  Context: The ionosphere of a comet is known to deflect the solar wind through
mass loading, but the interaction is dependent on cometary activity. We
investigate the details of this process at comet 67P using the Rosetta Ion
Composition Analyzer. Aims: This study aims to compare the interaction of the
solar wind and cometary ions during two different time periods in the Rosetta
mission. Methods: We compared both the integrated ion moments (density,
velocity, and momentum flux) and the velocity distribution functions for two
days, four months apart. The velocity distribution functions were projected
into a coordinate system dependent on the magnetic field direction and averaged
over three hours. Results: The first case shows highly scattered H+ in both ion
moments and velocity distribution function. The He2+ ions are somewhat
scattered, but less so, and appear more like those of H2O+ pickup ions. The
second case shows characteristic evidence of mass-loading, where the solar wind
species are deflected, but the velocity distribution function is not
significantly changed. Conclusions: The distributions of H+ in the first case,
when compared to He2+ and H2O+ pickup ions, are indicative of a narrow
cometosheath on the scale of the H+ gyroradius. Thus, He2+ and H2O+, with
larger gyroradii, are largely able to pass through this cometosheath. An
examination of the momentum flux tensor suggests that all species in the first
case have a significant non-gyrotropic momentum flux component that is higher
than that of the second mass-loaded case. Mass loading is not a sufficient
explanation for the distribution functions and momentum flux tensor in the
first case, and so we assume this is evidence of bow shock formation.
