Spectral Energy Distribution and Polarimetric Properties of Dust in the Interstellar Comet 3I/ATLAS
Abstract
The interstellar comet 3I/ATLAS exhibits unusual polarimetric properties compared with Solar System comets, while constraints on its fundamental physical properties, such as dust albedo and grain-size distribution, remain limited. We obtained new optical polarimetry near opposition with the Pirka Telescope, combined it with previously reported polarimetric measurements, and constructed a visible-to-mid-infrared spectral energy distribution (SED) from HST, VLT, SPHEREx, and JWST observations. The SED indicates that the coma is dominated by dark, absorbing dust, with an effective V-band albedo of peff∼0.04. Modeling the SED with a power-law grain-size distribution yields a size index of q=3.0--$3.3$. The mid-infrared spectral structure is better reproduced by adding a minor amorphous-silicate component. The combined polarimetric data further favor a highly porous scattering structure. Despite its unusual polarimetric behavior, the dust of 3I/ATLAS has an albedo and grain-size distribution within the range found for Solar System comets.
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BibTeX
@misc{choi2026spectral,
title = {{Spectral Energy Distribution and Polarimetric Properties of Dust in the Interstellar Comet 3I/ATLAS}},
author = {Seungwon Choi and Masateru Ishiguro and Hiroyuki Naito and Yoonsoo P. Bach and Jooyeon Geem and Bumhoo Lim and Moonkuk Hur and Sihu Ahn and Sunho Jin and Hisayuki Kubota and Seiko Takagi and Tatsuharu Ono and Max Mahlke and Carey Lisse and Tomohiko Sekiguchi and Makoto Watanabe},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.04919},
eprint = {2610.04919},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.04919},
}
RIS
TY - UNPB
TI - Spectral Energy Distribution and Polarimetric Properties of Dust in the Interstellar Comet 3I/ATLAS
AU - Seungwon Choi
AU - Masateru Ishiguro
AU - Hiroyuki Naito
AU - Yoonsoo P. Bach
AU - Jooyeon Geem
AU - Bumhoo Lim
AU - Moonkuk Hur
AU - Sihu Ahn
AU - Sunho Jin
AU - Hisayuki Kubota
AU - Seiko Takagi
AU - Tatsuharu Ono
AU - Max Mahlke
AU - Carey Lisse
AU - Tomohiko Sekiguchi
AU - Makoto Watanabe
PY - 2026
DA - 2026/10/04
PB - arXiv
DO - 10.48550/arxiv.2610.04919
UR - https://arxiv.org/abs/2610.04919
AB - The interstellar comet 3I/ATLAS exhibits unusual polarimetric properties compared with Solar System comets, while constraints on its fundamental physical properties, such as dust albedo and grain-size distribution, remain limited. We obtained new optical polarimetry near opposition with the Pirka Telescope, combined it with previously reported polarimetric measurements, and constructed a visible-to-mid-infrared spectral energy distribution (SED) from HST, VLT, SPHEREx, and JWST observations. The SED indicates that the coma is dominated by dark, absorbing dust, with an effective V-band albedo of p_eff∼0.04. Modeling the SED with a power-law grain-size distribution yields a size index of q=3.0--$3.3$. The mid-infrared spectral structure is better reproduced by adding a minor amorphous-silicate component. The combined polarimetric data further favor a highly porous scattering structure. Despite its unusual polarimetric behavior, the dust of 3I/ATLAS has an albedo and grain-size distribution within the range found for Solar System comets.
ER -