00:06We found the strongest evidence to date of possible biological activity on an exoplanet.
00:21DMS stands for dimethyl sulfide. This is a very important molecule because here on Earth,
00:26DMS is produced uniquely by life, microorganisms in the ocean like algae, phytoplankton,
00:33and theoretical studies have predicted for the last two decades that molecules like DMS would be
00:39very robust biomarkers on exoplanetary systems, including planets with hydrogen-rich atmospheres
00:46like Haitian worlds.
00:53K-18b is an exoplanet orbiting a red dwarf star about 124 light-years away. It has a mass of
01:01about
01:028.6 Earth masses and a radius of about 2.6 Earth radii, and it orbits in the habitable zone
01:10of its
01:10host star, which means if you put an Earth-like planet at its location, we would think of it as
01:15habitable.
01:20So the technique we used to determine the atmospheric composition of the planet is known
01:26as transit spectroscopy. What is happening is that you look at the planet as it transits in front of
01:32the 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,
01:43absorb some of that starlight. So by looking at a differential measurement when the planet is in
01:49front of the star or when it isn't, you can extract how much absorption is happening in the planet's atmosphere.
02:00So 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 was very
02:14tentative, so we looked this time at the planet again in a different wavelength range. And what we are
02:21finding is significantly stronger evidence at a three sigma level for the presence of either DMS or DMDS or
02:30both. Now DMDS, like DMS, is also a strong and unique biomarker here on Earth and had also been predicted
02:37to be a biomarker on planets with hydrogen-rich atmospheres. And that is what is new, is that
02:42there's a possibility of one or both of these molecules to be present in the atmosphere at a
02:48credible 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 five sigma. What
03:12is the difference between the three sigma and the three sigma? So we are pretty confident about our
03:19results at the significance that we are finding at this three sigma significance and that's partly
03:23because we have done enormous number of robustness checks. We have done it with multiple pipelines and
03:29within the same data reduction pipeline we have tried various assumptions on how we can reduce the data
03:35data. And no matter how we did it, the signal always persisted. And to us that's a great measure of
03:42our
03:42confidence in the detection at this level. But we should remain open-minded and get more observations so
03:49we can repeat the signal. That'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.
04:03So the question you may have is, have we found life on another planet? And this answer is simply no,
04:08not yet. Right? So we have to, as I always say, we have to be very careful in two directions.
04:15The
04:16detection we have made is at a level where it is very interesting. It's a landmark result, but it is
04:23not
04:24good enough to call it robust just yet. This is a big signal we are looking at. This is of
04:31very high
04:31importance. We need more observations to get it to that five sigma level where we would be much more
04:36confident, number one. The second aspect of that is that when we do detect and while we are making
04:42these observations, we also have to remind ourselves that while DMS has been predicted to be a robust
04:47biomarker, there is always a possibility that we may not have accounted for some physics that we don't
04:54know so far or some chemical process that we don't know of. So we want to remain open and do
05:00as much
05:00theoretical calculations, as many theoretical calculations and lab-based studies to say if there
05:05is any process which can get DMS in such an atmosphere at the levels that we are seeing.
05:16This is one of the most profound moments for me personally, as well as an astronomer. Because
05:25for 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. Because however
05:44you put it, we are seeing new chemical processes on a planet that could be habitable. And we have
05:51shown this in theoretical studies that that was possible. So this is, in my view, a transformational
05:58moment, not just for planetary science, not just for astronomy, but for finding our place in the universe as
06:05species.
06:07For more information, visit our website at www.xr.evs.gov.au
06:12and visit our website at www.xr.gov.au
06:12www.xr.gov.au
06:13www.xr.gov.au
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