AD - Go to https://surfshark.com/drbecky or use code DRBECKY at checkout to get 4 extra months of Surfshark VPN. | The planet K2-18b has been hitting the headlines again this month with the claim of a tentative detection of something known as dimethyl sulphide (DMS) in its atmosphere from this paper by Madhusudhan et al. (2025). DMS is a molecule that is only produced by microbial life here on Earth, but NO we have not detected alien life in this planet’s atmosphere. The detection itself of DMS is tentative, and the molecule itself, doesn’t necessarily mean life. This whole story is quite literally the definition of “extraordinary claims require extraordinary evidence”. Now if you’re thinking, wait haven’t I heard this before? Technically, yes, the same research group put out this paper in 2023 claiming an even more tentative detection of DMS, but the data they had from the James Webb Space Telescope, JWST, using NIRSpec wasn’t good enough to make a strong claim. So now they’ve got different data from MIRI on JWST, and now they’re claiming they have stronger evidence for DMS. But if you’ve been following me for a while you know that all of this hype around K2-18b has come with a lot of scientific debate with other research papers claiming there’s no evidence for DMS at all. And this past week or so since this research dropped has been no different, with this paper from Taylor (2025) also fitting to the new JWST MIRI data and claiming there’s no evidence for DMS at all. This is science in action and it is incredibly exciting to get to live through all of this debate! So let’s have a deep dive into this…
My previous video on the first claim of DMS in K2-18b's atmosphere with JWST (the NIRSpec data from Madhusdudhan et al. (2023) - https://www.youtube.com/watch?v=F360SGAlI8Y
My previous video on the counter-arguments against the DMS claim in the JWST NIRSpec data - https://www.youtube.com/watch?v=r0lGz73rluo
My previous video interviewing Jake Taylor about the discovery of photochemistry in a planet's atmosphere with JWST - https://www.youtube.com/watch?v=eW38rqLZMPg
Madhusudhan et al. (2025; K2-18b MIRI data claiming DMS) - https://arxiv.org/pdf/2504.12267
Taylor et al. (2025; reanalysis of same K2-18b MIRI data) - https://arxiv.org/pdf/2504.15916
Schimdt et al. (2025; reanalysis of K2-18b NIRSpec data) - https://arxiv.org/pdf/2501.18477
Madhusudhan et al. (2023; K2-18b NIRSpec data claiming DMS) - https://arxiv.org/pdf/2309.05566.pdf
Shorttle et al. (2024; K2-18b hydrogen atmosphere with magma ocean) - https://arxiv.org/pdf/2401.05864
Wogan et al. (2024; K2-18b is mini-Neptune) - https://arxiv.org/pdf/2401.11082
Hu et al. (2021; prediction of the molecules present in a hycean world atmosphere) - https://arxiv.org/pdf/2108.04745.pdf
Benneke et al. (2019; water vapour in K2-18b's atmosphere) - https://arxiv.org/pdf/1909.04642.pdf
Cloutier et al. (2019; K2-18b properties) - https://arxiv.org/pdf/1810.04731
Foreman-Mackey et al. (2015; K2-18b discovered in K2 data) - https://arxiv.org/pdf/1502.04715
Seager et al. (2013; biosignatures in hydrogen atmospheres) - https://arxiv.org/pdf/1309.6016.pdf
JWST proposal 2722 - https://www.stsci.edu/jwst/phase2-public/2722.pdf
JWST proposal 2372 - https://www.stsci.edu/jwst/phase2-public/2372.pdf
00:00 Introduction
04:29 The planet K2-18b: what we already know about it
13:16 Madhusudhan et al. (2025)’s claims of evidence of DMS
15:40 How strong their evidence is for their claimed detection of DMS
18:51 The counter-arguments against the detection
28:26 Bloopers
Video filmed on a Sony ⍺7 IV
Video edited by Martino Gasparrini: https://www.fiverr.com/mgs_editing
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👩🏽💻 I'm Dr. Becky Smethurst, an astrophysicist at the University of Oxford (Christ Church). I love making videos about science with an unnatural level of enthusiasm. I like to focus on how we know things, not just what we know. And especially, the things we still don't know. If you've ever wondered about something in space and couldn't find an answer online - you can ask me! My day job is to do research into how supermassive black holes can affect the galaxies that they live in. In particular, I look at whether the energy output from the disk of material orbiting around a growing supermassive black hole can stop a galaxy from forming stars.
http://drbecky.uk.com