Evidence for Two Modes of Water Release in Comet 103P/Hartley 2: Distributions of Column Density, Rotational Temperature, and Ortho-Para Ratio

We acquired high-resolution near-infrared spectra of H2O emission from comet 103P/Hartley-2 using NIRSPEC at Keck 2. Long-slit spectroscopy can directly probe the inner comae of comets via spectrally and spatially resolved measurements. This capability strengthens the quantitative view of conditions within the closest 200 km from the cometary nucleus, thereby providing direct constraints for models of density and temperature distributions in this collisionally dominated region of the coma. The near-Earth approach of comet 103P/Hartley 2 in 2010 presented an especially interesting opportunity to investigate the near-nucleus region of an active comet with substantial extended (vs. nuclear) release of water. We present spatially resolved measurements of rotational temperature and column density and discuss insights into the nature of volatile release. We also present spatially resolved measurements of the H2O ortho-para ratio (OPR). We compare these measurements with OPRs retrieved by various techniques during the 1998 and 2010 apparitions. We gratefully acknowledge support by the NSF Astronomy and Astrophysics Research Grants Program (PI/co-PI Bonev/Gibb), by the NASA Astrobiology Institute (PI: Meech, PI: Mumma), by the NASA Postdoctoral Program (Fellow: Paganini), and by NASA's Planetary Astronomy (PI: DiSanti; PI: Mumma; PI: Villanueva), Planetary Atmospheres (PI: Combi; PI: DiSanti; PI: Villanueva), and Discovery (PI: Meech) Programs. NOAO (through the Telescope System Instrumentation Program funded by NSF) and the University of Hawaii granted Keck-2 telescope time for this investigation.