3I/ATLAS became the main character when it came hurtling into our solar system last year, so it’s only fitting it gets a dramatic backstory.

After using the ALMA observatory in Chile to closely examine the interstellar visitor — widely believed to be some type of comet — astronomers discovered that it likely fled from a cold and isolated corner of the galaxy, they report in a new study published in the journal Nature, like some sort of cosmic refugee seeking warmth.

The clues came from examining the water vapor it released while passing through. As it flew near the Sun in November and began to heat up, it vented something to the tune of seventy Olympic swimming pools of water every day, providing a chance to study what materials it was harboring in its nucleus. (Other astronomers capitalizing on the opportunity even found that it contained the ingredients for life.)

When the astronomers peered into this vapor cloud, they found high amounts of deuterium, a heavy hydrogen isotope containing one proton and one neutron. The hydrogen atoms found in water molecules typically contain only the single proton. 

Scientists call water made of deuterium “heavy water,” and 3I/ATLAS is indeed a heavy hitter. The observations showed that the ratio of heavy water in the comet is 30 times higher than any regular comet that originated here in our own solar system, and forty times higher than the water found in the Earth’s oceans. Altogether, it’s more “than anything we’ve seen before in other planetary systems and planetary comets,” lead author Luis Salazar Manzano at the University of Michigan told BBC Sky at Night.

What the preponderance of heavy water suggests is that 3I/ATLAS formed in a cold and remote region of the Milky Way with less radiation, where there were fewer neighboring stars near its home star system. At an estimated age of at least seven billion years old, it formed well before our Sun, which is around 4.5 billion years old.

In addition to fleshing out 3I/ATLAS’s lonely backstory, it’s also a clue about how other star systems form. Study coauthor Teresa Paneque-Carreño at the University of Michigan said it was “proof that whatever the conditions were that led to the creation of our solar system are not ubiquitous throughout space.”

“That may sound obvious, but it’s one of those things that you need to prove,” she told Sky at Night.

More on space: Please Resist the Urge to Drink the Melted Sludge From 3I/ATLAS