comets: individual: 3I/ATLAS; Earth and Planetary Astrophysics; Astrophysics of Galaxies
Abstract :
[en] The interstellar comet 3I/ATLAS is only the third interstellar object to be discovered. Pre-perihelion measurements provide a unique opportunity to study its activity and composition, which may alter as it is heated in the coming months. We provide an initial baseline from optical spectroscopic observations obtained only two days after discovery, using the MUSE instrument on the VLT on 2025 July 3, while 3I was at 4.47 au from the Sun and 3.46 au from the Earth. These observations confirm the cometary nature of 3I, and reveal a red coma with a spectral slope of Å in the 5000-9000 Å range, redder than most Solar System comets but similar to the surface colour of some Solar System Trans-Neptunian Objects or Centaurs. We searched for but did not detect gas emission from C, NH, CN, and [O I], which is consistent with volatile non-detections for Solar System comets at this heliocentric distance. At present, the coma appears entirely dusty. Future observations of 3I as it comes closer to the Sun will provide an invaluable opportunity to witness the evolution of its activity, study its composition, test predictions of interstellar object population models, and compare 3I to Solar System comets.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Opitom, Cyrielle; Royal Observatory Edinburgh
Snodgrass, Colin; Royal Observatory Edinburgh
Jehin, Emmanuel ; Université de Liège - ULiège > Unités de recherche interfacultaires > Space sciences, Technologies and Astrophysics Research (STAR)
Bannister, Michele T.; School of Physical and Chemical Sciences–Te Kura Matū, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand
Bufanda, Erica; Royal Observatory Edinburgh
Deam, Sophie E.; Curtin University, Australia, International Centre for Radio Astronomy Research
Dorsey, Rosemary C.; University of Helsinki, Department of Physics
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
Hmiddouch, Said ; Université de Liège - ULiège > Unités de recherche interfacultaires > Space sciences, Technologies and Astrophysics Research (STAR)
Knight, Matthew M.; Physics Department, United States Naval Academy, 572C Holloway Road, Annapolis, MD 21402, USA,
Kokotanekova, Rosita; Bulgarian National Astronomical Observatory, International Space Science Institute, Switzerland
Leicester, Brayden; School of Physical and Chemical Sciences–Te Kura Matū, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand,
Marsset, Michaël; European Southern Observatory, Chile
Murphy, Brian; Royal Observatory Edinburgh
Okoth, Vincent; Royal Observatory Edinburgh
Ridden-Harper, Ryan; School of Physical and Chemical Sciences–Te Kura Matū, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand,
Vander Donckt, Mathieu ; Université de Liège - ULiège > Unités de recherche interfacultaires > Space sciences, Technologies and Astrophysics Research (STAR)
Ferellec, Léa; Royal Observatory Edinburgh
Hutsemekers, Damien ; Université de Liège - ULiège > Département d'astrophysique, géophysique et océanographie (AGO) > Space sciences, Technologies and Astrophysics Research (STAR)
Lippi, Manuela; Astronomical Observatory of Arcetri
Manfroid, Jean ; Université de Liège - ULiège > Département d'astrophysique, géophysique et océanographie (AGO)
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