your question at [email protected] mailto:[email protected]. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:00Emily Kwong?

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• 1:27Emily Kwong?

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• 2:09Speaker 01

  Hey, short wavers. Regina Barber here. And Emily Kwong. With our biweekly science news roundup, featuring the hosts of All Things Considered. And today, we have the legendary Elsa Chang. Elsa!

• 2:22Speaker 02

  Thank you for having me yet again. So what are we learning about today?

• 2:26Speaker 01

  So Elsa, we're giving you an update on the chances of life on an Earth-sized planet that orbits another star. Will complicate the saga of the Black Death with a story of how it may have been driven by volcanoes. What? And why sick ants let nestmates destroy them.

• 2:44Speaker 02

  Ew, dark. Okay.

• 2:47Speaker 01

  All of that on this episode of Short Wave, the science podcast from NPR.

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• 3:39Emily Kwong?

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• 4:29Speaker 01

  All right, Elsa, where do you want to start?

• 4:31Speaker 02

  Let's start with the Earth-sized planet around another star. Gina, go.

• 4:36Speaker 01

  Okay, so astronomers have already discovered more than 6,000 exoplanets, and those are planets that are orbiting other stars, not our Sun. And some of them are more promising spots to look for life than others, like this exoplanet called Trappist 1E. And this planet is rocky like Earth, it's the same size, it's orbiting at a distance that's smack dab in the habitable zone of the star, sometimes called the Goldilocks zone.

• 5:00Speaker 04

  Yes, it's at this really interesting distance from its host star. It gets a little bit less light than Earth does, but way more than Mars does. If there's life on it, we have the best chances of detecting it if it's present on Trappist 1E.

• 5:12Speaker 01

  That's Sukrit Ranjan, the lead author of a recent study about Trappist 1E, published in the journal Astrophysical Journal Letters. Now, what Sukrit is saying is that we have the best chances of finding life there in the Goldilocks zone, as opposed to some of these other exoplanet systems.

• 5:27Speaker 02

  This is so fascinating. Wait, just remind me, what are like the ingredients that scientists look for when deciding whether there can be life on a planet?

• 5:37Speaker 01

  Well, the reason this zone is important is because it's not too hot, such that water evaporates off the surface, and not too cold, such that the planet would be covered in ice. Another key ingredient for life on a planet is having an atmosphere.

• 5:50Speaker 04

  It turns out to be really hard, if it has an atmosphere, for it not to be habitable.

• 5:55Speaker 01

  That atmosphere allows liquid water to stick around, which is definitely good for life. But Elsa, there are other places in our solar system that scientists are looking at for possible life that also have atmospheres like Earth, places like Saturn's moon Titan. So this study looked at Trappist 1E and the potential existence of Titan-like exoplanets.

• 6:13Speaker 02

  Wow, okay, so how do they go about doing that?

• 6:17Speaker 01

  So when Trappist 1E orbits its star, it occasionally passes between the star and us viewing it, sort of eclipsing the star. So when that happens, the starlight goes through the exoplanet's atmosphere, if it has one, and studying that light can show if the atmosphere has certain molecules like CO2 or methane. And CO2 and methane could be, but don't have to be, signs of life.

• 6:38Speaker 02

  Oh, so wait, does this exoplanet have CO2 and methane? I hope.

• 6:43Speaker 01

  Drum roll. Sadly, no.

• 6:45Speaker 02

  Oh, wah wah.

• 6:47Speaker 01

  A more in-depth investigation of Trappist 1E revealed no CO2 and found that there may be no methane either.

• 6:54Speaker 02

  Oh.

• 6:55Speaker 01

  Oh, and by the way, the study also noted that the majority of these Titan-like exoplanets called exotitans most likely lack an atmosphere entirely.

• 7:02Speaker 04

  The answer we came out to was, man, exotitans, great idea, not looking super good.

• 7:08Speaker 02

  OK, so is he saying habitable planets might actually be rarer than scientists previously thought?

• 7:14Speaker 01

  Well, at least these kinds of habitable exoplanets. And these scientists said that we really just need like better telescopes to get to the bottom of this.

• 7:21Speaker 02

  All right. OK, well, this next study is a bit closer to home, Planet Earth, but we're going to time travel for this one, right? To the Middle Ages.

• 7:29Speaker 01

  Yeah, yes. And to one of the most defining events of that time, the Black Death, which killed one-third to one-half of the population of Europe. And we have a pretty good understanding of what caused the Black Death.

• 7:41Speaker 02

  It was rats, wasn't it? That's what I always thought.

• 7:43Speaker 01

  Close, Elsa. It was a bacterium from Central Asia, spread by fleas on rodents that hitched a ride from the shores of the Black Sea to what is now Italy in 1347. And the reason, Elsa, that scholars think so many rats were hitching a ride to Italy that year had to do with food. Hannah Barker, a historian at Arizona State University, discovered there was a reopening of the grain trade between the Mongol Empire and Genoa in 1347.

• 8:10Speaker 05

  They thought they were doing a good thing, bringing food to hungry people. They didn't realize that they were also carrying bacteria.

• 8:16Speaker 01

  And this raised a question, like, why were Italian states worried about famine that year? Martin Bauch, a historian in Germany, has a really cool hypothesis. He thinks it might have to do with volcanoes that erupted a few years prior.

• 8:29Speaker 06

  There must have been a major volcanic eruption when sulfate is put into the higher strata of the atmosphere, up to the stratosphere, then circling the globe for up to three years, and then at some point coming down.

• 8:41Speaker 01

  His team hypothesized that volcanic activity in 1345 led to extreme rainfall. It also led to widespread flooding and ultimately crop failure throughout Europe.

• 8:52Speaker 02

  This is quite a story. Okay, so what evidence do they have? Like, how do you prove volcanic activity from seven centuries ago?

• 9:04Speaker 01

  Totally. It's really interesting. So Martin and his colleague Ulf Buntgen looked at ancient tree ring samples, which found bad growth conditions in the years leading up to the plague. They looked at ice cores containing unusually high deposits of sulfate aerosols, which suggests volcano. And they published their findings in the journal Communications, Earth and Environment.

• 9:24Speaker 02

  This is amazing. Okay, let me just make sure I understand this. Volcanic activity led to some sort of climate downturn, which led to crop failure, which led to grain imports coming in that brought all these rats carrying the bacteria to Italy, and then a bunch of people died.

• 9:41Speaker 01

  Yep, beautifully summarized. Now, this is just a hypothesis, of course, but it suggests that one of the biggest pandemics in human history could have been connected to the climate.

• 9:49Speaker 02

  That is so interesting. Okay, moving on to our very last topic. Sick ants calling for their own extermination? What?

• 9:59Speaker 01

  Yeah, it's a-

• 10:00Speaker 02

  That's sick.

• 10:01Speaker 01

  Yeah, yeah, it's a gory tale, but for the common good. Okay, so a recent study in the journal Nature Communications found that sick ants send chemical messages to their nestmates, signaling that they're sick. Then worker ants pick up those signals and destroy the sick ants before they infect the others. Because, you know, like, a fungal infection could take out the whole colony.

• 10:23Speaker 02

  Wait, so these ants are like self-sacrificing?

• 10:25Speaker 01

  Yeah.

• 10:26Speaker 02

  That is dark. Okay, how does this happen exactly?

• 10:29Speaker 01

  Yeah, okay, so it turns out worker ants are paying close attention to the pupae. That's the stage when juvenile ants are still in their little cocoons. And it appears that when pupae have an infection, like a fungus, they send out a chemical message calling for those worker ants to destroy them. One of the study authors, Erica Dawson, explained the process to us. She says first, the worker ants peel off the cocoon.

• 10:55Speaker 05

  And then they bite holes in the pupae. And then they spray informic acid. And this basically serves to disinfect the infected pupa because it kills off the fungus.

• 11:07Speaker 01

  And while the acid kills off the fungus, it also kills the pupae. So in effect, the pupae is essentially calling for its own death.

• 11:15Speaker 02

  Saying, hey, I'm sick. Kill me now before I get you sick too?

• 11:20Speaker 01

  Yes, that is the dramatic monologue of these infected ants. Though there is a plot twist. The team looked at pupae that would eventually become queens, like ants that start their own colonies. And they found out two things. First, that these queen pupae didn't release the signal even when they were infected.

• 11:38Speaker 02

  Why not?

• 11:38Speaker 01

  Future queens, just, they don't signal when they're sick.

• 11:41Speaker 02

  They're above the self-sacrifice.

• 11:42Speaker 01

  Yes, they are. And also, the infected future queens could fight off the infection on their own.

• 11:47Speaker 02

  Bam, true queens. Just like Emily Kwong and Regina Barber from NPR's Science Podcast, Short Wave.

• 11:56Speaker 01

  Thanks, Elsa. Elsa, thank you so much for coming to talk with us about science and calling us queens because we are news queens.

• 12:05Speaker 02

  You guys are queens.

• 12:06Speaker 01

  Podcast queen recognizes news queen.

• 12:07Speaker 02

  Your highnesses, it has been an honor to join you.

• 12:10Speaker 01

  You're always welcome in our realm.

• 12:12Speaker 02

  Deeply vows.

• 12:13Speaker 01

  Yes.

• 12:22Speaker 01

  You can hear more of Elsa on Consider This, NPR's afternoon podcast about what the news means for you. And for more science stories just like this one, follow Short Wave on whatever app you're listening to. This episode was produced by Rachel Carlson and Jordan Marie Smith. It was edited by Rebecca Ramirez and Christopher Intagliata. Tyler Jones checked the facts. Maggie Luthar was the audio engineer. I'm Emily Kwong. And I'm Regina Barber. Thank you for listening to Short Wave, the science podcast from NPR.

• 13:01Speaker 03

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