Data from the James Webb Space Telescope on exoplanet K2-18b has revealed the "strongest hints yet of biological activity outside the solar system," according to a University of Cambridge study.
Does exoplanet K2-18b host alien life or not? Here's why the debate continues:
Does exoplanet K2-18b host alien life or not? Here's why the debate continues:
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00:00We found the strongest evidence to date of possible biological activity on an exoplanet.
00:13DMS stands for dimethyl sulfide. This is a very important molecule because here on Earth,
00:26the DMS is produced uniquely by life, microorganisms in the ocean like algae, phytoplankton, and theoretical
00:34studies have predicted for the last two decades that molecules like DMS would be very robust
00:40biomarkers on exoplanetary systems, including planets with hydrogen-rich atmospheres like
00:47Haishun wars.
00:54K-218b is an exoplanet orbiting a red dwarf star about 124 light years away. It has a mass
01:01of about 8.6 Earth masses and a radius of about 2.6 Earth radii, and it orbits in the habitable
01:09zone of its host star, which means if you put an Earth-like planet at its location, we would
01:14think of it as habitable.
01:21So the technique we used to determine the atmospheric composition of the planet is known as transit
01:27spectroscopy. What is happening is that you look at the planet as it transits in front
01:32of the host star. So the atmosphere of the planet, some of the starlight goes through the atmosphere
01:38of the planet before reaching the telescope. And the atmosphere, the molecules in the atmosphere,
01:44can absorb some of that starlight. So by looking at a differential measurement when the planet
01:49is in front of the star or when it isn't, you can extract how much absorption is happening
01:54in the planet's atmosphere.
02:01So two years ago in 2023, we reported a very tentative inference of DMS on this planet with a different
02:09set of observations with a different instrument in the 1 to 5 micron range. But the evidence
02:14was very tentative, so we looked this time at the planet again in a different wavelength range.
02:20And what we are finding is significantly stronger evidence at a three sigma level for the presence
02:27of either DMS or DMDS or both. Now DMDS, like DMS, is also a strong and unique biomarker here on Earth,
02:35and had also been predicted to be a biomarker on planets with hydrogen-rich atmospheres. And that is
02:41what is new, is that there's a possibility of one or both of these molecules to be present in the atmosphere
02:47at a credible level of significance. So while this is great evidence to keep looking, this is not enough
02:57to qualify it as a robust scientific discovery. For that, we need to reach the level of Phi Sigma. What does that mean?
03:03At Phi Sigma, you're talking about the chance of a fluke being about a part in a million.
03:16So we are pretty confident about our results at the significance that we are finding at this three sigma significance,
03:22and that's partly because we have done an enormous number of robustness checks. We have done it with multiple pipelines,
03:28and within the same data reduction pipeline, we have tried various assumptions on how we can reduce the data.
03:35And no matter how we did it, the signal always persisted. And to us, that's a great measure of our confidence in the detection at this level.
03:45But we should remain open-minded and get more observations so we can repeat the signal.
03:50That's the hallmark of science, the repeatability and increase in robustness
03:54till we get, till we are really, really satisfied. We are not there yet.
03:57So the question you may have is, have we found life on another planet? And this answer is simply no, not yet.
04:09Right? So we have to, as I always say, we have to be very careful in two directions.
04:15The detection we have made is at a level where it is very interesting. It's a landmark result,
04:22but it is not good enough to call it robust just yet. This is a big signal we are looking at.
04:30This is of very high importance. We need more observations to get it to that five sigma level
04:34where we would be much more confident, number one.
04:37The second aspect of that is that when we do detect, and while we are making these observations,
04:42we also have to remind ourselves that while DMS has been predicted to be a robust biomarker,
04:48there is always a possibility that we may not have accounted for some physics that we don't know so far
04:55or some chemical process that we don't know of. So we want to remain open
04:59and do as many theoretical calculations and lab-based studies to say if there is any process
05:06which can get DMS in such an atmosphere at the levels that we are seeing.
05:11This is one of the most profound moments for me personally, as well as an astronomer,
05:24because for the first time in the history of our species, we may actually be seeing signs of life elsewhere.
05:34On the other hand, this could also be a signal of a new chemical process
05:39that is not produced by life, and even that is a monumental breakthrough,
05:43because however you put it, we are seeing new chemical processes on a planet that could be habitable.
05:50And we have shown this in theoretical studies that that was possible.
05:54So this is, in my view, a transformational moment, not just for planetary science, not just for astronomy,
06:00but for finding our place in the universe as a species.
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