Contemporaneous Optical and Near-infrared Observations of the Interstellar Comet 3I/ATLAS Pre- and Postperihelion

Year: 2026

Type: article

Abstract: Interstellar objects provide a unique view into the formation of other star systems. Here we present spectroscopic observations of the recently discovered interstellar object 3I/ATLAS between a heliocentric distance of 3.7–1.8 au on either side of its travels through perihelion. We obtained several observations with the Keck-I/LRIS, Keck-II/NIRES, Gemini/GMOS, and UH88/SNIFS spectrographs, covering a wavelength range of 0.3–2.5 μ m. We report the continued emission of both Ni and CN, along with postperihelion detections of Fe and a weak detection of C 3 . We determine the spectral slope across optical and near-infrared (NIR) wavelengths and find a positive spectral slope in the optical, with values ranging from ∼21% to 27% in the blue regions (0.4–0.55 μ m) to ∼6%–10% in the red (0.65–0.9 μ m) regions. In contrast, the NIR showed a negative spectral slope of ∼−0.9% between 0.9 and 1.5 μ m and ∼−2.3% between 1.9 and 2.5 μ m. 3I/ATLAS shows a clear turnover in its spectral shape at ∼1.1 μ m, consistent with scattered sunlight from the dusty coma. Finally, in the NIR spectra presented in this work, we do not detect any of the water ice features that were identified in an earlier NIR observation of 3I/ATLAS. Our observations of 3I/ATLAS in the NIR show a similar shape to the NIR spectrum of 2I/Borisov as it approached perihelion.

Source: The Astronomical Journal

DOI: 10.3847/1538-3881/ae6b71

Authors: Kyle Medler, Willem B. Hoogendam, Christopher Ashall, Bin Yang, James J. Wray, Benjamin J. Shappee, Karen J. Meech, Michael A. Tucker, Katie Auchettl, Dhvanil D. Desai, Jason T. Hinkle, Andrew M. Hoffman, Mark E. Huber, David O. Jones, Ruining Zhao

Institutions: University of Hawaii System, Universidad Diego Portales, Georgia Institute of Technology, The Ohio State University, The University of Melbourne, University of California System, University of Illinois Urbana-Champaign, NSF-Simons AI Institute for the Sky, Chinese Academy of Sciences

Language: English

Topic: Astro and Planetary Science

Subfield: Space and Planetary Science

Field: Earth and Planetary Sciences

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $4,499

Funders: National Science Foundation, National Aeronautics and Space Administration, W. M. Keck Foundation, Simons Foundation, California Institute of Technology, Space Telescope Science Institute, Science Foundation Ireland, Korea Astronomy and Space Science Institute, Ministério da Ciência, Tecnologia, Inovações e Comunicações, Agencia Nacional de Investigación y Desarrollo

OpenAlex ID: W7164481548