This is a really interesting result [1]! We knew Comet 3I/ATLAS was an interstellar object because of its orbit, but the precise measurements done with ALMA by a team lead by a Ph.D. student (Luis E. Salazar Manzano from the University of Michigan), and supervised by Chilean assistant professor Teresa Paneque-Carreño [3], really show that its chemistry does not belong in our solar system.

In particular, the team found that 3I/ATLAS contains *at least 30 times* the proportion of semi-heavy water* found in comets from our own Solar System, which clearly indicates a different chemical history. The chemical processes leading to the enrichment of HDO usually require environments colder than about 30 Kelvin, which means the solar system in which 3I/ATLAS originated was colder than ours.

And this could be found because ALMA could observe the comet right after its perihelion, quite close to the sun, but observable with a radio telecope!

*Semi-heavy water [4] is water made with one atom of the most common isotope of hydrogen (protium), one atom of Deuterium (the next most common isotope of hydrogen, containing one proton and one neuron), and oxygen. It is sometimes called HDO, with D standing for Deuterium, or ¹H²HO. Compare with heavy water, which is made of two atoms of Deuterium and Oxygen, or D₂O (or ²H₂O).

#ALMA #AtacamaLargeMillimeterArray #AtacamaLargeMillimeterSubmillimeterArray #Comet3IATLAS #SolarSystemFormation #InterstellarObjects

[1] https://www.almaobservatory.org/en/press-releases/alma-reveals-interstellar-comet-3i-atlas-formed-in-a-far-colder-world-than-our-own/
[2] https://lsa.umich.edu/astro/people/graduate-students/lesamz.html
[3] https://terepaneque.com/info_english/
[4] https://en.wikipedia.org/wiki/Semiheavy_water