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The effects of coma anisotropies on the plasma environmentof comets have been studied by means of a 3-D hybridmodel which treats electrons as a massless, charge-neutralizing fluid,whereas ion dynamics are covered by a kinetic approach.From Earth-based observations as well as from in-situ spacecraft measurementsthe shape of the coma of many comets is ascertained to be anisotropic.However, most plasma simulation studies deploy a spherically symmetric activitypattern.In this paper anisotropy is studied by considering three different coma shape models.The first model is derived from the Haser model and is characterised byspherically symmetry.This reference model is then compared with two different neutral gas shape models:the dayside restricted model with no nightside activity and a cone shapedmodel with opening angle of π/2. In all models theintegrated surface activity is kept constant.The simulations have been done for the Rosetta targetcomet 67P/Churyumov-Gerasimenko for two heliocentric distances, 1.30 AU and 3.25 AU.It is found that shock formation processes are modified asa result of increasing spatial confinement. Characteristic plasma structures of cometssuch as the bow shock, magnetic barrier region and the ion composition boundaryexhibit a shift towards the sun. In addition, the cone shaped model leads to a strongincrease of the mass-loaded region which in turn leads to a smooth decelerationof the solar wind flow and an increasing degree ofmixture between the solar wind and cometary ion species.This creates an additional transport channel of the magnetic fieldfrom the magnetic barrier region away which in turn leadsto a broadening of this region. In addition, it leads to an ion compositionboundary which is only gradually developed

Mapping of coma anisotropies to plasma structures of weak comets: a 3-D hybrid simulation study