Multi-year Ground-Based Survey Photometry of Active Comet 103P/Hartley 2 and Centaur (2060) Chiron: A Tale of Two Comets in the Pre-LSST Era

[astro-ph.EP] Comets and Centaurs trace the evolution of trans-Neptunian objects (TNOs) into the inner solar system.

Their activity reflects the interplay between volatile sublimation, dust dynamics, and ring scattering. Yet the long-term behavior of individual objects is less constrained. To probe this evolutionary transition, we use wide-field survey photometry from the Asteroid Terrestrial-impact Last Alert System, Zwicky Transient Facility, and Las Cumbres Observatory observations of the Jupiter-family comet (JFC) 103P/Hartley 2 during its 2023/24 apparition, and the Centaur (2060) Chiron across 2020-2025, including its 2021 outburst.

For 103P, heliocentric activity slopes are asymmetric about perihelion, with a steep inbound index (nr,pre=−3.48±0.08) and flatter outbound value (nr,post=−1.16±0.04), consistent with enhanced relative dust contribution post-perihelion. Reduced brightness versus prior apparitions matches reported secular fading trends.

Dust mass-loss rates are ∼4-16 kg s⁻¹ for assumed grain properties. Colors exhibit a blueward trend near perihelion, consistent with enhanced gas contamination of the g-band, with possible phase-dependent scattering. A periodogram recovers a ∼18.7 hr activity-linked period near perihelion.

For Chiron, subtracting a quiescent baseline reveals exponential decay from the 2021 outburst on a ∼1.4 yr timescale. Seasonal phase curves flatten from βo=0.150±0.034 mag deg⁻¹ in 2021 to ≲0.09 mag deg⁻¹ by 2023-2025, converging with quiescent behavior.

Broad-band colors remain unchanged at ATLAS (c−o)=0.22±0.09 mag. This extended activity suggests a new epoch of persistent, low-level activity and/or evolving ring-scattering. These objects bracket the TNO-to-JFC evolutionary sequence, with 103P near the volatile-depleted end, and Chiron still volatile-rich and capable of episodic activity.

Joseph Murtagh, Megan E. Schwamb, Michael S. P. Kelley, Matthew M. Knight, Thomas Lehmann, Giannantonio Milani, A. Fraser Gillan, Alan Fitzsimmons, Ryan R. Lyttle, Matthew M. Dobson, Carrie E. Holt, Tim Lister, Joseph P. Chatelain, Sarah Greenstreet, Quanzhi Ye, Henry H. Hsieh, Denis Bodewits, Tracy X. Chen, Richard G. Dekany, Matthew J. Graham, Steven L. Groom, George Helou, Mansi M. Kasliwal, Ashish A. Mahabal, Reed Riddle

Comments: 32 pages, 12 figures, 8 tables, accepted for publication in PSJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2606.30280 [astro-ph.EP] (or arXiv:2606.30280v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2606.30280
Focus to learn more
Submission history
From: Joseph Murtagh
[v1] Mon, 29 Jun 2026 13:23:16 UTC (3,193 KB)
https://arxiv.org/abs/2606.30280

Astrobiology, Astrochemistry,