JWST and Gemini Observations of the Active Centaur 450P/LONEOS: Nucleus and Coma Characterizations

2026/05/22 by Charles A. Schambeau, Michael S. P. Kelley, Maria Womack +16 · 1 voice
Physics and Astronomy · #astro-ph.EP

paper · pdf · doi:10.3847/psj/ae685c

Abstract

Between 2019 and 2024, we used the Gemini-N and JWST observatories to conduct a detailed case study of the active Centaur 450P/LONEOS, whose orbit was significantly altered by a close Saturn encounter in 1992. Gemini-N GMOS optical images likely captured the first views of 450P's inactive nucleus, indicating a relatively small radius of R_N = 1.8±0.5 km and a surface color of g' - i' = 1.15±0.09. This places 450P on the red end of the neutral/gray Centaur population and may indicate comparatively limited solar-driven surface processing relative to other known active Centaurs. A coma developed as 450P changed its heliocentric distance, R_H, from 7.83 au to 7.24 au, with an estimated low dust production rate of ∼4-8 kg s^-1. JWST NIRSpec IFU Prism-mode spectra revealed an elongated dust morphology and a symmetric CO₂ gas distribution in the coma but no H₂O or CO emission features, with production rates of Q_CO2 = (6.99±0.07)×10²⁴ molec. s^-1, Q_H2O ≤ 1.2×10²⁴ molec. s^-1, and Q_CO ≤ 5.2×10²⁴ molec. s^-1. Absorption features at 2.0 and 3.0 μm indicate the presence of water ice, and a subtle 3.1 μm feature is consistent with crystalline water ice in larger grains. A Hapke-style model dominated by large (D_eff. = 5.9 μm) dust grains with a volumetric ice fraction of f_ice = 33% fits the spectrum. A thermal model incorporating 450P's orbital history since ∼1500 CE aligns with the observed onset of activity driven by CO₂ outgassing from amorphous water ice crystallization between 140-160 K.

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Discussions

• More Centaur JWST observations "JWST and Gemini Observations of the Active Centaur 450P/LONEOS: Nucleus and Coma Characterizations" arxiv.org/abs/2605.24260 [bsky, 2 points, 0 comments]