@drbecky_s: 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.... #comets #interstellar #Astronomy #3iATLAS

Dr Becky Smethurst

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Monday 18 May 2026 15:47:29 GMT