Near-perihelion Activity and Composition of 3I/ATLAS from JUICE/MAJIS Observations
Abstract
We present visible-to-infrared (0.5-5.56 μm) 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 μm and CO 2 at 4.3 μm 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 μm region to 1%-3% per 100 nm from 0.9 to 2.6 μm. 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 μm 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.
Related
- Very Large Telescope observations of interstellar comet 3I/ATLAS III: High-resolution monitoring of CN and forbidden oxygen emission across the perihelion passage with ESPRESSO
- Post-perihelion dust activity and a candidate icy-grain halo in long-period comet C/2023 A3 (Tsuchinshan--ATLAS)
- Multi-Wavelength Post-Perihelion Polarimetry of Interstellar Comet 3I/ATLAS
- Post-perihelion Photometric and Spectroscopic Monitoring of the Interstellar Comet 3I/ATLAS
- Juice/SWI during the Lunar-Earth-Gravity-Assist (LEGA) – Part 3: Observations of the Earth as calibration target
BibTeX
@article{bockeleemorvan2026nearperihelion,
title = {{Near-perihelion Activity and Composition of 3I/ATLAS from JUICE/MAJIS Observations}},
author = {D. Bockelée-Morvan and F Poulet and R.Y. Langevin and Benoît Seignovert and C. Leyrat and G. Piccioni and C Royer and S. Rodriguez and E. D’aversa and R. Brunetto and J. Carter and T. Cavalié and M. de Sanctis and E. Lellouch and A. Migliorini and C. Pilorget and E. Quirico and S. Robert and F. Tosi},
journal = {The Astrophysical Journal Letters},
year = {2026},
month = sep,
doi = {10.3847/2041-8213/ae8a47},
url = {https://hal.science/hal-05753495v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Near-perihelion Activity and Composition of 3I/ATLAS from JUICE/MAJIS Observations
AU - D. Bockelée-Morvan
AU - F Poulet
AU - R.Y. Langevin
AU - Benoît Seignovert
AU - C. Leyrat
AU - G. Piccioni
AU - C Royer
AU - S. Rodriguez
AU - E. D’aversa
AU - R. Brunetto
AU - J. Carter
AU - T. Cavalié
AU - M. de Sanctis
AU - E. Lellouch
AU - A. Migliorini
AU - C. Pilorget
AU - E. Quirico
AU - S. Robert
AU - F. Tosi
PY - 2026
DA - 2026/09/17
JO - The Astrophysical Journal Letters
DO - 10.3847/2041-8213/ae8a47
UR - https://hal.science/hal-05753495v1
AB - We present visible-to-infrared (0.5-5.56 μm) 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 μm and CO 2 at 4.3 μm 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 μm region to 1%-3% per 100 nm from 0.9 to 2.6 μm. 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 μm 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.
SN - 2041-8205
SN - 2041-8213
ER -