Variations in Volatile-Driven Activity of Comet C/2017 K2 (PanSTARRS) Revealed by Long-Term Multi-Wavelength Observations

Context. A comprehensive study of comets over a wide heliocentric distance range helps us understand the physical processes driving their activity and reveals compositional differences across dynamical groups. C/2017 K2 (PANSTARRS) is a Dynamically New Oort Cloud comet (DNC) that showed activity as far as 23.75 au and displayed a CO-rich coma at 6.72 au, making it a key object to investigate pre- and post-perihelion behavior.

Aims. We aim to study the long-term activity evolution and chemical composition of C/2017 K2 using photometry and spectroscopy, from October 2017 (rh = 15.18 au) pre-perihelion to April 2025 (rh = 8.46 au) post-perihelion.

Methods. Broad-band and narrow-band imaging from both TRAPPIST telescopes enabled us to produce an 8-year light curve, color analysis, and derivation of activity slopes. Production rates of OH, NH, CN, C₃, and C₂ were computed using a Haser model, along with the dust proxy A(0)fρ. High-resolution spectra from CRIRES+ and UVES at three epochs (May – September 2022) provided simultaneous observations of parent and daughter species as the comet crossed the water sublimation zone.

Results. The light curve of C/2017 K2 shows a complex evolution with varying slopes and a brightness plateau around perihelion, indicating multiple active species. Coma colors remained constant, suggesting uniform dust properties and similarity to other active long-period comets. Gas production rates indicate a typical C₂/CN composition with a high dust-to-gas ratio. Analysis of forbidden oxygen lines shows a transition from CO and CO₂-driven activity to water-driven sublimation inside 3 au. Infrared spectra reveal C/2017 K2 as a typical-to-enriched comet, with HCN identified as the main parent of CN, and C₂ likely originating from C2H2 rather than C₂H₆.

S. Hmiddouch, E. Jehin, M. Lippi, M. Vander Donckt, K. Aravind, D. Hutsemékers, J. Manfroid, A. Jabiri, Y. Moulane, Z. Benkhaldoun

Comments: 17 pages, 16 figures, 14 tables, Accepted for publication in A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2507.13451 [astro-ph.EP] (or arXiv:2507.13451v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2507.13451
Focus to learn more
Submission history
From: Said Hmiddouch
[v1] Thu, 17 Jul 2025 18:00:20 UTC (5,500 KB)
https://arxiv.org/abs/2507.13451
Astrobiology, Astrochemistry,