Water Production of Interstellar Comet 3I/ATLAS from SOHO/SWAN Observations after Perihelion
Year: 2026
Type: article
Abstract: The Solar Wind Anisotropies all-sky hydrogen Lyman-alpha camera on the Solar and Heliosphere Observatory observed the hydrogen coma of interstellar comet 3I/ATLAS, also called C/2025 N1 (ATLAS), beginning on 2025 November 6, 9 days after perihelion. Water production rates were calculated from each image of 3I/ATLAS using the methodology of J. T. T. Mäkinen and M. R. Combi, and fluorescence rates and g-factors were calculated using the daily solar Lyman-alpha fluxes from the LASP database ( https://lasp.colorado.edu/lisird/data ) corrected for solar rotation and for the comet’s heliocentric velocity. The method has been used for over 90 comet apparitions. A water production rate of 3.17 × 10 29 s −1 was found on November 6 when the comet was at a heliocentric distance of 1.40 au and at a sufficient solar elongation angle. It decreased over time after that, down to 1–2 × 10 28 s −1 around 40 days postperihelion (December 9).
Institutions: Finnish Meteorological Institute, Centre National de la Recherche Scientifique, Université de Versailles Saint-Quentin-en-Yvelines, Université Paris-Saclay, Sorbonne Université, Institut Pierre-Simon Laplace, Observatoire de Paris, LIRA - Laboratoire d'instrumentation et de recherche en astrophysique
Language: English
Topic: Astro and Planetary Science
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,400
OpenAlex ID: W7128062432