3I/ATLAS Studies Trace 1.5-Mile Object to Ancient Cold Outer Disk
Updated
Updated · Smithsonian Magazine · Jun 29
3I/ATLAS Studies Trace 1.5-Mile Object to Ancient Cold Outer Disk
3 articles · Updated · Smithsonian Magazine · Jun 29
Summary
Webb and ALMA studies now point to 3I/ATLAS forming in the frigid outer reaches of another star’s protoplanetary disk, making the third known interstellar object unlike comets seen in our solar system.
James Webb found almost no crystalline silicates in 3I’s dust, suggesting little inward-outward mixing in its home system and a quieter disk than the young solar system.
ALMA measured a heavy-water ratio about 30 times higher than solar system comets, implying formation below minus 405 degrees Fahrenheit; elevated carbon monoxide, carbon dioxide and methane support that deep-freeze origin.
Webb data published in June also showed unusually low carbon-13, hinting the object may have formed as long as 12 billion years ago and could be the oldest planetary body yet observed.
3I/ATLAS has already passed Jupiter’s orbit and is leaving the solar system, sharpening interest in future flyby missions such as ESA’s Comet Interceptor and in new surveys that could catch more interstellar visitors.
What secrets about the early universe are locked inside this 12-billion-year-old visitor from another star?
Is our solar system's turbulent formation a cosmic rarity compared to this ancient visitor's pristine home?
We missed the oldest object ever seen. Are our spacecraft fast enough to catch the next interstellar guest?
3I/ATLAS—The Third Interstellar Object: What Its Chemistry Reveals About Alien Worlds and the Early Galaxy
Overview
On July 1, 2025, astronomers announced the discovery of Comet 3I/ATLAS, first detected by the ATLAS survey telescope and officially designated as an interstellar comet. Its incredible speed and hyperbolic trajectory confirmed its origin from beyond our solar system, sparking immense scientific interest. Astronomers quickly determined that 3I/ATLAS poses no threat to Earth, as it will pass at a safe distance. This rare event has launched a global effort to study the comet’s unique chemistry and ancient origins, offering a valuable opportunity to learn about the building blocks of planets and the diversity of planetary systems across the galaxy.