New analysis of ALMA observations of interstellar comet 3I/ATLAS show its water carries a chemical signature pointing to a colder, more distant origin than any comet ever measured.

Water sampled from 3I/ATLAS (left) has 30 times the concentration of deuterated water molecules that Earth’s oceans do (right), as shown in this illustrated comparison. Credit: NSF/AUI/NSF NRAO/M. Weiss

We already knew interstellar comet 3I/ATLAS came from somewhere far beyond our solar system. Now scientists have more information on how alien that somewhere really is — a corner of the universe colder than, less irradiated than, and chemically distinct from the conditions that shaped our home.

A study published April 23 in Nature Astronomy reveals that 3I/ATLAS carries water with an extraordinary concentration of what’s known as deuterated water.…