A study published in The Astrophysical Journal Letters reports that interstellar comet 3I/ATLAS contains microscopic water-ice grains mixed with dust. The findings, based on observations from NASA’s James Webb Space Telescope, point to a composition unlike that typically seen in comets originating in our Solar System.
First identified in July 2025, 3I/ATLAS is the third known interstellar object observed passing through our cosmic neighborhood, after 1I/’Oumuamua and 2I/Borisov. Researchers used Webb’s infrared instruments to examine the object and its surrounding coma, the cloud of gas and debris released as sunlight warms the comet.
The team, led by Silvia Protopapa of the Southwest Research Institute, estimates that the comet may have formed more than 10 billion years ago in the disk of gas and dust around a young star. That would make it more than twice as old as the Solar System. It was later ejected from its original system by gravitational forces and spent billions of years traveling through space, according to the study.
The researchers found an unusual pattern in the light reflected by gases around 3I/ATLAS. Water ice in comets from the Solar System typically produces three distinct absorption features in the spectrum, but Webb’s measurements of 3I/ATLAS showed only one. Computer simulations indicated that its ice grains are heavily mixed with dust, whereas ice in local comets is generally purer.
The dust-to-ice mix may preserve clues about the conditions in which the comet formed. The study also notes similarities between 3I/ATLAS and trans-Neptunian objects, icy bodies beyond Neptune’s orbit. Both are associated with abundant frozen carbon dioxide and carbon-rich organic compounds. Previous research has reported one of the highest carbon dioxide concentrations recorded in 3I/ATLAS, which the SwRI says is consistent with formation in the cold, distant regions of its original system.
The researchers also raise the possibility that 3I/ATLAS is a fragment of a much larger icy body destroyed in a collision. Its dusty ice grains may offer evidence about how small materials in disks around young stars gather to form larger bodies.
Sources: Olhar Digital.