Dust Activity Evolution and Constraints on Icy Grains in the Interstellar Comet 3I/ATLAS

@misc{liu2026dust,
  title = {{Dust Activity Evolution and Constraints on Icy Grains in the Interstellar Comet 3I/ATLAS}},
  author = {Bin Liu and Xiaoping Zhang and Xiaodong Liu and Man-To Hui},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.21206},
  eprint = {2610.21206},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.21206},
}

TY  - UNPB
TI  - Dust Activity Evolution and Constraints on Icy Grains in the Interstellar Comet 3I/ATLAS
AU  - Bin Liu
AU  - Xiaoping Zhang
AU  - Xiaodong Liu
AU  - Man-To Hui
PY  - 2026
DA  - 2026/10/15
PB  - arXiv
DO  - 10.48550/arxiv.2610.21206
UR  - https://arxiv.org/abs/2610.21206
AB  - We present Zwicky Transient Facility observations of the interstellar comet 3I/ATLAS to characterize its dust-activity evolution before and after perihelion. Before perihelion, the effective scattering cross section C_e brightened across the inner 2×10^4 km as C_e∝ r_H^−γ, with γ increasing from 1.63±0.14 to 1.88±0.34 with aperture size. After perihelion, the heliocentric index decreased from 2.44±0.09 in the 5×10^3 km aperture to 1.54±0.09 in the 8×10^4 km aperture, indicating faster fading of the inner coma. Under adopted grain-size and residence-time assumptions, the implied dust mass-loss rates are ∼123--203 kg s^−1 before perihelion and ∼596--1412 kg s^−1 after perihelion. The morphology yields a sunward ejection-speed scale of v_ej∼(190±3)a_μm^−1/2 m s^−1 and an effective perpendicular velocity of v_⊥=(79±6)a_μm^−1/2 m s^−1. Post-perihelion surface-brightness profiles transiently steepened to k∼−2.7 in late November and early December, then became shallower and approached k=−1.5 by January. Matched g−r profiles show that this phase coincided with an anomalously blue outer coma that disappeared by January. We characterize the fading component with a projected destruction length of ℓ_DE∼(6.4--7.2)×10^4 km. Thermophysical sublimation calculations indicate that this scale, together with the order of magnitude of the water production near the main imaging epoch, is consistent with a_0∼5--10 μm icy grains containing a small absorbing carbonaceous fraction of f_C∼0.1%. These results suggest that the early post-perihelion coma likely contained a short-lived, volatile-bearing icy-grain component whose fading contributed to the outer-coma brightness and color evolution
ER  -