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arXiv · 2606.27535

JWST/MIRI Finds ISM-like Amorphous Silicates in Interstellar Comet 3I/ATLAS

Matthew Belyakov·Ian Wong·Carey M. Lisse·M. Ryleigh Davis·Bryce T. Bolin·Audrey Martin·Klaus M. Pontoppidan·Geoffrey A. Blake·Christine Chen·Michael E. Brown
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Abstract

We present the first spectroscopic mineralogical analysis of the dust coma of an interstellar object (ISO) from JWST mid-infrared spectroscopy of 3I/ATLAS (3I). 3I exhibits a strong 9- to 11-micron emissivity feature due to Si-O vibrational stretching modes that is commonly seen in asteroids, comets, disks, and the interstellar medium. Characterization of this 10-micron emissivity maximum reveals that 3I's dust composition is dominated by amorphous silicates, and that 3I is unlike Solar System comets, which show significant crystalline silicate dust. Instead, 3I's dust composition is more similar to circumstellar transition disks and the interstellar medium. We suggest 3I may have formed in a distant part of its home system out of interstellar medium-like material, without substantial incorporation of silicates condensed near its host star, unlike the mixing scenarios commonly suggested for the Solar System. Alternatively, 3I's original crystalline silicates may have been amorphized during its Gyr-long journey, although we find this alternative less likely due to 3I's mass loss rate and distinct 10-micron feature as compared to observed Solar System comets.

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Matthew Belyakov, Ian Wong, Carey M. Lisse, M. Ryleigh Davis, Bryce T. Bolin, Audrey Martin, Klaus M. Pontoppidan, Geoffrey A. Blake, Christine Chen, Michael E. Brown. 2026-09-16. JWST/MIRI Finds ISM-like Amorphous Silicates in Interstellar Comet 3I/ATLAS. https://arxiv.org/abs/2606.27535

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