Unraveling the dust activity of naked-eye comet C/2022 E3 (ZTF)

Abstract

A morphological and photometric analysis of the naked-eye long-period comet C/2022 E3 (ZTF) before perihelion is presented in this study. The observation images taken by the Zwicky Transient Facility survey telescope from July 2022 to October 2022 show a gradually brightening dust coma and a tail with a clear structure. The morphology of the dust coma reveals nonsteady-state emission with an ejection velocity lower than 14 m s$^{-1}$ for particles larger than 100 um. According to the syndyne-synchrone analysis, dust particles larger than about 10 um contribute significantly to the observed tail. The model simulations of the 10 October 2022 image suggest that the radii of large particles lingering near the nucleus range from 0.1 mm to 1 mm. Assuming that the nucleus of comet E3 is a homogeneous sphere with an albedo of 0.1, the photometry analysis sets the lower and upper limits of the nucleus radius to be $0.81\pm0.07$ km and $2.79\pm0.01$ km, respectively. The dust production rates increased continuously from $241\pm3$ kg s$^{-1}$ in July to $476\pm9$ kg s$^{-1}$ in October. The dependence of the ejection velocity $v_{\perp}$ perpendicular to the orbital plane of comet E3 on the particle size $a$ can be simplified as $v_{\perp}\propto a^{-1/2}$, which indicates that the dust emission is likely driven by gas. The water-production rate is inferred as $\sim 368\pm72$ kg s$^{-1}$ in October 2022, which is sustained by an equilibrium-sublimating area of $8.2\times10^6$ m$^2$ at least. The comparative analysis of the characteristics of comet E3 with those of comets belonging to different types shows that the activity profile of long-period comet E3 surprisingly aligns more closely with those of short-period comets within a heliocentric distance range of about [1.7, 3.4] AU, where the images of comet E3 that we used in this study were taken.