The near-nucleus gas coma of comet 67P/Churyumov-Gerasimenko prior to the descent of the surface lander PHILAE
2018
Context. The European Space Agency (ESA) Rosetta mission was the most comprehensive study of a comet ever performed. In
particular, the Rosetta orbiter, which carried many instruments for monitoring the evolution of the dusty gas emitted by the cometary
nucleus, returned an enormous volume of observational data collected from the close vicinity of the nucleus of comet 67P/Churyumov-
Gerasimenko.
Aims. Such data are expected to yield unique information on the physical processes of gas and dust emission, using current physical
model fits to the data. We present such a model (the RZC model) and our procedure of adjustment of this model to the data.
Methods. The RZC model consists of two components: (1) a numerical three-dimensional time-dependent code solving the
Eulerian/Navier-Stokes equations governing the gas outflow, and a Direct Simulation Monte Carlo (DSMC) gaskinetic code with
the same objective; and (2) an iterative procedure to adjust the assumed model parameters to best-fit the observational data at all
times.
Results. We demonstrate that our model is able to reproduce the overall features of the local neutral number density and composition
measurements of Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) Comet Pressure Sensor (COPS) and Double
Focusing Mass Spectrometer (DFMS) instruments in the period August 1 – November 30 of 2014. The results of numerical simulations
show that illumination conditions on the nucleus are the main driver for the gas activity of the comet. We present the distribution of
surface inhomogeneity best-fitted to the ROSINA COPS and DFMS in-situ measurements.
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