AILSA CHANG, HOST:
Time now for our science news roundup from Short Wave, NPR's science podcast. I'm joined by the show's two hosts, Regina Barber and Emily Kwong. Hello, hello.
REGINA BARBER AND EMILY KWONG: Hey, Ailsa.
CHANG: All right, so you have brought us, as always, three science stories that caught your attention this week. What are they?
REGINA BARBER, BYLINE: An update on the chances of life on an Earth-sized planet.
CHANG: Oh, cool.
EMILY KWONG, BYLINE: How the spread of the bubonic plague may have been driven by volcanoes.
CHANG: What?
BARBER: And why sick ants let nestmates destroy them.
CHANG: All right, let's start with the Earth-sized planet around another star. Gina, go.
BARBER: OK, 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.
SUKRIT RANJAN: 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.
KWONG: 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.
CHANG: 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?
KWONG: 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.
RANJAN: It turns out to be really hard, if it has an atmosphere, for it not to be habitable.
BARBER: That atmosphere allows liquid water to stick around, which is definitely good for life. But, Ailsa, 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.
CHANG: Wow. OK, so how did they go about doing that?
BARBER: 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.
KWONG: And CO2 and methane could be - but don't have to be - signs of life.
CHANG: Oh, so wait - does this exoplanet have CO2 and methane? I hope.
KWONG: Drumroll.
(SOUNDBITE OF DRUMMING)
KWONG: Sadly, no.
CHANG: Oh. Wah-wah.
(LAUGHTER)
KWONG: A more in-depth investigation of TRAPPIST-1e revealed no CO2 and found that there may be no methane, either.
CHANG: Oh.
KWONG: Oh, and by the way, the study also noted that the majority of these Titan-like exoplanets - called exo-Titans - most likely lack an atmosphere entirely.
RANJAN: The answer we came out to was, man, exo-Titans - great idea, not looking super good.
CHANG: OK, so is she saying habitable planets might actually be rarer than scientists previously thought?
BARBER: 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.
CHANG: 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?
KWONG: Yeah.
CHANG: To the Middle Ages.
KWONG: 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.
CHANG: It was rats, wasn't it? That's what I always thought.
BARBER: Close, Ailsa. 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.
KWONG: And the reason, Ailsa, 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.
HANNAH BARKER: They thought they were doing a good thing, bringing food to hungry people. They didn't realize that they were also carrying bacteria.
BARBER: 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.
MARTIN BAUCH: 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.
BARBER: His team hypothesized that volcanic activity in 1345 led to extreme rainfall. It also led to widespread flooding and ultimately crop failure throughout Europe.
CHANG: This is quite a story.
BARBER: Yeah.
KWONG: Yeah.
CHANG: OK, so what evidence do they have? Like, how do you prove volcanic activity from seven centuries ago?
KWONG: 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.
CHANG: Wow.
KWONG: And they published their findings in the journal Communications Earth & Environment.
CHANG: This is amazing. OK, let me just make sure I understand this. Volcanic activity led to some sort of climate downturn...
BARBER: Yeah.
CHANG: ...Which led to crop failure...
BARBER: Yep.
CHANG: ...Which led to grain imports coming in that brought all these rats carrying the bacteria to Italy, and then a bunch of people died.
BARBER: Yep.
KWONG: 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.
CHANG: That is so interesting. OK, moving on to our very last topic - sick ants calling for their own extermination. What?
BARBER: Yeah, it's like...
CHANG: That's sick.
BARBER: Yeah. Yeah, it's a gory tale, but for the common good, OK? 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.
CHANG: Wait, so these ants are, like, self-sacrificing?
KWONG: Yeah.
CHANG: That is dark. OK, how does this happen, exactly.
KWONG: Yeah. OK, 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.
BARBER: Ouch.
KWONG: One of the study authors, Erika Dawson, explained the process to us. She says, first, the worker ants peel off the cocoon.
ERIKA DAWSON: And then they bite holes in the pupae, and then they spray in formic acid. And this basically serves to disinfect the infected pupa because it kills off the fungus.
BARBER: 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.
CHANG: Saying, hey, I'm sick - kill me now before I get you sick, too?
KWONG: Yes, that is the dramatic monologue of these infected ants.
(LAUGHTER)
KWONG: 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.
CHANG: Why not?
KWONG: Future queens just - they don't signal when they're sick.
CHANG: (Laughter) They're above the self-sacrifice.
KWONG: Yes, they are. And also, the infected future queens could fight off the infection on their own.
CHANG: Bam. True queens.
(LAUGHTER)
CHANG: Just like Emily Kwong and Regina Barber...
KWONG: Yeah. Wow.
CHANG: ...From NPR's science podcast Short Wave.
KWONG: Thanks, Ailsa.
CHANG: Which, everyone, you can follow on the NPR app or whatever podcasting app you want for new scientific discoveries. Thanks to both of you.
BARBER: Thank you.
KWONG: Thank you, Ailsa.
(SOUNDBITE OF LOLA YOUNG SONG, "CONCEITED") Transcript provided by NPR, Copyright NPR.
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