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Astronomers utilizing the NASA/ESA/CSA James Webb Space Telescope have actually discovered that the water ice in the interstellar comet 3I/ATLAS is blended with dark, rocky product in small grains. The grains’ spectral attributes vary from those of ice grains in planetary system comets however look like the spectra of some icy worlds beyond Neptune.
Protopapa et alutilized Webb to compare the interstellar comet 3I/ATLAS with icy bodies in our Solar System; the contrast provides hints to the early development of planetary foundation; at leading right, both 3I/ATLAS and the icy planetary system comet C/2024 E1 reveal a strong water-ice absorption band near 3 microns, however the interstellar comet has extremely weak or missing bands near 1.5 and 2.0 microns; its spectrum more carefully looks like the typical spectrum of a class of icy worlds beyond Neptune whose spectra likewise reveal co2 ice and organics (bottom right); the artist’s principle (left, not to scale) compares the fairly pure ice grains with different dust, as translated for many planetary system comets, with the dust-rich ice aggregates the research study presumed for 3I/ATLAS. Image credit: SwRI/ Silvia Protopapa/ NASA/ ESA/ CSA/ JWST.
“Interstellar comets are little icy bodies that formed in the disks of gas and dust around other stars and are now travelling through our Solar System,” stated Dr. Silvia Protopapa, an astronomer at the Southwest Research Institute.
“As 3I/ATLAS heats up, gas leaving from its interior brings ice and dust grains into the surrounding cloud, or coma.”
“Those grains hold ideas to the conditions where the comet was born.”
Dr. Protopapa and coworkers observed 3I/ATLAS with Webb’s NIRSpec instrument on 3 dates: August 6, 2025, December 22, 2025, and April 1, 2026.
These covered about 8 months around the comet’s closest technique to the Sun on October 29, 2025.
The spectra reveal a strong water-ice absorption plus gas emission from water, co2 and carbon monoxide gas.
The weaker water-ice signatures, which are normally seen in icy comets, were faint or missing.
According to the group’s modeling, the very best description is grains smaller sized than a couple of micrometers, each a mix of water ice and refractory product.
“The grains of 3I/ATLAS have to do with the exact same size as those in our own comets,”Dr. Protopapa stated.
“What appears to set them apart is just how much dust is blended into the ice.”
The April 2026 spectrum likewise means a 2nd population of bigger, micron-sized ice-rich grains.
“We can’t yet inform whether the modifications with time are the outcome of the Sun heating the grains in a different way at each observation, or of brand-new product exposed as the comet’s surface area worn down near the Sun,” stated Dr. Michael Kelley, an astronomer at the University of Maryland.
“Both are possible, and informing them apart is among the open concerns we intend to deal with.”
The reserchers likewise compared 3I/ATLAS with other comets and with numerous classes of trans-Neptunian things.
They recommend icy planetesimals formed around various stars might share a continuum of ice grain homes, from pure ice to ice blended with refractory product, with 3I/ATLAS towards the refractory-rich end.
“At very first look, 3I/ATLAS looks various from the icy comets we understand,” Dr. Protopapa stated.
“But when we positioned it along with far-off icy worlds in our own Solar System, it no longer kept an eye out of location.”
“This recommends that the icy foundation of worlds, here and around other stars, might share ice in the kind of small, micron-scale grains, varying from reasonably pure ice to ice blended with dust, with 3I/ATLAS towards the dirty end.”
“If verified, this shared variety of grain homes might suggest that the physical kind of water ice is developed early, in planet-forming disks, and is at least partially protected in the icy bodies that form there.”
The outcomes appear in the Astrophysical Journal Letters
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Silvia Protopapa et al2026. JWST Reveals Refractory-rich Water Ice in Interstellar Comet 3I/ATLAS: Evidence for a Continuum of Grain Properties throughout Protoplanetary Disks. ApJL 1011, L11; doi: 10.3847/ 2041-8213/ aea60d
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