Gibt es Leben auf dem Exoplaneten K2-18b?

0:00 [Music] K-2-18B. No, it's not a character from Star Wars. It's a planet two and a half times the size of Earth and 700 trillion miles away, and it could be home to living organisms. And the atmosphere analyzed from K-2-18B shows molecules that can only be produced by living organisms. [Music] Welcome to "Rätsel der Wissenschaft", the standard podcast about the big questions of humanity.

0:38 I'm David Renert. And I'm Tanja Traxler. We deal with every second Wednesday with the big and small mysteries in our universe. Today we're talking about a planet that has been in science for the past months for a very long time. K-2-18B. Researchers want to discover clues to life in the atmosphere of this distant exoplanet.

1:04 What's behind it? It's been 30 years since the Swiss astronomers who first discovered an exoplanet called the Yellow and Michel Major, a planet that circles a sun-like star, but which isn't our sun. The search for planets outside the solar system was still in the children's genes, but in the three decades it's usually exploded.

1:32 In the meantime, almost 6,000 exoplanets are confirmed and they are coming up new. There are many different worlds, such as bizarre planets, or huge, single exoplanets, and many promising candidates for the search for extraterrestrial life. In the past months, such a candidate has made a lot of noise.

2:00 The exoplanet K-2-18B, which is about 124 light-years away from us in the Sternbild-Löwe, is not just an Earth-village. It has 8.6 Earth masses and the 2.4 times radius of our planet is much larger than the Earth. It is also so close to its star that it needs 33 days to round it around. Because its sun is much smaller than ours, it is still in the so-called habitable zone.

2:33 In other words, it could be liquid water and thus also the basic conditions for life on this planet. A few years ago, concrete evidence was found that K-2-18B could actually be an ocean planet. This alone is not a sensation, because many planets in the habitable zone of its star are already known today.

2:57 We already know some of the mutable ocean planets. And such so-called sub-Neptunas, like K-2-18B, which are somewhere in their properties between the star planets and the gas giants, are not necessarily the first addresses for the search for life. A recently published study has recently thrown a new light on K-2-18B.

3:25 A research team about Niko Matusudan from the University of Cambridge wants to discover a much more promising biosignature in the atmosphere of this planet, a molecule that also comes to Earth and is almost exclusively produced by multiple living beings. It is about the methyl sulfide, a short DMS, which is the largest part of plankton, says Niko Matusudan.

3:54 DMS on Earth is primarily produced by life, like almost all of it is produced by life. There are arguments that it could be produced by some other means, but there hasn't been a clear evidence that it could be produced in the quantities that we are seeing. We are talking about 10 to 100 parts per million, large quantities, that is thousands of times larger than what we see on Earth.

4:20 So if you find this molecule at those amounts, it is very hard to argue based on current knowledge that you can make it in those quantities without biology. Niko Matusudan and his team evaluated these results as the strongest evidence of biological activity apart from our solar system, which was discovered the year before.

4:43 This is a pretty big claim, and it remains unnoticeable outside of the astronomical field. The news of a possible discovery of distant life was about the whole world. So this distant exoplanet only survived in the ocean. The excitement was large in the field after the researchers published their results.

5:05 But quickly, there were also doubts. Are these DMS measurements strong enough and could the signatures not also come from completely different molecules? And is it really true that K2-18b is an ocean world? For extraterrestrial claims, extraterrestrial evidence is also needed. The discovery of life in space would definitely not be a small thing, because we also found no biological activity on earth.

5:48 Such claims are also under enormous evidence. Even if Niko Matusudan and his colleagues reported very carefully about the evidence and did not immediately talk about an discovery, the debate about K2-18b immediately took place after the publication of their study. Some researchers believe that this exoplanet does not have any water on the surface, but could rather be a lava world.

6:17 And even if definitely complex molecules around K2-18b are proof, the question is whether the signal for the methyl sulfide is clearly enough. And that's exactly what there are doubts about. Since the publication of the study, more publications have already appeared about this exoplanet, the alternative explanations for the results.

6:43 The astronomer from Cambridge greets this criticism and the increased interest in research on K2-18b, as we have told us. Criticisms are huge. It's not just any scientific result. It's not just any experiment, any observation that we are making. What we are finding and what if these come out to be true, the implications are enormous.

7:21 Criticisms can be scientific and emotional. There are all kinds of criticism, but the real duty we have in science is to give due respect and attention to all the criticisms, but then pay specific attention to criticisms that have a scientific merit. And then if there is, then we take that and then we implement that ourselves.

7:43 So we also are our worst critics. Madhusudan and colleagues have conducted new analyses of the data and compared the suspicious DMS signatures from this exoplanet atmosphere with 650 molecules. This has never been done before in such a way. The result is likely to be more likely that K2-18b is actually a promising candidate for life.

8:16 every molecule, almost every molecule that has what is it the molecular cross-section data, align data, experimental data on Earth. We search for all those molecules in the data sets we have and currently there are only a couple of molecules that come close. So there is DMS obviously that still after all that search we are still finding that DMS is a promising candidate. So there are two other molecules. There is a molecule called methyl acrylonitrile which is a complex molecule, again a complex molecule and there is literally no way of producing it that we know currently it's a complex molecule. We don't know of any way of producing it abiotically without life. There is also another molecule diethyl sulfide. Again there is no known source on Earth or any planetary

9:05 atmosphere. We are not just talking about Earth. Any astronomical source be it other planetary atmospheres or the interstellar medium or wherever you look. We saw it is an interesting time in the sense that they're either from life or they're from complex chemical processes that we don't understand and however you put it whatever you find it's going to be a big breakthrough.

9:28 We also have to consider that the exoplanet research is a very young field. Practically everything we know about planets outside the solar system was discovered within the last 30 years and in many areas the research is still at the very beginning. For example, with the research of atmospheres of the exoplanet.

9:57 The research team uses the best instrument that people have at the moment and that is the James Webb Space Telescope. How the combination of an exoplanet atmosphere can be analyzed at all, that's what Luca Fossati of the Grazer Institute for Space Research of the Austrian Academy of Sciences explains.

10:18 The main way that is currently used to study the atmospheres is through a methodology that's called transmission spectroscopy. It requires to have a planet that is in transit so that transits the host star that passes in front of the star as we look at the star and then there is part of the stellar light that goes through the atmosphere and then this stellar light essentially gets imprinted on the signature of what is in the atmosphere and what are the physical properties of the atmosphere of the planet. When the planet is out of transit and we do one minus the other one divided by the hour and we get the signature of the planet of the planetary atmosphere.

10:57 Because of the large size of the mirror the sensitivity is unprecedented you know that level of sensitivity for example k218b you know if you want to do this with any other facility before like Hubble Space Telescope which had a much narrower wavelength range you know what you get the level of sensitivity what you get with 50 hours 60 hours of hst time you get it with only 10 hours with JWST. The second thing is the spectral coverage in other words the wavelength range what wavelengths of light you can look at before JWST again going back to the Hubble Space Telescope which is still operational the maximum wavelengths you can could probe where in the near infrared up to about 1.8 micron max. With JWST you can go up to 20 microns so this combination

12:03 of extreme sensitivity and this broad wavelength range means that you can look at more molecules more chemicals because the molecules usually have strong absorption bands in the infrared. By expanding this wavelength range you're opening that window into you know planets elsewhere into their chemical composition but the sensitivity means that you can also go to smaller and cooler planets you can look at smaller and cooler planets and you can tease out their composition much better and that enables us to look at now for the first time habitable zone exoplanets like K218b. Nico Madoussoudan and his colleagues have already secured a new observation time for K218b with the web telescope but what now if the suspicion of biological activities is actually

12:52 hardened how could we ever find out for sure that there is life on an distant exoplanet and how it looks the search for life on the earth is faced with many major challenges one of which is how the final proof is supposed to look like if we don't just bump into microbe or other living beings in the solar system that with great effort but still somehow reachable for us what then to send a space probe to an exoplanet is unfortunately not achievable today and would really last forever without it so it could easily happen that we will find strong hints of life in space but no final answers will be received how do you go forward with these problems this is the reality of all astronomical observations right how do you know black holes exist right how do you

14:03 know neutron stars exist or any astronomical phenomenon exist it's all remote observations so I don't think this is any different the reason we are even asking this question is because supernovae don't happen on earth right black holes don't happen on earth so we are used to thinking them as cosmic phenomena which we can only learn remotely so we are happy we are comfortable with that notion but something like life and geological process all of that happen on earth and in plants in the solar system so our standards change we are like now to establish life we have to go there touch it smell it know it and then that is when we will qualify as life so in my view the moment you're talking about life elsewhere we should be thinking of life as a cosmic phenomenon

14:50 and if you do that then just like any other cosmic phenomenon we will have ways to establish whether or not there is life and it could be a probability it could be a probabilistic approach is that we can say with a very high degree of certainty that it is life because we can rule out all the other processes based on simulations experiments all of those things that we can conduct on earth for similar environments live as a cosmic phenomenon that would be also philosophically exciting and definitely a paradigm change our egocentric species would probably not hurt but to be honest I already know now should we ever find such hints on life in the hall that are strong and vulnerable I am sure much too curious to find myself with

15:39 probabilities well we will maybe see it for today we say thank you for listening and we are looking forward to seeing you again next time at Rätsel of the science every second Wednesday everywhere where there is a podcast I am David Renard and I am Tania Draxer this episode was produced by Christoph Neuwirt until next time until then k218 b is two and a half times the size of earth and it's 700 trillion miles away the James Webb Space Telescope is so powerful it can analyze the chemical composition of the atmosphere for the light that passes through it and the small red star it orbits