How does measuring deuterium tell us where a COMET formed? #shorts

Comets are often called dirty snowballs, and their water acts like a frozen time capsule of the conditions and chemistry of where they formed. So this is why since 3I Atlas was discovered back in July 2025, its been all hands on deck to observe it with what feels like every telescope we have, from Hubble, JWST, TESS, Parker Solar Probe, and even Perseverance from the surface of Mars. But now, a paper published by Salazar-Manzano and collaborators has revealed something really interesting about the chemistry of water on this interstellar visitor. So Salazar-Manzano et al. (2026) used the ALMA ratio telescope in Chile, a big array of antenna that work together to make one big telescope in order to detect the infrared light given out by both normal water, H2O and something known as heavy water HDO. So instead of 2 hydrogen atoms, heavy water has a deuterium atom. It’s still hydrogen, it’s just a bit heavier because its got a neutron as well as a proton in the centre of the atom. Hence heavy hydrogen, and heavy water. This was the very first measurement of deuterium in an interstellar object, which is exciting in itself but also what it reveals. So yes comets and asteroids in the solar system also have water, and lots of it. Comets are often called dirty snowballs, and their water acts like a frozen time capsule of the conditions and chemistry of where they formed. And the ratio of heavy water, with deuterium, to normal water is really sensitive to the temperature of where an object formed: the colder the environment, the more deuterium gets locked in, and the more heavy water you get.... Video filmed on a Sony ⍺7 IV Video edited by Martino Gasparrini: [email protected] Video produced by Marina Hui & Dr Becky Smethurst --- 📚 My book, "A Brief History of Black Holes", out NOW in hardback, paperback, e-book and audiobook (which I narrated myself!): http://lnk.to/DrBecky --- 👕 My merch, including JWST designs, are available here (with worldwide shipping!): https://dr-becky.teemill.com/ --- 🎧 Royal Astronomical Society Podcast that I co-host: podfollow.com/supermassive --- 🔔 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. 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