You’ve heard the news! Astronomers are reporting the discovery of biosignatures at K2-18b. Is this proof of life or should we all be more skeptical? It’s in the news and people are claiming aliens… but is it aliens? Let’s see what the data actually says.
Show Notes
- Discovery of K2-18b
- Habitable Zone
- Planet Characteristics
- Planet’s Composition
- Red Dwarf Star Activity
- Hydrosian World Definition
- Hubble Telescope Observation
- Molecular Complexity
- Atmospheric Composition
- Technological Advancement
- Spectral Analysis of Exoplanet Atmosphere:
- Dimethyl Sulfide as a Potential Biosignature
- Follow-up Observations for Clarification
- Biosignature Search
- JWST Observation
- Media Coverage
- Scientific Significance
- Exoplanet Atmosphere Composition
- Potential Biological Implication
- Dimethyl Sulfide in Space
- Skepticism in Scientific Research
- Red Flag in Scientific Claims
- Importance of Data Reprocessing
- Alternative Explanation for Atmospheric Composition
- Exoplanet Classification
Transcript
Fraser Cain: Astronomy Cast, Episode 754 What’s Happening with K2-18b? Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know.
I’m Fraser Cain. I’m the publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of Cosmos Quest. Hey Pamela, how are you doing?
Dr. Pamela Gay: I am doing well. It is owls being very loud stage of spring here. What stage have you reached?
Fraser Cain: I’ve reached maximum tulip in my garden, deer assaults on my garden, which now I think I’ve got them fended off at this point, but I say this every year, and of course they just wait and bide their time and feast on my happiness. But I have something that I wanted to get off my chest here, which is that you may not know this, but I’m the publisher of Universe Today.
Dr. Pamela Gay: Yes you are.
Fraser Cain: Yes I am.
Dr. Pamela Gay: You really, really are.
Fraser Cain: This is a space news website, which you’re going to see its articles come up all the time in Google News and Apple News and on Reddit and around the Internet. I also have a YouTube channel where I come on and I talk about space news, and I interview new patrons that come on to Universe Today and I’ll talk about, they’ll say, ask where they found me. They found me on AstronomyCast.
They originally started listening to AstronomyCast, and then they admit that they never realized that I did anything else other than be the co-host on AstronomyCast, that they didn’t realize that I was also the publisher of Universe Today, and I literally say it every single episode. Every episode. I am the publisher of Universe Today.
I have a day job. I run a space news website. We produce 10 articles a day about space and astronomy.
We are one of the most popular space news websites on the Internet. We are breaking tons of stories. That’s what we do.
I don’t know how much louder I can say this, but I just need to get this off my chest. I am the publisher of Universe Today.
Dr. Pamela Gay: He really, really is. The two of us have to have day jobs because your Patreon contributions go to paying Ali Rich and Aviva to maintain all the stuff you see.
Fraser Cain: We don’t take any money from this. You and I receive no paycheck, no salary, no cut. We just do this for the lulz.
Dr. Pamela Gay: My day job is CosmoQuest, and I pick up consulting gigs left and right.
Fraser Cain: Voiceover work.
Dr. Pamela Gay: Yeah.
Fraser Cain: Yeah.
Dr. Pamela Gay: I will voiceover if you wish me to. And then you are out there doing, you do the best interviews in our profession, I think.
Fraser Cain: Thank you. I appreciate that. Well, of course, this is the training.
You are the training. Does that ever occur to you, that you’re the person who I trained all my interviewing on? That is fair.
Yeah, that’s you. All right. You’ve heard the news.
Astronomers are reporting the discovery of biosignatures of K2-18b. Is this proof of life, or should we all be more skeptical? All right.
Hmm. This has been a week, a month, a few weeks now.
Dr. Pamela Gay: It all started in 2015, so it’s been a decade.
Fraser Cain: Yes. It has been a decade. It all started with the launch of the Kepler spacecraft, so it’s been two decades.
Fair. And the number, 18. It was early on in one of the planets that Kepler detected.
All right. So, man, I don’t even know where to start on this. So why don’t you unfold the story as you understand it going back for this decade?
Dr. Pamela Gay: All right. So back in 2015, the Kepler mission detected a red dwarf star, a little tiny, itty-bitty little red dwarf star that had something transiting in front of it. They measured the period.
The period was, today is going to be a I look at my notes kind of day. The period of this was 32.9 days, which for a red dwarf star, which is putting out just a few percentage of the amount of light our sun puts out, that close in 32.9 day period put this world that kept passing in front of its star into the habitable zone, that distance from the star where liquid water is able to exist. And in fact, this world at this distance around this itty-bitty tiny star is receiving about the same amount of energy per square meter on its surface that the earth is receiving.
Right. So that was the discovery. Now, when you find a planet going around an itty-bitty little tiny star that is fairly close, it’s about 124 light years away, that is fairly large, it’s 2.3 times the radius of the earth, and it isn’t huge. It’s 8.9 times the mass of the earth. So this is what we call a sub-Neptune or super earth. We’re still trying to figure out the definitions here.
Fraser Cain: And one of the things that’s kind of interesting about this world, even though it is that much bigger and that much more massive, the density works out that the actual surface gravity is not significantly higher than what it is on earth. So rockets would work. Like I think the gravity is like 1.1, 1.2, like it’s higher gravity, but not a lot.
Dr. Pamela Gay: And it’s only about half the density of the earth. So it’s not one of these super fluffy worlds, but it’s also not clearly a super terrestrial rocky world. So we know it’s fundamentally different than our planet, but we’re intrigued because it’s close enough that we can start looking at its atmosphere and its atmosphere is something we can separate away from its star’s light.
Fraser Cain: So I guess let’s fast forward a little bit into a couple of years later, a team of researchers floated this idea, pardon the pun, of these Haitian worlds, that the way you might explain a world that has that kind of density is that it has a lot of water, not just like an ocean of water, but hundreds, maybe thousands of kilometers deep of water on its surface. Surrounded by a fairly thick envelope of hydrogen that you could get this, you know, that with the hydrogen atmosphere, that is an incredible greenhouse gas that is able to keep the water warm. And so you have what will be liquid water across the entire surface of this planet.
These are these Haitian worlds.
Dr. Pamela Gay: Now at the same time, this Haitian world is orbiting an angry little red star. One of the problems with red dwarf stars is they can let off tremendous flares and this one is particularly active. So we are in a situation where, yes, the world could potentially be one of these Haitian worlds, hydrogen plus ocean.
It looks like it should be pronounced Haitian, it’s Haitian, just to be overly specific.
Fraser Cain: So someone proposed another one, Hydrosian, which I kind of like.
Dr. Pamela Gay: That one’s easier to say.
Fraser Cain: Yeah. And it’s like hydrogen and ocean. Hydrosian. Yeah. That makes so much more sense. Yeah, it’s a good one.
So we have to make that stick, Hydrosian world.
Dr. Pamela Gay: So even if there is the potential for life to evolve in this world, it’s going to have to survive basically radiation attacks from its star. But with a thick ocean, the oceans block most of that. So we’re potentially looking at space whales if we’re really lucky, but we don’t think we’re lucky here.
Fraser Cain: A meter of water and you’ve got protection from radiation. That thick hydrogen atmosphere, you’ve got a protection from radiation. So these would be working together.
And just with these Haitian worlds, it’s kind of interesting because of that global warming effect because of that sort of trapping in of the heat, it actually really extends the habitable zone of one of these planets that normally the habitable zone, people consider it’s a Earth-like world orbiting around the Sun-like star. Ours is from say Venus to Mars and Earth is in between. We’ve got three planets in the habitable zone, but clearly Venus and Mars aren’t habitable.
But with this Haitian, Hydrosian world, that you could go much farther out, all the way out to say the asteroid belt and still have liquid water on the surface of the planet, even farther. People have even proposed that these could be say orbiting around like a brown dwarf or a gas giant in interstellar space, that a rogue planet could have enough tidal effects that are keeping the planet warm, that it could have liquid water on the surface of this planet. So it’s a really fascinating idea and a totally alternative way that a planet could evolve over time.
Dr. Pamela Gay: And since we have cool planet, cool idea, there’s Hubble time in that. So in 2019, a paper came out looking at observations made by the Hubble Space Telescope. And the Hubble Space Telescope sees a little bit into the infrared.
It’s not optimized to see into the infrared. It doesn’t have all the cooling stuff that it had when it launched. And it doesn’t have all of the sunshades and stuff that the JWST has, but it can see further into the infrared than we can here on the surface of our planet.
And the infrared is where you get a lot of these molecular lines that occur from the spin and the essentially stretch motions of molecules. And so they looked a little bit into the infrared with Hubble Space Telescope. They took spectra of the star.
They took spectra while the planet was in front of the star. They subtract these two to look for the difference. They were able to see a spectra from the planet, and they found in that snippet of spectra they were able to see lines that were consistent with absorption from water molecules in the planet’s atmosphere.
Now the catch is, what determines where we have these different spectral lines is the various energy levels in atoms. So you have electrons jumping between different energy levels. We all probably learned that somewhere in middle school or high school.
And in molecules, we have similar things that occur related to the rotation and essentially jiggling of molecules.
Fraser Cain: That’s the scientific term.
Dr. Pamela Gay: I’m going to go with it. It’s easier than trying to explain.
Fraser Cain: There can also be wiggling and jiggling. Anyway, please continue.
Dr. Pamela Gay: So these different energy levels in molecules are much more numerous. The more complicated the molecule, the more lines it’s going to have. And it can get super trickstery to try and understand exactly what a line you’re looking at happens to be, because when you pull up the data tables, there’s all these different lines that could occur in roughly the same wavelength.
And so they said this is consistent with the discovery of water, and because it appeared to change over time, it is consistent with potentially clouds in the atmosphere of this world. But it was a very low sigma detection. And it was also the kind of thing where other molecules could explain it.
Methane is in a very similar area in the spectra. This was low resolution spectra. And so you couldn’t look for a whole series of specific lines that said, this is definitely water.
This is definitely methane.
Fraser Cain: They just had this small chunk. Well, fast forward to the greatest observatory that humanity has ever built, and placing space changed a lot.
Dr. Pamela Gay: So then along came the James Webb Space Telescope, and it took its own spectra. And all this press came out about this particular discovery. So here we have fast forwarded all the way to 2023.
And in 2023, a new paper came out with JWST observations done in the same manner. Look at star, look at planet in front of star, subtract, get your data. We’re now looking at a different swath of the electromagnetic spectrum.
We are seeing more different lines. And what they were able to see was a whole series of what was really noisy, noisy, ugly data that was consistent with methane bands. So bands of emission or absorption rather, due to methane being in the atmosphere.
Fraser Cain: And I think it’s really important to say, like the leap from Hubble to Webb is an order of magnitude. That when Webb came online, one of the first pictures that they shared was the spectra that was taken by this telescope of the atmospheres of planets that it is providing just unambiguous answers to the chemicals that are floating in these atmospheres. Carbon dioxide, carbon monoxide, water vapor, and even methane.
Like they’re seeing these chemicals and what before was like, maybe, maybe, you’re saying there’s a chance. Now we’re getting this really definitive answer. And so then that is now allowing a next layer of chemicals.
The ones that are harder to spot are starting to, now we’re into the maybe, maybe land again.
Dr. Pamela Gay: The, the thing is like looking at these results, they, the graphic they released is trickstery. The graphic they released shows this extremely high resolution, gorgeous spectra within these pixels above and below, above and below. And.
Fraser Cain: But that was the previous one. This is the one a couple of years ago, right? Yeah.
Okay.
Dr. Pamela Gay: Yeah. Yeah. Yeah.
And, and those points are like, okay, you’re saying that that beautiful, gorgeous spectra is a best fit fit to the JWST points. And me, who, who for part of my career did high, high resolution spectroscopy until I learned I really hate doing high resolution spectroscopy, uh, looked at this and was like, Oh, well, I can see why you called that a fit. And I believe the methane results.
I firmly believe the methane results, everything works for methane. The carbon dioxide results are a whole lot messier. And so I’m like, maybe, maybe, and then they’re making these claims back in this 2023 data that maybe there’s this molecule called dimethyl sulfide that is also in this set of spectra.
And because the data was unclear and because dimethyl sulfide is, is one of those molecules we’re super interested in, it’s a complex molecule. It’s considered to potentially be a biomarker. They were able to get more time to go back and get more clarity, more photons that would allow them to see more clearly what’s in the spectra.
Fraser Cain: And I think it’s really important to sort of, you know, talk about this dimethyl sulfide, that, that here on earth, the presence of dimethyl sulfide in the atmosphere of earth is a signature of life, that we have marine bacteria that are producing dimethyl sulfide as a outcome. And this is gathering in the atmosphere. And when you measure it, you can trace this directly to life.
And so this is the holy grail. Astronomers have been searching for some kind of biosignature that methane, carbon dioxide, carbon monoxide, ozone, oxygen, all of these chemicals have a perfectly abiotic explanation. And so with all of the big superstars out of the running, you’re left with these other molecules that are more complex, that seem to have life requiring, phosphine, advenous, another example of a potential biosignature.
And astronomers are really hoping that they can figure out some kind of molecule that when they detect the presence of it in the atmosphere of an exoplanet, that tells you that there is life there. And as I’m sure listeners to the show are becoming increasingly aware that these molecules have not been found. But dimethyl sulfide, phosphine, these are some of the best candidates that have been found so far.
So fast forward again, and the astronomers get more time on James Webb. And this is the announcement that we have all heard in the last couple of weeks.
Dr. Pamela Gay: Yeah. And so this has been a trickstery announcement. So the first part of it was…
Fraser Cain: This is a three trickstery episode. You’ve used that term now. It really is.
Dr. Pamela Gay: Holy cow, Yakala.
Fraser Cain: All right.
Dr. Pamela Gay: So in looking at their additional JWST data, they made the one sigma, which means it has a 30% chance of being correct, result that they found dimethyl sulfide. So one sigma, that’s really low probability.
Fraser Cain: And nobody gets out of bed for one sigma.
Dr. Pamela Gay: No. They then went on… The paper was fully conservative, very carefully not making claims of life or anything, just saying this could be a biomarker.
Not citing the fact that we’ve found dimethyl sulfide.
Fraser Cain: We’ll get skeptical in a second here. But let’s give the sort of the exciting, breathless announcement, and then we’ll move on to all the skepticism.
Dr. Pamela Gay: So while the paper was nice and conservative, the interviews, especially the one with the sun, which is not a tabloid, but it’s a tabloid in the UK, was very, this could be life. This could be the discovery. Use different words, but that’s what they said without saying it.
And so this got a whole lot of people and a whole lot of headlines with the, we have discovered an unambiguous biosignature. This is it, folks. So you’ve seen that on one side.
And then on the other side, you’ve seen all the grumpy scientists. Right.
Fraser Cain: Yes. Yeah. Yeah.
And in the paper, they claim a three sigma detection of dimethyl sulfide, as well as a detection of dimethyl disulfide, which is a version of dimethyl sulfide.
Dr. Pamela Gay: That’s the one side. Yeah.
Fraser Cain: And a three sigma detection is a pretty strong detection. Like this has astronomers getting out of bed, taking attention, walking over, rubbing their eyes, looking again. Three sigma is 99.5% certain. Is that right? 97%. I forget which one it is.
Is it 97?
Dr. Pamela Gay: So three sigma is 99.7. 99.7. Okay.
Fraser Cain: 99.7% chance that this signal is there and it is not a mistake. That is not a statistical error that just happens to be showing you this. You couldn’t cash that in at the bank at this point.
Now you’re not at the six sigma where it’s 99.9999. I’m going to pause and correct you.
Dr. Pamela Gay: The carbon dioxide was at three sigma and the dimethyl sulfide was one sigma hmm Okay, you sure? Uh-huh I’m looking at Ethan’s article.
Fraser Cain: Okay. All right. I’ll I’ll I Will take your word for that, but I thought it is the DMS was the one that they were hitting three sigma at but okay Um, we’ll we’ll we’ll dig into the point being Which is now we’re about to shift to this So first so the the best possible version of this right is that that astronomers are detecting the presence of methane carbon dioxide and dimethyl sulfide in the atmosphere of this world that its Chemical composition the density all of this is matching this idea of a high shin world a hydrogen world Come on stick term. Um and That this is the first compelling evidence of Some kind of biological process that is acting on some other world And if it really is a giant world a giant ocean world Surrounded by this thick layer of hydrogen, which is food for bacteria. You can imagine that there is some kind of thriving ecosystem that is producing various chemicals and pumping dimethyl sulfide and other waste gases out into the atmosphere of this world that Carbon dioxide methane.
These are not long-lived chemicals in the atmosphere of a world in at a at a sort of Astronomical eon and so there must be some source that is continually replenishing This material so that is the that is the best possible version of what this discovery could mean and this and that’s why everyone’s Is so excited about it so now prepare the skeptical Cold water as we begin to pour
Dr. Pamela Gay: well, both methane and DMS dimethyl sulfide molecules are short-lived and require Replenishment if they’re going to be seen That doesn’t mean it has to be life, right? so We have already Detected dimethyl sulfide in a comet and we have detected it in a Nebula We we know it’s out there
Fraser Cain: Hanging out in outer space, right and we actually reported on this just a couple of days ago in universe today that That there is chemistry like it’s been detected in deep space Detected on comets like it clearly can form in an abiotic environment and That now chemists are starting to work out the mechanisms for how this comes together and you just get starlight operating on chemicals of various Elements and they come together into these interesting molecules that you can get dimethyl sulfide in an abiotic environment It is not a smoking gun biosignature.
Dr. Pamela Gay: Its detection is interesting But it is it there are other avenues that you can get this chemical That’s like the first issue So the second issue is people going through and doing reanalysis of the data Can reanalyze the data and come up with other? Best fit models that don’t require DMS to be there, right?
Fraser Cain: So just reanalyzing the actual data that was Released with the paper people are being skeptical that they are finding that in fact What they say is a very strong three-signature detection might actually be not detecting dimethyl sulfide at all that it is very close on the On the spectrum to other chemicals and that you could be seeing other things that there’s a lot of room for disagreement in this and that’s The other part where a lot of I’m seeing a lot of papers where people are saying that you know That you can’t claim that it’s such a strong detection.
Dr. Pamela Gay: Yeah, you can just you can give it as a tentative detection And the other issue and this is gonna sound like a silly red flag, but it is Scientists are supposed to be skeptical. We are supposed to be people who are like there are multiple explanations for our data Here’s how well each of these things fit and this research team Gets grouchy if you point out to them things like there’s other ways to process the data. There are other interpretations of is this Organic origins or is this just it exists because molecules do things and When your researchers get grouchy when you say, okay, let’s consider another solution That is weirdly a red flag.
Fraser Cain: Mm-hmm and you can think of examples of people who Have put out bold claims people have questioned the results and they have not responded with oh, you’re right I made a terrible mistake.
Dr. Pamela Gay: Let me go back and do some work Instead, you know, thank you for you know for showing me that I’ve cut the that I was down the wrong road they dig in and And history has shown us With the phosphine results at Venus with the methane results at IO That we’re gonna find Biosignatures and Sometimes when we reprocess the data we realize Something went wrong. That’s what happened with the phosphine data when they went back and they redid the data reduction pipeline Yeah
Fraser Cain: And I think and the other thing and this is a this is a paper that we reported on universe today Like a year ago That you can have a completely different world that would also explain the findings that if you had a molten world With a lava ocean on the surface of it and various volcanic gases that are bubbling up and surrounding the planet that would give you a very similar atmospheric composition that you get carbon dioxide and methane and even dimethyl sulfide out of volcanoes blasting around on the surface and that feels like a perfectly viable possibility, so So I think hopefully Those of you who’ve been watching the science unfold have been have heard We’re running a simulation of the way Pamela and I approach these kinds of matters You you know what Paul Matt Sutter always says that if it’s interesting, it’s probably wrong and that extraordinary claims Thanks to Carl Sagan require extraordinary evidence. And this is the world that we’re in it is the most Exciting It is the most is the deepest philosophical question that humanity can ask.
Are we alone in the universe and and anyone who Proposes to provide an answer to this question has got to show up with with plenty of evidence or maintain an incredibly weak Hold on the evidence that they’ve performed so far and so we are at the very beginning of this conversation And to say that life has been found is a is a dramatic over simplification of what’s been found we it is and I think the thing you want to take away is You’re watching the scientific community perform in the way that it should they are being Skeptical they push back they are being combative and that is wonderful This is how science works and if anyone says I go scientists all just you know, they all just agree that this is the truth Watch this Conversation unfold and see if you still feel that way at the end of it
Dr. Pamela Gay: Sarah Horst has a great thread over on blue sky and this is definitely one of those opportunities to see scientists being their most crunchy as We curmudgeon at one another.
Fraser Cain: Yeah.
Dr. Pamela Gay: Yeah, when we do find life, it’s going to be more than a couple of molecules that we need to say that’s what we discovered.
And the worst part about this, in some ways, it’s a lot of the planetary modelers are like, calling that a super earth is just wrong. And that’s actually a baby Neptune, baby Neptune. Yeah, it doesn’t matter.
All planets are wonderful.
Fraser Cain: Thanks, Pamela.
Dr. Pamela Gay: Thank you, Fraser.
And thank you, all of our patrons out there. We wouldn’t be here without you. And more to the point, we wouldn’t have people to make us sound smarter without you.
So this week, I would like to thank Keith Murray, Thomas Gazetta, Steve Rutley, Maxim Levitt, Bebop Apocalypse, Dr. Whoa, Danny McGlitchin, Jean-Baptiste Lemontier, Fredo Salvo, Just Me and the Cat, Van Ruckman, TC Starboy, Michael Perchata, Bury Gowan, Bure Andro-Loves-Vol, Ed David, Buzz Parsec, Joe Holstein, Kenneth Ryan, Wanderer M101, Felix Goop, Dr. Jeff Collins, Greg Davis, MHW1961, Super Symmetrical, Bart Flaherty, Matthew Horsman, J.
Alex Anderson, Kimberly Reich, James Roger, Scott Beaver, Daniel Loosley, Greg Viles, Mark Steven Raznick, Janelle, Michelle Cullen, The Air Major, The Big Squish Squatch, Justin Proctor, Don Mundus, Mark Phillips, Larry Zotz, Stephen Miller, Paul Esposito, Ron Thorson, and Daniel Jonathan. Thank you all so very much. Thanks, everyone.
And we’ll see you next week. Bye-bye. You’re listening to the 365 Days of Astronomy podcast.
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