00:00:00: [Music]

00:00:04: K-2-18B.

00:00:06: No, it's not a character from Star Wars.

00:00:08: It's a planet two and a half times the size of Earth

00:00:10: and 700 trillion miles away,

00:00:12: and it could be home to living organisms.

00:00:15: And the atmosphere analyzed from K-2-18B shows molecules

00:00:20: that can only be produced by living organisms.

00:00:23: [Music]

00:00:33: Welcome to "Rätsel der Wissenschaft",

00:00:35: the standard podcast about the big questions of humanity.

00:00:38: I'm David Renert.

00:00:40: And I'm Tanja Traxler.

00:00:42: We deal with every second Wednesday

00:00:44: with the big and small mysteries in our universe.

00:00:49: Today we're talking about a planet

00:00:51: that has been in science for the past months

00:00:53: for a very long time.

00:00:56: K-2-18B.

00:00:58: Researchers want to discover clues to life

00:01:01: in the atmosphere of this distant exoplanet.

00:01:04: What's behind it?

00:01:06: It's been 30 years since the Swiss astronomers

00:01:09: who first discovered an exoplanet

00:01:13: called the Yellow and Michel Major,

00:01:15: a planet that circles a sun-like star,

00:01:19: but which isn't our sun.

00:01:22: The search for planets outside the solar system

00:01:25: was still in the children's genes,

00:01:27: but in the three decades it's usually exploded.

00:01:32: In the meantime, almost 6,000 exoplanets are confirmed

00:01:37: and they are coming up new.

00:01:40: There are many different worlds,

00:01:43: such as bizarre planets,

00:01:45: or huge, single exoplanets,

00:01:48: and many promising candidates for the search

00:01:52: for extraterrestrial life.

00:01:55: In the past months, such a candidate

00:01:58: has made a lot of noise.

00:02:00: The exoplanet K-2-18B,

00:02:03: which is about 124 light-years away from us

00:02:06: in the Sternbild-Löwe,

00:02:08: is not just an Earth-village.

00:02:10: It has 8.6 Earth masses

00:02:13: and the 2.4 times radius of our planet

00:02:17: is much larger than the Earth.

00:02:19: It is also so close to its star

00:02:22: that it needs 33 days to round it around.

00:02:26: Because its sun is much smaller than ours,

00:02:29: it is still in the so-called habitable zone.

00:02:33: In other words, it could be liquid water

00:02:36: and thus also the basic conditions for life on this planet.

00:02:40: A few years ago, concrete evidence was found

00:02:44: that K-2-18B could actually be an ocean planet.

00:02:49: This alone is not a sensation,

00:02:51: because many planets in the habitable zone

00:02:55: of its star are already known today.

00:02:57: We already know some of the mutable ocean planets.

00:03:01: And such so-called sub-Neptunas, like K-2-18B,

00:03:07: which are somewhere in their properties

00:03:10: between the star planets and the gas giants,

00:03:14: are not necessarily the first addresses

00:03:17: for the search for life.

00:03:19: A recently published study

00:03:21: has recently thrown a new light on K-2-18B.

00:03:25: A research team about Niko Matusudan

00:03:28: from the University of Cambridge

00:03:30: wants to discover a much more promising biosignature

00:03:33: in the atmosphere of this planet,

00:03:36: a molecule that also comes to Earth

00:03:40: and is almost exclusively produced by multiple living beings.

00:03:44: It is about the methyl sulfide, a short DMS,

00:03:48: which is the largest part of plankton,

00:03:52: says Niko Matusudan.

00:03:54: DMS on Earth is primarily produced by life,

00:03:58: like almost all of it is produced by life.

00:04:01: There are arguments that it could be produced by some other means,

00:04:05: but there hasn't been a clear evidence

00:04:08: that it could be produced in the quantities that we are seeing.

00:04:11: We are talking about 10 to 100 parts per million,

00:04:15: large quantities, that is thousands of times larger

00:04:18: than what we see on Earth.

00:04:20: So if you find this molecule at those amounts,

00:04:23: it is very hard to argue based on current knowledge

00:04:27: that you can make it in those quantities without biology.

00:04:31: Niko Matusudan and his team

00:04:34: evaluated these results as the strongest evidence

00:04:37: of biological activity apart from our solar system,

00:04:40: which was discovered the year before.

00:04:43: This is a pretty big claim,

00:04:45: and it remains unnoticeable

00:04:47: outside of the astronomical field.

00:04:49: The news of a possible discovery of distant life

00:04:52: was about the whole world.

00:04:54: So this distant exoplanet only survived in the ocean.

00:04:59: The excitement was large in the field

00:05:02: after the researchers published their results.

00:05:05: But quickly, there were also doubts.

00:05:08: Are these DMS measurements strong enough

00:05:11: and could the signatures

00:05:13: not also come from completely different molecules?

00:05:16: And is it really true that K2-18b is an ocean world?

00:05:21: For extraterrestrial claims,

00:05:36: extraterrestrial evidence is also needed.

00:05:38: The discovery of life in space

00:05:40: would definitely not be a small thing,

00:05:43: because we also found no biological activity on earth.

00:05:48: Such claims are also under enormous evidence.

00:05:52: Even if Niko Matusudan and his colleagues

00:05:55: reported very carefully about the evidence

00:05:59: and did not immediately talk about an discovery,

00:06:02: the debate about K2-18b

00:06:05: immediately took place after the publication of their study.

00:06:08: Some researchers believe that this exoplanet

00:06:11: does not have any water on the surface,

00:06:14: but could rather be a lava world.

00:06:17: And even if definitely complex molecules

00:06:20: around K2-18b are proof,

00:06:23: the question is whether the signal

00:06:26: for the methyl sulfide is clearly enough.

00:06:30: And that's exactly what there are doubts about.

00:06:33: Since the publication of the study,

00:06:35: more publications have already appeared

00:06:37: about this exoplanet,

00:06:39: the alternative explanations for the results.

00:06:43: The astronomer from Cambridge greets this criticism

00:06:46: and the increased interest in research

00:06:49: on K2-18b, as we have told us.

00:07:09: Criticisms are huge. It's not just any scientific result.

00:07:13: It's not just any experiment, any observation that we are making.

00:07:16: What we are finding and what if these come out to be true,

00:07:19: the implications are enormous.

00:07:21: Criticisms can be scientific and emotional.

00:07:24: There are all kinds of criticism,

00:07:26: but the real duty we have in science

00:07:29: is to give due respect and attention to all the criticisms,

00:07:33: but then pay specific attention to criticisms

00:07:36: that have a scientific merit.

00:07:38: And then if there is, then we take that

00:07:40: and then we implement that ourselves.

00:07:43: So we also are our worst critics.

00:07:46: Madhusudan and colleagues have conducted new analyses of the data

00:07:56: and compared the suspicious DMS signatures

00:07:59: from this exoplanet atmosphere with 650 molecules.

00:08:02: This has never been done before in such a way.

00:08:05: The result is likely to be more likely

00:08:08: that K2-18b is actually a promising candidate for life.

00:08:16: every molecule, almost every molecule that has what is it the molecular cross-section data,

00:08:21: align data, experimental data on Earth. We search for all those molecules in the data sets we have

00:08:27: and currently there are only a couple of molecules that come close. So there is DMS obviously that

00:08:34: still after all that search we are still finding that DMS is a promising candidate. So there are

00:08:39: two other molecules. There is a molecule called methyl acrylonitrile which is a complex molecule,

00:08:44: again a complex molecule and there is literally no way of producing it that we know currently it's

00:08:52: a complex molecule. We don't know of any way of producing it abiotically without life. There is

00:08:58: also another molecule diethyl sulfide. Again there is no known source on Earth or any planetary

00:09:05: atmosphere. We are not just talking about Earth. Any astronomical source be it other planetary

00:09:11: atmospheres or the interstellar medium or wherever you look. We saw it is an interesting time in the

00:09:16: sense that they're either from life or they're from complex chemical processes that we don't

00:09:22: understand and however you put it whatever you find it's going to be a big breakthrough.

00:09:28: We also have to consider that the exoplanet research is a very young field.

00:09:40: Practically everything we know about planets outside the solar system was discovered within

00:09:45: the last 30 years and in many areas the research is still at the very beginning.

00:09:52: For example, with the research of atmospheres of the exoplanet.

00:09:57: The research team uses the best instrument that people have at the moment and that is

00:10:03: the James Webb Space Telescope. How the combination of an exoplanet atmosphere

00:10:09: can be analyzed at all, that's what Luca Fossati of the Grazer Institute for Space Research

00:10:16: of the Austrian Academy of Sciences explains.

00:10:18: The main way that is currently used to study the atmospheres is through a methodology that's

00:10:23: called transmission spectroscopy. It requires to have a planet that is in transit so that

00:10:29: transits the host star that passes in front of the star as we look at the star and then there is

00:10:34: part of the stellar light that goes through the atmosphere and then this stellar light essentially

00:10:40: gets imprinted on the signature of what is in the atmosphere and what are the physical properties

00:10:47: of the atmosphere of the planet. When the planet is out of transit and we do one minus the other

00:10:52: one divided by the hour and we get the signature of the planet of the planetary atmosphere.

00:10:57: Because of the large size of the mirror the sensitivity is unprecedented you know that

00:11:21: level of sensitivity for example k218b you know if you want to do this with any other facility

00:11:27: before like Hubble Space Telescope which had a much narrower wavelength range you know what you

00:11:32: get the level of sensitivity what you get with 50 hours 60 hours of hst time you get it with

00:11:40: only 10 hours with JWST. The second thing is the spectral coverage in other words the wavelength

00:11:46: range what wavelengths of light you can look at before JWST again going back to the Hubble Space

00:11:51: Telescope which is still operational the maximum wavelengths you can could probe where in the near

00:11:55: infrared up to about 1.8 micron max. With JWST you can go up to 20 microns so this combination

00:12:03: of extreme sensitivity and this broad wavelength range means that you can look at more molecules

00:12:11: more chemicals because the molecules usually have strong absorption bands in the infrared.

00:12:17: By expanding this wavelength range you're opening that window into you know planets elsewhere into

00:12:23: their chemical composition but the sensitivity means that you can also go to smaller and cooler

00:12:28: planets you can look at smaller and cooler planets and you can tease out their composition

00:12:31: much better and that enables us to look at now for the first time habitable zone exoplanets like

00:12:37: K218b. Nico Madoussoudan and his colleagues have already secured a new observation time for K218b

00:12:45: with the web telescope but what now if the suspicion of biological activities is actually

00:12:52: hardened how could we ever find out for sure that there is life on an distant exoplanet and how it looks

00:13:07: the search for life on the earth is faced with many major challenges one of which is how

00:13:18: the final proof is supposed to look like if we don't just bump into microbe or other living beings in the

00:13:25: solar system that with great effort but still somehow reachable for us what then

00:13:32: to send a space probe to an exoplanet is unfortunately not achievable today and would

00:13:40: really last forever without it so it could easily happen that we will find strong hints of life in

00:13:48: space but no final answers will be received how do you go forward with these problems this is the

00:13:55: reality of all astronomical observations right how do you know black holes exist right how do you

00:14:03: know neutron stars exist or any astronomical phenomenon exist it's all remote observations

00:14:08: so I don't think this is any different the reason we are even asking this question is because

00:14:14: supernovae don't happen on earth right black holes don't happen on earth so we are used to

00:14:21: thinking them as cosmic phenomena which we can only learn remotely so we are happy we are comfortable

00:14:26: with that notion but something like life and geological process all of that happen on earth

00:14:31: and in plants in the solar system so our standards change we are like now to establish life we have

00:14:36: to go there touch it smell it know it and then that is when we will qualify as life so in my view

00:14:43: the moment you're talking about life elsewhere we should be thinking of life as a cosmic phenomenon

00:14:50: and if you do that then just like any other cosmic phenomenon we will have ways to establish

00:14:56: whether or not there is life and it could be a probability it could be a probabilistic approach

00:15:01: is that we can say with a very high degree of certainty that it is life because we can rule

00:15:07: out all the other processes based on simulations experiments all of those things that we can

00:15:13: conduct on earth for similar environments live as a cosmic phenomenon that would be

00:15:19: also philosophically exciting and definitely a paradigm change our egocentric species would

00:15:26: probably not hurt but to be honest I already know now should we ever find such hints

00:15:32: on life in the hall that are strong and vulnerable I am sure much too curious to find myself with

00:15:39: probabilities well we will maybe see it for today we say thank you for listening and we are looking forward

00:15:47: to seeing you again next time at Rätsel of the science every second Wednesday everywhere

00:15:52: where there is a podcast I am David Renard and I am Tania Draxer this episode was produced by Christoph Neuwirt

00:15:58: until next time until then k218 b is two and a half times the size of earth and it's 700 trillion

00:16:07: miles away the James Webb Space Telescope is so powerful it can analyze the chemical

00:16:12: composition of the atmosphere for the light that passes through it and the small red star it orbits