Great comet C/2023 A3 (Tsuchinshan-ATLAS): dust loss before perihelion

TL;DR

This study analyzes the dust loss and activity onset of comet C/2023 A3 (Tsuchinshan-ATLAS) before perihelion, estimating dust ejection velocities, nucleus size, activity timing, and stability, indicating the nucleus survived without disintegration.

Contribution

It provides the first detailed analysis of dust ejection velocities, activity onset, and nucleus stability for comet C/2023 A3 based on archival imaging data.

Findings

Dust ejection velocity v_perp ~ 65±5 β^{1/2} m/s

Nucleus radius estimated at ~5.9 km

Dust activity likely began on 25 July 2022 at 9.1 au

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 nearly in a steady state during the observations. Analysis of the dust distribution perpendicular to the orbital plane reveals that the ejection velocity is $v_{\perp}\sim(65\pm5)\,\beta^{1/2}$ m s$^{-1}$, where $\beta$ 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 $\sim\!5.9\pm0.2$ 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 \SI{20}{\micro\meter} and the size distribution index is $s = 3.4$ in tail. The dust loss rate is determined to be $(1.7 \pm 0.8) \times 10^2$ 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.