The Inbound Gas and Dust Evolution of Interstellar Comet 3I/ATLAS from Optical Spectroscopy and Multiband Photometry*
14 affiliations
- 1Universidad de Alicante
- 2Universitat de Barcelona (UB)
- 3Université Côte d’Azur
- 4V.N. Karazin Kharkiv National University
- 5Astronomical Institute of the Slovak Academy of Sciences
- 6Main Astronomical Observatory of the National Academy of Sciences of Ukraine
- 7Adam Mickiewicz University
- 8Institut für Geophysik und Extraterrestrische Physik
- 9Astronomical Observatory of Taras Shevchenko National University of Kyiv
- 10University of Helsinki
- 11South African Astronomical Observatory
- 12Stellenbosch University
- 13Ulugh Beg Astronomical Institute
- 14Université PSL
Abstract
Interstellar objects (ISOs) provide direct constraints on the composition and evolution of extrasolar planetary systems. As the third confirmed ISO, comet 3I/ATLAS offers a rare opportunity to study pristine material from another star system. We present a systematic multiband monitoring campaign conducted from 2025 July to September. To minimize systematic uncertainties, we utilized a homogeneous dataset of Sloan Digital Sky Survey (SDSS) g ′ , r ′ , i ′ , z s and Johnson–Cousins BVR imaging obtained with MuSCAT3/4 on the 2.0 m Faulkes Telescopes and the 1.5 m Maidanak telescope. We employed a novel multiaperture technique that provides a robust, distance-independent characterization of the coma, alongside optical spectroscopy from SALT and the Nordic Optical Telescope. 3I/ATLAS exhibited a stable reddish color with no significant secular variation during its inbound journey. Spectroscopic analysis reveals carbon-chain depletion, with CN as the only prominent molecular emission. Coma morphology, analyzed via azimuthal averaging and rotational gradient filters, shows a persistent sunward jet at a position angle of ∼280 ∘ , indicating sustained and localized outgassing from a high-latitude active region. Modeling of light scattering demonstrates that the observed colors and polarization are consistent with dense aggregates of organic matter and silicate minerals, while water-ice sublimation remained insufficient to alter the optical properties. The stability of the coma structures and the homogeneous nature of our dataset indicate that 3I/ATLAS underwent a steady activation phase, preserving a volatile-rich but carbon-chain-poor composition. This characterization points to an object formed in a distinct protoplanetary environment and provides a definitive record of its pre-perihelion evolution.
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BibTeX
@article{santanaros2026inbound,
title = {{The Inbound Gas and Dust Evolution of Interstellar Comet 3I/ATLAS from Optical Spectroscopy and Multiband Photometry*}},
author = {T. Santana-Ros and Alexey V. Sergeyev and Oleksandra V. Ivanova and Sofiia Mykhailova and Johannes Markkanen and Igor V. Luk'yanyk and T. Kwiatkowski and Dagmara Anna Oszkiewicz and Antti Penttilä and Nicolas Erasmus and K. E. Ergashev and Yu. N. Krugly},
journal = {The Astrophysical Journal},
year = {2026},
month = aug,
doi = {10.3847/1538-4357/ae8dbb},
url = {https://doi.org/10.3847/1538-4357/ae8dbb},
note = {CC BY},
}
RIS
TY - JOUR
TI - The Inbound Gas and Dust Evolution of Interstellar Comet 3I/ATLAS from Optical Spectroscopy and Multiband Photometry*
AU - T. Santana-Ros
AU - Alexey V. Sergeyev
AU - Oleksandra V. Ivanova
AU - Sofiia Mykhailova
AU - Johannes Markkanen
AU - Igor V. Luk'yanyk
AU - T. Kwiatkowski
AU - Dagmara Anna Oszkiewicz
AU - Antti Penttilä
AU - Nicolas Erasmus
AU - K. E. Ergashev
AU - Yu. N. Krugly
PY - 2026
DA - 2026/08/18
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/ae8dbb
UR - https://doi.org/10.3847/1538-4357/ae8dbb
AB - Interstellar objects (ISOs) provide direct constraints on the composition and evolution of extrasolar planetary systems. As the third confirmed ISO, comet 3I/ATLAS offers a rare opportunity to study pristine material from another star system. We present a systematic multiband monitoring campaign conducted from 2025 July to September. To minimize systematic uncertainties, we utilized a homogeneous dataset of Sloan Digital Sky Survey (SDSS) g ′ , r ′ , i ′ , z s and Johnson–Cousins BVR imaging obtained with MuSCAT3/4 on the 2.0 m Faulkes Telescopes and the 1.5 m Maidanak telescope. We employed a novel multiaperture technique that provides a robust, distance-independent characterization of the coma, alongside optical spectroscopy from SALT and the Nordic Optical Telescope. 3I/ATLAS exhibited a stable reddish color with no significant secular variation during its inbound journey. Spectroscopic analysis reveals carbon-chain depletion, with CN as the only prominent molecular emission. Coma morphology, analyzed via azimuthal averaging and rotational gradient filters, shows a persistent sunward jet at a position angle of ∼280 ∘ , indicating sustained and localized outgassing from a high-latitude active region. Modeling of light scattering demonstrates that the observed colors and polarization are consistent with dense aggregates of organic matter and silicate minerals, while water-ice sublimation remained insufficient to alter the optical properties. The stability of the coma structures and the homogeneous nature of our dataset indicate that 3I/ATLAS underwent a steady activation phase, preserving a volatile-rich but carbon-chain-poor composition. This characterization points to an object formed in a distinct protoplanetary environment and provides a definitive record of its pre-perihelion evolution.
SN - 0004-637X
SN - 1538-4357
ER -