Discovery and Preliminary Characterization of a Third Interstellar Object: 3I/ATLAS
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| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| author | Seligman, Darryl Z. Micheli, Marco Farnocchia, Davide Denneau, Larry Noonan, John W. Hsieh, Henry H. Santana-Ros, Toni Tonry, John Auchettl, Katie Conversi, Luca Devogèle, Maxime Faggioli, Laura Feinstein, Adina D. Fenucci, Marco Ferrais, Marin Frincke, Tessa Gillon, Michaël Hainaut, Olivier R. Hart, Kyle Hoffman, Andrew Holt, Carrie E. Hoogendam, Willem B. Huber, Mark E. Jehin, Emmanuel Kareta, Theodore Keane, Jacqueline V. Kelley, Michael S. P. Lister, Tim Mandt, Kathleen Manfroid, Jean Marčeta, Dušan Meech, Karen J. Miftah, Mohamed Amine Morgan, Marvin Ocaña, Francisco Peña-Asensio, Eloy Shappee, Benjamin J. Siverd, Robert J. Taylor, Aster G. Tucker, Michael A. Wainscoat, Richard Weryk, Robert Wray, James J. Yaginuma, Atsuhiro Yang, Bin Ye, Quanzhi Zhang, Qicheng |
| author_facet | Seligman, Darryl Z. Micheli, Marco Farnocchia, Davide Denneau, Larry Noonan, John W. Hsieh, Henry H. Santana-Ros, Toni Tonry, John Auchettl, Katie Conversi, Luca Devogèle, Maxime Faggioli, Laura Feinstein, Adina D. Fenucci, Marco Ferrais, Marin Frincke, Tessa Gillon, Michaël Hainaut, Olivier R. Hart, Kyle Hoffman, Andrew Holt, Carrie E. Hoogendam, Willem B. Huber, Mark E. Jehin, Emmanuel Kareta, Theodore Keane, Jacqueline V. Kelley, Michael S. P. Lister, Tim Mandt, Kathleen Manfroid, Jean Marčeta, Dušan Meech, Karen J. Miftah, Mohamed Amine Morgan, Marvin Ocaña, Francisco Peña-Asensio, Eloy Shappee, Benjamin J. Siverd, Robert J. Taylor, Aster G. Tucker, Michael A. Wainscoat, Richard Weryk, Robert Wray, James J. Yaginuma, Atsuhiro Yang, Bin Ye, Quanzhi Zhang, Qicheng |
| contents | We report initial observations aimed at the characterization of a third interstellar object. This object, 3I/ATLAS or C/2025 N1 (ATLAS), was discovered on 2025 July 1 UT and has an orbital eccentricity of $e\sim6.1$, perihelion of $q\sim 1.36$ au, inclination of $\sim175^\circ$, and hyperbolic velocity of $V_\infty\sim 58$ km s$^{-1}$. We report deep stacked images obtained using the Canada-France-Hawaii Telescope and the Very Large Telescope that resolve a compact coma. Using images obtained from several smaller ground-based telescopes, we find minimal light curve variation for the object over a $\sim4$ day time span. The visible/near-infrared spectral slope of the object is 17.1$\pm$0.2 %/100 nm, comparable to other interstellar objects and primitive solar system small bodies (comets and D-type asteroids). 3I/ATLAS will be observable through early September 2025, then unobservable by Earth-based observatories near perihelion due to low solar elongation. It will be observable again from the ground in late November 2025. Although this limitation unfortunately prohibits detailed Earth-based observations at perihelion when the activity of 3I/ATLAS is likely to peak, spacecraft at Mars could be used to make valuable observations at this time. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2507_02757 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Discovery and Preliminary Characterization of a Third Interstellar Object: 3I/ATLAS Seligman, Darryl Z. Micheli, Marco Farnocchia, Davide Denneau, Larry Noonan, John W. Hsieh, Henry H. Santana-Ros, Toni Tonry, John Auchettl, Katie Conversi, Luca Devogèle, Maxime Faggioli, Laura Feinstein, Adina D. Fenucci, Marco Ferrais, Marin Frincke, Tessa Gillon, Michaël Hainaut, Olivier R. Hart, Kyle Hoffman, Andrew Holt, Carrie E. Hoogendam, Willem B. Huber, Mark E. Jehin, Emmanuel Kareta, Theodore Keane, Jacqueline V. Kelley, Michael S. P. Lister, Tim Mandt, Kathleen Manfroid, Jean Marčeta, Dušan Meech, Karen J. Miftah, Mohamed Amine Morgan, Marvin Ocaña, Francisco Peña-Asensio, Eloy Shappee, Benjamin J. Siverd, Robert J. Taylor, Aster G. Tucker, Michael A. Wainscoat, Richard Weryk, Robert Wray, James J. Yaginuma, Atsuhiro Yang, Bin Ye, Quanzhi Zhang, Qicheng Earth and Planetary Astrophysics Astrophysics of Galaxies Instrumentation and Methods for Astrophysics We report initial observations aimed at the characterization of a third interstellar object. This object, 3I/ATLAS or C/2025 N1 (ATLAS), was discovered on 2025 July 1 UT and has an orbital eccentricity of $e\sim6.1$, perihelion of $q\sim 1.36$ au, inclination of $\sim175^\circ$, and hyperbolic velocity of $V_\infty\sim 58$ km s$^{-1}$. We report deep stacked images obtained using the Canada-France-Hawaii Telescope and the Very Large Telescope that resolve a compact coma. Using images obtained from several smaller ground-based telescopes, we find minimal light curve variation for the object over a $\sim4$ day time span. The visible/near-infrared spectral slope of the object is 17.1$\pm$0.2 %/100 nm, comparable to other interstellar objects and primitive solar system small bodies (comets and D-type asteroids). 3I/ATLAS will be observable through early September 2025, then unobservable by Earth-based observatories near perihelion due to low solar elongation. It will be observable again from the ground in late November 2025. Although this limitation unfortunately prohibits detailed Earth-based observations at perihelion when the activity of 3I/ATLAS is likely to peak, spacecraft at Mars could be used to make valuable observations at this time. |
| title | Discovery and Preliminary Characterization of a Third Interstellar Object: 3I/ATLAS |
| topic | Earth and Planetary Astrophysics Astrophysics of Galaxies Instrumentation and Methods for Astrophysics |
| url | https://arxiv.org/abs/2507.02757 |