Thermal Balance and Water Ice Sublimation on the Surface of Hyperactive Comet 103P/Hartley 2

Abstract

AbstractHyperactive comets have attracted attention due to their high water production rate with an unclear mechanism, though some hypotheses have been proposed to explain it. Based on the thermal theories of the comet nuclei, this paper studied a comet surface thermal model considering the sublimation of H2O. In this paper, a method for solving the sublimation rate of water ice by infrared spectroscopy is proposed. The method adopts the assumption of subpixel temperature nonuniformity on the comet nucleus surface and uses the numerical solution of the Fredholm equation. We use the HRI‐IR spectrum (1.05–4.8 μm) data by EPOXI to analyze the pixel‐by‐pixel water sublimation rate of hyperactive comet 103P/Hartley 2. The results show that sublimation exists in most areas of the surface with or without surface roughness, and most of the water production rate (70%–90%) may come from the comet nucleus when Gauss random surface roughness is adopted. According to the sublimation law, it is estimated that the sublimation temperature of water ice on 103P is above 180 K. If the dust‐to‐ice volume ratio is 3:1, the sublimation temperature is about 200–210 K, which indicates that the water ice may sublimate underneath. This may explain why exposed water ice on the surface can hardly be observed while the active fraction of this comet is up to 100%.