Updated

Updated · The Conversation · Jul 2

Astronomers Trace 3I/Atlas to 12 Billion Years Ago as Spectra Reveal Unusual CO2-Rich Chemistry

Updated

Updated · The Conversation · Jul 2

Astronomers Trace 3I/Atlas to 12 Billion Years Ago as Spectra Reveal Unusual CO2-Rich Chemistry

Q: Can this 12-billion-year-old comet be traced back to the specific star system where it was born?

No. Astronomers can infer when and under what conditions 3I/Atlas formed, but they cannot identify its exact parent star system. The strongest evidence comes from its chemistry and isotopes. Its unusually high deuterium-to-hydrogen ratio shows it formed in an extremely cold environment, and its elevated carbon-12 to carbon-13 ratio suggests it condensed from ancient material roughly 11 to 12 billion years ago, early in the Milky Way’s history. Those measurements make 3I/Atlas a rare “galactic fossil,” but they do not provide a unique return address. Its motion through space also does not solve the problem. By the time 3I/Atlas reached our solar system, it had likely spent billions of years traveling between stars, with repeated gravitational nudges from stars and the galaxy itself altering its path. Over that timescale, reconstructing a precise trajectory back to one system becomes effectively impossible. Researchers can still narrow the picture in broad terms. Current studies suggest it may have formed in an ancient, cold planetary system in the Milky Way’s thick disk, and if its parent star was Sun-like, that star may no longer even exist in a recognizable form. As one of the lead researchers noted, these measurements are much better at revealing formation conditions than pinpointing a birthplace. So 3I/Atlas can be traced to an era and environment in the early galaxy, not to a specific star.

3 articles · Updated · The Conversation · Jul 2

Three new studies say interstellar comet 3I/Atlas formed about 12 billion years ago and carries a chemical mix unlike any known solar system object.
James Webb spectroscopy found water, carbon dioxide, methane, cyanides, sulphides, and iron and nickel atoms, with especially high CO2 and unusually low ammonia marking it as an outsider.
A roughly 1% deuterium-to-hydrogen ratio in its water points to formation in an extremely cold environment below 30 Kelvin, where heavy hydrogen becomes locked into ice.
Its exceptionally high 12C/13C ratio acts as a cosmic clock, indicating birth in the early Milky Way and reinforcing earlier estimates that the comet is at least 7 billion years old.
3I/Atlas is only the third interstellar object ever identified, but upcoming surveys from NEO Surveyor and the Vera C. Rubin Observatory could raise such discoveries by an order of magnitude.

Sources

The Conversation1d ago

Astronomers Uncover Interstellar Comet 3I/Atlas's Unique Composition and 12-Billion-Year-Old Origin

dailybeirut.com4h ago

Mysterious Comet 3I/Atlas Reveals Unique Composition · Daily Beirut

ScienceAlert8h ago

Comet From Outside Our Solar System Has Chemistry Unlike Anything We've Ever Seen Before : ScienceAlert

5 Sources

As new telescopes find more interstellar visitors, what other ancient cosmic relics will soon be discovered in our backyard?

Can this 12-billion-year-old comet be traced back to the specific star system where it was born?

Is this alien comet proof that the building blocks for planets and life are vastly different across our galaxy?

3I/ATLAS: Unveiling a 12-Billion-Year-Old Interstellar Visitor and Its Impact on Astronomy

Overview

The discovery of 3I/ATLAS in July 2025 marked a milestone in astronomy as it became the third confirmed interstellar object, thanks to recent advances in astronomical technology and the efforts of the ATLAS survey team. Officially designated C/2025 N1 (ATLAS), this object displayed cometary features and was quickly targeted for intensive observation. Its detection highlights how new capabilities now allow astronomers to spot these rare visitors, opening up opportunities to study material from beyond our solar system and deepening our understanding of the galaxy’s ancient history and chemical diversity.

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