Webb observations of interstellar comet 3I/ATLAS

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The NASA/ESA/CSA James Webb Space Telescope observed interstellar comet 3I/ATLAS on 6 August 2025 using its Near-Infrared Spectrograph. The research team is analysing Webb’s data, with a preprint now available online. Webb is one of several space telescopes studying this comet, helping to reveal its size, physical properties, and chemical composition. For example, the NASA/ESA Hubble Space Telescope and NASA’s recently launched SPHEREx mission have also observed it. While the comet poses no threat to Earth, such observations support astronomers in their ongoing mission to find, track, and better understand objects in our Solar System.

ESA astronomer Marco Micheli from the Agency's Near-Earth Object Coordination Centre is a co-author on the paper. Marco helped measure the trajectory of 3I/ATLAS accurately enough for Webb to be able to capture it within the very small field of view of the NIRSpec instrument.

"It was quite challenging!" says Marco. "It was very important to successfully capture the comet inside of Webb’s images and enable these new insights into its structure and composition."

[Image description: Three-panel infrared image of comet 3I/ATLAS taken by Webb on 6 August 2025. The left panel shows the overall infrared image with a bright white core fading to red, orange, and blue. The centre and right panels show flux maps highlighting CO₂ at 4.3 μm and H₂O at 2.7 μm, respectively, with insets showing spectral line profiles confirming molecular signatures.]