Webb Finds Dust-Rich Water Ice in Interstellar Comet 3I/ATLAS Across 3 Observations
Updated
Updated · Sci.News · Oct 26
Webb Finds Dust-Rich Water Ice in Interstellar Comet 3I/ATLAS Across 3 Observations
3 articles · Updated · Sci.News · Oct 26
Summary
3I/ATLAS contains water ice blended with dark rocky material in tiny grains, a Webb result that sets the interstellar comet apart from typical icy comets in the Solar System.
Three NIRSpec observations from August 2025 to April 2026 showed a strong 3-micron water-ice band plus water, carbon dioxide and carbon monoxide gas, while the usual 1.5- and 2.0-micron ice signatures were faint or absent.
Modeling points to grains smaller than a few micrometers that mix ice and refractory material; the April 2026 spectrum also hinted at a second population of larger, more ice-rich grains.
Spectra from 3I/ATLAS more closely matched some trans-Neptunian icy worlds than most known comets, suggesting planet-forming disks around different stars may produce a continuum from relatively pure ice to dustier ice.
That continuum, if confirmed, would imply the physical form of water ice is set early in protoplanetary disks and can survive into the icy bodies those disks create.