A comet that drifted between the stars for millions or even billions of years before entering our Solar System carries water with roughly 30 times more heavy hydrogen than a typical comet here, suggesting its ice formed in an extraordinarily cold alien planetary system.

ALMA and Webb found extreme deuterium enrichment in 3I/ATLAS water, preserving a chemical record of ice formed below roughly 30 kelvin in another planetary system. The post A comet that drifted between the stars for millions or even billions of years before entering our Solar System carries water with roughly 30 times more heavy hydrogen than a typical comet here, suggesting its ice formed in an…