Surface activity of H2O and CO2 on comet 103P/Hartley2 derived from EPOXI/HRI images

Abstract

On November 4, 2010, the EPOXI extended the mission of the Deep Impact spacecraft, flew by comet 103P/Hartley 2, and made a series of spectral images in both the infrared and the visible. The High-Resolution Instrument Infrared Spectrometer (HRI-IR) observed the comet and its surrounding coma, enabling maps in the light of the infrared emissions of H${}_2$O at $2.7\mu m$ and CO${}_2$ at $4.3\mu m$ to be made. We have extended an inversion method originally developed to map out potential activity on the surface of comet 67P/Churyumov–Gerasimenko from ROSINA mass spectrometer measurements as part of the Rosetta mission to enable making similar nucleus surface activity maps from 2-D images of H${}_2$O and CO${}_2$ in the inner coma of Hartley 2. Processed close-up column density images show the existence of extended sources for H${}_2$O and CO${}_2$. Column density profiles specific to an icy grain extended source are derived based on a simple Monte Carlo grain model, and are used to remove the effects of an extended source from a set of 11 spectral maps of each species taken within 1 h of closest approach. We apply the inversion technique to the processed HRI-IR spectral images to calculate the distribution of potential surface activity of both species over the whole surface. Comparisons are made between the processed images, fitted images from the inversion model, and synthetic images generated by the Direct Simulation Monte Carlo (DSMC) coma model, demonstrating that the derived surface activity distributions can reproduce most patterns in the observed images. Production rates from direct nucleus sublimation during the closet approach period are characterized based on the DSMC model results.