Work

Near-perihelion Activity and Composition of 3I/ATLAS from JUICE/MAJIS Observations

Year: 2026

Type: article

Abstract: We present visible-to-infrared (0.5–5.56 μ m) observations of the interstellar comet 3I/ATLAS obtained with the Moons and Jupiter Imaging Spectrometer aboard the Jupiter Icy Moons Explorer spacecraft between 2025 November 2 and 25, shortly after perihelion. The fluorescence emission from H 2 O at 2.7 μ m and CO 2 at 4.3 μ m is detected at heliocentric distances of 1.36–1.68 au. A weak dust-scattered continuum is identified from which we determine the spectral slope, with values ranging from ∼15% per 100 nm in the 0.65–0.9 μ m region to 1%–3% per 100 nm from 0.9 to 2.6 μ m. Spatially resolved measurements show that the radial distributions of H 2 O and CO 2 species are consistent with release in the near-nucleus environment. We derive H 2 O production rates that decreased from 8 × 10 28 s −1 to 4 × 10 28 s −1 over the period November 2–25, while the CO 2 /H 2 O ratio remained nearly constant at ∼10%. The heliocentric evolution of the CO 2 production rate indicates activity controlled by solar heating. Combined with published CO measurements and the low gas expansion velocities, our analyses support a scenario in which CO 2 plays a major role in driving the activity of 3I/ATLAS near perihelion. In addition, broad emission features are identified in the 3.2–3.6 μ m region that cannot be explained by the fluorescence of common cometary CH–bearing volatiles. Their spectral characteristics are consistent with aliphatic C–H functional groups and provide tentative evidence for the release of complex organic material from dust grains in the coma.

Source: The Astrophysical Journal Letters

DOI: 10.3847/2041-8213/ae8a47