Evolution of water production of 67P/Churyumov-Gerasimenko: An empirical model and a multi-instrument study

We examine the evolution of the water production of comet 67P/Churyumov-Gerasimenko during the Rosetta mission (June 2014 to May 2016) based on in situ and remote sensing measurements made by Rosetta instruments, Earth-based telescopes and through the development of an empirical coma model. The derivation of the empirical model is described and the model is then applied to detrending spacecraft position effects from the ROSINA data. The inter-comparison of the instrument datasets shows a high level of consistency and provides insights into the water and dust production. We examine different phases of the orbit, including the early mission (beyond 3.5 AU) where the ROSINA water production does not show the expected increase with decreasing heliocentric distance. A second important phase is the period around the inbound equinox, where the peak water production makes a dramatic transition from northern to southern latitudes. During this transition, the water distribution is complex, but is driven by rotation and active areas in the north and south. Finally, we consider the perihelion period, where there may be evidence of time dependence in the water production rate. The peak water production, as measured by ROSINA, occurs 18-22 days after perihelion at 3.5 ± 0.5 × 1028 water molecules/s. We show that the water production is highly correlated with ground-based dust measurements, possibly indicating that several dust parameters are constant during the observed period. Using estimates of the dust/gas ratio we use our measured water production rate to calculate a uniform surface loss of 2-4 meters during the current perihelion passage.