[en] 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 ∼ 6.1, perihelion of q ∼ 1.36 au, inclination of ∼175°, and hyperbolic velocity of V∞ ∼ 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 ∼4 day time span. The visible/near-infrared spectral slope of the object is 17.1% ± 0.2%/100 nm, comparable to other interstellar objects and primitive solar system small bodies (comets and D-type asteroids). Moreover, 3I/ATLAS will be observable through early 2025 September, then unobservable by Earth-based observatories near perihelion due to low solar elongation. It will be observable again from the ground in late 2025 November. 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.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Seligman, Darryl Z.; Michigan State University, Department of Physics and Astronomy
Micheli, Marco; ESA NEO Coordination Centre, Largo Galileo Galilei 1, I-00044 Frascati (RM), Italy
Farnocchia, Davide; Jet Propulsion Laboratory
Denneau, Larry; University of Hawaii, Manoa, Institute for Astronomy
Noonan, John W.; Auburn University, Department of Physics
Hsieh, Henry H.; Planetary Science Institute, Arizona
Santana-Ros, Toni; Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Carr. San Vicente del Raspeig, s/n, 03690 San Vicente del Raspeig, Alicante, Spain, Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (UB), c. Martí Franquès, 1, 08028 Barcelona, Catalonia, Spain
Tonry, John; University of Hawaii, Manoa, Institute for Astronomy
Auchettl, Katie; University of Melbourne, Department of Physics, University of California, Santa Cruz, Department of Astronomy and Astrophysics
Conversi, Luca; ESA NEO Coordination Centre, Largo Galileo Galilei 1, I-00044 Frascati (RM), Italy
Devogèle, Maxime; ESA NEO Coordination Centre, Largo Galileo Galilei 1, I-00044 Frascati (RM), Italy
Faggioli, Laura; ESA NEO Coordination Centre, Largo Galileo Galilei 1, I-00044 Frascati (RM), Italy
Feinstein, Adina D.; Michigan State University, Department of Physics and Astronomy
Fenucci, Marco; ESA NEO Coordination Centre, Largo Galileo Galilei 1, I-00044 Frascati (RM), Italy
Ferrais, Marin ; Université de Liège - ULiège > Département d'astrophysique, géophysique et océanographie (AGO) > COMets METeors and Asteroids (COMETA) ; Florida Space Institute, University of Central Florida, 12354 Research Parkway, Orlando, FL 32828, USA
Frincke, Tessa; Michigan State University, Department of Physics and Astronomy
Gillon, Michaël ; Université de Liège - ULiège > Département d'astrophysique, géophysique et océanographie (AGO)
Hainaut, Olivier R.; European Southern Observatory, Germany
Hart, Kyle; University of Hawaii, Manoa, Institute for Astronomy
Hoffman, Andrew; University of Hawaii, Manoa, Institute for Astronomy
Holt, Carrie E.; Las Cumbres Observatory Global Telescope
Hoogendam, Willem B.; University of Hawaii, Manoa, Institute for Astronomy
Huber, Mark E.; University of Hawaii, Manoa, Institute for Astronomy
Jehin, Emmanuel ; Université de Liège - ULiège > Unités de recherche interfacultaires > Space sciences, Technologies and Astrophysics Research (STAR)
Kareta, Theodore; Dept. of Astrophysics and Planetary Science, Villanova University, Villanova, PA, USA, Lowell Observatory, 1400 W Mars Hill Rd, Flagstaff, AZ 86001, USA
Keane, Jacqueline V.; U.S. National Science Foundation, 2415 Eisenhower Avenue, Alexandria, VA 22314, USA
Kelley, Michael S. P.; University of Maryland, Department of Astronomy
Lister, Tim; Las Cumbres Observatory Global Telescope
Mandt, Kathleen; NASA Goddard Space Flight Center, Maryland
Manfroid, Jean ; Université de Liège - ULiège > Département d'astrophysique, géophysique et océanographie (AGO)
Marčeta, Dušan; University of Belgrade, Department of Astronomy
Meech, Karen J.; University of Hawaii, Manoa, Institute for Astronomy
Miftah, Mohamed Amine; Space sciences, Technologies &, Astrophysics Research (STAR) Institute Université de Liége 4000 Liege, Belgium
Morgan, Marvin; University of California, Santa Barbara, Department of Physics and Astronomy
Ocaña, Francisco; ESA NEO Coordination Centre, Largo Galileo Galilei 1, I-00044 Frascati (RM), Italy
Peña-Asensio, Eloy; Technical University of Milan, Italy
Shappee, Benjamin J.; University of Hawaii, Manoa, Institute for Astronomy
Siverd, Robert J.; University of Hawaii, Manoa, Institute for Astronomy
Taylor, Aster G.; University of Michigan, Department of Astronomy
Tucker, Michael A.; Center for Cosmology &, Astroparticle Physics, The Ohio State University, Columbus, OH, USA, Department of Astronomy, The Ohio State University, Columbus, OH, USA
Wainscoat, Richard; University of Hawaii, Manoa, Institute for Astronomy
Weryk, Robert; University of Western Ontario, Department of Physics and Astronomy
Wray, James J.; Georgia Institute of Technology, Earth and Atmospheric Sciences
Yaginuma, Atsuhiro; Michigan State University, Department of Physics and Astronomy
Yang, Bin; Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Santiago, Chile
Ye, Quanzhi; University of Maryland, Department of Astronomy, Boston University, Department of Astronomy
