Interstellar Comet: Water 14 Times Heavier Than Earth's express
Comet 3I/ATLAS was spotted when it entered the Solar System from interstellar space. The James Webb Telescope split the light from its gas cloud into a rainbow, a spectrum, and in this pattern, the lines of rare molecules with deuterium (heavy hydrogen) appeared.
For 3I/ATLAS, this 'thermometer' is off the charts: for every 30 ordinary hydrogen atoms, there's one deuterium atom — in Earth's oceans, that ratio is hundreds of times poorer. This means the comet was born in the icy darkness of a distant protoplanetary disk — a region where planets are just beginning to coalesce from cosmic dust and gas. This alien world is far colder than the cloud that gave birth to our Sun and Earth.
The deuterium abundance points to a comet birth temperature below –250°C — colder than the eternal shadows on the Moon.
Interstellar wanderers like 3I/ATLAS come to life in the pages of science fiction: for example, in Arthur C. Clarke's novel 'Rendezvous with Rama'.