K2-18b: did JWST really find evidence of life on this exoplanet?

AD |  To try everything Brilliant has to offer for free for a full 30 days, visit and you’ll also get 20% off an annual premium subscription. | Back in 2023, we saw the first ever claim that JWST had discovered a possible signature of life in the atmosphere of an exoplanet, a planet orbiting another star in our galaxy the Milky Way. But the evidence for the claim that dimethyl sulphide exists in K2-18b’s atmosphere was weak. Now, in the past few months of 2024, we’ve had two new papers analysing the data from K2-18b which both claim there are other models that can explain K2-18b just as well, with the same level of statistical backing. So what is going on here? So let’s dive into what’s going on so you can all make up your own mind. Madhusudhan et al. (2023; hycean world with DMS evidence) - Shorttle et al. (2024; hydrogen atmosphere with magma ocean) - Wogan et al. (2024; mini-Neptune) - Hu et al. (2021; prediction of the molecules present in a hycean world atmosphere) - Benneke et al. (2019; water vapour in K2-18b’s atmosphere) - Cloutier et al. (2019; K2-18b mass) - Foreman-Mackey et al. (2015; K2-18b discovered in K2 data) - Seager et al. (2013; biosignatures in hydrogen atmospheres) - JWST proposal 2722 - JWST proposal 2372 - 00:00 - Introduction 02:45 - What do we know about K2-18b so far? 05:21 - Madhusudhan et al. (2023) - K2-18b is a hydrogen atmosphere with a liquid water ocean with dimethyl sulphide 09:33 - Shorttle et al. (2024) - K2-18b has hydrogen atmosphere with a magma ocean 11:05 - Wogan et al. (2024) - K2-18b is just a mini-Neptune 13:19 - What data do we need to figure this out? 16:37 - Bloopers My previous video on K2-18b: My previous video on the markers for life JWST is looking for: Video filmed on a Sony ⍺7 IV --- 🎧 Royal Astronomical Society Podcast that I co-host: --- 📚 My new book, “A Brief History of Black Holes“, out NOW in paperback, e-book and audiobook (which I narrated myself!): --- 📚 “The Year In Space“ celebrating all things space in 2022 from me and the rest of the Supermassive Podcast team: --- 👕 My new merch, including JWST designs, are available here (with worldwide shipping!): --- 🔔 Don’t forget to subscribe and click the little bell icon to be notified when I post a new video! --- 👩🏽‍💻 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.