Webb Finds 1-Micron Dusty Ice Grains in 3I/ATLAS, Hinting at a 7-Billion-Year Origin
Updated
Updated · The Economic Times · Nov 1
Webb Finds 1-Micron Dusty Ice Grains in 3I/ATLAS, Hinting at a 7-Billion-Year Origin
3 articles · Updated · The Economic Times · Nov 1
Summary
Webb data showed interstellar object 3I/ATLAS contains unusually dusty water-ice grains about 1 micron or smaller, producing a strong 3-micron absorption feature while expected 1.5- and 2.0-micron signals were weak or absent.
Observations gathered from August 2025 to April 2026 suggest the ice is heavily mixed with dust, a property that sets 3I/ATLAS apart even though the grain sizes resemble those seen in Solar System comets.
A separate Nature Astronomy study used methane’s deuterium-to-hydrogen ratio in December 2025 observations at 2.5 AU to suggest the object may have formed in a star system older than the Sun—possibly more than 7 billion years old.
Researchers said the grain properties changed as the comet moved away from the Sun, but it is still unclear whether solar heating or erosion exposing fresher material drove that shift.
The findings give scientists a rare look at material from another planetary system and may show that some icy building blocks around other stars share traits with those in our own Solar System.