Great comet C/2023 A3 (Tsuchinshan–ATLAS): Dust loss before perihelion

¹ State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Taipa, Macau 999078, PR China
² School of Aeronautics and Astronautics, Shenzhen Campus of Sun Yat-sen University, Shenzhen, Guangdong 518107, PR China

^★ Corresponding authors: mthui@must.edu.mo; manto@hawaii.edu

Received: 19 March 2025
Accepted: 28 April 2025

Abstract

In this study, the dust loss of comet C/2023 A3 (Tsuchinshan–ATLAS) is investigated through the analysis of archival images. By measuring the surface brightness profile of the coma, we determined that the comet maintained a nearly steady state during the observations. Analysis of the dust distribution perpendicular to the orbital plane reveals that the ejection velocity is v_⊥ ~ (65 ± 5)β^1/2 m s⁻¹, where β is inversely proportional to the size of the dust grains. From the dust scattering cross-section measurement, we estimated the upper limit of the nucleus radius to be ~5.9 ± 0.2 km, assuming a geometric albedo of 0.04. Based on the extrapolation of the scattering cross-section over time, the onset time of significant dust activity is estimated to be 25 July 2022, corresponding to a heliocentric distance of 9.1 au, with the activity mechanism at this distance likely being the phase transition from amorphous to crystalline ice. Our simulation reveals that the minimum dust size is 20 μm and the size distribution index is s = 3.4 in tail. The dust loss rate is determined to be (1.7 ± 0.8) × 10² kg s⁻¹, based on the derived average size of the particles and the rate of change of the scattering cross-section over time. Through a simplistic model, we evaluate that the nucleus of the comet remains stable against tidal effects, sublimation, and rotational instability, and disfavour the fate of disintegration. The result is consistent with observations that the nucleus has survived.