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Water Production Rates in Comets: Evidence for Physical Evolution of Cometary Surfaces

Presentation #210.03 in the session “Comets”. Cross-listed as presentation #105.07.

Published onOct 03, 2021
Water Production Rates in Comets: Evidence for Physical Evolution of Cometary Surfaces

Using observations from the Lowell Observatory narrowband photometry database, we examine trends in water production among comets based on dynamical classes. Our program began in 1976, and to date includes observations of nearly 220 comets. Of these, over 190 have measured OH fluxes, which are converted to production rates for OH and are then readily converted to H2O production rates. We use these water production values for several investigations, including deriving each comet’s extrapolated water production rate at perihelion, calculating the surface area required to produce the observed water production for each comet (i.e. the effective active area), and finding the fractional active area for over 50 of these objects with published nucleus sizes. Our large sample allows us to not only look at these properties within the ensemble of comets, but to also examine differences among these objects based on their dynamical ages. Clear trends emerge for each of these analyses based on the bulk division of Jupiter-family (JF) comets, presumed to mostly originate from the Kuiper belt, and non-JF comets, presumed to mostly originate from the Oort cloud. Within the non-JF comets, the dynamically younger objects overall have higher extrapolated water production rates at perihelion than do the dynamically older members. We also see a clear trend in their effective active areas, with the dynamically new comets having the largest values while the older, Halley-type comets have the smallest. Though few of the younger comets have measured nucleus sizes, this trend persists when looking at the active fractions. Taken together, this provides clear evidence for the evolution of the surfaces of these comets towards lower activity. In comparison, the JF comets have overall smaller water production rates at perihelion. They exhibit a wide range of active areas and active fractions, which we conclude is a result of the JF comets having a full range of relative ages, i.e. physical evolution of their surfaces, with objects continually being moved in from the Kuiper belt, and resulting in varying amounts of time that these comets have spent in the inner solar system.

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