Interstellar 3I/ATLAS Is Unusually Rich in Heavy Water

Researchers at RIKEN attribute the odd isotope ratios of interstellar object 3I/ATLAS to the low metallicity of its birth cloud. Its water shows a deuterium-to-hydrogen ratio of about 1%, versus 0.015–0.03% for typical solar system comets.

• D/H in 3I/ATLAS water is about 1%, versus 0.015–0.03% for solar system comets
• Its C-12/C-13 ratio is 123–191, against ~90 in the solar system and ~68 in the interstellar medium
• Methane D/H in 3I/ATLAS is about 3%, versus 0.2% in comet 67P
• Low metallicity boosts deuterium: less CO, weaker atomic hydrogen flux and lower cosmic-ray ionization